Mechanisms of carbapenem resistance among a collection of Enterobacteriaceae clinical isolates in a Texas city.
ABSTRACT Fourteen Enterobacteriaceae isolates with ertapenem MIC >2 mg/mL were analyzed to identify mechanisms of resistance. All isolates produced extended-spectrum beta-lactamase or AmpC beta-lactamase with variable, but decreased, expression of outer membrane proteins. One Enterobacter cloacae produced derepressed AmpC beta-lactamase, 1 Escherichia coli expressed plasmid-mediated AmpC beta-lactamase, and 1 E. cloacae produced a carbapenemase.
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ABSTRACT: The emergence and spread of resistance in Enterobacteriaceae are complicating the treatment of serious nosocomial infections and threatening to create species resistant to all currently available agents. Approximately 20% of Klebsiella pneumoniae infections and 31% of Enterobacter spp infections in intensive care units in the United States now involve strains not susceptible to third-generation cephalosporins. Such resistance in K pneumoniae to third-generation cephalosporins is typically caused by the acquisition of plasmids containing genes that encode for extended-spectrum beta-lactamases (ESBLs), and these plasmids often carry other resistance genes as well. ESBL-producing K pneumoniae and Escherichia coli are now relatively common in healthcare settings and often exhibit multidrug resistance. ESBL-producing Enterobacteriaceae have now emerged in the community as well. Salmonella and other Enterobacteriaceae that cause gastroenteritis may also be ESBL producers, which is of relevance when children require treatment for invasive infections. Resistance of Enterobacter spp to third-generation cephalosporins is most typically caused by overproduction of AmpC beta-lactamases, and treatment with third-generation cephalosporins may select for AmpC-overproducing mutants. Some Enterobacter cloacae strains are now ESBL and AmpC producers, conferring resistance to both third- and fourth-generation cephalosporins. Quinolone resistance in Enterobacteriaceae is usually the result of chromosomal mutations leading to alterations in target enzymes or drug accumulation. More recently, however, plasmid-mediated quinolone resistance has been reported in K pneumoniae and E coli, associated with acquisition of the qnr gene. The vast majority of Enterobacteriaceae, including ESBL producers, remain susceptible to carbapenems, and these agents are considered preferred empiric therapy for serious Enterobacteriaceae infections. Carbapenem resistance, although rare, appears to be increasing. Particularly troublesome is the emergence of KPC-type carbapenemases in New York City. Better antibiotic stewardship and infection control are needed to prevent further spread of ESBLs and other forms of resistance in Enterobacteriaceae throughout the world.American Journal of Infection Control 07/2006; 34(5 Suppl 1):S20-8; discussion S64-73. · 2.73 Impact Factor
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ABSTRACT: Membrane permeability is the first step involved in resistance of bacteria to an antibiotic. The number and activity of efflux pumps and outer membrane proteins that constitute porins play major roles in the definition of intrinsic resistance in Gram-negative bacteria that is altered under antibiotic exposure. Here we describe the genetic regulation of porins and efflux pumps of Escherichia coli during prolonged exposure to increasing concentrations of tetracycline and demonstrate, with the aid of quantitative real-time reverse transcriptase-polymerase chain reaction methodology and western blot detection, the sequence order of genetic expression of regulatory genes, their relationship to each other, and the ensuing increased activity of genes that code for transporter proteins of efflux pumps and down-regulation of porin expression. This study demonstrates that, in addition to the transcriptional regulation of genes coding for membrane proteins, the post-translational regulation of proteins involved in the permeability of Gram-negative bacteria also plays a major role in the physiological adaptation to antibiotic exposure. A model is presented that summarizes events during the physiological adaptation of E. coli to tetracycline exposure.PLoS ONE 01/2007; 2(4):e365. · 3.73 Impact Factor
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ABSTRACT: A Klebsiella pneumoniae clinical isolate was resistant to cefoxitin, cefotaxime, ceftazidime, ceftazidime- clavulanate, piperacillin-tazobactam (MICs, >256 g/ml in all cases), and meropenem (MIC, 16 g/ml) and was intermediate to imipenem (MIC, 8 g/ml). Decreased expression of the OmpK36 porin and expression of an SHV-2 -lactamase contributed to the observed resistance to these -lactam-containing agents. Expanded-spectrum cephalosporins play an important role in the treatment of infections due to Klebsiella pneumoniae. However, the presence of a carbapenemase or the expression of AmpC or SHV-2 -lactamases combined with decreased outer membrane permeability provide resistance to these agents (3, 7, 10). In this report, we investigate the resistance mechanisms in a K. pneumoniae clinical isolate resistant to oxyiminocephalos- porins, -methoxycephalosporins, and carbapenems. K. pneu- moniae 103624 was isolated from blood cultures of a 60-year- old male with pneumonia. He was neutropenic following chemotherapy for Hodgkin's lymphoma, developed pneumo- nia, and was treated empirically with ceftazidime. After receipt of antibiotic susceptibility test results, treatment was changed to a combination of imipenem, gentamicin, and ciprofloxacin. Following 2 weeks of treatment, all signs of pneumonia had resolved. The patient had received 7 days of treatment with piperacillin-tazobactam and ceftazidime 6 weeks prior to this episode. The susceptibility of K. pneumoniae 103624 to anti- microbials (Table 1) indicated resistance to -methoxycepha- losporins (cefoxitin); oxyiminocephalosporins (cefotaxime and ceftazidime); -lactam--lactamase inhibitor combinations such as ceftazidime-clavulanate, piperacillin-tazobactam (MICs, 256 g/ml in all cases), and amoxicillin-clavulanate (MICs, 64 and 32 g/ml, respectively); and meropenem (MIC, 16 g/ml), and intermediate status for imipenem (MIC, 8 g/ ml). However, the strain was susceptible to all of the non-- lactam compounds tested, such as gentamicin, amikacin, to- bramycin, ciprofloxacin, and tetracycline. Isoelectric focusing analysis of K. pneumoniae 103624 was performed as previously described (13) and yielded one single -lactamase band with pI 7.6 that was inhibited by clavulanate but not by EDTA. Plasmid analysis of K. pneumoniae 103624 showed that the organism carried two plasmids of 3 and 90 kb designated p3 and p90, respectively. The plasmid carrying the -lactamase gene (p90) was identified after conjugation-medi- ated transfer to Escherichia coli K-12 14R525 and selection on amoxicillin (50 g/ml) and nalidixic acid (30 g/ml). It was associated with resistance to ceftazidime and cefotaxime and did not confer resistance to other antibiotics, including cefox- itin, imipenem, and meropenem (Table 1). Transconjugants were more resistant to ceftazidime-clavulanate and piperacil- lin-tazobactam but remained susceptible to gentamicin, ami- kacin, ciprofloxacin, and tetracycline (MICs of 0.125, 1.0, 0.125, and 0.5 g/ml, respectively). Isoelectric focusing analysis also revealed a single -lactamase band with pI 7.6 that was inhibited by clavulanate. PCR amplification using the SHV primers GCCCGGGTTATTCTTATTTGTCGC and TCTT- TCCGATGCCGCCGCCAGTCA (5-to-3 sequences) (11) and restriction fragment length polymorphism (RFLP) analysis of the PCR amplicon from isolate 103624 with NheI produced two fragments of 770 and 247 bp, confirming the presence of the SHV-2 gene, and an unrestricted product of 1,017 bp, which indicated the additional presence of SHV-1. The same PCR-RFLP analysis applied to the transconjugant produced only the 770- and 247-bp fragments, corresponding to the pres- ence of SHV-2 alone. This was further confirmed by DNA sequencing (Applied Biosystems sequencer and dye-termina- tor chemistry). These data indicated that K. pneumoniae 103624 expresses a plasmid-borne extended-spectrum -lacta- mase, SHV-2, and implied that another nontransferable mech- anism should be responsible for the observed resistance to expanded-spectrum cephalosporins, cefoxitin, and carbapen- ems. Since porin deficiency is a well-established mechanism of resistance in K. pneumoniae and other species, the outer mem- brane of the isolate was characterized. Outer membrane proteins (OMPs) and porins were isolated by differential solubilization in sodium lauryl sarkosinate and by a combination of methods, respectively, as described before (1). Electrophoretic analysis was performed in sodium dodecyl sulfate (SDS)-11% polyacrylamide gels as described previously (6).Antimicrobial Agents and Chemotherapy - ANTIMICROB AGENTS CHEMOTHER. 01/2002; 46(11):3679-3682.