Gun Jo Woo

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-β-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.

VanB phenotype-vanA genotype Enterococcus faecium with heterogeneous expression of teicoplanin resistance.

ABSTRACT Six VanB phenotype-vanA genotype isolates of Enterococcus faecium with heterogeneous expression of teicoplanin resistance which gave rise to an outbreak at a Korean tertiary care teaching hospital have IS1216V in the coding region of vanS. This could be the underlying cause of the VanB phenotype-vanA genotype with heterogeneous expression of teicoplanin resistance.

Novel variants of the qnrB gene, qnrB22 and qnrB23, in Citrobacter werkmanii and Citrobacter freundii.

Resistance to quinolones in Gram-negative bacteria is usually mediated by the following: (i) chromosomal mutations that alter the target enzymes, DNA gyrase and topoisomerase IV, in their quinolone resistance-determining regions (QRDR), (ii) changes in drug entry (loss of porin channels), and (iii) the presence of plasmid-mediated quinolone resistance (PMQR) determinants [qnrA, qnrB, qnrS, qnrC, and qnrD, coding for Qnr proteins that protect DNA gyrase from quinolone attack; aac(6′)-Ib-cr, coding for a protein that acetylates quinolones; and qepA, coding for a quinolone efflux pump] (2, 12). The recent worldwide emergence of PMQR due to the qnr and aac(6′)-Ib-cr genes is a concerning fact among human and animal Gram-negative pathogens (8). n nThe aim of this study was to determine the prevalence of qnr genes among 93 consecutive nonrepetitive Enterobacteriaceae of animal origin and to characterize positive isolates. These isolates were collected from chickens (n = 37) and pigs (n = 56) at five farms near the city of Seoul (South Korea) in 2007. n nThe presence of PMQR determinants and QRDR mutations was investigated by PCR-based detection and sequencing (2, 5, 6). The qnrA, qnrS, qnrC, qnrD, aac(6′)-Ib-cr, and qepA genes were not found. Two isolates (2.2%) were found to carry qnr-like genes (Citrobacter werkmanii PS012 and Citrobacter freundii S008). Sequence analysis identified two novel qnrB variants, qnrB22 and qnrB23, in C. werkmanii PS012 (isolated from a pig at the Daeyoung Farm) and C. freundii S008 (isolated from a chicken at the Hanmi Farm), respectively. These new variants were assigned according to the qnr numbering scheme shown in the Lahey website (http://www.lahey.org/qnrStudies). The qnrB22 gene had 99.7% nucleotide identity with qnrB4. The qnrB23 gene had 99.9% nucleotide identity with qnrB9. The deduced QnrB22 product had two amino acid substitutions (Ser36Cys and Gly188Val) compared with the amino acid sequence of QnrB4. Compared with the amino acid sequence of QnrB9, QnrB23 showed one amino acid substitution (Asn27Tyr). n nC. werkmanii PS012 showed a reduced susceptibility (MIC > 0.125 μg/ml) to fluoroquinolones (ofloxacin, norfloxacin, levofloxacin, and ciprofloxacin) (Table u200b(Table1).1). C. freundii S008 was nonsusceptible (resistant or intermediate) to the fluoroquinolones (Table u200b(Table1).1). The MICs were determined by E-test (AB Biodisk, Solna, Sweden) and interpreted according to Clinical and Laboratory Standards Institute guidelines (4). The QRDR mutations associated with fluoroquinolone resistance were not detected in the two isolates (Table u200b(Table11). n n n nTABLE 1. n nCharacteristics of the two Citrobacter isolates, their transconjugants, Escherichia coli DH5α transformants, and reference (recipient or host) strains n n n nThe transfer of qnrB22- and qnrB23-harboring plasmids to Escherichia coli J53 AzideR was accomplished through mating experiments described previously (9). Transconjugants were selected on Mueller-Hinton agar plates containing sodium azide (150 μg/ml) and ciprofloxacin (0.125 μg/ml). Fluoroquinolone (or nalidixic acid) MICs of the two transconjugants (TrcPS012 and TrcS008) were similar to those of the donor strains (Table u200b(Table1).1). Strain TrcS008, carrying qnrB23, had MIC values for nalidixic acid and fluoroquinolones that were higher than those of TrcPS012, harboring qnrB22 (Table u200b(Table11). n nThe PCR amplicons of the qnrB22 and qnrB23 genes were cloned into the vector pCR-BluntII-TOPO and transformed into the E. coli DH5α host strain (Invitrogen, Karlsruhe, Germany). Primers used were as follows: for cloning of qnrB22, 5′-ATGACTCTGGCGTTAGTTGG-3′ and 5′-TTAACCCATGACAGCGATACCAA-3′; and for cloning of qnrB23, 5′-ATGACGCCATTACTGTATAAAAAAACA-3′ and 5′-CTAGCCAATAATCGCGATGCC-3′. A decrease in quinolone susceptibility was observed with both transformants, even though the qnrB23-carrying transformant showed higher MICs than that carrying qnrB22 (Table u200b(Table1).1). Fluoroquinolone (or nalidixic acid) MICs of two transformants (TrfPS012 and TrfS008) were lower than those of two transconjugants (TrcPS012 and TrcS008), which was compatible with a recent finding (11). The differences observed between transconjugants and transformants might be related to recipient susceptibility (E. coli DH5α was more susceptible than E. coli J53 AzideR), plasmid copy number, and/or the presence of additional PMQR determinants in the two plasmids. n nThe conjugative plasmids of C. werkmanii PS012 and C. freundii S008 showed identical patterns (showing 13 distinct bands) and similar molecular sizes (about 23 kb) in restriction fragment length polymorphism analysis after digestion with BglII, as described previously (1). qnrB22- and qnrB23-harboring plasmids belonged to an incompatibility group, IncL/M, according to a PCR-based replicon-typing scheme (3). These results suggest that conjugative IncL/M plasmids might play a role in the dissemination and evolution of qnrB genes. The association of various antibiotic resistance genes, including PMQR determinants with conjugative IncL/M plasmids from human isolates of the Enterobacteriaceae, has been described in several reports (7, 10, 13, 14). Despite the currently low prevalence (2.2%) of qnrB22 and qnrB23, surveillance for bacterial isolates carrying these resistance determinants in animals is warranted.