The Emergence of Bacteroides pyogenes as a Human Pathogen of Animal Origin: A Narrative Review
by
, , , , and
Carola Mauri
*,†
,
Chiara Giubbi
†,
Alessandra Consonni
,
Elena Briozzo
,
Elisa Meroni
,
Francesco Luzzaro
and
Silvia Tonolo
Clinical Microbiology and Virology Unit, “A. Manzoni” Hospital, 23900 Lecco, Italy
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Microorganisms 2025, 13(6), 1200; https://doi.org/10.3390/microorganisms13061200
Submission received: 7 March 2025
/
Revised: 21 May 2025
/
Accepted: 22 May 2025
/
Published: 24 May 2025
(This article belongs to the Section Medical Microbiology)
Abstract
:Bacteroides pyogenes is a Gram-negative obligate anaerobe rod. It is naturally found in the oral microbiome of cats and dogs, which represents a primary source of disease for humans. The present review provides an update on the role of B. pyogenes as a pathogen responsible for infections in humans. Indeed, an increasing number of B. pyogenes infections have been reported in recent years, including skin and soft tissue infections as well as severe diseases like osteomyelitis, Lemierre’s syndrome, and bloodstream infection. Pre-analytical and analytical phases are crucial to guarantee the isolation of anaerobic bacteria, including B. pyogenes. Moreover, the introduction of MALDI-TOF mass spectrometry and 16S rRNA sequencing in clinical microbiology laboratories may be partially responsible for the increasing number of reports of B. pyogenes infections. However, the mechanisms underlying the pathogenicity of B. pyogenes remain poorly understood and require further investigations. Indeed, despite common antimicrobial susceptibilities, infections frequently persist and require multiple courses of antibiotics. In addition, based on literature data, this review indicates that treatment of skin and soft tissue infections often necessitates surgical procedures and hospitalization.
1. Introduction
The genus Bacteroides belongs to the Bacteroidaceae family, the order Bacteroidales, the class Bacteroidia, and the phyla Bacteroidota (1 of 41 bacterial phyla), and includes at least fifty species [1]. Bacteria belonging to the genus Bacteroides are obligately anaerobic Gram-negative, non-spore-forming, non-motile rods. These bacteria have a critical role as commensal organisms in the human gut but are also involved in human disease, having a potential pathogenic role outside the gut [2]. Among anaerobes, Bacteroides are the most frequently isolated in clinical specimens [3]. In particular, Bacteroides fragilis was the first member of the genus recognized in 1898 as a human pathogen [4] and, to date, is still considered the most virulent [3]. Bacteroides thetaiotaomicron, Bacteroides uniformis, and Bacteroides vulgatus are considered other clinically relevant species.
Advances in microbiological diagnostic techniques, including the increasing use of Matrix-Assisted Laser Desorption Ionization–time-of-flight Mass Spectrometry (MALDI-TOF MS), and the use of 16S rRNA sequencing have allowed the increasing isolation of “new” or previously rarely described organisms, including Bacteroides pyogenes.
B. pyogenes (py.o’ge.nes. Gr. n. pyum pus; Gr. v. gennaio produce; M.L. adj. pyogenes pus-producing) was first described with Bacteroides suis from the abscesses and feces of pigs by Benno et al. in 1983 [5] and then isolated from uteri of dairy cows with metritis and from horses’ wounds [6,7,8]. In 1997, Forsblom and colleagues reported the presence of B. pyogenes and Bacteroides tectum as major components of the anaerobic, Gram-negative, saccharolytic microflora of dogs and their possible role in the development of periodontal disease [9].
Sakamoto et al. studied the B. pyogenes genome, concluding that B. suis and B. tectus are heterotypic synonyms of B. pyogenes, showing 100% similarity for the hsp60 and 16S rRNA genes [10]. Four years later, analysis by whole-genome sequencing of these three strains revealed the diversification of B. pyogenes strains isolated from different animals [11]. Sakamoto et al. concluded that further genome analysis will improve our understanding of this species [11]. B. pyogenes is included in the Bacteroides fragilis group [12].
B. pyogenes is usually considered an uncommon but significant human pathogen. However, an increasing number of reports are currently describing its isolation in human clinical specimens, particularly in those collected from wounds [3,13]. Indeed, B. pyogenes is a component of the oral microbiota of animals, like dogs and cats [9,14], and can be transmitted to humans through animal bites. The high numbers of domestic dogs and cats in the European Union in 2023, estimated at over 65 million and 75 million, respectively [15,16], highlights the possible growing impact of B. pyogenes in the development of human infections.
2. Materials and Methods
2.1. Search Strategy and Inclusion and Exclusion Criteria
This narrative review aims to summarize all the data on B. pyogenes infections in humans published in the literature. Information regarding patients’ demographics, clinical characteristics, site of infection, clinical presentation, and treatment provided were described. There was a particular focus on data regarding microbiological characteristics and methodologies used for identification and antimicrobial susceptibility testing (AST). By using the PubMed/Medline database, searches for relevant articles were performed with the following item: “(Bacteroides pyogenes)”. Studies providing original data, such as case reports and letters to the editor providing information on B. pyogenes infections in humans and published up to 31 January 2025 were included in the review. Studies regarding infections and/or colonization in animals were excluded from the analysis. The references of included articles were also examined to identify any studies potentially missed in the initial search.
2.2. Data Extraction
After the initial screening, the following data were extracted from each included study: publication year, age and gender of patients, type of infection, contact with animals, treatment (antibiotic therapy and/or surgical procedure), underlying disease, and hospitalization. Other relevant microbiological data were collected: type of sample, method of identification, antimicrobial susceptibility testing profile and co-isolated bacteria.
3. Results
3.1. Literature Search
The search strategy yielded 42 references; 36 articles were excluded based on exclusion criteria as previously described. Overall, 16 studies were included and analyzed: 9 case reports, 5 letters to the editor and 2 articles, describing a total of 39 cases of infection.
3.2. Epidemiology of B. pyogenes Infections
B. pyogenes is an obligate anaerobe commensal from the oral cavity of cats and dogs. B. pyogenes infections have been described in the United States [17,18] and different countries from Europe [3,13,19,20,21,22], Asia [23,24,25,26,27,28], and Oceania [29,30].
Table 1 reports clinical features of B. pyogenes infections described in the literature. Skin and soft tissue infections, mainly associated with animal bites, are the most frequent human infections caused by this microorganism [3,13,17,19,22,23,24,26,29]. B. pyogenes can also be responsible for severe diseases, such as bloodstream infections [13,22,23,27], bone infections including osteomyelitis [3,19,20], joint prosthesis infections [21], and intra-abdominal infections [3,25,27]. A case of Lemierre’s syndrome [18], one multiple lung abscess [30], and one urinary tract infection [3] were also described (Table 1 and Table 2). Notably, in some cases, a single patient can develop an infection from B. pyogenes in different anatomical sites, as reported by Park and colleagues, who described the presence of B. pyogenes in blood and material from a liver abscess [27], or by Chen and colleagues, who identified B. pyogenes in blood and purulent exudate from a head injury [23].
The medical history of patients is not always complete and often underlying pathologies are not reported. However, in some cases, underlying diseases were described, with the most frequently reported being diabetes and history of oncology (Table 2 and Supplementary Table S1).
In most cases, B. pyogenes infections are described in patients reporting close contact with animals (e.g., bites, licks), confirming that direct contact with animals should be considered the main route of transmission of B. pyogenes. Except for the case report by Chen and colleagues describing an infection after a snow leopard bite [23], in all other cases the contact with companion animals (cats and dogs) seems to be the main route of transmission (Table 1 and Table 2). This phenomenon may be linked to the closer contact between companion animals and humans. Nevertheless, in some cases B. pyogenes infections seem to be unrelated to animal bites, where contact with animals is not documented in the medical history of the patient or did not occur (Table 1 and Table 2). Minor scratches and bites caused by pets are not always reported to the healthcare facility.
Previous studies on Pasteurella multocida, a facultative anaerobic Gram-negative coccobacillus present in the oral and respiratory tracts of cats and dogs, hypothesized that the contamination of a wound with animal fluids or animal air, as well as the ingestion of food contaminated by the animal, may be associated with the onset of opportunistic infections, particularly in patients with comorbidities or in treatment with immunosuppressant [31]. For this reason, future studies on B. pyogenes are required to investigate potential transmission mechanisms other than animals’ bites.
Most references describe polymicrobial infections between B. pyogenes and other pathogens (Table 2 and Table 3). When more pathogens are detected, the specific contribution of B. pyogenes in the development of the infection cannot be conclusively assessed. Anaerobic bacteria, such as Fusobacterium spp. and Pasteurella spp., are among the coinfecting pathogens most frequently identified. In particular, P. multocida is considered responsible for skin and soft tissue infections, but it can be more rarely associated with severe infections such as bone and joint prosthesis infections, endocarditis, sepsis, and meningitis, particularly in immunocompromised hosts [32,33].
3.3. Pathogenesis of B. pyogenes Infections
Despite the clinical significance of B. pyogenes infections, the mechanisms underlying its pathogenicity remain poorly understood. Usually, limited superficial soft tissue infections and abscesses are reported among healthy individuals. However, immunocompromised patients or those with important comorbidities may develop severe and/or systemic infections.
The pathogenicity of Bacteroides spp. includes the presence of a polysaccharide capsule, release of lipopolysaccharide, evasion of host immune response, production of proteolytic enzymes and hemolysin, release of enterotoxin, and aerotolerance [2]. Limited data on specific virulence factors of B. pyogenes are currently available; however, its ability to thrive in anaerobic conditions and cause systemic infections suggests the presence of mechanisms helping tissue invasion and immune evasion. B. pyogenes produces metabolic products such as succinic acid and acetic acid, which are thought to contribute to its survival in the anaerobic environments of host tissues [34]. It also demonstrates resistance to several host defense mechanisms, including phagocytosis by immune cells. The exact role of B. pyogenes in biofilm formation, a critical factor for chronic infection, needs to be better investigated [35]. Furthermore, there is evidence suggesting that B. pyogenes may harbor genetic elements conferring resistance to certain antimicrobial agents, complicating treatment regimens.
3.4. Diagnosis of B. pyogenes in Humans
Pre-analytical and analytical phases are crucial for guaranteeing the isolation of anaerobic bacteria, including B. pyogenes. Anaerobic infections may be underestimated because of difficulties related to their isolation and identification. Similarly to Pasteurella spp., B. pyogenes should be considered a potential etiological agent of soft tissue infections resulting from scratching, biting, or licking by domestic animals [31].
Proper sample collection is essential and should ideally be performed before the start of antibiotic therapy. Specimens must be free from contamination with commensal microbiota and representative of the infection site (aspirates and tissue biopsies should be preferred to swabs). All samples should be deeply inserted into anaerobic transport media or collected directly in oxygen-free containers. The transport to the laboratory should be at room temperature within two hours from the collection [36].
3.4.1. Identification of B. pyogenes
Diagnosis of B. pyogenes infection in clinical specimens can be achieved by isolating the pathogen from a culture or using molecular methods.
For culture-based methods, it is essential to provide appropriate conditions for the isolation of anaerobic bacteria, both in terms of culture medium and incubation environment. Specimens should be adequately inoculated on specific culture media, for example, Columbia Agar or Schaedler agar with 5% sheep blood and incubated for 48–72 h in anaerobic conditions (e.g., using anaerobic pouches, boxes, or jars) [3,36].
Table 4 summarizes the methods used for the identification of B. pyogenes in previously published reports. The identification of B. pyogenes with traditional biochemical methods may be inaccurate due to phenotypically similar species. Indeed, prior to the implementation of MALDI-TOF MS and 16S rRNA sequencing in diagnostics of bacterial infections, the identification of anaerobic microorganisms, such as B. pyogenes, was performed using biochemical methods, such as the VITEK-2 ANC card (bioMérieux, Marcy l’Etoile, France) or API Rapid ID 32A (bioMérieux, Marcy l’Etoile, France). Erroneous results of biochemical tests may be responsible for misidentification of the microorganism: Prevotella oralis and Prevotella melaninogenica were among the species more frequently misidentified [18,21,28,29] (Table 4).
The introduction of MALDI-TOF MS and 16S rRNA sequencing in clinical microbiology laboratories may be partially responsible for the increasing number of reports of B. pyogenes infections in last years. The accuracy of MALDI-TOF MS [37] and 16S rRNA gene sequencing [38] to correctly identify anaerobic microorganisms has been widely demonstrated (Table 4). Both techniques have shown good performance in the identification of B. pyogenes [3,13,18,21,22,23,24,25,27,28,29], but MALDI-TOF MS is more frequently used in routine diagnostics because of its rapidity and reduced costs. However, to provide a correct identification of all microorganisms [36] and, in particular B. pyogenes [27,29], it is fundamental to maintain updated databases of identification instruments. Data libraries for anaerobes should include reference strains as well as clinical isolates corroborated by sequencing methods [36]. Park and colleagues reported a misidentification of B. pyogenes with B. uniformis using Vitek MS (bioMérieux, Marcy l’Etoile, France) (Table 3 and Table 4) [27].
3.4.2. Antimicrobial Susceptibility of B. pyogenes
Culture-based methods are fundamental to guaranteeing the execution of antimicrobial susceptibility testing. Drug susceptibility testing of B. pyogenes isolates should be performed according to the most recent International Guidelines of European Committee on Antimicrobial Susceptibility Testing (EUCAST) [39] or the Clinical & Laboratory Standards Institute (CLSI) [40]. The current version of EUCAST Guidelines, version 15.0, provides indications for the interpretation of the results of susceptibility testing of B. pyogenes for ampicillin–sulbactam, amoxicillin–clavulanic acid, piperacillin–tazobactam, ertapenem, imipenem, meropenem, clindamycin, and metronidazole, while the use of CLSI criteria offers the possibility to report results of other molecules; for example, moxifloxacin. Moreover, EUCAST Guidelines for the interpretation of amoxicillin–clavulanic acid were first published in Version 13.1 in June 2023. For this reason, most of the studies currently available interpret their results using CLSI criteria.
The use of different international guidelines with different antibiotic breakpoints for the interpretation of antimicrobial susceptibility testing makes the comparison of results between studies difficult. As reported in Table 3 and Table 5, data on antimicrobial susceptibility testing are not always clearly reported. However, in most of the cases, EUCAST criteria were used for the interpretation of the results (n = 13) [3], while CLSI criteria were used in five cases [17,22,28,29] and EUCAST with CLSI (for amoxicillin–clavulanate and moxifloxacin) were applied in eight cases [13,19,20]. In three cases, no indication of the criteria used for the interpretation of the results of antimicrobial susceptibility testing were reported [21,24,26].
Antibiotic resistance among Bacteroides spp. has increased over the past decade [36,41]. Unlike other Bacteroides spp., B. pyogenes has been shown to be highly susceptible to most of the molecules usually tested. Cunha and colleagues, in their study on B. pyogenes strains from the uteri of cows with metritis, described the presence of a beta-lactam resistance gene (cfxA2) in the four isolated tested. Moreover, they observed the presence of the tetQ gene, encoding for a ribosomal protection protein conferring resistance to tetracycline, and the sul2 gene, encoding for a dihydropteroate synthase type-2 and imparting sulfonamide resistance in some of the isolates [8]. Moreover, a study on the genomics of isolates belonging to the B. fragilis group excluded the presence of overexpression of the cfiA gene in B. pyogenes. The cfiA gene, responsible for carbapenem resistance, was, however, present in some of the B. fraglis isolates tested [42].
As described in Table 5, metronidazole, amoxicillin–clavulanate, and clindamycin were the antibiotics whose activity was most frequently tested against B. pyogenes strains. In most of the cases, beta-lactams associated with beta-lactamase inhibitors, carbapenems, clindamycin, and metronidazole demonstrated good in vitro activity against most B. pyogenes isolates (Table 5) [3,13,21,22,24]. Moreover, B. pyogenes showed a good susceptibility to penicillins [22,26], even though all seven isolates identified by Majewska and colleagues were found to be resistant [3].
4. Treatment and Outcomes of B. pyogenes Infections
Given the susceptibility of B. pyogenes to many classes of antimicrobials, the treatment of infections is often based on beta-lactams, such as amoxicillin–clavulanate, piperacillin–tazobactam and ceftriaxone, and/or metronidazole (Supplementary Table S1). The selection of the appropriate regimen of treatment should take into account the outcome of antimicrobial susceptibility testing, while the duration should be evaluated based on the site of the infection and response to the treatment. Moreover, in most cases, B. pyogenes was co-isolated with other pathogens, further hindering the selection of appropriate antibiotic therapy (Table 3).
Despite appropriate antimicrobial therapy, in the presence of animal bites and scratch-related infections, correct wound hygiene and close follow-up are fundamental to avoid complications. In particular, the adequate management of those infections requires the control of their focus. In addition to antimicrobial treatment, surgical procedures, such as incision or debridement, and hospitalization are frequently required to treat B. pyogenes infections and guarantee their favorable evolution (Table 2 and Supplementary Table S1).
5. Conclusions
The present narrative review summarizes the characteristics of infections by B. pyogenes in humans by gathering all the published articles in the PubMed literature.
B. pyogenes infections may affect any organ and system but mainly involve skin and soft tissues. In any wound resulting from an animal bite or scratch, primarily cats and dogs, anaerobes like B. pyogenes should be suspected as the causative agents of the infection. The contact with the saliva of the animal in the absence of a bite could be sufficient to allow infection with B. pyogenes. Careful medical history-taking and microbiological confirmation of the infection are essential for accurate diagnosis and choice of appropriate treatment.
The introduction of MALDI-TOF MS and 16S rRNA sequencing in clinical microbiology laboratories has allowed the identification of species of bacteria previously unassociated with human infections or rarely reported, such as B. pyogenes. Although B. pyogenes has been shown to be highly susceptible to most of the molecules usually tested in vitro except penicillin, antimicrobial susceptibility testing of the isolated strains is recommended. Despite the susceptibility to antibiotics, the treatment of infections caused by B. pyogenes often necessitates surgical procedures, hospitalization, and intravenous therapies. Meticulous monitoring of the infection’s progression is critical to ensure effective clinical management. While the pathogenic mechanisms of other Bacteroides spp. have been described, specific investigation on the pathogenic potential of B. pyogenes is still required to better understand the mechanisms underlying the development of infections caused by this microorganism.
Supplementary Materials
The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/microorganisms13061200/s1, Supplementary Table S1: Clinical features of Bacteroides pyogenes infections reported in the literature, including age, gender, clinical presentation, underlying illness and risk factors, medical history, contact with animals, treatment, and outcome.
Author Contributions
C.M. and C.G. equally contributed to this work. C.M. conceptualized the work. C.M. and C.G. analyzed literature data and drafted the manuscript. E.B., A.C., and E.M. performed the literature search and drafted the manuscript. F.L. and S.T. supervised the activities and revised the manuscript. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Informed Consent Statement
Not applicable.
Data Availability Statement
No new data were created or analyzed in this study. Data sharing is not applicable to this article.
Conflicts of Interest
The authors declare no conflicts of interest.
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Table 1.
Clinical features of Bacteroides pyogenes infections reported in the literature, including age, gender, type of infection, contact with animals, and treatment.
Table 1.
Clinical features of Bacteroides pyogenes infections reported in the literature, including age, gender, type of infection, contact with animals, and treatment.
| Author Year Reference | Age, Gender | Type of Infection | Contact with Animals | Treatment |
|---|---|---|---|---|
| 2025 Chen [23] | 33, M | Subcutaneous abscess | Snow leopard bite | Multiple antibiotic therapies and surgical procedure |
| 2024 Lee [30] | 55, M | Multiple lung abscesses | Recent exposure to cats and dogs but no known bites | Multiple antibiotic therapies and surgical procedure |
| 2024 Sadhwani [17] | 81, F | Intramuscular abscess | Cat bite | Multiple antibiotic therapies and surgical procedure |
| 2023 Vecilla [13] 2023 Vecilla [20] case report regarding #1 2023 Vecilla [19] case report regarding #6 | #1 50, M | Jaw osteomyelitis and masseter myositis | Contact with his cat but no bites or scratches | Antibiotic therapy and surgical procedure |
| #2 62, F | Cellulitis on the arm | Cat bite | Antibiotic therapy | |
| #3 79, M | Surgical wound infection (tracheostomy) | Unknown | Antibiotic therapy | |
| #4 82, M | Bacteremia | Unknown | Antibiotic therapy | |
| #5 22, M | Ear, nose, and throat infection (fistula) | Unknown | Surgical procedure | |
| #6 40, M | Osteomyelitis of the second metacarpal with bone destruction of its head | Cat bite | Multiple antibiotic therapies and surgical procedure | |
| #7 37, F | Cellulitis on the hand | Cat bite | Antibiotic therapy | |
| #8 57, M | Infected ulcer on the leg | Unknown | Antibiotic therapy | |
| 2021 Takahashi [25] | 79, F | Appendiceal abscess | No history of animal contact | Multiple antibiotic therapies and surgical procedure |
| 2021 Shenoy [24] | 55, M | Diabetic foot infection | Contact with domestic animals such as street dogs, cats, and cattle, without history of any animal bite | Multiple antibiotic therapies and surgical procedures |
| 2021 Majewska [3] | #1 67, M | Soft tissue necrosis within oral cavity and osteomyelitis of the mandible bone | No history of animal contact | Antibiotic therapy and surgical procedure |
| #2 70, M | Odontogenic infection, chronic maxillary sinusitis (left) and osteomyelitis of the jaw bone | No history of animal contact | Antibiotic therapy and surgical procedure | |
| #3 84, F | Phlegmon on the skin and necrotic lesions with fistulas | No history of animal contact | Antibiotic therapy and surgical procedure | |
| #4 35, M | Trauma: multiple fracture of mandibular bones with displacement | No history of animal contact | Multiple antibiotic therapies and surgical procedure | |
| #5 67, M | Osteomyelitis | No history of animal contact | Multiple antibiotic therapies and surgical procedures | |
| #6 73, M | Cholecystitis | No history of animal contact | Antibiotic therapy | |
| #7 89, F | Phlegmon of the right hand | Cat bite | Antibiotic therapy and surgical procedure | |
| #8 72, F | Urinary tract infection | No history of animal contact | Antibiotic therapy and surgical procedure | |
| #9 79, F | Subcutaneous tissue inflammation and phlegmon of the right foot | No history of animal contact | Surgical procedure | |
| #10 10, F | Skin and soft tissue infection | Dog bite | Not reported | |
| #11 35, F | Skin and soft tissue infection | Dog bite | Not reported | |
| #12 39, F | Skin and soft tissue infection | Animal contact not clear (incomplete medical history) | Not reported | |
| #13 55, M | Skin and soft tissue infection | Animal contact not clear (incomplete medical history) | Not reported | |
| 2021 Goggin [18] | 7, M | Lemierre’s syndrome | Contact with 3 domestic dogs, that often slept with him and roused him in the morning by licking his head, neck, and ears. No history of any animal bite | Multiple antibiotic therapies and surgical procedure |
| 2019 Gual-de-Torrella [21] | 53, F | Abscess from the surgical wound of primary knee arthroplasty of the patella. Eschar of the surgical wound | Contact with her domestic dog, without history of bites or scratches (patient has an open surgical wound) | Multiple antibiotic therapies and surgical procedure |
| 2018 Umemura [26] | 53, F | Abscess on the left foot | Cat bite | Multiple antibiotic therapies and surgical procedure |
| 2016 Park [27] | 77, F | Bacteremia secondary to liver abscess | No history of animal bite | Antibiotic therapy and surgical procedure |
| 2016 Lau [29] | #1 46, F | Skin and soft tissue infection | Dog bite on the left index finger | Multiple antibiotic therapies and surgical procedure |
| #2 46, M | Skin and soft tissue infection | Cat bite on the right lower leg | Multiple antibiotic therapies and surgical procedures | |
| #3 69, F | Abscess on the right forearm | Cat bite | Multiple antibiotic therapies and surgical procedure | |
| #4 47, F | Skin and soft tissue infection | Dog bite on the left index finger | Multiple antibiotic therapies and surgical procedure | |
| #5 76, M | Skin and soft tissue infection | Contact with his two dogs without history of any animal bite | Multiple antibiotic therapies and surgical procedures | |
| #6 10, M | Skin and soft tissue infection | Dog bite on the right-hand 1st webspace | Multiple antibiotic therapies and surgical procedures | |
| #7 67, M | Joint infection | Cat bite on the left-hand 2nd metacarpophalangeal joint | Multiple antibiotic therapies and surgical procedures | |
| 2016 Kim [28] | 51, F | Bloodstream infection | No history of animal contact | Multiple antibiotic therapies |
| 2011 Madsen [22] | 60, M | Skin and soft tissue infection, and bacteremia | Cat bite on the left wrist | Multiple antibiotic therapies and surgical procedures |
Abbreviations: F: Female; M: Male.
Table 2.
Summary of Bacteroides pyogenes infections reported in the literature.
| Gender | 21 M; 18 F |
|---|---|
| Age | Range: 7–89 Average: 55.6 |
| Type of infection | Skin and soft tissue infection, n = 24 Bone infection, n = 5 Intra-abdominal infection, n = 4 Bloodstream infection, n = 1 Intramuscular abscess, n = 1 Joint prosthesis infection, n = 1 Lemierre’s syndrome, n = 1 Lung abscess, n = 1 Urinary tract infection, n = 1 |
| Contact with animal | Yes, n = 22 (16 animal bites: cats, n = 10; dogs, n = 5; snow leopard, n = 1; 6, no history of animal bite); No history of animal contact, n = 10 Animal contact not clear or incomplete medical history, n = 7 |
| Monomicrobial infection | 9 samples |
| Polymicrobial infection | 30 samples (6 patients with more than one samples; at least 1 was polymicrobial) Other anaerobic bacteria, n = 24 (Pasteurella spp. n = 10) Only aerobic bacteria, n = 6 |
| Underlying disease | Medical history not always complete, n = 10 No underlying disease, n = 11 Diabetes mellitus, n = 6 Oncologic history, n = 3 Diabetes mellitus and oncologic history, n = 3 Hepatitis infection, n = 2 Recent surgery, n = 1 Cardiac disease, n = 1 Systemic Lupus Erythematosus, n = 1 |
| Hospitalization | Yes, n = 31 (3 patients in ICU wards) No, n = 8 (Range: 2–61 days, average: 16 days) |
| Treatment | Antibiotic and surgical reatment, n= 26 Only antibiotic treatment, n = 7 Only surgical treatment *, n = 2 Treatment not reported, n = 4 |
Abbreviations: F: Female; M: Male. * Information regarding antibiotic therapy after surgical treatment was not reported.
Table 3.
Laboratory features of Bacteroides pyogenes infections reported in the literature, including type of infection, identification method used, antimicrobial susceptibility, and co-pathogens isolated.
Table 3.
Laboratory features of Bacteroides pyogenes infections reported in the literature, including type of infection, identification method used, antimicrobial susceptibility, and co-pathogens isolated.
| Author Year Reference | Type of Sample | Method of Identification | Antibiotic Resistance Phenotype (MIC mg/L) | Co-Isolated Bacteria |
|---|---|---|---|---|
| 2025 Chen [23] | Purulent exudate | 16S rRNA sequencing | NR | Fusobacterium necrophorum; Pasteurella multocida |
| Venous blood | ||||
| 2024 Lee [30] | Lung abscesses | NR | AST not performed because it was expected to be susceptible to metronidazole | Different bacteria for 4 years. In the sample with B. pyogenes: Fusobacterium nucleatum and mixed anaerobes |
| 2024 Sadhwani [17] | Intraoperative sample from abscess | NR | AMC-susceptible | Pasteurella multocida |
| 2023 Vecilla [13] 2023 Vecilla [20] case report regarding #1 2023 Vecilla [19] case report regarding #6 | #1 Pus from masseter muscle abscess | MALDI-TOF mass spectrometry | AMC-, CLI-, IMP-, MEM-, MTZ-, MXF-, TZP-susceptible | No (monomicrobial) |
| #2 Swab from wound | MALDI-TOF mass spectrometry | AMC-, CLI-, IMP-, MEM-, MTZ-, MXF-, TZP-susceptible | No (monomicrobial) | |
| #3 Swab from surgical wound | MALDI-TOF mass spectrometry | AMC-, CLI-, IMP-, MEM-, MTZ-, MXF-, TZP-susceptible | Proteus mirabilis, Gemella morbillorum, Streptococcus mitis, and Corynebacterium amycolatum | |
| #4 Blood culture | MALDI-TOF mass spectrometry | AMC-, CLI-, IMP-, MEM-, MTZ-, MXF-, TZP-susceptible | No (monomicrobial) | |
| #5 Pus from fistula | MALDI-TOF mass spectrometry | AMC-, CLI-, IMP-, MEM-, MTZ-, MXF-, TZP-susceptible | P. mirabilis, Klebsiella oxytoca, and Streptococcus constellatus | |
| #6 Intraoperatively taken tissue | MALDI-TOF mass spectrometry | AMC-, CLI-, IMP-, MEM-, MTZ-, MXF-, TZP-susceptible | Pasteurella multocida | |
| #7 Pus from abscess | MALDI-TOF mass spectrometry | AMC-, CLI-, IMP-, MEM-, MTZ-, MXF-, TZP-susceptible | Pasteurella multocida | |
| #8 Swab from a wound | MALDI-TOF mass spectrometry | AMC-, CLI-, IMP-, MEM-, MTZ-, MXF-, TZP-susceptible | Pseudomonas aeruginosa and Prevotella intermedia | |
| 2021 Takahashi [25] | Intraoperative appendiceal abscess obtained by intra-abdominal drainage | MALDI-TOF mass spectrometry Biochemical test (identified as Prevotella melaninogenica) 16S rRNA sequencing | NR | Escherichia coli; Bacteroides thetaiotaomicron; Peptostreptococcus micros |
| 2021 Shenoy [24] | Intraoperative soft tissue specimens | MALDI-TOF mass spectrometry Biochemical test (identified as Prevotella oralis) 16S rRNA sequencing | CLI-, IPM-, MEM-, MTZ-, PIP-susceptible. Β-lactamase-negative | MRSA; Streptococcus dysgalactiae |
| 2021 Majewska [3] | #1 Pus from an abscess | MALDI-TOF mass spectrometry | AMC-, IPM-, MTZ-susceptible; CLI-, PEN-resistant | Eikenella corrodens, Enterococcus faecalis; Streptococcus pneumoniae |
| #2 Swab from the alveolar jaw | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-susceptible; PEN-resistant | Enterococcus faecalis; Streptococcus parasanguinis | |
| #3 Wound swab | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-susceptible; PEN-resistant | Staphylococcus epidermidis | |
| #4 Intraoperative tissue | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-, PEN-susceptible | Fusobacterium nucleatum; Streptococcus anginosus | |
| #4 Transtracheal aspirate | MALDI-TOF mass spectrometry | No (monomicrobial) | ||
| #5 Intraoperatively taken tissue | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-, PEN-susceptible | Finegoldia magna; Proteus mirabilis | |
| #6 Bile | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-, PEN-susceptible | Clostridium perfringens; Escherichia coli | |
| #7 Pus from an abscess | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-susceptible; PEN-resistant | No (monomicrobial) | |
| #8 Urine (ureteral catheter) | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-, PEN-susceptible | Veilonella atypica | |
| #9 Wound swab | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-, PEN-susceptible | No (monomicrobial) | |
| #9 Wound swab (29 days later) | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-susceptible; PEN-resistant | MRSA; Enterococcus faecalis; Pseudomonas aeruginosa; Alcaligenes faecalis | |
| #10 Wound swab | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-, PEN-susceptible | Fusobacterium nucleatum; Pasteurella multocida | |
| #11 Wound swab | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-susceptible; PEN-resistant | Peptostreptococcus harei; Cutibacterium acnes | |
| #12 Wound swab | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-susceptible; PEN-resistant | Fusobacterium nucleatum; Staphylococcus aureus | |
| #13 Wound swab | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-, PEN-susceptible | Pasteurella canis | |
| 2021 Goggin [18] | Intraoperative samplefrom abscess | Biochemical test (identified as Prevotella oralis) 16S rRNA sequencing | NR | Alcaligenes xylosoxidans spp. xylosoxidans, Gemella species, Granulicatella elegans, Staphylococcus epidermidis, non-hemolytic diphtheroides |
| 2019 Gual-de-Torrella [21] | Four intraoperative specimens (osteoarticular biopsy, wound exudate, joint fluid, synovial tissue) and prosthesis | MALDI-TOF mass spectrometry | AMC-, CLI-, IPM-, MTZ-, PEN-, TZP-susceptible | Peptostreptococcus canis |
| Prosthesis, osteoarticular biopsy, joint fluid (after 10 days of treatment) | MALDI-TOF mass spectrometry (recovered only from the prosthesis culture) | NR | No (monomicrobial) | |
| 2018 Umemura [26] | Pus discharge from abscess | MALDI-TOF mass spectrometry | PEN-, cephem-, and new quinolone-susceptible | No, but minocycline (3 weeks of therapy) might have killed other pathogens before the culture |
| 2016 Park [27] | Blood culture | MALDI-TOF mass spectrometry (identified as Bacteroides pyogenes by Bruker system; identified as Bacteroides uniformis by VITEK MS) Biochemical test for blood culture sample (identified as Prevotella oralis) 16S rRNA sequencing for blood culture sample | NR | No (monomicrobial) |
| Pus from liver abscess | Klebsiella pneumoniae | |||
| 2016 Lau [29] | #1 Wound swab | MALDI-TOF mass spectrometry Biochemical test (performed only on 5 isolates, identified as Prevotella oralis, n = 4; and Prevotella melaninogenica, n = 1) 16S rRNA sequencing | NR | No (monomicrobial) |
| #2 Wound swab | NR | Pasteurella multocida | ||
| #3 Wound swab | NR | No (monomicrobial) | ||
| #4 Wound swab | NR | Pasteurella canis Pasteurella stomatis Staphylococcus pseudointermedius | ||
| #5 NA | AMC 0.094, MTZ 0.50, MXF 0.047, PEN 0.016, TZP 0.064 | Staphylococcus aureus Morganella morganii Atopobium deltae | ||
| #6 Wound swab | NR | Pasteurella dagmatis | ||
| #7 Wound swab | AMC 0.032, MTZ 0.025, MXF 0.047, PEN 0.016, TZP 0.016 | No (monomicrobial) | ||
| 2016 Kim [28] | Blood culture | Biochemical test (identified as Prevotella oralis) 16S rRNA sequencing | CLI > 256, CRO 0.064, MEM 0.016, MTZ 0.5, PEN 0.032, TZP 0.016 | No (monomicrobial) |
| 2011 Madsen [22] | Pus discharge from abscess | Biochemical test (identified as Bacteroides capillosus) 16S rRNA sequencing | CLI, MEM, MTZ, PEN, TZP susceptible | Pasteurella multocida |
| Blood culture | No (monomicrobial) |
Abbreviations: NR: not reported; NA: not available; AMC: amoxicillin–clavulanate; CLI: clindamycin; CRO: ceftriaxone; IPM: imipenem; MEM: meropenem; MRSA: methicillin-resistant Staphylococcus aureus; MTZ: metronidazole; MXF: moxifloxacin; PEN: penicillin; PIP: piperacillin; TZP: piperacillin–tazobactam. Cases with absence of bacterial growth in the aforementioned studies were omitted.
Table 4.
Methods used for Bacteroides pyogenes identification previously reported in the literature.
Table 4.
Methods used for Bacteroides pyogenes identification previously reported in the literature.
| Type of Identification | N. of Test | Results | Instrument |
|---|---|---|---|
| MALDI-TOF mass spectrometry | 33 | Bacteroides pyogenes was misidentified as: Bacteroides uniformis (n = 1, by Vitek MS) In 5 samples, the Vitek MS instrument was not able to identify the pathogen | Bruker (n = 17) Vitek MS (n = 21) Not Reported (n = 1) |
| Biochemical test | 11 | Bacteroides pyogenes was misidentified as: Prevotella oralis (n = 8) Prevotella melaninogenica (n = 2) Bacteroides capillosus (n = 1) | VITEK 2 ANC Card (n = 9) API Rapid ID 32A anaerobe identification system (n = 2) |
| 16S rRNA sequencing | 14 | Bacteroides pyogenes Matching score: 94–100% | Sanger Sequencing (n = 10) Next-Generation Sequencing (n = 2) Not Reported (n = 2) |
Table 5.
Antimicrobial susceptibility testing results of Bacteroides pyogenes infections reported in the literature.
Table 5.
Antimicrobial susceptibility testing results of Bacteroides pyogenes infections reported in the literature.
| Antibiotic | N. of Test Performed | Susceptible N. (%) |
|---|---|---|
| Amoxicillin–clavulanate | 25 | 25 (100%) |
| Clindamycin | 25 | 23 (92%) |
| Imipenem | 23 | 23 (100%) |
| Meropenem | 11 | 11 (100%) |
| Metronidazole | 28 | 28 (100%) |
| Moxifloxacin | 10 | 10 (100%) |
| Penicillin | 19 | 12 (63.2%) |
| Piperacillin–tazobactam | 13 | 13 (100%) |
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Mauri, C.; Giubbi, C.; Consonni, A.; Briozzo, E.; Meroni, E.; Luzzaro, F.; Tonolo, S. The Emergence of Bacteroides pyogenes as a Human Pathogen of Animal Origin: A Narrative Review. Microorganisms 2025, 13, 1200. https://doi.org/10.3390/microorganisms13061200
AMA Style
Mauri C, Giubbi C, Consonni A, Briozzo E, Meroni E, Luzzaro F, Tonolo S. The Emergence of Bacteroides pyogenes as a Human Pathogen of Animal Origin: A Narrative Review. Microorganisms. 2025; 13(6):1200. https://doi.org/10.3390/microorganisms13061200
Chicago/Turabian StyleMauri, Carola, Chiara Giubbi, Alessandra Consonni, Elena Briozzo, Elisa Meroni, Francesco Luzzaro, and Silvia Tonolo. 2025. "The Emergence of Bacteroides pyogenes as a Human Pathogen of Animal Origin: A Narrative Review" Microorganisms 13, no. 6: 1200. https://doi.org/10.3390/microorganisms13061200
APA StyleMauri, C., Giubbi, C., Consonni, A., Briozzo, E., Meroni, E., Luzzaro, F., & Tonolo, S. (2025). The Emergence of Bacteroides pyogenes as a Human Pathogen of Animal Origin: A Narrative Review. Microorganisms, 13(6), 1200. https://doi.org/10.3390/microorganisms13061200
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