Search Results (43)

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

Background/Objectives: In an era of increasing bacterial resistance, Enterococcus, as a reservoir of antibiotic resistance genes, poses a serious threat to public health. Methods: This study conducted antibiotic susceptibility tests, whole-genome sequencing, and bioinformatics analysis on 89 Enterococcus isolates from chickens, pigs, cattle, and sheep in Ningxia Autonomous Region. Results: The resistance rates of Enterococcus to clindamycin, cefoxitin, sulfamethoxazole, and tamoxifen were all above 95%, and 96.6% (86/89) of the isolates were multi-antibiotic resistant. There were significant differences in resistance phenotypes among different species, with Enterococcus from pigs showing significantly higher resistance than those from other animals. optrA was commonly found in Enterococcus from pigs, accounting for 61.5% (8/13). ST480, ST16, ST116, and ST300 were the main MLST types, and ST16 was one of the important pathogenic Enterococcus types. Conclusions: The study revealed the occurrence of inter-species transmission events of Enterococcus. In conclusion, this study comprehensively described the resistance spectrum, sequence characteristics, and transmission features of resistance genes in Enterococcus isolated from farm animals, and emphasized the possibility of the spread of resistance genes carried by Enterococcus from farm animals to humans. Full article

Background/Objectives: Despite clear benefits, conventional rubber dam use remains low due to barriers that often originate during undergraduate training. To examine a potential approach to mitigating these barriers, this study evaluated the efficacy and feasibility of OptraDam^® Plus, a user-friendly alternative to the conventional rubber dam, in preclinical simulation training. Methods: In this 2 × 2 crossover trial, preclinical undergraduate students were randomly assigned to two groups to perform two types of dental isolation, conventional rubber dam and OptraDam^® Plus, in alternating sequences on a dental simulator. The efficacy and feasibility of both systems were evaluated based on application time, isolation quality, and students’ perceptions. Results: Data from 94 randomized students were collected and analyzed. Although students’ performance was suboptimal with both systems, there were significant differences in efficacy and feasibility between them. Application time was shorter with the conventional rubber dam (mean reduction 77 s; 95% CI 4–151; p = 0.039), whereas using OptraDam^® Plus was associated with 51% lower odds of achieving a higher isolation quality category (OR 0.49; p = 0.011). In addition, students perceived the conventional rubber dam to be superior to the OptraDam^® Plus in achieving higher-quality dental isolation and in their confidence in using it. Conclusions: OptraDam^® Plus cannot be considered a suitable alternative to the conventional rubber dam in preclinical simulation training due to its inferior efficacy and feasibility. The findings of this study challenge the assumption that utilization of newer marketed “user-friendly” rubber dam systems necessarily overcome the core technical barriers faced by undergraduate students. Full article

Linezolid (LNZ) is a synthetic oxazolidinone antibiotic that inhibits bacterial protein synthesis through binding to ribosomal RNA, also preventing the assembly of the initiation complex during translation. It is one of the last-line therapeutic options for serious infections caused by problematic Gram-positive pathogens, including vancomycin-resistant and multidrug-resistant Enterococcus species. Data from recent large-scale studies show a 2.5-fold increase in the prevalence of clinical LNZ-resistant enterococci (LRE) over the past decade with a global detection rate of 1.1% for LNZ-resistant E. faecium (LREfm) and 2.2% for LNZ-resistant E. faecalis (LREfs). Most reported cases have originated from China, followed by South Korea and the United States. LREfm typically belongs to the high-risk clonal complex 17, whereas LREfs demonstrates a heterogeneous population structure. Mutations in the 23S rRNA and ribosomal proteins, as well as acquired resistance genes such as cfr, optrA, and poxtA are involved in the development of LNZ resistance among enterococci. Whole-genome sequencing (WGS) has been recognized as a gold standard for identifying the underlying molecular mechanisms. It exposes that numerous LRE isolates possess multiple LNZ resistance determinants and mutations, further complicating the treatment strategies. The present review article summarizes all known mutational and non-mutational LNZ resistance mechanisms and presents a global overview of WGS-based studies with emphasis on resistome analysis of clinical LREfs and LREfm isolates published in the literature during the period 2014–2025. 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

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

This study investigates the occurrence, antimicrobial resistance (AMR) profiles, virulence factors, and plasmid composition of Enterococcus species isolated from salad ingredients in the United Arab Emirates (UAE). Four hundred salad vegetable items collected from local markets, over ten months through 2023, were screened, yielding an Enterococcus detection rate of 85.5% (342/400). E. casseliflavus was the most commonly identified species (50%), followed by E. faecium (20%) and E. faecalis (16%). Among 85 Enterococcus isolates tested for antimicrobial susceptibility, 55.3% displayed resistance to at least one agent, with 18.8% classified as multidrug-resistant (MDR). All isolates were not resistant to ampicillin, linezolid, teicoplanin, tigecycline, and high-level gentamicin. Intrinsic phenotypic resistance to vancomycin was found in E. gallinarum and E. casseliflavus, while low-level (<5%) ciprofloxacin and erythromycin resistance was sporadically detected in E. faecium and E. faecalis. Whole-genome sequencing (WGS) of 14 isolates (nine E. faecium, four E. faecalis, and one E. casseliflavus) unveiled a complex resistome. We report the first detection in salad vegetables of vancomycin resistance genes (vanC, vanXY-C2) in a vancomycin-susceptible E. faecalis isolate. Identifying tetM, ermB, and optrA genes in the studied isolates further underscored emerging resistance to tetracyclines, macrolides, and oxazolidinones. Concurrently, virulence gene analysis revealed 74 putative virulence factors, with E. faecalis harboring a higher diversity of biofilm-related and exoenzyme-encoding genes. One E. faecalis strain carried the cytolysin cluster (cylI, cylS, cylM), highlighting its pathogenic potential. Plasmid profiling identified 19 distinct plasmids, ranging from 3845 bp to 133,159 bp. Among the genome-sequenced isolates, mobilizable plasmids (47.3%) commonly carried AMR genes, especially tet(L) and tet(M), whereas conjugative plasmids (10.5%) did not harbor resistance determinants. These findings highlight that salad vegetables can still harbor and potentially transmit Enterococcus strains with clinically relevant resistance determinants and virulence traits. Enhancing foodborne AMR surveillance with WGS and targeted interventions is key to controlling its spread in the food. Full article

Background: The emergence of linezolid resistance, mediated by genes such as optrA and cfr(D), poses a growing public health threat. While these genes have been detected in clinical and animal-derived Enterococcus species, their presence in underexplored species like Enterococcus saccharolyticus remains undocumented, leaving a significant gap in our understanding of their dissemination and stability. Method: E. saccharolyticus GXN23C125Es was screened for the presence of known linezolid resistance genes via PCR analysis. Conjugation and stability experiments were used to evaluate the transferability and stability of the resistance genes. The complete genome of GXN23C125Es was obtained using both the Illumina and Nanopore platforms. Results: We report the first identification of optrA and cfr(D) in GXN23C125Es from chicken feces in China. Whole-genome sequencing revealed multiple plasmid-borne resistance genes, including optrA, cfr(D), fexA, and erm(A). Stability testing demonstrated that optrA was highly stable, while cfr(D) was rapidly lost without selective pressure. Conclusions: These findings highlight E. saccharolyticus as a potential reservoir for linezolid resistance genes, underscoring the need for enhanced surveillance of resistance determinants in animal-associated bacteria. Understanding the dissemination dynamics of optrA and cfr(D) is crucial for mitigating their impact on public health and guiding antimicrobial resistance management strategies. Full article

Linezolid-non-susceptible Enterococcus faecalis (LNSEf) has emerged as a critical clinical concern worldwide, yet data from Latin American settings remain scarce. This study aimed to investigate the molecular epidemiology and mechanisms underlying LNSEf in a Mexican tertiary care university hospital, focusing on clinical correlates and clonal relationships. A total of 392 non-duplicated E. faecalis isolates were collected over 12 months, of which 24 with minimum inhibitory concentrations ≥4 µg/mL underwent whole-genome sequencing to identify specific resistance determinants (optrA, cfrA, 23S rRNA mutations) and to perform multilocus sequence typing (MLST) and phylogenetic analyses. Of the 392 isolates, 6.12% showed linezolid non-susceptibility, predominantly linked to plasmid- or chromosomally encoded optrA; only two isolates carried cfrA. No mutations were detected in 23S rRNA domain V or ribosomal proteins L3/L4. Clinically, LNSEf strains were associated with immunosuppression, previous surgical interventions, and prolonged hospital stays. Although most LNSEf isolates retained susceptibility to ampicillin, vancomycin, and daptomycin, they exhibited high rates of resistance to other antibiotic classes, particularly aminoglycosides and fluoroquinolones. These findings underscore the emergence of LNSEf in this region, highlighting the need for robust genomic surveillance, strict infection control, and judicious antimicrobial stewardship to curb further dissemination. Full article

Background/Objectives: Enterococcus is one of the major nosocomial pathogens. The present status of antimicrobial resistance determinants and virulence factors was analyzed for current Enterococcus causing infectious diseases in Bangladesh. Methods: Clinical isolates of Enterococcus recovered from various specimens in a tertiary care hospital were analyzed. Antimicrobial susceptibility was measured by a broth microdilution test, and resistance genes/virulence factors were detected by uniplex/multiplex PCR, along with sequencing analysis as required. The sequence type (ST) of E. faecalis and E. faecium was identified based on a multilocus sequence typing (MLST) scheme. Results: For a one-year period, a total of 143 isolates (135 E. faecalis, 7 E. faecium, and 1 E. hirae) were collected. Although all E. faecalis isolates were susceptible to penicillin, high resistance rates were noted against erythromycin (87%) and levofloxacin (62%). High-level resistance to gentamicin was detected in 30% of E. faecalis and 86% of E. faecium. Vancomycin resistance due to vanA was identified in one isolate each of E. faecalis (ST1912, CC116) and E. faecium (ST80, CC17). Three E. faecalis isolates (2.2%) with ST32 or ST1902 were resistant to linezolid, harboring optrA-fexA. Conclusions: The present study identifies the vancomycin-resistant Enterococcus harboring vanA from humans in Bangladesh and shows the potential spread of optrA in multiple lineages of E. faecalis. Full article

Linezolid is an oxazolidinone antibiotic and is considered a last-resort treatment option for serious infections caused by problematic Gram-positive pathogens, including vancomycin-resistant enterococci. The present study aimed to explore the linezolid resistance mechanisms and genomic characteristics of two vancomycin-susceptible Enterococcus faecalis isolates from Bulgaria. The strains designated Efs2503-bg (inpatient from Pleven) and Efs966-bg (outpatient from Varna) were recovered from wounds in 2018 and 2023, respectively. Antimicrobial susceptibility testing, whole-genome sequencing, multilocus sequence typing, and phylogenomic analysis based on 332 linezolid-resistant E. faecalis genomes were performed. Efs2503-bg was high-level resistant to linezolid (MIC > 256 mg/L) and displayed the G2576T mutation affecting three of the four 23S rDNA loci. Efs966-bg (MIC = 8 mg/L) carried a plasmid-located optrA determinant surrounded by fexA and ermA. No mutations in the genes encoding for ribosomal proteins L3, L4, and L22 were detected. The isolates belonged to the sequence types ST6 (Efs2503-bg) and ST1102 (Efs966-bg). Phylogenomic analysis revealed that Efs2503-bg and Efs966-bg are genetically distinct, with a difference of 12,051 single-nucleotide polymorphisms. To our knowledge, this is the first report of linezolid-resistant enterococci in Bulgaria. Although the global incidence of linezolid-resistant enterococci is still low, their emergence is alarming and poses a growing clinical threat to public health. Full article

Background/Objectives: The spread of antibiotic resistance, particularly through Enterococcus spp., in wastewater treatment plants (WWTPs) poses significant public health risks. Given that research on antibiotic-resistant enterococci and their antibiotic-resistance genes in aquatic environments is limited, we evaluated the role of Enterococcus spp. in WWTPs by comparing the antibiotic resistance rates, gene prevalence, biofilm formation, and residual antibiotics in the influent and effluent using culture-based methods. Methods: In 2022, influent and effluent samples were collected from 11 WWTPs in South Korea. Overall, 804 Enterococcus strains were isolated, and their resistance to 16 antibiotics was assessed using the microdilution method. Results: High resistance to tetracycline, ciprofloxacin, kanamycin, and erythromycin was observed. However, no significant differences in the overall resistance rates and biofilm formation were observed between the influent and effluent. Rates of resistance to ampicillin, ciprofloxacin, and gentamicin, as well as the prevalence of the tetM and qnrS genes, increased in the effluent, whereas resistance rates to chloramphenicol, florfenicol, erythromycin, and tylosin tartrate, along with the prevalence of the optrA gene, decreased. E. faecium, E. hirae, and E. faecalis were the dominant species, with E. faecalis exhibiting the highest resistance. Conclusions: Our results suggest that WWTPs do not effectively reduce the rates of resistant Enterococcus spp., indicating the need for continuous monitoring and improvement of the treatment process to mitigate the environmental release of antibiotic-resistant bacteria. Full article

In an aquaponic system, fish and plants are cultivated together in a symbiotic environment where they mutually benefit, using significantly less water than traditional farming methods. The main aim of this study was to investigate the occurrence of antimicrobial resistance in two aquaponic systems implemented in two Chilean high schools using rainbow trout and lettuce cultures. When water samples (fish tank, biofilter, and plant raft) were analyzed over a three-month period, no resistance to oxytetracycline was detected, whereas the occurrence of resistance to florfenicol was rather small, ranging from 0.01% to 3.1% of bacterial culturable counts. Eighteen isolates were recovered from various sources as representatives of the florfenicol-resistant population, and all of them belonged to the Pseudomonas genus, showing a multi-drug-resistance phenotype and exhibiting simultaneous resistance to 7–13 antimicrobials. All isolates exhibited resistance to amoxicillin, chloramphenicol, florfenicol, and furazolidone and susceptibility to meropenem, oxytetracycline, oxolinic acid, flumequine, ciprofloxacin, and enrofloxacin. Five and two isolates carried the amphenicol-resistance-encoding genes floR and cmlA, respectively, whereas no carriage of integrons or the fexA, fexB, pexA, optrA, and cfr genes encoding for florfenicol resistance was detected. Eleven isolates carried plasmids, but only two of them were able to transfer their plasmid content by conjugation. The knowledge of the microbiome associated with aquaponic systems is still scarce, and their role as potential reservoirs of antimicrobial-resistant bacteria and related genes of these systems must be elucidated. Full article

The impact of soil fertilization with animal manure on the spread and persistence of antibiotic resistance in the environment is far from being fully understood. To add knowledge about persistence and correlations between antibiotic residues and antibiotic resistance genes (ARGs) in fertilized soil, a longitudinal soil mesocosm study was conducted. Soil samples were collected from the mesocosms immediately before spreading and then afterward at fifteen time points during a 320-day observation period. Eight ARGs (ermB, sul1, tetA, tetG, tetM, cfr, fexA, and optrA) and the class 1 integron-integrase gene, intI1, were determined in both pig slurry and soil, as well as residues of 36 antibiotics. Soil chemical and biochemical parameters were also measured. Twelve antibiotics were detected in the slurry in the range of 3 µg kg⁻¹–3605 µg kg⁻¹, with doxycycline, lincomycin, and tiamulin being the most abundant, whereas ermB, sul1, and tetM were the predominant ARGs. Before spreading, neither antibiotic residues nor ARGs were detectable in the soil; afterwards, their concentrations mirrored those in the slurry, with a gradual decline over the duration of the experiment. After about three months, the effect of the amendment was almost over, and no further evolution was observed. Full article

Oxazolidinone resistance, especially transmissible resistance, is a major public health concern, and the origin of this resistance mechanism is not yet resolved. This study aims to delve into the phylogenetic origin of the transmissible oxazolidinone resistance mechanisms conferring cross-resistance to other drugs of human and veterinary importance. The amino acid sequences of the five cfr ribosomal methylases and optrA and poxtA were used as queries in searches against 219,549 bacterial proteomes in the NCBI RefSeq database. Hits with >40% amino acid identity and >80% query coverage were aligned, and phylogenetic trees were reconstructed. All five cfr genes yielded highly similar trees, with rlmN housekeeping ribosomal methylases located basal to the sister groups of S-adenosyl-methionine-dependent methyltransferases from various Deltaproteobacteria and Actinomycetia, including antibiotic-producing Streptomyces species, and the monophyletic group of cfr genes. The basal branches of the latter contained paenibacilli and other soil bacteria; they then could be split into the clades [cfr(C):cfr(E)] and [[cfr:cfr(B)]:cfr(D)], always with different Bacillaceae in their stems. Lachnospiraceae were encountered in the basal branches of both optrA and poxtA trees. The ultimate origin of the cfr genes is the rlmN housekeeping ribosomal methylases, which evolved into a suicide-avoiding methylase in antibiotic producers; a soil organism (Lachnospiraceae, Paenibacilli) probably acted as a transfer organism into pathogenic bacteria. In the case of optrA, the porcine pathogenic Streptococcus suis was present in all branches, while the proteins closest to poxtA originated from Clostridia. Full article