Search Results (281)

Introduction: Borderline oxacillin-resistant Staphylococcus aureus (BORSA) represents a rare and poorly characterized phenotype of S. aureus. Its detection remains challenging, even in modern clinical laboratories. Moreover, there is no consensus on the optimal therapeutic approach, and treatment strategies remain controversial. In this report, we present a rare case of BORSA bacteremia and discuss potential approaches to improve its detection and management. Case presentation: A 39-year-old woman with systemic lupus erythematosus was admitted for a suspected exacerbation, complicated by multiple serositis and nephritis. She was on chronic treatment with methylprednisolone and hydroxychloroquine. On admission, she was afebrile. Laboratory investigations revealed elevated C-reactive protein and increased D-dimer levels. Later, she developed a septic peripheral venous thrombophlebitis, and treatment was adjusted to amoxicillin–clavulanate. Blood cultures grew S. aureus, prompting a switch to intravenous oxacillin based on a negative penicillin-binding protein 2a test. A discrepancy in the antimicrobial susceptibility test was observed, with cefoxitin showing susceptibility and oxacillin resistance. Further characterizations were carried out, confirming a BORSA infection. Treatment was switched to linezolid and ciprofloxacin with good recovery. Conclusions: This case highlights the complexity of managing a patient with an uncommon and poorly documented infection. The lack of data on BORSA infections and the difficulties in detecting and treating them led to a prolonged delay in the appropriate management of this patient. Full article

Enterococcus spp. are opportunistic and nosocomial pathogens. Intensive pig farms have been recently described as important hotspots for antibiotic resistance and reservoirs of potentially pathogenic enterococci, including other species than the most known E. faecalis and E. faecium. Here, we identified Linezolid-resistant non-E. faecalis and E. faecium (NFF) Enterococcus strains isolated from different production stages (suckling piglets, weaning pigs, and fatteners) across six intensive pig farms. The transferability of the linezolid-resistance determinants was assessed by bacterial conjugation and strains were also characterized for biofilm production, hemolytic and gelatinase activity. Among 64 identified NFF Enterococcus strains, 27 were resistant to at least three different antibiotic classes and 8/27 specifically to Linezolid. E. gallinarum and E. casseliflavus both transferred their Linezolid resistance determinants to the main pathogenic species E. faecium. Remarkably, this is the first report of the optrA gene transfer from E. casseliflavus to E. faecium by conjugation, which can greatly contribute to the spread of antibiotic resistance genes among pathogenic enterococcal species. The “weaning pigs” stage exhibited a significantly higher number of antibiotic-resistant enterococci than the “fatteners”. These findings highlight the importance of monitoring pig farms as hotspots for the spread of antibiotic-resistant enterococci, especially in the early stages of production. Furthermore, they underscore the significant role of NFF Enterococcus species as carriers of antibiotic resistance genes, even to last-resort antibiotics, which may be transferable to the major enterococcal species. Full article

Background: Broad-spectrum antibiotics are often used for suspected infections in patients with hematologic malignancies due to the risk of severe infections. Although antibiotic use can lead to antimicrobial resistance and microbiome dysbiosis, the effects of antibiotics on the microbiome and resistome in patients with acute myeloid leukemia (AML) undergoing remission induction chemotherapy (RIC) are not well understood. Methods: Various statistical models were utilized to examine the effects of antibiotic administration on the microbiome and resistome over time, as well as differences in AR-infection (ARI) and colonization (ARC) by important CDC-threats in 119 AML patients. Results: A greater number of unique antibiotic classes administered correlated with a loss of unique antibiotic resistance genes (ARGs) (R = −0.39, p = 0.008). Specifically, although a greater number of oxazolidinone administrations was correlated with a greater loss of diversity (R = −0.58, p < 0.001), each additional day of linezolid reduced the risk of ARC by ~30% (HR: 0.663, p = 0.047) and decreased the odds of acquiring genes predicted to confer macrolide (HR: 0.50, p = 0.026) resistance. Conclusions: The number of antibiotic administrations and the types of antibiotics used can influence the risk of antibiotic resistance gene (ARG) expansion and ARC events in AML patients undergoing RIC. While certain antibiotics may reduce microbial diversity, they are not always linked to an increase in ARGs or ARC events. Full article

Background/Objectives: Methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP) represent important antimicrobial resistance threats related to companion animals, which can directly or indirectly lead to adverse health effects in humans and animals living in close contact. Characterizing the phenotypic resistance of MRSA and MRSP to a panel of antimicrobials relevant to both veterinary and human medicine is crucial within a “One Health” framework. Methods: In this study, a total of 79 presumptive MRSA isolates (34 from cats, 45 from dogs) and 110 presumptive MRSP isolates (105 from dogs, 5 from cats) from clinical cases were analysed. Real-time PCR was used to detect the presence of mecA and mecC genes, and susceptibility testing was performed using the Sensititre EUST2 panel. Results: Most of the isolates (88.9%, 168/189) were positive for the mecA gene, while a minority (1.1%, 2/189) were mecC-positive (2 MRSA, 1 dog, 1 cat). MRSP isolates exhibited acquired resistance to a broader range of antibiotics compared to MRSA strains. Furthermore, several isolates demonstrated acquired resistance to antibiotics considered critically important for human medicine. Resistance to vancomycin was found in an MRSP isolate from a dog, and resistance to linezolid in an MRSP isolate from a cat. This study reveals that 83.3% (30/36) of MRSA isolates from dogs and 89.3% (25/28) from cats were multidrug-resistant organisms, while MRSP isolates exhibited multidrug resistance in 99% (101/102) of cases for dogs and 100% (4/4) for cats. Conclusions: The extremely high level of multidrug resistance, with some isolates resistant to critically important antibiotics used in human medicine, highlight the importance of monitoring antimicrobial susceptibility in MRSA and MRSP isolates collected from cats and dogs in a One Health perspective. Full article

The antimicrobial resistance (AMR) surveillance network has been monitoring bloodstream bacterial pathogens and their resistance since 1999 in Tunisia. We report the long-term trends in the distribution of bloodstream bacterial pathogens and their resistance patterns from this surveillance database. We analyzed antibiotic resistance rates in 11 tertiary teaching hospital laboratories under the AMR surveillance network during 2011–2023, focusing on six priority bacterial pathogens, using the Cochrane–Armitage test for trend analysis. Of 22,795 isolates, K. pneumoniae (38.5%) was the most common, followed by S. aureus (20.4%), E. coli (13.6%), and A. baumannii (10.3%). Carbapenem resistance was highest in A. baumannii (77%), followed by Pseudomonas aeruginosa (29.3%), K. pneumoniae (19.4%), and Enterobacter cloacae (6.8%). Carbapenem-resistant Enterobacterales and third-generation cephalosporin-resistant Enterobacterales (3GCREB) increased from 10.6% to 26.3% (p-value < 0.001), and from 39% to 50.2%, respectively, during 2011–2023 (p-value < 0.001). Vancomycin resistance (38.3%) and the emergence of linezolid resistance in 2019 (2.4%) were reported in E. faecium isolates. Resistance to carbapenems and 3GC is a major challenge to controlling BSI in Tunisia. The national AMR surveillance network helps monitor annual patterns and guides empirical therapy. An integrated database combining clinical profiles and resistance data via real-time data-sharing platforms could improve clinical decision-making. Full article

Objectives: Linezolid resistance among Enterococcus species poses a growing clinical and public health concern, especially due to the dissemination of transferable resistance genes, such as optrA. This study aimed to evaluate the prevalence of linezolid resistance and to characterize the molecular epidemiology and genetic contexts of optrA-positive linezolid-resistant Enterococcus (LRE) isolates from clinical and animal sources in South Korea. Methods: A total of 2156 Enterococcus isolates, collected through nationwide surveillance from hospitalized patients and healthy livestock (pigs, cattle, and chickens) between 2017 and 2019, were retrospectively analyzed. Phenotypic susceptibility testing, optrA gene screening, and whole-genome sequencing were performed to investigate genetic environments and phylogenetic relationships. Results: The prevalence of linezolid resistance was 0.2% in clinical isolates, 3.3% in pigs, 4.3% in cattle, and 1.4% in chickens. optrA-positive linezolid-resistant isolates were less frequent, with rates of 0.1%, 1.4%, 0.9%, and 1.0%, respectively. Multilocus sequence typing identified sequence types (STs) 330 and ST476 in E. faecalis from humans, with no shared STs between human and livestock isolates. The optrA gene was located either chromosomally, frequently associated with transposon Tn6674, or on multidrug resistance plasmids. Notably, optrA variants exhibited host-specific distribution patterns. Phylogenetic analysis demonstrated considerable genomic diversity, and Korean ST476 isolates were genetically related to international strains reported from livestock, poultry products, and wild birds, suggesting potential global dissemination. Conclusions: This study provides a comprehensive, nationally representative assessment of linezolid resistance in South Korea. The findings highlight the zoonotic potential and possible international dissemination of optrA-carrying ST476 lineages, underscoring the need for integrated One Health surveillance to monitor and control the spread of transferable resistance genes. Full article

The emergence of antimicrobial resistance (AMR) in Clostridium difficile (C. difficile), particularly to last-line antibiotics such as linezolid, represents a critical challenge in clinical settings. This study investigates the genomic epidemiology of linezolid-resistant C. difficile, focusing on the distribution and mutational patterns of the chloramphenicol–florfenicol resistance (cfr) gene and its association with multidrug resistance. We analyzed 514 clinical isolates (354 from NCBI Pathogen Detection, 160 from EnteroBase), revealing distinct prevalence patterns among cfr subtypes: cfr(C) was dominant (156/354 NCBI strains; 101/160 EnteroBase strains), whereas cfr(B) frequently harbored missense mutations (p.R247K, p.V294I, and less commonly p.A334T). The cfr(E) subtype was exclusively identified in ribotype 027 (RT027) strains. Notably, cfr(C) exhibited a strong association with RT017, correlating with a conserved 99 bp genomic deletion. Phylogenetic analysis linked cfr-carriage to predominant sequence types (ST1 in NCBI strains, ST37 in EnteroBase isolates). Furthermore, the co-occurrence of cfr with additional AMR genes conferred resistance to macrolides (erythromycin, azithromycin) and tetracyclines, indicating a convergent evolution toward multidrug resistance. These findings underscore the interplay between cfr mutations, hypervirulent ribotypes, and AMR dissemination, necessitating enhanced surveillance to mitigate the spread of resistant C. difficile lineages. Full article

(1) Background: Spontaneous bacterial peritonitis (SBP) is associated with a 20% mortality and is mainly caused by Gram-negative bacteria (GNB); Gram-positive bacteria (GPB) were predominant in some areas; and increased antibiotic resistance was recorded. (2) Methods: A retrospective study was performed between 2018 and 2024. The type of isolated strains, antibiotic susceptibility, and mortality (in-hospital; 30-day; 90-day; and 1-year) were estimated; multivariate analyses evaluated predictive factors for in-hospital mortality risk. (3) Results: 45 culture-positive SBP, 28 culture-negative SBP, 6 bacterascites, and 670 control ascites were diagnosed; GPB represented 60%; two Candida peritonitis and 11 polymicrobial peritonitis (21.6%) were noted (without surgery; peritoneal dialysis; or tegumentary lesion). High resistance rates to cephalosporins and quinolones, and high carbapenem resistance for nosocomial GNB were recorded. A low resistance rate to Tigecycline was noted in all infection types; GPB was susceptible to Linezolid and Vancomycin; and GNB was susceptible to Aztreonam and Colistin. In-hospital mortality was 26.7% (40% for GNB-SBP; 20% for GPB-SBP), similar to culture-negative SBP (21.3%), and higher than in the control group (9%); long-term mortality remained higher. (4) Conclusions: microbial changes to GPB etiology and increasing resistance were noted, but with a lower mortality compared to GNB; higher mortality rates up to 1 year for culture-positive and culture-negative SBP were recorded Full article

This study examines temporal patterns in pathogens isolated from prosthetic joint infection (PJI) cases and antimicrobial resistance patterns at a Romanian orthopedic center. We have conducted a retrospective cohort study that included 674 patients undergoing hip or knee replacement revision surgery between January 2016 and December 2023. From these, 102 confirmed PJI cases requiring surgical intervention were selected for analysis. We isolated 27 microorganisms from acute PJI cultures and 82 from chronic PJIs. Staphylococcus epidermidis (33 cases, 30.3%; 95% CI 22.0–40.3) was the predominant pathogen, with coagulase-negative Staphylococci (22 cases, 20.18%; 95% CI 0.9–41.3) and Enterobacteriaceae (13 cases, 11.9%; 95% CI 6.4–18.3) also prevalent. Methicillin resistance was identified in 43.6% of coagulase-negative staphylococci and 45.5% of Staphylococcus aureus isolates. All Gram-positive isolates remained susceptible to vancomycin, linezolid, and tigecycline. Among Gram-negative bacilli, Klebsiella oxytoca and Proteus mirabilis showed resistance to third-generation cephalosporins, with phenotypic profiles suggestive of extended-spectrum β-lactamase (ESBL) production. All Escherichia coli, Enterobacter spp., and Citrobacter freundii strains were fully susceptible to tested agents, while Pseudomonas aeruginosa exhibited reduced susceptibility to ciprofloxacin, aztreonam, and imipenem. Among the isolated strains, 47 were multidrug-resistant (MDR), with Staphylococcus aureus accounting for the highest MDR count, including methicillin resistance. The distribution of microorganism types and MDR strains remained consistent throughout the study period, with no significant association between infection type and MDR strain presence or between infection site and microorganism presence except for a strong association between MDR strains and the type of microorganism (p < 0.05). The microbial profile and resistance patterns in PJIs have remained stable over eight years. Our observations do not suggest that MDR PJIs are more commonly acute cases, contrary to what has been highlighted in previous reports. The ongoing prevalence of MDR strains underscores the importance of targeted antimicrobial treatments based on local susceptibility profiles. Full article

Vancomycin-resistant Enterococcus faecium represents an emerging threat in healthcare settings. The aim of this study was to investigate biomolecular characteristics of 31 E. faecium isolates from patients in two hospitals of Molise region, central Italy. Particularly, antimicrobial resistance profiles and prevalence of resistance and virulence genes were analyzed, as well as the clonal relationships and sequence types (STs). Antimicrobial susceptibility and genes associated with resistance and virulence were evaluated using automated system and PCR assays, respectively. SmaI-based pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing were performed following standardized protocols. All strains exhibited resistance to vancomycin and teicoplanin, and high rates were detected for other antibiotics, except for linezolid. PFGE identified 18 clusters and 26 pulsotypes (Simpson’s index, 0.98). ST80, ST1478, and ST2164 were identified, with ST80 as the most frequent (77.4%). The resistance genes vanA, aac(6′)-Ie-aph(2″)-Ia, aph(3′)-IIIa, and ermB were detected in 90.3%, 93.6%, 93.6%, and 90.3% of the strains, respectively, while the esp gene was prevalent (61.3%) amongst virulence genes. The study findings highlight the predominance of multidrug-resistant clones and virulence determinants among E. faecium strains circulating in the regional hospitals, reinforcing the urgency of implementing targeted molecular surveillance and robust antimicrobial stewardship strategies to contain their spread. Full article

This study aimed to evaluate the virulence of 36 clinical isolates estimated as blood culture contaminants (BCCs). MALDI-TOF MS classified all isolates as coagulase-negative staphylococci (CoNS) with the highest percentage of S. epidermidis (77.78%). All tested strains formed biofilms with greater ability at room temperature than 37 °C. CoNS were sensitive to vancomycin (0% resistance) and had relatively low resistance to linezolid and rifampicin (8.33 and 22.22% resistance). The highest resistance was observed for penicillin (94.44%). Moreover, we observed the transfer of antibiotic resistance genes from the tested CoNS to S. aureus and even to E. coli, although with lower efficiency. CoNS in planktonic form were completely combated by antiseptics after 10 and 60 s exposition, and activity against biofilms was time-dependent. The complete elimination of biofilms was observed after a 180 s exposure to Kodan and CITROclorex, and this exposure to Rivanol and Octenidyne showed still viable cells (>0.9 log CFU/mL). Our findings showed that a careful selection of antiseptics and extending the exposure time before blood collection can reduce the occurrence of blood culture contamination. However, our most important finding is the indication that CoNS naturally occurring on human skin and mucous membranes exhibit antibiotic resistance, and what is more, determinants of antibiotic resistance are transferred to both closely related Gram-positive bacteria and phylogenetically distant Gram-negative bacteria. Thus, our findings shed new light on CoNS—they indicate the necessity of their control due to the effective transfer of mobile genetic elements harboring antibiotic resistance genes, which may contribute to the spread of resistance genes and deepening the antibiotic crisis. Full article

Methicillin-resistant Staphylococcus aureus (MRSA) is a devastating global health concern. Hypervirulent strains are on the rise, causing morbidities and mortalities worldwide. In tertiary care hospitals, critically ill patients, those undergoing invasive procedures, and pediatric and geriatric patients are at risk. It is not fully clear how strains adapt and specialize in humans and emerge despite the well-established commonality of the S. aureus genome from humans and animals. This study investigates the influence of age-, gender-, and source-specific profiles (clinical, intensive care unit (ICU vs. non-ICU)) on the evolution of hospital-associated (HA)-MRSA versus community-associated (CA)-MRSA lineages. A total of 253 non-duplicate S. aureus isolates were obtained from May 2023 to March 2025. The patients were stratified by age and gender in ICUs and non-ICUs. Standard microbiology methods and Clinical and Laboratory Standards Institute (CLSI) guidelines were used for identification and susceptibility testing, with cefoxitin and oxacillin disk diffusions and molecular diagnosis confirming MRSA. Mann–Whitney U and Chi-square tests assessed the demographic distributions, clinical specimen sources, and MRSA/methicillin-sensitive S. aureus (MSSA) prevalence. Of 253, 41.9% originated from ICUs (71% male; 29% female) and 58.1% from non-ICU wards (64% male; 36% female). In both settings, MRSA colonized the two extremes of age (10–29 and 70+) for males and females, with different mid-life peaks or declines by gender. However, the overall demographic distribution did not differ significantly between the ICU and non-ICU groups (p = 0.287). Respiratory specimens constituted 37% and had the highest MRSA rate (42%), followed by blood (24.5%) and wounds (10.3%). In contrast, MSSA dominated wounds (20.3%). Overall, 73.9% were resistant to cefoxitin and cefotaxime, whereas vancomycin, linezolid, daptomycin, and tigecycline remained highly effective. Younger non-ICU patients (10–29) had higher MSSA, whereas older ICU ones showed pronounced HA-MRSA profiles. By the virtue of methicillin resistance, all MRSA were classified as multidrug resistance. Thus, MRSA colonization of the two extremes of life mostly in ICU seniors and the dominance of invasive MSSA and CA-MRSA patterns in non-ICU youth imply early age- and gender-specific adaptations of the three lineages. MRSA colonizes both ICU and non-ICU populations at extremes of age and gender specifically. High β-lactam resistance underscores the importance of robust stewardship and age- and gender-specific targeting in screening. These findings also indicate host- and organ-specificity in the sequalae of MSSA, CA-MRSA, and HA-MRSA evolutionary dynamics, emphasizing the need for continued surveillance to mitigate MRSA transmission and optimize patient outcomes in tertiary care settings. Full article

Background: Animal-associated antimicrobial-resistant staphylococci pose a One Health concern, as they can spread into the environment and cause serious infections. Yet, donkeys in Nigeria have been largely overlooked as potential reservoirs of these pathogens. Aim/Objectives: To isolate Staphylococcus aureus from donkeys in Obollo-Afor, southeast Nigeria, assess their antimicrobial resistance profiles, and evaluate their virulence potential. Materials and Methods: Staphylococci were isolated from the nasal swabs of 250 donkeys, using mannitol salt agar, confirmed biochemically, with Staphylococcus aureus identified via a latex agglutination test and mass spectrometry. The resistance profiles of the isolates, including in regard to methicillin, inducible clindamycin, and β-lactamase production, were determined using disc diffusion, while vancomycin resistance was assessed through the use of agar dilution. The virulence factors were evaluated phenotypically. Results: Of the 250 samples, 11 (4.4%) contained S. aureus and 239 (95.6%) grew other Staphylococcus species. The resistance rates of the 11 S. aureus isolates to gentamicin, penicillin, tigecycline, cefoxitin, linezolid, and chloramphenicol were 45.5%, 66.7%, 54.5%, 27.3%, 36.4%, and 18.1%, respectively. The phenotypic methicillin-resistant S. aureus prevalence was 1.2%. Additionally, 23.5% of the S. aureus isolates were multidrug resistant, with a mean antibiotic resistance index of 0.25. All the S. aureus isolates exhibited virulence factors like clumping factor expression, catalase, caseinase, lecithinase, and gelatinase activity, while the occurrence of haemagglutinin, biofilm, pellicle, and hemolysin occurred in 27.3%, 54.5%, 36.4%, 72.2%, respectively. Conclusion: Although a small percentage of donkeys in Nigeria may harbor S. aureus, these animals are potentially spreading antimicrobial resistance, including multidrug and methicillin resistance, to humans and the environment. Full article

The emergence of multidrug-resistant and extensively drug-resistant Mycobacterium tuberculosis strains poses serious challenges to global tuberculosis control, highlighting the urgent need to elucidate the mechanisms underlying multidrug resistance. In this study, we screened for spontaneous bortezomib (BTZ)-resistant Mycobacterium smegmatis (Msm) mutants and identified a strain, Msm-R1-2, exhibiting 16- and 64-fold increases in minimum inhibitory concentrations (MICs) to BTZ and linezolid (LZD), respectively, compared to the parental strain. Whole-genome sequencing revealed resistance-associated mutations in two functionally distinct genes: MSMEG_1380, encoding a transcriptional regulator involved in efflux pump expression, and MSMEG_0965, encoding a porin protein. CRISPR-Cpf1-assisted gene knockout and editing experiments confirmed that single mutations in either MSMEG_1380 or MSMEG_0965 caused low-level resistance (4-fold MIC increase) to BTZ and LZD, while dual mutations conferred resistance levels comparable to Msm-R1-2, with 16- and 64-fold increases in MICs for BTZ and LZD, respectively. An ethidium bromide accumulation assay demonstrated that mutations in MSMEG_0965 reduce cell wall permeability, contributing to multidrug resistance. Furthermore, quantitative real-time PCR showed that mutations in MSMEG_1380 upregulate the mmpS5-mmpL5 efflux system. Together, these dual mechanisms function synergistically: restricted drug entry combined with enhanced drug efflux confers robust multidrug resistance. These findings provide novel insights into the evolutionary mechanisms of resistance in mycobacteria. Full article

Enterococcus species are used as One Health indicators of antimicrobial resistance (AMR) in humans, animals, and the environment. A surveillance study in beef cows and calves isolated Enterococcus casseliflavus along with E. faecium, E. faecalis, and E. hirae. Given the high prevalence of E. casseliflavus, we elected to characterize this species to better understand its role in the antimicrobial resistance of enterococci in cows and calves. Almost 12% of E. casseliflavus isolates exhibited multidrug resistance with the majority being resistant to lincomycin (99%), followed by quinupristin–dalfopristin (34%), ciprofloxacin (9.6%), tylosin (4.5%), erythromycin (2.7%), tetracycline (1.8%), tigecycline (1.5%), daptomycin (0.6%), streptomycin (0.3%), and kanamycin (0.3%). All E. casseliflavus were susceptible to chloramphenicol, penicillin, streptomycin, nitrofurantoin, gentamicin, and linezolid. Whole genome antimicrobial resistance gene profiling identified vanC-type intrinsic vancomycin resistance genes in all E. casseliflavus, with the vanC4XYT gene cluster being dominant (67%) followed by vanC2XYT (31%) and vanC3XYT (1.5%). Resistance genes for erythromycin (ermB) and tetracycline (tetM) were rarely identified (2.1% and 1.2%, respectively) within E. casseliflavus genomes. No resistance genes were identified to explain either the quinupristin–dalfopristin or ciprofloxacin resistance in these isolates. A core genome phylogenetic tree revealed two clades that exhibited no distinct association with the age of the host, time of sample collection, or the farm sampled. The open nature of the E. casseliflavus pan-genome highlighted its intraspecies diversity. These findings suggest that E. casseliflavus is likely a low-risk species in terms of contributing to antimicrobial resistance in the cow–calf sector. Full article