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.

Antimicrobial Resistance Profile of Acinetobacter spp. Isolates from Retail Meat Samples under Campylobacter-Selective Conditions.

Acinetobacter strains are widely present in the environment. Some antimicrobial-resistant strains of this genus have been implicated in infections acquired in hospitals. Genetic similarities have been reported between Acinetobacter strains in nosocomial infections and those isolated from foods. However, the antimicrobial resistance of Acinetobacter strains in foods, such as meat, remains unclear. This study initially aimed to isolate Campylobacter strains; instead, strains of the genus Acinetobacter were isolated from meat products, and their antimicrobial resistance was investigated. In total, 58 Acinetobacter strains were isolated from 381 meat samples. Of these, 32 strains (38.6%) were from beef, 22 (26.5%) from pork, and 4 (4.8%) from duck meat. Antimicrobial susceptibility tests revealed that 12 strains were resistant to more than one antimicrobial agent, whereas two strains were multidrug-resistant; both strains were resistant to colistin. Cephalosporin antimicrobials showed high minimal inhibitory concentration against Acinetobacter strains. Resfinder analysis showed that one colistin-resistant strain carried mcr-4.3; this plasmid type was not confirmed, even when analyzed with PlasmidFinder. Analysis of the contig harboring mcr-4.3 using BLAST confirmed that this contig was related to mcr-4.3 of Acinetobacter baumannii. The increase in antimicrobial resistance in food production environments increases the resistance rate of Acinetobacter strains present in meat, inhibits the isolation of Campylobacter strains, and acts as a medium for the transmission of antimicrobial resistance in the environment. Therefore, further investigations are warranted to prevent the spread of antimicrobial resistance in food products.

Characterization of oxazolidinone and phenicol resistance genes in non-clinical enterococcal isolates from Korea.

OBJECTIVES: To investigate the distribution and genetic characteristics of linezolid-resistant enterococci. METHODS: Enterococcus faecalis and Enterococcus faecium strains were isolated from pigs, equipment, grounds, and employees of 19 Korean swine farms in 2017. Antimicrobial susceptibility testing was then performed and linezolid resistance genes were detected via PCR. For genetic epidemiological characterization, multilocus sequence typing and whole-genome sequencing data were analysed. RESULTS: Twenty-eightE. faecalis and five E. faecium strains were isolated from 1026 samples obtained from the 19 farms. Ten sequence types were identified among the E. faecalis strains, of which ST256 (42.9%) and ST86 (25%) were the most abundant. The oxazolidinone and phenicol resistance genes poxtA, optrA, and fexA were detected in isolates of E. faecalis (100%, 85.7%, and 67.9%, respectively) and E. faecium (100%, 60%, and 80%, respectively). The minimum inhibitory concentrations of linezolid in these isolates ranged from 2 mg/L to 12 mg/L. The whole-genome sequencing data indicated that fexA was located upstream of poxtA. CONCLUSIONS: This is the first study to report the detection of poxtA in isolates that were both susceptible and resistant to linezolid in Korea. These results demonstrate the importance of antimicrobial resistance monitoring programmes, including regular antimicrobial susceptibility testing and resistance gene expression analysis, to facilitate the control of the spread of antibiotic resistance in non-clinical settings in Korea.

Emergence of Transferable mcr-9 Gene-Carrying Colistin-Resistant Salmonella enterica Dessau ST14 Isolated from Retail Chicken Meat in Korea.

Colistin is an important antibiotic currently used to manage infections caused by multidrug-resistant pathogens in both humans and livestock animals. A new mobile colistin-resistance (mcr-9) gene was recently discovered; this discovery highlighted the need for rigorous monitoring of bacterial resistance against colistin. Salmonella is one of the major pathogens responsible for foodborne illnesses; however, there is minimal information regarding the presence of mcr genes in foodborne Salmonella strains. The aim of this study was to investigate the presence of mcr genes among 178 Salmonella strains isolated from chicken meat in Korea. Antimicrobial susceptibility was measured using the broth microdilution method. Bioinformatics characterization of colistin-resistant strains and genetic environment of the mcr-9 gene were analyzed using next-generation sequencing. Transferability of the mcr-9 carrying colistin-resistant Salmonella strain was tested using broth-mating conjugation. Thirteen of the 178 Salmonella isolates showed colistin resistance, but only one strain, Salmonella Dessau ST14 (KUFSE-SAL043) from a traditional chicken market in Korea, carried an mcr family gene, mcr-9. This strain also carried other acquired antimicrobial resistance genes such as blaTEM-1B, qnrS1, and aac(6')-Iaa. Only the IncX1 plasmid replicon type was detected in this strain. In the strain KUFSE-SAL043, the mcr-9 gene was located between two insertion sequences, IS903B and IS26, followed by the downstream regulatory genes qseB-like and qseC-like, which were located between IS1R and ΔIS1R. Conjugation tests revealed that the mcr-9 gene was successfully transferred to Escherichia coli J53 at a mean frequency of 2.03 × 10-7. This is the first report of a transferable mcr-9 gene in Salmonella isolated from chicken meat in Korea, highlighting the possibility of transfer of colistin resistance. Therefore, the wide use of colistin should be reconsidered, and a One Health perspective should be adopted to monitor the antimicrobial resistance of Enterobacteriaceae strains in humans, livestock, and the environment.

Characterization of Extended-Spectrum ß-Lactamase-Producing Escherichia coli Isolated from Fresh Produce and Agricultural Environments in Korea.

ABSTRACT: This study was conducted to characterize Escherichia coli strains and evaluate the spread of antimicrobial resistance among these strains from fresh produce and farm environments in Korea. We then conducted phenotypic and genetic studies on antimicrobial-resistant isolates. We determined the genetic epidemiological characteristics of isolates that produced extended-spectrum ß-lactamase (ESBL) and confirmed plasmid transfer in isolates that carried blaCTX-M-type genes. E. coli strains were isolated from 8 samples of fresh produce and 152 samples from the farm environment collected from May 2014 to June 2016. Cephalosporin resistance was the most prevalent (61.8%) type of resistance among the isolates. Five ESBL-producing strains with high genetic homology with E. coli of human or livestock origin were identified. Lateral transfer of plasmids harboring blaCTX-M-type genes to transconjugants was successful. Two isolates from Chinese cabbage and from water samples collected from a nearby stream harbored the ISEcp1-blaCTX-M-55-orf477 operon and were confirmed as sequence type 1196 and the same type of plasmid replicon, suggesting that cross-contamination was highly likely. A high-risk clone of sequence type 69 (clonal complex 69) isolates was also recovered from the farm environment. This study provides genetic evidence that antimicrobial resistance factors in E. coli from farm environments originate in the clinic or in livestock, highlighting the fact that good agricultural practices in farming are important to inhibit the spread of antimicrobial resistance to bacteria on fresh produce.

Characterization of Vancomycin-Resistant Enterococcus faecalis and Enterococcus faecium Isolated from Fresh Produces and Human Fecal Samples.

Increased enterococcal infections in hospitals and multidrug-resistant and vancomycin-resistant enterococci (VRE) isolated from humans, animals, and food sources raised public health concern on the presence of VRE in multiple sources. We performed a comparative analysis of the antimicrobial resistance and genetics of VRE isolates derived from fresh produce and human fecal samples. Of 389 Enterococcus isolates, 8 fecal and 3 produce isolates were resistant to vancomycin and teicoplanin; all harbored vanA gene. The VRE isolates showed multidrug-resistant properties. The isolates from fresh produce in this study showed to have the common shared characteristics with the isolates from humans by the results of antimicrobial resistance, multilocus sequence typing, and Tn 1546 transposon analysis. Therefore, VRE isolates from fresh produce are likely related to VRE derived from humans. The results suggested that VRE may contaminate vegetables through the environment, and the contaminated vegetables could then act as a vehicle for human infections. Ongoing nationwide surveillance of antibiotic resistance and the promotion of the proper use of antibiotics are necessary.

Characterization of antimicrobial resistance and quinolone resistance factors in high-level ciprofloxacin-resistant Enterococcus faecalis and Enterococcus faecium isolates obtained from fresh produce and fecal samples of patients.

BACKGROUND: The emergence of fluoroquinolone-resistant enterococci is worldwide. Antimicrobial resistance was characterized and the effect of quinolone-resistance factors was analyzed in high-level ciprofloxacin-resistant (HLCR) Enterococcus faecalis and Enterococcus faecium isolated from fresh produce and fecal samples of patients. RESULTS: Among the 81 ciprofloxacin-resistant Enterococcus isolates, 46 showed high levels of ciprofloxacin resistance, resistance to other quinolone antibiotics, and multidrug resistance profiles. The virulence factors esp and hyl were identified in 27 (58.7%) and 25 (54.3%) of isolates, respectively. Sequence type analysis showed that 35 strains of HLCR E. faecium were clonal complex 17. Eleven strains of HLCR E. faecalis were confirmed as sequence type (ST) 28, ST 64 and ST 125. Quinolone resistance-determining region mutation was identified in HLCR Enterococcus isolates; with serine being changed in gyrA83, gyrA87 and parC80. This result shows that gyrA and parC mutations could be important factors for high-level resistance to fluoroquinolones. CONCLUSION: No significant differences were observed in antimicrobial resistance patterns and genetic characteristics among the isolates from fresh produce and fecal samples. Therefore, good agricultural practices in farming and continuous monitoring of patients, food and the environment for Enterococcus spp. should be performed to prevent antimicrobial resistance and enable reduction of resistance rates. © 2016 Society of Chemical Industry.

World Health Organization Ranking of Antimicrobials According to Their Importance in Human Medicine: A Critical Step for Developing Risk Management Strategies to Control Antimicrobial Resistance From Food Animal Production.

Antimicrobial use in food animals selects for antimicrobial resistance in bacteria, which can spread to people. Reducing use of antimicrobials-particularly those deemed to be critically important for human medicine-in food production animals continues to be an important step for preserving the benefits of these antimicrobials for people. The World Health Organization ranking of antimicrobials according to their relative importance in human medicine was recently updated. Antimicrobials considered the highest priority among the critically important antimicrobials were quinolones, third- and fourth-generation cephalosporins, macrolides and ketolides, and glycopeptides. The updated ranking allows stakeholders in the agriculture sector and regulatory agencies to focus risk management efforts on drugs used in food animals that are the most important to human medicine. In particular, the current large-scale use of fluoroquinolones, macrolides, and third-generation cephalosporins and any potential use of glycopeptides and carbapenems need to be addressed urgently.

Molecular Characterization of Plasmids Encoding CTX-M ß-Lactamases and their Associated Addiction Systems Circulating Among Escherichia coli from Retail Chickens, Chicken Farms, and Slaughterhouses in Korea.

Extended-spectrum ß-lactamases (ESBLs), particularly those of the CTX-M types, are the predominant resistance determinants of Escherichia coli that are rapidly spreading worldwide. To determine CTX-M types, E. coli isolates were collected from retail chickens (n = 390) and environmental samples from chicken farms (n = 32) and slaughterhouses (n = 67) in Korea. Fifteen strains harboring blaCTX-M genes were isolated from 358 E. coli isolates. The most common CTX-M type was eight of CTX-M-15, followed by six of CTX-M-1 and one of CTX-M- 14. The blaCTX-M genes were identified in the isolates from retail chickens (n = 9), followed by feces, water pipes, floors, and walls. Conjugations confirmed the transferability of the plasmids carrying blaCTX-M genes to the recipient E. coli J53 strain. Furthermore, eight addiction systems carried by the replicons in CTX-M types were confirmed. The dominant system was identified as ccdAB, vagCD, and pndAC in donor strains and transconjugants. The clonal relationship between the two strains carrying blaCTX-M genes indicates that E. coli may transmit from the farm to retail chickens, suggesting a possible public health risk. Our findings demonstrate that the detection of CTX-M types in E. coli isolates is important for tracking ESBL production in animals, and suggest linkage of multiple addiction systems in plasmids bearing blaCTX-M genes.

Prevalence of CTX-M-15 Extended-Spectrum ß-Lactamase-Producing Salmonella Isolated from Chicken in Korea.

A total of 162 Salmonella isolates were isolated in samples from poultry farms, slaughterhouses, retail chicken meats, and human feces between 2012 and 2013. All extended-spectrum ß-lactamase-producing isolates had bla(CTX-M-15) gene sequence in their plasmids. This genotype may be related to multidrug resistance. Repetitive sequence-based polymerase chain reaction patterns among CTX-M-15 isolates were classified into 12 indistinguishable groups. CTX-M-15 isolates had various plasmid replicon types; however, the most frequent type was FIIS. This result suggests that bla(CTX-M-15) could be propagated via plasmid transfer.

Transfer of tetracycline resistance genes with aggregation substance in food-borne Enterococcus faecalis.

Enterococcus faecalis has the ability to conjugate with the aid of aggregation substance (AS) and inducible sex pheromones to exchange genetic elements in food matrix. To evaluate the food safety condition and the transferable factor, 250 tetracycline-resistant food-borne E. faecalis were collected in Korea. Among the isolates, a majority of tetracycline-resistant isolates (49.6 %) harbored both the tet(M) and tet(L) genes together, followed by tet(M) (19.6 %), and tet(L) (6.8 %) alone. Also, we found the combination of tet(L)/tet(M)/tet(O) or tet(M)/tet(O). We identified two tet(S) genes including the isolate carrying tet(M) + tet(S) genes. Additionally, most E. faecalis were positive for cpd and ccf (both 96.8 %) followed by cob (57.2 %). Through mating experiments, we confirmed E. faecalis possessing the Int-Tn gene and/or any AS gene successfully transferred tet genes to JH2-2 E. faecalis, whereas neither E. faecalis carrying AS genes nor the Int-Tn gene showed the conjugation. Pulsed-field gel electrophoresis results supported a distinct pattern, implying transfer of genetic information. Our study revealed a high occurrence of tetracycline resistance genes in E. faecalis from various foods. The widespread dissemination of tetracycline resistance genes would be promoted to transfer tetracycline resistance genes by pheromone-mediated conjugation systems.

Prevalence and characterization of antimicrobial-resistant Escherichia coli isolated from conventional and organic vegetables.

To compare the characteristics and to identify the epidemiological relationships of Escherichia coli isolated from organic and conventional vegetables, the antimicrobial resistance and genetic properties of E. coli were investigated from 2010 to 2011. E. coli was isolated from 1 of 111 (0.9%) organic vegetables and from 20 of 225 (8.9%) conventional vegetables. The majority of strains were isolated from the surrounding farming environment (n=27/150 vs. 49/97 in organic vs. conventional samples). The majority of the vegetable strains were isolated from the surrounding farming environments. E. coli isolated from organic vegetables showed very low antimicrobial resistance rates except for cephalothin, ranging from 0% to 17.9%, while the resistance rates to cephalothin (71%) were extremely high in both groups. E. coli isolates expressed various resistance genes, which most commonly included blaTEM, tet(A), strA, strB, and qnrS. However, none of the isolates harbored tet(D), tet(E), tet(K), tet(L), tet(M), or qnrA. The transferability of tet gene, tet(A), and tet(B) was identified in tetracycline-resistant E. coli, and the genetic relationship was confirmed in a few cases from different sources. With regard to the lower antimicrobial resistance found in organic produce, this production mode seems able to considerably reduce the selection of antimicrobial-resistant bacteria on vegetables.

Increase of multidrug efflux pump expression in fluoroquinolone-resistant Salmonella mutants induced by ciprofloxacin selective pressure.

Multidrug-resistant foodborne pathogens are a leading public health concern, as antimicrobial resistance can lead to therapeutic failure. In this study, a ciprofloxacin-susceptible Salmonella Istanbul (Sal10-FC-KU12) was isolated from chicken meat obtained from a market in Korea to induce ciprofloxacin-resistant mutants (SalML, SalMM, and SalMH). Minimum inhibitory concentrations (MICs) of 12 antibiotics were measured in the presence or absence of an efflux pump inhibitor. Expression levels of efflux pump-related genes (acrB, acrF, marA, ramA, rob, and soxS) were determined using quantitative reverse transcription polymerase chain reaction (qRT-PCR). Elevated MICs for the derived mutants were shown to result from the action of the efflux pump, with increased expression of marA, ramA, and acrB compared with the wild-type strain. The results of this study suggest that continued use of ciprofloxacin might induce the emergence of Salmonella mutants resistant not only to fluoroquinolones, but also to several other classes of antimicrobials.

Molecular characterization of high-level gentamicin-resistant Enterococcus faecalis from chicken meat in Korea.

Because the intrinsically antimicrobial-resistant Enterococcus has acquired high-level aminoglycoside resistance genes, treating enterococcal infections is difficult. In this study, of the 101 food-borne Enterococcus faecalis isolates collected from retail chicken meat between 2003 and 2010, 11 high-level gentamicin-resistant (HLGR) E. faecalis isolates (MICs>2,048 µg/mL) were found. Molecular characterization was performed to determine the basis of this resistance. All HLGR E. faecalis isolates encoded aac(6')-Ie-aph(2″)-Ia and harbored at least 3 virulence traits in the asa1, esp, gelE, efaA, ace, and cylA genes. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were performed to characterize their molecular epidemiology. A total of 8 sequence types (STs), including 3 novel STs, were identified (ST35, ST82, ST116, ST202, ST300, ST403, ST407, and ST420). ST82, which is associated with amyloid arthropathy in poultry, was the most prevalent ST among HLGR E. faecalis isolates (4 out of 11 isolates, 36.4%); all other STs were identified in the isolates as well. The STs of food-borne HLGR E. faecalis in this study have been confirmed as corresponding to clinical isolates in the MLST database (DB), except for ST300 and the new STs. Three out of 11 isolates belonged to CC116, including ST116, ST407, and ST420. This study characterized HLGR E. faecalis isolates and provided evidence for the spread of HLGR E. faecalis with virulence factors to chicken sources in Korea. The emergence of food-borne HLGR E. faecalis suggests that chicken could be a potential source of transmission of antimicrobial resistance and virulence factors.

wksl3, a New biocontrol agent for Salmonella enterica serovars enteritidis and typhimurium in foods: characterization, application, sequence analysis, and oral acute toxicity study.

Of the Salmonella enterica serovars, S. Enteritidis and S. Typhimurium are responsible for most of the Salmonella outbreaks implicated in the consumption of contaminated foods in the Republic of Korea. Because of the widespread occurrence of antimicrobial-resistant Salmonella in foods and food processing environments, bacteriophages have recently surfaced as an alternative biocontrol tool. In this study, we isolated a virulent bacteriophage (wksl3) that could specifically infect S. Enteritidis, S. Typhimurium, and several additional serovars. Transmission electron microscopy revealed that phage wksl3 belongs to the family Siphoviridae. Complete genome sequence analysis and bioinformatic analysis revealed that the DNA of phage wksl3 is composed of 42,766 bp with 64 open reading frames. Since it does not encode any phage lysogeny factors, toxins, pathogen-related genes, or food-borne allergens, phage wksl3 may be considered a virulent phage with no side effects. Analysis of genetic similarities between phage wksl3 and four of its relatives (SS3e, vB_SenS-Ent1, SE2, and SETP3) allowed wksl3 to be categorized as a SETP3-like phage. A single-dose test of oral toxicity with BALB/c mice resulted in no abnormal clinical observations. Moreover, phage application to chicken skin at 8°C resulted in an about 2.5-log reduction in the number of Salmonella bacteria during the test period. The strong, stable lytic activity, the significant reduction of the number of S. Enteritidis bacteria after application to food, and the lack of clinical symptoms of this phage suggest that wksl3 may be a useful agent for the protection of foods against S. Enteritidis and S. Typhimurium contamination.

Phylogenetic group distribution and prevalence of virulence genes in Escherichia coli isolates from food samples in South Korea.

We analyzed the distribution of phylogenetic groups of foodborne Escherichia coli isolates. We also investigated the prevalence of virulence-associated genes of diarrheagenic E. coli. In total, 162 E. coli isolated from foods (raw meat, fish, and processed foods) were collected in Korea. Approximately 90% of the foodborne isolates belonged to phylogenetic groups A and B1, whereas 1.2% were allocated to group B2, and 9.3% to D. Multiplex polymerase chain reaction (PCR) assays were used to detect the following: stx (1) and stx (2) to identify Shiga toxin-producing E. coli (STEC), eae and bfpA to identify enteropathogenic E. coli (EPEC), ipaH for enteroinvasive E. coli, CVD432 for enteroaggregative E. coli, and lt and st for enterotoxigenic E. coli (ETEC). The presence of daaD in diffusely adherent E. coli was examined by singleplex PCR. Of the 162 foodborne E. coli isolates, three (1.9%) were confirmed to be pathogenic E. coli: STEC, ETEC, and atypical EPEC based on their possession of stx (1), st, and eae, and the pathogenic strains were isolated in beef, rockfish, and pork, respectively. Molecular typing was conducted by multilocus sequence typing to investigate the genetic relationships among the pathogenic strains. All isolates positive for virulence genes had different mulilocus sequence typing profiles representing different sequence types (ST) of ST101, ST1815, and ST1820. These results indicate that some food samples were contaminated with pathogenic E. coli.

Characterization of antimicrobial resistance of Escherichia coli recovered from foods of animal and fish origin in Korea.

Antimicrobial-resistant Escherichia coli is transferred from food-producing animals to humans through the food chain. We investigated the prevalence of antimicrobial resistance and resistance determinants and characterized the integrons of foodborne E. coli in Korea. In total, 162 E. coli isolates from commercial foods (raw meat, fish, and processed foods) were collected by the National Antimicrobial Resistance Management Program from 2004 to 2006. Susceptibility to 20 antibiotics was tested by disk diffusion, and resistance determinants were detected using PCR and genomic sequence analysis. The isolates were highly resistant to antibiotics commonly used in livestock farming. Resistance to tetracycline (74.7%) was the most frequently observed, followed by streptomycin (71%) and ampicillin (51.2%). Class 1 integrons were detected in 13 isolates (8%), and nine of these integrons were located on conjugative plasmids. None of the isolates produced extended-spectrum ß -lactamase. One isolate (0.6%) harbored bla(CMY-2), which was located on a conjugative plasmid. Although the qnr gene was not detected, aac(6'9)-Ib-cr was present in two isolates (1.2%). This is the first report of aac(6'9)-Ib-cr in food isolates. Three or four amino acid substitutions at positions 83 and 87 in gyrA and at positions 80 and/or 84 in parC were found in six isolates, representing high resistance to ciprofloxacin (MIC ≥ 16 mg/liter). These results suggest that E. coli isolates carrying resistance genes and integrons are present in the Korean food chain.

Characterization of the quinolone resistance mechanism in foodborne Salmonella isolates with high nalidixic acid resistance.

Sixteen Salmonella strains resistant to nalidixic acid isolated from kimbab, the most popular ready-to-eat (RTE) food in Korea, and chicken meat were selected for this study. The resistant strains were shown to have high minimal inhibitory concentrations (MICs) against nalidixic acid (512~4096 µg/mL). Among them, 4 Salmonella enterica serovar Haardt isolates showed multi-drug resistance (MDR) patterns with reduced susceptibility to fluoroquinolone (0.5 µg/mL of ciprofloxacin MICs). The mechanisms of quinolone resistance in the nalidixic acid resistant strains were characterized by PCR and sequence analysis. The presence of plasmid-mediated quinolone resistance (PMQR) genes and amino acid changes in the quinolone resistance determining region (QRDR) were investigated by PCR-based detection and sequencing, and the efflux pump inhibition test was also done using phe-arg-ß-naphthylamide (PAßN). Although PMQR genes were not detected in any of the tested strains, the QRDR mutations were found in this study: single mutation in gyrA (Asp87Tyr, Asp87Gly, and Asp87Asn), double mutations in gyrA (Ser83Thr) and parC (Thr57Ser), and single mutation in parC (Thr57Ser). MICs of nalidixic acid were reduced by 2- to 32-folds by the efflux pump inhibitor, PAßN. Pulsed-field gel electrophoresis (PFGE) was carried out to confirm the epidemiological relationship between the nalidixic acid resistant strains. The PFGE patterns were classified into 6 groups at cutoff level of 70~100% correlation on the dendrogram. Some strains of serotype Haardt and Enteritidis showed several values of genomic identity in accordance with strains, sources, and isolation year. We suggest that point mutation on QRDR and efflux pump systems involved in antimicrobials had independent effects on drug-resistance regardless of bacterial genomic variation.

Distribution and transferability of tetracycline resistance determinants in Escherichia coli isolated from meat and meat products.

Escherichia coli is used to assess the hygienic quality of food products and the dissemination of antimicrobial resistance. In particular, tetracycline-resistant E. coli can be chosen as an indicator of antibiotic resistant bacteria because it has a high frequency of occurrence. The purpose of this study was to investigate the distribution and transfer of tetracycline resistance determinants in meatborne E. coli. A total of 121 tetracycline-resistant E. coli isolates were collected from meat and meat products (raw meat, fish, and processed foods) from 2004 to 2006 in Korea. Among these isolates, tet(A) (52.4%) was the most frequent tetracycline resistance determinant, followed by tet(B) (41.3%), whereas tet(C) (1.7%) and tet(D) (0.8%) were less frequently identified. Two isolates (1.6%) contained two tet genes simultaneously, tet(A) and tet(B). Minimal inhibitory concentrations (MICs) to tetracycline family antibiotics, such as tetracycline, minocycline, doxycycline, oxytetracycline, and chlortetracycline were higher for isolates carrying the tet(B) gene compared to isolates carrying tet(A) (P<0.0001). Conjugation experiments were performed by the broth mating method; 119 isolates (98.3%) containing at least one of the tet genes were shown to transfer tetracycline resistance to recipient E. coli J53. Also, we observed high diversity of tetracycline-resistant E. coli isolates in meat and meat products in Korea by using XbaI pulsed-field gel electrophoresis (PFGE) typing. This study suggests that the high prevalence of tetracycline-resistant E. coli in meat may be due to the high transferability of tet determinants.

Prevalence and diversity of carbapenemases among imipenem-nonsusceptible Acinetobacter isolates in Korea: emergence of a novel OXA-182.

Increase in multidrug-resistant Acinetobacter poses a serious problem in Korea. In this study, 190 imipenem (IPM)-nonsusceptible (NS) Acinetobacter isolates from 12 Korean hospitals in 2007 were used to determine species, prevalence, and antimicrobial susceptibility of OXA carbapenemase- and metallo-ß-lactamase (MBL)-producing isolates. bla(OXA)-23-like and ISAba1-asssociated bla(OXA)-51-like genes were detected in 80% and 12% of 178 IPM-NS Acinetobacter baumannii isolates, respectively. A novel bla(OXA)-182 was detected in 12 IPM-NS A. baumannii isolates. Twelve out of 14 MBL-producing isolates were non-baumanniiAcinetobacter. A. baumannii isolates with OXA carbapenemase were more often resistant to aminoglycosides, ciprofloxacin, and tigecycline than non-baumannii Acinetobacter isolates with MBL. Identical pulsed- field gel electrophoresis patterns were observed in 89% of A. baumannii isolates with bla(OXA)-23-like gene. In conclusion, extremely rapid increase of IPM-NS A. baumannii in previous Korean studies was mainly due to clonal spread of OXA-23-producing A. baumannii isolates. A novel OXA-182 emerged in Korea.