Nationwide Surveillance on Antimicrobial Resistance Profiles of Enterococcus faecium and Enterococcus faecalis Isolated from Healthy Food Animals in South Korea, 2010 to 2019

Species prevalence, virulence genes, and antibiotic resistance of enterococci from food-producing animals at a slaughterhouse in Turkey

Healthy cattle, sheep, and goats can be reservoirs for gastrointestinal pathogenic fecal enterococci, some of which could be multidrug-resistant to antimicrobials. The objective of this study was to determine the prevalence and diversity of Enterococcus species in healthy sheep, goat, and cattle carcasses, as well as to analyze the antimicrobial resistance phenotype/genotype and the virulence gene content. During 2019-2020, carcass surface samples were collected from 150 ruminants in a slaughterhouse. A total of 90 enterococci, comprising five species, were obtained. The overall prevalence of enterococci was found to be 60%, out of which 37.7% were identified as Enterococcus (E.) hirae, 33.3% as E. casseliflavus, 15.5% as E. faecium, 12.2% as E. faecalis, and 1.1% as E. gallinarum. Virulence-associated genes of efaA (12.2%) were commonly observed in the Enterococcus isolates, followed by gelE (3.3%), asaI (3.3%), and ace (2.2%). High resistance to quinupristin-dalfopristin (28.8%), tetracycline (21.1%), ampicillin (20%), and rifampin (15.5%) was found in two, four, four, and five of the Enterococcus species group, respectively. The resistance of Enterococcus isolates to 11 antibiotic groups was determined and multidrug resistant (MDR) strains were found in 18.8% of Enterococcus isolates. Characteristic resistance genes were identified by PCR with an incidence of 6.6%, 2.2%, 1.1%, 1.1%, 1.1%, and 1.1% for the tetM, ermB, ermA, aac(6')Ie-aph(2")-la, VanC1, and VanC2 genes in Enterococcus isolates, respectively. Efflux pump genes causing multidrug resistance were detected in Enterococcus isolates (34.4%). The results showed that there were enterococci in the slaughterhouse with a number of genes linked to virulence that could be harmful to human health.

Assessment of Zn and Cu in piglets' liver and kidney: impact in fecal Enterococcus spp.?

Zinc and copper have been used as growth promotors in alternative to antibiotics in pig's diet. The aim was the ascertainment of the Zn and Cu concentrations in piglets' liver and kidney and their impact in the reduced susceptibility to Zn, Cu, and antibiotics in enterococci, used as microbiota biomarker. Zn and Cu were determined in the livers and kidneys of 43 piglets slaughtered in Portugal, by flame atomic absorption spectrometry. Enterococci were isolated from feces for determining the identification of species (E. faecalis, E. faecium, and Enterococcus spp.); susceptibility to vancomycin, ciprofloxacin, linezolid, tigecycline, ampicillin, imipenem, and metals; and Cu tolerance genes. In piglets with Zn and Cu high or toxic levels, enterococci had reduced susceptibility to ions, reinforced by the presence of Cu tolerance genes and by resistance to antibiotics. The study relevance is to show the relationship between these metals' levels and decreased susceptibility to Cu, Zn, and antibiotics by enterococci. From the results, it could be supposed that the piglets were being fed with high doses of Zn and Cu which could select more resistant bacteria to both antibiotics and metals that could spread to environment and humans.

Molecular epidemiology, phenotypic and genomic characterization of antibiotic-resistant enterococcal isolates from diverse farm animals in Xinjiang, China

Multidrug-resistant (MDR) bacteria in farm environments can be transferred to humans through the food chain and occupational exposure. Enterococcus infections caused by linezolid resistant enterococci (LRE) are becoming more challenging to treat as their resistance to antibiotics intensifies. Therefore, this study investigated the molecular epidemiology, phenotypic and genomic characterization of enterococci in seven species of farm animals (sheep, chicken, swine, camel, cattle, equine, pigeon) anal swab from Xinjiang, China by agar dilution method, polymerase chain reaction (PCR), whole-genome sequencing (WGS) and bioinformatics analysis. A total of 771 samples were collected, 599 (78 %) were contaminated with Enterococcus spp., among which Enterococcus faecalis (350/599) was dominant. Antimicrobial susceptibility testing showed that high resistance was observed in rifampicin (80 %), tetracycline (71 %), doxycycline (71 %), and erythromycin (69 %). The results of PCR showed the highest prevalent antibiotic resistance genes (ARGs) were aac(6')-aph(2″) (85 %), followed by tet(M) (73 %), erm(B) (62 %), and aph(3')-IIIa (61 %). Besides, 29 optrA-carrying E. faecalis isolates belonging to 13 STs (including 3 new alleles) were detected, with ST714 (31 %, 9/29) being the dominant ST type. The phylogenetic tree showed that optrA-carrying E. faecalis prevalent in the intensive swine farm is mainly caused by clonal transmission. Notably, optrA gene in Enterococcus spp. isolate from camel was first characterized here. WGS of E. faecalis F109 isolate from camel confirmed the colocalization of optrA with other five ARGs in the same plasmid (pAFL-109F). The optrA-harboring genetic context is IS1216E-fexA-optrA-erm(A)-IS1216E. This study highlights the prevalence of MDR Enterococcus (≥88 %) and four ARGs (≥75 %) in swine (intensive farming), cattle (commercial farming), and chickens (backyard farming) are high and also highlights that optrA-carrying E. faecalis of farm animals incur a transmission risk to humans through environment, food consumption and others. Therefore, antibiotic-resistant bacteria (ARB) monitoring and effective control measures should be strengthened and implemented in diverse animals.

Antimicrobial Resistance Profiles of Enterococcus faecium and Enterococcus faecalis Isolated from Healthy Dogs and Cats in South Korea

Enterococcus spp. are typically found in the gastrointestinal tracts of humans and animals. However, they have the potential to produce opportunistic infections that can be transmitted to humans or other animals, along with acquired antibiotic resistance. In this study, we aimed to investigate the antimicrobial resistance profiles of Enterococcus faecium and Enterococcus faecalis isolates obtained from companion animal dogs and cats in Korea during 2020-2022. The resistance rates in E. faecalis towards most of the tested antimicrobials were relatively higher than those in E. faecium isolated from dogs and cats. We found relatively higher resistance rates to tetracycline (65.2% vs. 75.2%) and erythromycin (39.5% vs. 49.6%) in E. faecalis isolated from cats compared to those from dogs. However, in E. faecium, the resistance rates towards tetracycline (35.6% vs. 31.5%) and erythromycin (40.3% vs. 35.2%) were comparatively higher for dog isolates than cats. No or very few E. faecium and E. faecalis isolates were found to be resistant to daptomycin, florfenicol, tigecycline, and quinupristin/dalfopristin. Multidrug resistance (MDR) was higher in E. faecalis recovered from cats (44%) and dogs (33.9%) than in E. faecium isolated from cats (24.1%) and dogs (20.5%). Moreover, MDR patterns in E. faecalis isolates from dogs (27.2%) and cats (35.2%) were shown to encompass five or more antimicrobials. However, E. faecium isolates from dogs (at 13.4%) and cats (at 14.8%) were resistant to five or more antimicrobials. Taken together, the prevalence of antimicrobial-resistant enterococci in companion animals presents a potential public health concern.

Molecular Characterization of Enterococcus faecalis and Enterococcus faecium Isolated from a Meat Source in Shahrekord Local Markets, Iran

Enterococcus faecalis (E. faecalis) and E. faecium (E. faecium) are commensals of the gastrointestinal biota of humans and animals and are considered opportunistic pathogens. This study aimed to improve the knowledge about E. faecalis and E. faecium isolated from meat. To this end, 104 meat samples were collected from sheep, goats, cattle, and calves from Shahrekord local markets in Iran. Presumptive colonies of E. faecalis and E. faecium were isolated from the samples and subjected to identification tests. Antimicrobial susceptibility was determined using the Kirby-Bauer disc diffusion method, and polymerase chain reaction (PCR) was performed to detect some virulence genes. Furthermore, randomly amplified polymorphic DNA typing and repetitive element sequence-based PCR fingerprinting were used to show the clonal relatedness of the isolates. The results revealed that enterococci were present in 90 out of 104 samples. Specifically, E. faecalis and E. faecium were the commonly isolated species, with the predominance of E. faecalis, which exhibited high resistance to streptomycin (95%) but was susceptible to vancomycin (85.6%). Virulence genes detection showed that ccf and cpd genes were the most prevalent genes in both species. In addition, the molecular typing method indicated that the isolates belonged to separate subgroups. This study shows the contamination of meat products by potential pathogens and resistant enterococci. There is a need to implement regular surveillance to monitor the emergence of antimicrobial-resistant E. faecalis and E. faecium in food, particularly in meat production.

Prevalence and Associated Factors of optrA-Positive-Enterococcus faecalis in Different Reservoirs around Farms in Vietnam

Linezolid is an antibiotic of last resort for the treatment of infections caused by Gram-positive bacteria, including vancomycin-resistant enterococci. Enterococcus faecalis, a member of enterococci, is a significant pathogen in nosocomial infections. E. faecalis resistance to linezolid is frequently related to the presence of optrA, which is often co-carried with fex, phenicol exporter genes, and erm genes encoding macrolide resistance. Therefore, the common use of antibiotics in veterinary might promote the occurrence of optrA in livestock settings. This is a cross-sectional study aiming to investigate the prevalence of optrA positive E. faecalis (OPEfs) in 6 reservoirs in farms in Ha Nam province, Vietnam, and its associated factors and to explore genetic relationships of OPEfs isolates. Among 639 collected samples, the prevalence of OPEfs was highest in flies, 46.8% (51/109), followed by chickens 37.3% (72/193), dogs 33.3% (17/51), humans 18.7% (26/139), wastewater 16.4% (11/67) and pigs 11.3%, (14/80). The total feeding area and total livestock unit of the farm were associated with the presence of OPEfs in chickens, flies, and wastewater. Among 186 OPEfs strains, 86% were resistant to linezolid. The presence of optrA was also related to the resistant phenotype against linezolid and levofloxacin of E. faecalis isolates. Close genotypic relationships identified by Pulsed Field Gel Electrophoresis between OPEfs isolates recovered from flies and other reservoirs including chickens, pigs, dogs, and wastewater suggested the role of flies in the transmission of antibiotic-resistant pathogens. These results provided warnings of linezolid resistance although it is not used in livestock.

Antibiotic Resistance among Gastrointestinal Bacteria in Broilers: A Review Focused on Enterococcus spp. and Escherichia coli

Chickens can acquire bacteria at different stages, and bacterial diversity can occur due to production practices, diet, and environment. The changes in consumer trends have led to increased animal production, and chicken meat is one of the most consumed meats. To ensure high levels of production, antimicrobials have been used in livestock for therapeutic purposes, disease prevention, and growth promotion, contributing to the development of antimicrobial resistance across the resident microbiota. Enterococcus spp. and Escherichia coli are normal inhabitants of the gastrointestinal microbiota of chickens that can develop strains capable of causing a wide range of diseases, i.e., opportunistic pathogens. Enterococcus spp. isolated from broilers have shown resistance to at least seven classes of antibiotics, while E. coli have shown resistance to at least four. Furthermore, some clonal lineages, such as ST16, ST194, and ST195 in Enterococcus spp. and ST117 in E. coli, have been identified in humans and animals. These data suggest that consuming contaminated animal-source food, direct contact with animals, or environmental exposure can lead to the transmission of antimicrobial-resistant bacteria. Therefore, this review focused on Enterococcus spp. and E. coli from the broiler industry to better understand how antibiotic-resistant strains have emerged, which antibiotic-resistant genes are most common, what clonal lineages are shared between broilers and humans, and their impact through a One Health perspective.

Determination of the Prevalence and Antimicrobial Resistance of Enterococcus faecalis and Enterococcus faecium Associated with Poultry in Four Districts in Zambia

The presence of antimicrobial-resistant Enterococci in poultry is a growing public health concern worldwide due to its potential for transmission to humans. The aim of this study was to determine the prevalence and patterns of antimicrobial resistance and to detect drug-resistant genes in Enterococcus faecalis and E. faecium in poultry from four districts in Zambia. Identification of Enterococci was conducted using phenotypic methods. Antimicrobial resistance was determined using the disc diffusion method and antimicrobial resistance genes were detected using polymerase chain reaction and gene-specific primers. The overall prevalence of Enterococci was 31.1% (153/492, 95% CI: 27.1–35.4). Enterococcus faecalis had a significantly higher prevalence at 37.9% (58/153, 95% CI: 30.3–46.1) compared with E. faecium, which had a prevalence of 10.5% (16/153, 95% CI: 6.3–16.7). Most of the E. faecalis and E. faecium isolates were resistant to tetracycline (66/74, 89.2%) and ampicillin and erythromycin (51/74, 68.9%). The majority of isolates were susceptible to vancomycin (72/74, 97.3%). The results show that poultry are a potential source of multidrug-resistant E. faecalis and E. faecium strains, which can be transmitted to humans. Resistance genes in the Enterococcus species can also be transmitted to pathogenic bacteria if they colonize the same poultry, thus threatening the safety of poultry production, leading to significant public health concerns.

Meta-analysis of the global prevalence of Enterococcus spp. in foods: Antibiotic resistance profile of Enterococcus faecalis and Enterococcus faecium

Aim: The objective of this study was to evaluate the prevalence and diversity of Enterococcus spp. and antibiotic-resistant Enterococcus faecalis and Enterococcus faecium isolates in different foods worldwide.

Method and Result: This study used meta-analytical methods. Besides, Web of Science (n= 705), Medline (n= 6), and Scopus (n= 1.338) were searched for studies in the years 1995-2021 using related keywords. Results showed that the pooled prevalence for Enterococcus spp. and antibiotic-resistant of E. faecalis and E. faecium isolates were found 0.41 (95% C.I. 0.34-0.47), 0.25 (95% C.I. 0.13-0.38), respectively. According to the results of the subgroup analysis, the lowest and highest prevalence of Enterococcus spp. in food types were calculated for red meat (0.56), and fermented foods (0.29). Also, as a result of subgroup analyses by country the highest prevalence of Enterococcus spp. was calculated in studies conducted in Slovakia (0.74). In contrast, the lowest prevalence was calculated in studies conducted in Georgia (0.07).

Conclusion: The meta-analyses improved our understanding of the prevalence of Enterococcus spp. and the antibiotic resistance of E. faecalis and E. faecium isolates in different foods and provided results that can be useful as input for quantitative microbiological risk evaluation modeling.

Significance and Impact of Study: We demonstrated the antibiotic resistance of E. faecalis and E. faecium in foods and gaps that could be addressed in the future. Therefore, it is believed that the results compiled herein will contribute to the epidemiological surveillance of the presence and antibiotic resistance of E. faecalis and E. faecium in foods.

Concurrent Determination of Tigecycline, Tetracyclines and Their 4-Epimer Derivatives in Chicken Muscle Isolated from a Reversed-Phase Chromatography System Using Tandem Mass Spectrometry

A quantitative and qualitative method using a high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) detection approach was developed and validated for the analysis of tigecycline, four tetracyclines and their three 4-epimer derivatives in chicken muscle. Samples were extracted repeatedly with 0.1 mol/L Na2EDTA–McIlvaine buffer solution. After vortexing, centrifugation, solid-phase extraction, evaporation and reconstitution, the aliquots were separated using a C8 reversed-phase column (50 mm × 2.1 mm, 5 µm) with a binary solvent system consisting of methanol and 0.01 mol/L trichloroacetic acid aqueous solution. The typical validation parameters were evaluated in accordance with the acceptance criteria detailed in the guidelines of the EU Commission Decision 2002/657/EC and the U.S. Food and Drug Administration Bioanalytical Method Validation 05/24/18. The matrix-matched calibration curve was linear over the concentration range from the limit of quantitation (LOQ) to 400 μg/kg for doxycycline, and the calibration graphs for tetracycline, chlortetracycline, oxytetracycline, their 4-epimer derivatives and tigecycline showed a good linear relationship within the concentration range from the LOQ to 200 μg/kg. The limits of detection (LODs) for the eight targets were in the range of 0.06 to 0.09 μg/kg, and the recoveries from the fortified blank samples were in the range of 89% to 98%. The within-run precision and between-run precision, which were expressed as the relative standard deviations, were less than 5.0% and 6.9%, respectively. The applicability was successfully demonstrated through the determination of residues in 72 commercial chicken samples purchased from different sources. This approach provides a novel option for the detection of residues in animal-derived food safety monitoring.

Analysis of virulence genes, drug resistance detection, and pathogenicity in Enterococcus from farm animals

This study aimed to investigate the presence of eight virulence genes (ace, asa1, esp, efaA, gelE, cylA, agg, fsr) in Enterococcus from a variety of animals and to explore the drug resistance and pathogenicity. This could provide a theoretical basis for clinical treatment of Enterococcus infections. Anal swabs from pigs, chickens, cattle, and dogs in farms and pet hospitals were collected for Enterococcus isolation and identification. Eight virulence genes were detected (PCR method), and drug resistance was assessed (drug-sensitive paper method). The strains containing different virulence genes were then divided into EV1, EV2, and EV3 groups. The LD₅₀ and pathogenicity was examined by intra-peritoneal injection to infect mice. Differences were found in the detection rates of virulence genes in Enterococcus from the different animals. The highest overall detection rate was for the esp gene (78.0%), and the lowest for the cylA gene (15.5%). Eight genes were detected most frequently in Enterococcus from dogs and least frequently from cattle. Among the Enterococcus strains from four variety of animals, drug resistance was highest against sulfamethoxazole (100%), cefotaxime (>97%), and cefotaxitin (>93%). Drug resistance was lowest against vancomycin (0%), levofloxacin (<12%) and ciprofloxacin (<13%). The LD₅₀ for each of the three groups was EV1_LD50=8.71×10⁹CFU， EV2_LD50=2.34×10¹⁰CFU，and EV3_LD50=9.33×10¹⁰CFU. The Enterococcus12LD₅₀ dose group caused significant clinical symptoms in mice, with pathological effects on the heart, liver, lungs, and kidneys, and particularly on the urinary system. The abundance of Enterococcus virulence genes, drug resistance, and pathogenicity vary among different animal origins, and the pathology caused by Enterococcus requires effective treatment protocols based on species and regional characteristics.

Enumeration, Antimicrobial Resistance, and Virulence Genes Screening of Enterococcus spp. Isolated from Retail Chicken Carcasses in the United Arab Emirates

Enterococci have recently emerged as nosocomial pathogens worldwide. Their ubiquitous nature determines their frequent finding in foods as contaminants. In this study, we aimed to determine the counts, species diversity, antimicrobial resistance profile, and to screen for a set of virulence genes among enterococci. Enterococcus were identified from 75.7% (125/165) of chilled chicken carcasses, belonging to seven companies, sampled from retail markets in Abu Dhabi Emirate, United Arab Emirates (U.A.E.). Overall, the samples, with a mean Enterococcus count of 2.58 log₁₀ colony-forming unit (CFU)/g with a standard deviation of ±1.17 log₁₀ CFU/g. Among the characterized Enterococcus isolates (n = 90), Enterococcus faecalis was the predominant species (51.1%), followed by Enterococcus faecium (37.8%). Using Vitek2 automated antimicrobial sensitivity panel, we found none of the E. faecalis nor E. faecium to be resistant to ampicillin, teicoplanin, vancomycin, or tigecycline. A third of the E. faecalis (28.3%) and E. faecium (35.3%) were resistant to high-level gentamicin. Over half of E. faecalis (54.3%) were resistant to ciprofloxacin, and the same was in about a third of E. faecium isolates (29.4%). Linezolid resistance was identified in 10 E. faecalis and 7 E. faecium isolates belonging to samples from three companies. All of the linezolid-resistant isolates harbored oxazolidinone resistance optrA gene. Virulence-associated genes (asa1 and gelE) were significantly (p < 0.05) more detected among E. faecalis compared to E. faecium isolates recovered in this study. Over half of the E. faecalis (25/46) and E. faecium (20/34) isolates were identified as multidrug-resistant. This study provides further insight into virulence genes and their association with the dissemination of multidrug-resistant E. faecalis and E. faecium in supermarket chicken meat in the U.A.E. This is probably the first description of the optrA gene in enterococci from supermarket chicken meat in the U.A.E. and from Arab countries. This study adds to the regional and global understanding of antimicrobial resistance spread in foods of animal origin.

Complete genome analysis of bacteriophage EFC1 infecting Enterococcus faecalis from chicken

A novel lytic Enterococcus faecalis phage, EFC1, was isolated from the sewage of a farm in Handan, China, and its genome was analyzed and described. The phage could infect 87.5% of the chicken-derived Enterococcus faecalis preserved in our laboratory. The genome of phage EFC1 consists of a circular double-stranded DNA with a length of 56,099 bp and a G + C content of 39.96%, containing 89 predicted protein-coding genes as well as 2 tRNAs, which are involved in phage intron, structure, transcription, packaging, DNA replication, modification, cell lysis, and other functions, indicating the genetic and functional characteristics of this phage. Genome comparison analysis revealed that phage EFC1 can be regarded as new genus Saphexavirus phage in the Siphoviridae family.

High-Resolution Genotyping Unveils Identical Ampicillin-Resistant Enterococcus faecium Strains in Different Sources and Countries: A One Health Approach

Multidrug-resistant (MDR) Enterococcus faecium (Efm) infections continue to increase worldwide, although epidemiological studies remain scarce in lower middle-income countries. We aimed to explore which strains circulate in E. faecium causing human infections in Tunisian healthcare institutions in order to compare them with strains from non-human sources of the same country and finally to position them within the global E. faecium epidemiology by genomic analysis. Antibiotic susceptibility testing was performed and transfer of vancomycin-vanA and ampicillin-pbp5 resistance was performed by conjugation. WGS-Illumina was performed on Tunisian strains, and these genomes were compared with Efm genomes from other regions present in the GenBank/NCBI database (n = 10,701 Efm genomes available May 2021). A comparison of phenotypes with those predicted by the recent ResFinder 4.1-CGE webtool unveiled a concordance of 88%, with discordant cases being discussed. cgMLST revealed three clusters [ST18/CT222 (n = 13), ST17/CT948 strains (n = 6), and ST203/CT184 (n = 3)], including isolates from clinical, healthy-human, retail meat, and/or environmental sources in different countries over large time spans (10–12 years). Isolates within each cluster showed similar antibiotic resistance, bacteriocin, and virulence genetic patterns. pbp5-AmpR was transferred by VanA-AmpR-ST80 (clinical) and AmpR-ST17-Efm (bovine meat). Identical chromosomal pbp5-platforms carrying metabolic/virulence genes were identified between ST17/ST18 strains of clinical, farm animal, and retail meat sources. The overall results emphasize the role of high-resolution genotyping as provided by WGS in depicting the dispersal of MDR-Efm strains carrying relevant adaptive traits across different hosts/regions and the need of a One Health task force to curtail their spread.

Molecular characterization and antimicrobial resistance of Enterococcus faecalis isolated from seafood samples

Background

Enterococcus faecalis is considered an opportunistic foodborne pathogen. The present study aimed to assess the prevalence, antimicrobial resistance, virulence characters, and molecular typing of E. faecalis strains isolated from seafood samples.

Methods

Two hundred and seventy‐six seafood samples were collected. E. faecalis was isolated from samples using bacterial culture. Furthermore, the disk diffusion assessed their antimicrobial resistance. Also, the distribution of virulence factors was determined using polymerase chain reaction (PCR) assay. Random amplified polymorphic DNA (RAPD) method was used for their molecular typing.

Results

Fifty‐six of 276 (20.2%) seafood samples were contaminated with E. faecalis. Fish harboured the highest contamination rate (30.0%). Isolates harboured the highest resistance rate towards oxacillin (100%), tetracycline (100%), erythromycin (100%), cefoxitin (89.2%), cefazolin (87.5%), trimethoprim‐sulfamethoxazole (85.7%), rifampin (69.6%), clindamycin (69.6%), and gentamicin (64.2%) antimicrobials. Efa (100%), ebpA (89.2%), ebpB (58.9%), ebpC (53.5%), and esp (51.7%) were the most commonly detected virulence factors among E. faecalis isolates. RAPD–PCR analysis showed 11 different molecular clusters considering the closeness of more than 80%.

Conclusion

Seafood samples were considered reservoirs of virulence and resistant E. faecalis strains. Different molecular clusters of isolates may reflect their diverse sources of contamination.

Prevalence and Characteristics of Phenicol-Oxazolidinone Resistance Genes in Enterococcus Faecalis and Enterococcus Faecium Isolated from Food-Producing Animals and Meat in Korea

The use of phenicol antibiotics in animals has increased. In recent years, it has been reported that the transferable gene mediates phenicol-oxazolidinone resistance. This study analyzed the prevalence and characteristics of phenicol-oxazolidinone resistance genes in Enterococcus faecalis and Enterococcus faecium isolated from food-producing animals and meat in Korea in 2018. Furthermore, for the first time, we reported the genome sequence of E. faecalis strain, which possesses the phenicol-oxazolidinone resistance gene on both the chromosome and plasmid. Among the 327 isolates, optrA, poxtA, and fexA genes were found in 15 (4.6%), 8 (2.5%), and 17 isolates (5.2%), respectively. Twenty E. faecalis strains carrying resistance genes belonged to eight sequence types (STs), and transferability was found in 17 isolates. The genome sequences revealed that resistant genes were present in the chromosome or plasmid, or both. In strains EFS17 and EFS108, optrA was located downstream of the ermA and ant(9)-1 genes. The strains EFS36 and EFS108 harboring poxtA-encoding plasmid cocarried fexA and cfr(D). These islands also contained IS1216E or the transposon Tn554, enabling the horizontal transfer of the phenicol-oxazolidinone resistance with other antimicrobial-resistant genes. Our results suggest that it is necessary to promote the prudent use of antibiotics through continuous monitoring and reevaluation.

Bacterial Antibiotic Resistance: The Most Critical Pathogens

Antibiotics have made it possible to treat bacterial infections such as meningitis and bacteraemia that, prior to their introduction, were untreatable and consequently fatal. Unfortunately, in recent decades overuse and misuse of antibiotics as well as social and economic factors have accelerated the spread of antibiotic-resistant bacteria, making drug treatment ineffective. Currently, at least 700,000 people worldwide die each year due to antimicrobial resistance (AMR). Without new and better treatments, the World Health Organization (WHO) predicts that this number could rise to 10 million by 2050, highlighting a health concern not of secondary importance. In February 2017, in light of increasing antibiotic resistance, the WHO published a list of pathogens that includes the pathogens designated by the acronym ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) to which were given the highest "priority status" since they represent the great threat to humans. Understanding the resistance mechanisms of these bacteria is a key step in the development of new antimicrobial drugs to tackle drug-resistant bacteria. In this review, both the mode of action and the mechanisms of resistance of commonly used antimicrobials will be examined. It also discusses the current state of AMR in the most critical resistant bacteria as determined by the WHO's global priority pathogens list.

Bacterial Antibiotic Resistance: The Most Critical Pathogens

Antibiotics have made it possible to treat bacterial infections such as meningitis and bacteraemia that, prior to their introduction, were untreatable and consequently fatal. Unfortunately, in recent decades overuse and misuse of antibiotics as well as social and economic factors have accelerated the spread of antibiotic-resistant bacteria, making drug treatment ineffective. Currently, at least 700,000 people worldwide die each year due to antimicrobial resistance (AMR). Without new and better treatments, the World Health Organization (WHO) predicts that this number could rise to 10 million by 2050, highlighting a health concern not of secondary importance. In February 2017, in light of increasing antibiotic resistance, the WHO published a list of pathogens that includes the pathogens designated by the acronym ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) to which were given the highest "priority status" since they represent the great threat to humans. Understanding the resistance mechanisms of these bacteria is a key step in the development of new antimicrobial drugs to tackle drug-resistant bacteria. In this review, both the mode of action and the mechanisms of resistance of commonly used antimicrobials will be examined. It also discusses the current state of AMR in the most critical resistant bacteria as determined by the WHO's global priority pathogens list.