ObjectivesThis study investigated the fluoroquinolone-resistant mechanism of 56 clinical cases of A baumannii infection from 23 non-tertiary hospitals, collected between 2004 and 2006.MethodsSusceptibility testing was performed by broth microdilution and Epsilometer test. Analyses of quinolone resistance-determining region (QRDR) were done by sequencing. The activity of the efflux pump was measured using inhibitors.ResultsThe sequences from selected 56 isolates were divided into seven groups (I-VII) on the basis of mutations in gyrA (S83L), parC (S80L, S80W and S84K) and gyrB (containing the novel mutations E679D, D644Y and A677V). The 27 isolates with triple mutations in gyrA, gyrB and parC (groups IV-VII) showed higher levels of resistance to ciprofloxacin (minimal inhibitory concentration [MIC] of 16-256 μg/mL) than the 26 isolates with double mutations in gyrA and parC (groups II and III, MIC of 8-64 μ g/mL; p < 0.05). Alterations in the efflux pump were observed in four isolates with the parC S80L mutation (group II) or E84K mutation (group VII), but no effect was observed in an isolate with the parC S80 W mutation (group III).ConclusionThese results suggest that triple mutations in clinical isolates of A baumannii contribute to the development of high levels of resistance to fluoroquinolones and that mutations in parC S80L or E84K (groups II and VII) may contribute to alterations in efflux pump activity in A baumannii.

PurposeSince November 2006, imipenem-resistant Acinetobacter baumannii isolates have increased in Kyung Hee University Hospital in Seoul, Korea. The purpose of this study was to determine the genetic basis and molecular epidemiology of outbreak isolates.Materials and MethodsForty-nine non-repetitive isolates of the 734 IRAB strains were investigated in order to determine their characteristics. The modified Hodge and the ethylenediaminetetraacetic acid (EDTA)-disk synergy test were performed for the screening of carbapenemase and metallo-β-lactamase production. Multiplex polymerase chain reaction (PCR) assays were performed for the detection of genes encoding for OXA-23-like, OXA-24-like, OXA-58-like and OXA-51-like carbapenemase. Pulsed-field gel electrophoresis (PFGE) was performed for strain identification.ResultsAll isolates showed 100% resistance to ciprofloxacin and gentamicin, 97.9% resistance to cefepime, piperacillin/tazobactam, aztreonam, ceftazidime and piperacillin, 93.9% resistance to tobramycin and 57.1% resistance to amikacin. All of the 49 isolates (100%) showed positive results in the modified Hodge test and negative results in the EDTA-disk synergy test. They all (100%) possessed the encoding gene for an intrinsic OXA-51-like carbapenemase and an acquired OXA-23-like carbapenemase in the multiplex PCR assay. PFGE patterns revealed that all isolates were clonally related from A1 to A14.ConclusionIt is concluded that all of the 49 IRAB isolates acquired resistance to imipenem by producing OXA-23 carbapenemase and they might have originated from a common source.

We characterized two new streptogramin A resistance genes from quinupristin-dalfopristin-resistant Enterococcus faecium JS79, which was selected from 79 E. faecium isolates lacking known genes encoding streptogramin A acetyltransferase. A 5,650-bp fragment of HindIII-digested plasmid DNA from E. faecium JS79 was cloned and sequenced. The fragment contained two open reading frames carrying resistance genes related to streptogramin A, namely, genes for an acetyltransferase and an ATP efflux pump. The first open reading frame comprised 648 bp encoding 216 amino acids with a predicted left-handed parallel ␤-helix domain structure; this new gene was designated vatG. The second open reading frame consisted of 1,575 bp encoding 525 amino acids with two predicted ATPase binding cassette transporters comprised of Walker A, Walker B, and LSSG motifs; this gene was designated vgaD. vgaD is located 65 bp upstream from vatG, was detected together with vatG in 12 of 179 quinupristin-dalfopristin-resistant E. faecium isolates, and was located on the same plasmid. Also, the 5.6-kb HindIII-digested fragment which was observed in JS79 was detected in nine vgaD-and vatG-containing E. faecium isolates by Southern hybridization. Therefore, it was expected that these two genes were strongly correlated with each other and that they may be composed of a transposon. Importantly, vgaD is the first identified ABC transporter conferring resistance to streptogramin A in E. faecium. Pulsed-field gel electrophoresis patterns and sequence types of vgaD-and vatG-containing E. faecium isolates differed for isolates from humans and nonhumans.

We identified 25 high-level mupirocin-resistant (MuH) and 21 low-level mupirocin-resistant (MuL) Staphylococcus aureus isolates from eight long-term-care facilities (LTCFs). The pulsed-field gel electrophoresis patterns of 19 MuH and 19 MuL isolates from two facilities were identical for 18 and 15 isolates, respectively. The most predominant mupA restriction fragment length polymorphism type was found in 21 MuH isolates. We conclude that clonal transmission of MuH and MuL S. aureus strains occurred in these LTCFs. This is the first report of clonal transfer of mupirocin resistance in LTCFs.Colonization and infection with Staphylococcus aureus are common in older people in long-term-care facilities (LTCFs) (1, 2, 4). The prevalence of S. aureus colonization and infection, which result primarily from methicillin-resistant strains, has recently been reported by chronic care facilities worldwide (1,3,6,7). Mupirocin calcium ointment is a topical antibiotic indicated for the eradication of nasal carriage of staphylococci, including methicillin-resistant strains. Mupirocin alone or in combination with other antimicrobial agents decreases S. aureus colonization among residents of LTCFs (3,7,8,20). Several outbreaks of methicillin-resistant S. aureus colonization and infection in LTCFs have been reported, and until now, it was thought that the application of mupirocin ointment might help break the chain of transmission. However, the extensive use of this agent has led to the rapid emergence of mupirocinresistant strains in different parts of the world (9,16,11,13,18,19). To our knowledge, there are no reports on the prevalence and outbreak of mupirocin-resistant S. aureus in LTCFs. In South Korea, mupirocin ointment has been used since 1994 to eradicate staphylococcal infection in hospitals, and the prevalence and mechanisms of mupirocin-resistant staphylococci were first reported in 2003 (23).We investigated the clonal transmission of high-level mupirocin-resistant (MuH) and low-level mupirocin-resistant (MuL) S. aureus and the mupA gene polymorphisms of MuH S. aureus strains in LTCFs. Seven hundred forty-nine swab specimens were obtained from patients of eight LTCFs from July to August 2002. Nasal swab specimens were obtained from 632 patients (one isolate per patient), and 117 infection swab samples were obtained from infected sites (e.g., sore, wound, or trachea) present in these patients. Swab specimens were cultured on staphylococcal broth (Trypticase soy broth [TSB]) medium for 24 h at 35°C. Mannitol salt agar and mannitol salt oxacillin agar supplemented with 6 g/ml oxacillin were used to isolate S. aureus and methicillin-resistant S. aureus, respectively. Initial identification was based on colony morphology, Gram staining, the coagulase test using the Staphaureux latex agglutination kit (Murex Biotech Ltd., Dartford, United Kingdom), and thermonuclease production with DNase medium (Becton Dickinson, Franklin Lakes, NJ). When necessary, further confirmatory tests were performed using a Vitek system (bioMerieux,...