Antimicrobial susceptibility studiesPlasmid-mediated, inducible AmpC β-lactamase (DHA-1)-producing Enterobacteriaceae at a Korean hospital: wide dissemination in Klebsiella pneumoniae and Klebsiella oxytoca and emergence in Proteus mirabilis
Introduction
β-Lactamase production is the predominant mechanism for resistance to β-lactam antibiotics in Gram-negative bacilli. Resistance due to extended-spectrum β-lactamase (ESBL) appeared in Klebsiella pneumoniae and in other enterobacterial species, but they remained susceptible to cephamycins (Philippon et al., 2002).
Plasmid-mediated AmpC β-lactamases were first detected in 1988 (Bauernfeind et al., 1989, Bauernfeind et al., 1998, Papanicolaou et al., 1990), and subsequently various AmpC enzymes have been found, particularly in Klebsiella spp., Escherichia coli, and Proteus mirabilis (Paterson et al., 2003, Philippon et al., 2002). The majority of plasmid-mediated AmpC enzymes are expressed constitutively, with the exceptions of DHA, ACT-1, and CFE-1. DHA-1 was first reported in 1992 in Salmonella enteritidis in Saudi Arabia and France (Gaillot et al., 1997), DHA-2 in K. pneumoniae in France (Fortineau et al., 2001), ACT-1 in K. pneumoniae in the United States (Reisbig and Hanson, 2002), and CFE-1 in Citrobacter freundii in Japan (Nakano et al., 2004).
In Korea, cefoxitin-resistant E. coli and K. pneumoniae has been increasingly noted. A recent investigation detected 15 isolates with undetermined blaDHA subtype (Song et al., 2002). Recently, we have increasingly noted presence of induction-positive isolates of K. pneumoniae at a tertiary care hospital laboratory.
Some of the plasmid-mediated AmpC enzyme-producing isolates are susceptible to third-generation cephalosporins and aztreonam in vitro (Philippon et al., 2002), but their clinical utility is uncertain. As for DHA-producing organisms, even in vitro susceptibility data are limited, because only a few studies have been reported (Alvarez et al., 2004, Yan et al., 2002). In addition to the treatment problem, accurate differentiating methods for plasmid-mediated AmpC β-lactamase-producing isolates are required to improve surveillance and infection control (Perez-Perez and Hanson, 2002), but the current guidelines from the National Committee for Clinical Laboratory Standards (NCCLS, 2004) do not include any recommendation. Recently, Perez-Perez and Hanson (2002) recommended the use of multiplex PCR to identify family-specific AmpC β-lactamase genes.
The aim of this study was to determine the phenotypic and genetic characteristics of induction-positive strains of E. coli, Klebsiella spp., and P. mirabilis isolated at a Korean hospital. We also investigated the susceptibility, inoculum effect on the minimum inhibitory concentrations of antimicrobial agents, and the molecular epidemiological features of blaDHA-1 allele-positive strains.
Section snippets
Screening of inducible AmpC β-lactamase– and ESBL-producing isolates
Bacterial strains were isolated from patients at a Korean tertiary care hospital between June and December 2002. Species were identified by conventional methods or by using the Vitek GNI system (bioMérieux, Marcy l'Etoile, France). Cefoxitin-resistant E. coli, Klebsiella spp., and P. mirabilis isolates, detected by the disk diffusion method (NCCLS, 2002) using commercial disks and Mueller-Hinton agar (Becton Dickinson, Cockeysville, MD), were tested for induction by applying cefoxitin and
Detection of DHA-producing isolates
Of the 3,109 unduplicated isolates of E. coli, K. pneumoniae, K. oxytoca, and P. mirabilis tested, 15.0%, 29.0%, 16.8%, and 9.7%, respectively, were resistant to cefoxitin (Table 1). Of the cefoxitin-resistant isolates, induction was observed in 8 of 291 (2.7%) E. coli, 55 of 261 (21.1%) K. pneumoniae, 8 of 25 (32.0%) K. oxytoca, and 1 of 12 (8.3%) P. mirabilis isolates.
blaDHA alleles were detected by PCR in all of the 72 induction-positive isolates. All of these isolates showed positive PCR
Discussion
Plasmid-mediated AmpC β-lactamase-producing gram-negative bacilli are being found increasingly in many parts of the world (Philippon et al., 2002), but reports on DHA-producing organisms are relatively rare. CMY-1-producing K. pneumoniae and E. coli have been prevalent and single amino acid-substituted CMY-1b (CMY-10) has emerged in Korea (Bauernfeind et al., 1998). Therefore, most of the plasmid-mediated AmpC β-lactamases in Korea was presumed to be these enzymes until other types were
Acknowledgment
This study was supported by the Yonsei University Research Fund (2003-35).
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Risk factors and clinical features of infections caused by plasmid-mediated AmpC β-lactamase-producing Enterobacteriaceae
2009, International Journal of Antimicrobial AgentsCitation Excerpt :Use of antibiotics, especially an oxyimino-cephalosporin, is also an important risk factor for acquisition of an ESBL-producing organism [14,20,21]. With respect to plasmid AmpC-producing Enterobacteriaceae, however, there are only a surprisingly few studies to assess risk factors and clinical outcome, although there are several reports of nosocomial outbreaks [22–24] and increasing prevalence [3–5,25]. We previously reported that clinical features and outcomes of the patients infected with plasmid AmpC-producing K. pneumoniae are similar to those of patients infected with ESBL-producers [8].
Spread of multidrug-resistant Proteus mirabilis isolates producing an AmpC-type β-lactamase: epidemiology and clinical management
2009, International Journal of Antimicrobial AgentsCitation Excerpt :Very little is known in terms of the clinical management and outcome of infections caused by enterobacteria producing acquired CBLs [8]. In P. mirabilis, the production of acquired CBLs belonging to different lineages (ACC, CMY/LAT and DHA) has been occasionally reported from Europe, the USA and Asia [7,9–12]. No major outbreaks have been reported yet.
Emerging problems with plasmid-mediated DHA and CMY AmpC β-lactamases in Enterobacteriaceae in Singapore
2007, International Journal of Antimicrobial AgentsFalse susceptibility to cefotetan reported by MicroScan for DHA-type AmpC β-lactamase-producing Klebsiella pneumoniae
2007, Clinical Microbiology and InfectionPrevalence and mechanisms of decreased susceptibility to carbapenems in Klebsiella pneumoniae isolates
2007, Diagnostic Microbiology and Infectious DiseaseCitation Excerpt :Further studies are needed to elucidate the relationship between carbapenems MICs and factors affecting them. In conclusion, although the prevalence of carbapenem resistance was very low in Korean isolates of K. pneumoniae collected in 2003, considering the recent report that SHV-12– and DHA-1–producing isolates of K. pneumoniae are widely disseminated at Korean hospitals (Kim et al., 2005; Yong et al., 2005), it might have increased. Therefore, there is a need for continuous monitoring of carbapenem susceptibility and of carbapenemase production.