Search Results (1,654)

Background: Erysipelothrix rhusiopathiae is an important zoonotic pathogen in poultry, yet little is known about its antimicrobial resistance (AMR) dynamics in avian hosts. With growing concerns about subtherapeutic antimicrobial use in animal agriculture, poultry-origin isolates represent a potential but under-characterized reservoir of resistance genes. Methods: We phenotypically tested 38 E. rhusiopathiae strains isolated from geese, ducks, and turkeys in Hungary (2024) using broth microdilution against 18 antimicrobial agents, following Clinical Laboratory Standards Institute (CLSI) guidelines. Nineteen phenotypically resistant strains were selected for whole-genome sequencing (Illumina platform), followed by de novo hybrid assembly, gene annotation (Prokka, CARD, VFDB), mobile element detection (Mobile Element Finder), and phylogenetic inference (autoMLST). Results: All isolates were susceptible to β-lactams, including penicillin, amoxicillin, and third-generation cephalosporins. Resistance to tetracyclines (up to 10.5%) and florfenicol (5.3%) was most frequently detected. Genomic analysis revealed the presence of tetM (9/19), tetT (2/19), and erm(47) (2/19) genes, all associated with chromosomally integrated mobile elements, ICE Tn6009 and IS ISErh6. Phylogenomic analysis demonstrated tight clustering into four clades, suggesting clonal expansion. Notably, one strain harbored a 64.8 kb genomic island carrying ermC, the first such finding in poultry-derived E. rhusiopathiae. Conclusions: Our data highlights the early emergence of mobile AMR determinants in E. rhusiopathiae from poultry and suggests that horizontal gene transfer may drive resistance even in chromosomally encoded contexts. The genomic stability and phylogenetic homogeneity of avian isolates underscore the need for targeted AMR surveillance in poultry sectors to mitigate potential zoonotic transmission risks. Full article

Background/Objectives: Infections caused by multidrug-resistant methicillin-resistant Staphylococcus pseudintermedius (MRSP) strains are becoming increasingly common in veterinary medicine. Depending on which tet genes are present, MRSP isolates may exhibit resistance to all tetracyclines or resistance to tetracycline and doxycycline with susceptibility to minocycline. As minocycline may be a potential treatment option, our study aimed to verify this hypothesis. We have compared phenotypic resistance to tetracyclines with the presence of the tet(K), tet(L), tet(M), and tet(O) genes and conducted the molecular characterization of 50 clinical MRSP isolates of canine origin. Methods: The presence of the tet genes was determined by PCR. Molecular characterization included multilocus sequence typing (MLST) and staphylococcal cassette chromosome mec (SCCmec) typing. Results: Among the 50 examined clinical MRSP isolates, sequence type ST71 with the SCCmec II–III cassette was predominant (n = 27; 54%). Among these isolates, the tet genes were either absent or present only as the tet(K) gene, resulting in susceptibility to all tetracyclines, tetracycline and doxycycline resistance, and minocycline susceptibility. In contrast, isolates carrying the SCCmec type V cassette (n = 20; 40%) were resistant to all tetracyclines tested and belonged to ST551, ST2851 (new), ST2869 (new) and ST672. These genotypes were most often characterized by the presence of a single tet(M) gene; two genes, tet(M) and tet(K); or three genes, tet(M), tet(K) and tet(O). Notably, 28 out of 50 isolates (56%) showed minocycline susceptibility, and 19 (38%) were minocycline-susceptible and resistant to tetracycline and doxycycline. Conclusions: The obtained results indicate that genotype ST551 and its related ST2851 carry the SCCmec type V and typically contain two or even three tet genes with the tet(M) gene, which confers resistance to all tetracyclines, including minocycline. These genotypes are becoming more common in Poland, and thus, minocycline may be unsuitable for the treatment of MRSP infections in our geographical region. However, in other countries, distinct MRSP genotypes exhibiting minocycline susceptibility may predominate, such as those belonging to clonal complex 71 and carrying the SCCmec type II–III cassette. In the case of such strains, minocycline may be a therapeutic option. Therefore, it is advisable to monitor the spread of MRSP clones carrying different tet genes and exhibiting varying minocycline resistance profiles. Full article

Streptococcus dysgalactiae subsp. equisimilis (SDSE) has historically been recognized as a human pathogen, yet β-hemolytic streptococci consistent with SDSE have been documented in pigs for nearly a century. To investigate the population structure of porcine SDSE and the phylogenetic relationships between swine and human strains, we characterized 41 isolates recovered from diseased pigs in Quebec, Canada (2019–2022). Infected animals spanned all major production stages and frequently presented with invasive disease, including arthritis, endocarditis, and sudden death. Core-genome phylogenetics resolved two heterogeneous porcine clades separated by long internal branches and clearly distinct from dominant human SDSE lineages. Most porcine isolates were emm-negative or contained structurally altered emm regions compared with human strains. Analysis of Lancefield antigen loci identified a predominant group C lineage and a minority group L lineage, recapitulating historical serogroup distributions described since the early-20th century. Phenotypic testing showed susceptibility to β-lactams and florfenicol but high levels of resistance to tetracycline, macrolides and lincosamides. Detected antimicrobial resistance (AMR) genes correlated well with phenotypes, and multidrug resistance was frequent. Hybrid genome assemblies revealed integrative and mobilizable elements carrying AMR determinants. Collectively, our data indicate that porcine SDSE represents a long-standing, genetically structured, host-adapted population with notable AMR potential, underscoring the need for continued swine SDSE genomic surveillance. Full article

Background/Objectives: The widespread use of antibiotics in livestock has raised concerns about commensal gut bacteria, such as lactic acid bacteria (LAB), acting as reservoirs for antimicrobial resistance. This study aimed to characterize the antibiotic resistance profiles of LAB isolated from livestock feces by combining phenotypic susceptibility testing with whole-genome sequencing (WGS) to identify antibiotic resistance genes (ARGs) and their genomic context. Methods: Four LAB strains from farm animal fecal samples were subjected to antibiotic susceptibility testing for 9 antibiotics (ampicillin, gentamicin, kanamycin, clindamycin, chloramphenicol, erythromycin, streptomycin, tetracycline, and vancomycin) using MIC determinations. WGS was performed on each isolate to detect ARGs using curated databases and to determine the chromosomal or plasmid location of these genes. Results: All four isolates exhibited phenotypic resistance to at least one antibiotic class, most frequently to aminoglycosides. However, discrepancies between phenotype and genotype were noted: resistance to aminoglycosides was common despite the absence of known aminoglycoside-resistance genes, suggesting intrinsic, uptake-related mechanisms. In contrast, one strain carried the chromosomal lsa(D) gene but remained susceptible to clindamycin. WGS revealed that all strains harbored the chromosomal van(T) gene, while one isolate carried three additional plasmid-borne ARGs—erm(B), cat(A), and tet(W)—conferring resistance to macrolide–lincosamide–streptogramin antibiotics, chloramphenicol, and tetracycline. Another strain encoded van(Y), lsa(D), and arr on its chromosome. The detection of multiple plasmid-located ARGs in a single LAB isolate highlights their potential for horizontal gene transfer. Conclusions: This study provides a detailed phenotypic and genomic insight into antibiotic resistance in gut-derived LAB from livestock. The findings highlight that commensal LAB can harbor clinically relevant ARGs—sometimes on mobile genetic elements—without always expressing corresponding resistance phenotypes. Such LAB may serve as a hidden reservoir for antibiotic resistance, raising the risk of ARG dissemination through the food chain. These results underscore the importance of vigilant monitoring and genomic screening of LAB, especially those considered for use in foods or feed, to ensure they do not contribute to the spread of antimicrobial resistance. Full article

Aeromonas salmonicida is a major pathogen in aquaculture, and its ability to form biofilms contributes significantly to antibiotic resistance and chronic infections. This study investigated the effects of four antibiotics—ampicillin, amoxicillin, oxytetracycline, and doxycycline—at various concentrations on bacterial growth, biofilm formation, and gene expression related to antibiotic resistance and quorum sensing (QS) in two subspecies: A. salmonicida subsp. masoucida (ASM) and A. salmonicida subsp. salmonicida (ASS). Bacterial isolates from Atlantic salmon were identified using 16S rRNA and vapA gene sequencing. Growth inhibition was more pronounced in ASS than ASM under high antibiotic concentrations. Conversely, sub-inhibitory concentrations (sub-MICs) enhanced biofilm formation in both subspecies, particularly in ASM. PCR results showed that tetA and tetE resistance genes were present only in ASM. qRT-PCR analysis revealed that expression of QS-related genes (ahyI and ahyR) was generally downregulated under tetracycline treatment, while litR expression varied across antibiotic conditions and strains. Some isolates showed increased litR expression alongside elevated biofilm formation, suggesting involvement of additional regulatory mechanisms. These results highlight the potential for sub-MIC antibiotic exposure to promote biofilm development and modulate gene expression, emphasizing the need for careful antibiotic use in aquaculture and providing insight into alternative pathogen control strategies. Full article

Background/Objectives: Helicobacter pylori infection remains a significant health concern, as increasing antimicrobial resistance compromises the efficacy of eradication. Understanding regional antimicrobial resistance profiles is crucial for optimizing eradication strategies. In this study, we aimed to evaluate the antimicrobial susceptibility patterns and identify the factors influencing H. pylori culture success. Methods: In this prospective study, 697 gastric tissue samples were collected from consecutive patients who underwent upper endoscopy between November 2023 and May 2025. Tissue samples obtained by forceps biopsy or recovered from rapid urease test kits were cultured for H. pylori. Antimicrobial susceptibility testing was performed using the agar dilution method; factors associated with successful culture were analyzed using logistic regression. Results: Among 488 patients with H. pylori infection, culture and antimicrobial susceptibility testing were successful in 387 (79.3%). The overall antimicrobial resistance rates were 17.8%, 27.1%, 29.5%, 0.3%, and 32.8% for amoxicillin, clarithromycin, metronidazole, tetracycline, and levofloxacin, respectively. Notably, 27.6% (107/387) of the isolates were resistant to two or more antibiotics. Using multivariate analysis, the use of fresh biopsy tissue (odds ratio [OR]: 1.646, 95% confidence interval [CI]: 1.046–2.591, p = 0.031), transport interval (OR: 0.911, 95% CI: 0.853–0.973, p = 0.005), and presence of prior eradication therapy (OR: 0.318, 95% CI: 0.156–0.648, p = 0.002) were identified as significant predictors of culture success. Conclusions: The high rate of clarithromycin resistance underscores the need for susceptibility-guided eradication strategies in this region. Optimizing sample handling, particularly by minimizing transport time and using fresh biopsy tissue, may improve culture yields. Full article

Equine bacterial abortion presents substantial economic and One Health challenges; however, comprehensive epidemiological data from China are limited. This study sought to ascertain the overall prevalence of key pathogens—namely, Chlamydia spp., Coxiella burnetii, Salmonella abortus equi, and Brucella spp.—in equine populations in northwestern China. In this study, we aimed to further elucidate the characteristics of co-infections, profile antimicrobial resistance genes, and identify associated risk factors. Conducted as a cross-sectional analysis across four provinces, we collected 508 blood samples and 24 abortion tissue samples from 15 farms. Pathogen detection was performed using ELISA and real-time PCR, complemented by a targeted PCR panel screening for 29 AMR genes. The highest prevalence was observed for S. abortus equi (serology: 35.03%; molecular: 23.03%), followed by C. burnetii (28.94%; 15.35%) and Chlamydia spp. (18.90%; 14.17%). No PCR-confirmed cases of Brucella spp. were detected, despite low-level seropositivity. Notably, donkeys and horses aged 5–10 years exhibited higher positivity rates, and co-infections were common, particularly S. abortus equi + C. burnetii (n = 44). Among the 196 PCR-positive samples, extended-spectrum beta-lactamase (ESBL) genes were predominant, with CTX-M (n = 158) and TEM-1 (n = 106) being the most prevalent. Additionally, we identified a high prevalence of genes conferring resistance to fluoroquinolones (qnrA/B), tetracyclines (tetM), macrolides (ermA/B/C), and sulfonamides (sul1), along with sporadic occurrences of carbapenemase genes. This study presents the inaugural comprehensive analysis of pathogen prevalence and associated antimicrobial resistance (AMR) gene carriage in equine abortion cases in northwest China. The findings highlight the imperative for integrated serological and molecular surveillance, revealing a significant discrepancy between empirical therapeutic approaches and the prevalent resistance genotypes. Consequently, this research lays the groundwork for evidence-based biosecurity measures and antimicrobial stewardship within a One Health framework. Full article

Escherichia coli (E. coli) is a ubiquitous opportunistic pathogen in nature and serves as an important reservoir for antibiotic resistance genes. The tet(X4) gene is a key determinant mediating tigecycline resistance. Although its core resistance mechanism, encoding a flavin-dependent monooxygenase, has been elucidated, the broader impact of the tet(X4) gene on the secondary regulatory networks of E. coli remains not fully understood. In recent years, multiple studies have indicated that the tet(X4) gene participates in pathways contributing to resistance to other antibiotics by regulating the expression of various genes. In this study, E. coli tet(X4) gene deletion and complementation strains were constructed to investigate the mechanisms by which the tet(X4) gene influences the growth characteristics and antibiotic resistance of E. coli. The minimum inhibitory concentrations (MICs) of 24 different antibiotics, as well as the degradation capacities of tetracycline and tigecycline, were determined for the wild-type, deletion, and complementation strains. In addition, a four-week starvation stress experiment was performed under both the presence and absence of sub-inhibitory concentrations of tigecycline, during which the bacterial growth curves, survival rates, and MIC variations were analyzed. Transcriptomic sequencing of the wild-type, deletion, and complementation strains identified 531 differentially expressed genes associated with ABC transporter activity, drug metabolism, and bacterial two-component systems. These findings provide reliable evidence for elucidating the mechanism by which the tet(X4) gene affects E. coli resistance, offering valuable insights into the prevention and control of tigecycline-resistant E. coli infections. Full article

Escherichia coli sequence type 648 (ST648), a lineage within the clinically important phylogroup F, has disseminated worldwide in humans and animals. In this study, we performed whole-genome sequencing and comparative genomic analysis for two New Delhi metallo-beta-lactamase (bla_NDM-5) carrying E. coli strains: ECsOL198, recovered from a wild Eurasian otter in Northern Lebanon, and ECOL247, isolated from a hospitalized leukemia patient. Both isolates belonged to phylogroup F and serotype O9:H4, and exhibited IncFIA, IncFIB, and IncFII plasmids. They shared a similar antimicrobial resistance profile, including a carbapenemase gene (bla_NDM-5), β-lactamase genes (bla_TEM-1, bla_CTX-M-15, and bla_OXA-1), and other genes that confer resistance to aminoglycosides (acc(3)-Ile, aadA2), sulfonamides (sul1), tetracyclines (tet(A)), and fluoroquinolones (mutations in gyrA and parC). Both isolates also carried common virulence-associated genes related to adhesion, iron acquisition, environmental persistence, and immune evasion. Whole-genome multilocus sequence typing (wgMLST) revealed that both isolates formed a distinct subclade closely related to a bloodstream-derived ST648 isolate from India, indicating limited relatedness to global clones. These findings highlight the transmission of nearly clonal multidrug-resistant E. coli ST648 in both clinical and non-clinical settings, raising concerns about the threat to public health. Full article

Antimicrobial resistance (AMR) among commensal Escherichia coli from poultry is a growing concern for food safety and public health. This study investigated AMR patterns in E. coli isolated from broiler neck skin at slaughter, comparing organic, antibiotic-free (ATB-free), and conventional production systems. A total of 375 samples were collected from two Italian slaughterhouses and tested by broth microdilution following EU protocols. E. coli was recovered from 358 samples, and 37.9% were presumptively positive for ESBL/AmpC-producing strains. Conventional broilers showed the highest resistance to ampicillin (73.8%), sulfonamides (72.5%), and fluoroquinolones (nalidixic acid, 62.5%; ciprofloxacin, 67.5%), while organic and ATB-free systems showed significantly lower levels. Intermediate resistance occurred for trimethoprim (21.4–47.9%) and tetracycline (36–54%), and low prevalence (<10%) was found for gentamicin, tigecycline, and third-generation cephalosporins. No relevant resistance was detected to colistin or carbapenems (≤1.2%). Total E. coli counts did not differ among systems, suggesting differences in resistant strain proportions rather than bacterial load. ATB-free flocks processed after conventional batches displayed higher resistance, indicating possible cross-contamination during slaughter. These results highlight the influence of farming practices and slaughterhouse hygiene on AMR dissemination, underscoring the need for integrated farm-to-slaughter control strategies. Full article

Background/Objective: Sewage sludge (biosolids) is increasingly reused as a fertilizer to recycle nutrients and close material cycles; however, concerns persist regarding antibiotics and antimicrobial resistance. This study evaluated the agronomic safety and microbiological integrity of biosolid fertilization in soybean and maize systems, with particular attention to grain quality and food safety. Methods: Soybean and maize were cultivated in greenhouse microcosms under biosolid or mineral fertilization. Soil, roots, shoots, and grains were analyzed for antibiotic residues using LC–MS/MS and antibiotic-resistant bacteria (ARB) using culture-based assays. Minimum inhibitory concentrations for isolates from grains were compared with clinical breakpoints to verify phenotypic susceptibility. Multivariate analyses (PCA) integrating real-time antibiotic concentrations and updated resistance indicators were performed using centered and scaled data. Results: Fluoroquinolones were the predominant residues introduced by biosolids and exhibited consistent time-dependent declines across all treatments, although low concentrations remained detectable at 90 d in several soil–fertilizer–crop combinations. Tetracyclines, macrolides, and sulfonamides showed similar decreasing trends, with planted soils displaying faster dissipation than bulk control soils. Biosolid fertilization increased shoot biomass by 1.5–2.3-fold and nitrogen, phosphorus, and potassium uptake by 30–60% without impairing soybean nodulation or nitrogenase function. ARB was observed in all soils, including mineral and plant-free controls, indicating a natural background resistome. Ciprofloxacin-resistant isolates were detected in one simple sampling point, and MDR proportions were transient (67%), returning to their background levels by 45–90 days. PCA showed that crop presence, not fertilizer type, was the primary driver of microbial ordination, and that antibiotic concentrations and resistance indicators were only weakly aligned, indicating a limited selective pressure. No antibiotic residues or phenotypically resistant bacteria were detected in the soybean or maize grains. Conclusions: Updated residue, resistance, and multivariate data confirmed that biosolids did not induce, amplify, or transfer antibiotic resistance and maintained complete grain safety. Properly treated biosolids function as safe, agronomically beneficial fertilizers aligned with One Health goals, enhancing crop productivity without compromising food quality or increasing antimicrobial resistance. Full article

Background: Antimicrobial resistance (AMR) is a growing public health concern affecting both medicine and food safety. While Listeria monocytogenes is the primary pathogen of concern, Listeria innocua—commonly found in food and food-processing environments—may serve as a reservoir for resistance genes and a useful indicator of species for surveillance. This study aimed to assess the phenotypic antibiotic susceptibility and detect resistance-associated genes in L. innocua isolates from meat products and processing environments in Poland. Methods: A total of 51 L. innocua isolates were analyzed, originating from raw and processed meat products as well as meat-processing environments. Antimicrobial susceptibility was determined using the disc diffusion method against 18 antibiotics representing multiple classes. Phenotypic resistance was interpreted following CLSI guidelines (CLSI, 2020). Isolates exhibiting resistance or intermediate resistance were further screened for resistance-associated genes using PCR. Results: All isolates were fully susceptible to ampicillin, benzylpenicillin, chloramphenicol, gentamicin, rifampin, trimethoprim-sulfamethoxazole, and vancomycin. High susceptibility was observed for ciprofloxacin, erythromycin, meropenem, trimethoprim, and nitrofurantoin, with only sporadic intermediate responses. Moderate resistance levels were noted for streptomycin (10%) and tetracycline (12%). The lowest susceptibility was recorded for clindamycin and linezolid, with most isolates exhibiting intermediate or resistant phenotypes. Universal resistance to cefotaxime and oxacillin was found. Eighteen distinct resistance patterns were identified. PCR confirmed the presence of several resistance-associated genes, including mecA, lnuA, lnuB, cfr, optrA, and poxtA, consistent with observed phenotypes. Conclusions: This study provides the first detailed characterization of AMR in L. innocua from Polish meat and processing environments. The findings highlight its heterogeneous resistance profiles and potential role as a reservoir of clinically relevant resistance genes. Incorporating L. innocua into surveillance programs may strengthen early detection of emerging resistance and enhance food safety monitoring. Full article

Staphylococcus aureus is a common foodborne pathogen, posing significant concern due to the emergence of its multidrug-resistant (MDR) strains. The aim of this study was to assess the antibiotic resistance profiles in S. aureus isolated from raw poultry, the associated resistance genes, and their ability to form biofilms. S. aureus was isolated and identified using conventional microbiological methods. Antimicrobial susceptibility profiles were assessed using the disk diffusion method, and biofilm-forming ability was evaluated using the microtiter plate assay. The presence of antimicrobial resistance genes was determined by PCR. A total of 45 isolates were isolated. High resistance rates were observed against penicillin (88.9%), tetracycline (86.7%) and doxycycline (66.7%). Of the isolates, 71.1% were classified as multidrug-resistant (MDR) organisms, and 60% exhibited a multiple antibiotic resistance index greater than 0.2. PCR analysis revealed the presence of the resistance genes blaZ (86.7%), mecA (27.3%), tet(M) (46.2%), tet(K) (35.9%), tet(S) (59%), erm(B) (51.9%), and erm(C) (59.3%). A total of 44 isolates were biofilm producers: 46.7% were weak producers, 46.7% were moderate producers, and 4.4% were strong producers. These findings highlight a significant public health concern, emphasizing the need for stringent hygiene practices and continuous monitoring to limit the spread of resistant pathogens through the food chain. Full article

Introduction: Streptococcus suis is a zoonotic pathogen of great relevance to the swine industry, characterized by high genetic diversity and multiple serovars (SVs) with varying clinical prevalence. Biofilm formation represents a key factor in its virulence, antimicrobial resistance and infection persistence. Methods: We integrated gene expression profiling of biofilm-associated genes by RT-qPCR and antimicrobial susceptibility in planktonic and mature biofilm against five antibiotics in S. suis field isolates belonging to SV1, SV2, SV7 and SV9. Results: Expression of quorum sensing and adhesion genes (luxS, fbps, sadP and srtA) was significantly higher in SV2, the poorest biofilm formers, and inversely correlated with biofilm biomass, suggesting these factors act during early biofilm establishment. Correlation analysis indicated coordinated regulation among genes involved in quorum sensing, adhesion and capsule synthesis. Antimicrobial susceptibility testing revealed a high frequency of non-wild type phenotypes in planktonic cells for tetracycline, erythromycin and clindamycin (>80%), while ampicillin and ciprofloxacin were less frequent. Mature biofilms exhibited a significant increase in antimicrobial tolerance for all antibiotics tested, with SV2 showing the greatest susceptibility. Conclusions: These data highlight serovar-specific biofilm regulation patterns and enhanced drug tolerance in established S. suis biofilms. Full article

Bovine mastitis is a prevalent infectious disease in dairy cattle, causing inflammation, pain, reduced milk yield, and economic losses. Antibiotic therapy is the mainstay of treatment, yet irresponsible use can lead to the presence of antibiotic residues in milk and contribute to the emergence of antimicrobial resistance (AMR), posing significant risks to public health and food safety. This review aims to provide a comprehensive synthesis of current knowledge on mastitis management, antibiotic use and resulting residues in milk, their public health and environmental impacts, and alternative strategies to reduce antibiotic dependence, framed within a One Health–One Welfare perspective. Antibiotic residues in milk are closely linked to treatment practices, withdrawal period compliance, and regulatory oversight, with prevalence ranging from <1% in some European countries to over 80% in parts of Africa. Residues, particularly from β-lactams, tetracyclines, and quinolones, can disrupt human intestinal microbiota, promote resistant bacterial strains, trigger immunological reactions, and interfere with dairy processing. Environmental contamination through excreted antibiotics further facilitates the spread of resistance. Sustainable alternatives, including probiotics, phytotherapy, vaccines, and improved farm biosecurity, show promise in reducing antibiotic use while maintaining animal welfare and productivity. Antibiotic therapy remains essential for mastitis control, but its consequences on milk safety, public health, and AMR require prudent management. Integrating monitoring, adherence to withdrawal periods, and sustainable alternatives within a One Health–One Welfare framework is critical for ensuring safe, responsible, and environmentally sustainable dairy production. Full article