KPC screening by updated BD Phoenix and Vitek 2 automated systems.

Current BD Phoenix and Vitek 2 methodologies were assessed as screens for KPC ß-lactamases. Using carbapenem MICs or expert system interpretations as screens, both systems exhibited high (97%) sensitivity in tests with 103 well-characterized Gram-negative isolates, 77 of which were KPC producers.

In vitro activity of tigecycline against multidrug-resistant Acinetobacter baumannii and selection of tigecycline-amikacin synergy.

Polymyxin B, minocycline, and tigecycline were the most potent of 10 antibiotics against 170 isolates of multidrug-resistant Acinetobacter baumannii. In time-kill studies, the exposure of a highly tigecycline-resistant isolate to tigecycline resulted in enhanced susceptibility to amikacin and synergistic bactericidal activities of the two drugs.

Cefdinir: an oral alternative to parenteral cephems.

Cost savings are possible if oral cephems of equivalent efficacy can be substituted for parenteral cephems. An in vitro study was performed to compare the activity of cefdinir, cefoxitin, cefazolin, ceftriaxone, ceftazidime, and cefepime against 243 clinical isolates of human pathogens. Activities were determined by National Committee for Clinical Laboratory Standards microbroth dilution methodology using an inoculum of approximately 5 x 10(5) CFU/mL. Cefdinir was the single or equally most potent agent against Streptococcus pyogenes, penicillin-susceptible Streptococcus pneumoniae, methicillin-susceptible Staphylococcus aureus, and Klebsiella pneumoniae isolates that produced a variety of beta-lactamase types. Cefdinir was less potent than ceftriaxone, ceftazidime, and cefepime against Haemophilus influenzae, but was 2- to 8-fold more potent than cefoxitin and 8- to 32-fold more potent than cefazolin. Cefdinir was slightly less potent than ceftazidime, against beta-lactamase-positive Moraxella catarrhalis. These data support clinical consideration of cefdinir as an alternative to parenteral cephems in infections where adequate tissue levels can be safely assured.

Convenient test using a combination of chelating agents for detection of metallo-beta-lactamases in the clinical laboratory.

Although transmissible metallo-beta-lactamases (MBLs) are a serious threat to beta-lactam antibiotic therapy, the CLSI currently does not recommend testing methods for the detection of MBLs. The aim of this study was to evaluate the capability of double-disk tests (DDTs) by using disks containing a combination of the chelators 2-mercaptopropionic acid (MPA) and Tris-EDTA (TE) to detect MBLs. Sixteen isolates (4 Acinetobacter baumannii isolates, 6 Pseudomonas aeruginosa isolates, 1 Serratia marcescens isolate, 1 Aeromonas hydrophila isolate, 1 Aeromonas veronii isolate, 2 Chryseobacterium meningosepticum isolates, and 1 Stenotrophomonas maltophilia isolate) producing IMP-1, IMP-1-like, IMP-18, GIM-1, SPM-1, VIM-2, VIM-2-like, and chromosomal MBLs and 20 isolates (7 Klebsiella pneumoniae isolates, 3 Escherichia coli isolates, 5 Enterobacter cloacae isolates, 2 S. marcescens isolates, 1 Proteus mirabilis isolate, and 2 A. baumannii isolates) producing non-MBL carbapenemases, AmpC beta-lactamases, and extended-spectrum beta-lactamases were tested. The DDT method was evaluated by using four types of chelator disks (TE, high-strength TE, MPA, and TE plus 20 microl of MPA [at various concentrations]) and the beta-lactams imipenem (IPM), meropenem (MEM), ertapenem (ERT), and ceftazidime (CAZ). DDTs with IPM and a TE disk supplemented with 1:320 MPA detected all MBLs and yielded no false-positive results. Some, but not all, MBL producers were detected in IPM-based tests involving the single chelator TE or MPA alone or by ERT- or CAZ-based tests. IPM-based tests with MPA concentrations other than 1:320 and all MEM-based tests had suboptimal sensitivities or specificities. DDT with IPM and a TE disk supplemented with 20 microl of 1:320 MPA appears to be convenient for the detection of MBLs in the clinical laboratory.

Comparison of Phoenix and VITEK 2 extended-spectrum-beta-lactamase detection tests for analysis of Escherichia coli and Klebsiella isolates with well-characterized beta-lactamases.

The VITEK 2 and Phoenix extended-spectrum beta-lactamase (ESBL) detection systems, which comprise confirmatory tests and expert systems, were evaluated for their ability to discriminate between 102 well-characterized strains of ESBL-positive or -negative Escherichia coli, Klebsiella pneumoniae, and Klebsiella oxytoca. At least 38 distinct ESBLs were included. The strains were chosen to include some known to cause false-positive and false-negative CLSI ESBL confirmatory test results. Therefore, enzyme characterizations, rather than CLSI tests, were the reference methods for the Phoenix and VITEK 2 evaluations. A third arm of the study was conducted with the Phoenix test using two normally inactive expert rules intended to enhance ESBL detection, in addition to using the currently available software. The Phoenix ESBL confirmatory test and unmodified expert system exhibited 96% sensitivity and 81% specificity for ESBL detection. Activation of the two additional rules increased sensitivity to 99% but reduced the specificity to 58%. The VITEK 2 ESBL confirmatory test exhibited 91% sensitivity, which was reduced to 89% sensitivity by its expert system, while its specificity was 85%. Many of the expert system interpretations of both instruments were helpful, but some were suboptimal. The VITEK 2 expert system was potentially more frustrating because it provided more inconclusive interpretations of the results. Considering the high degree of diagnostic difficulty posed by the strains, both ESBL confirmatory tests were highly sensitive. The expert systems of both instruments require modification to update and enhance their utility.

Prevalence of newer beta-lactamases in gram-negative clinical isolates collected in the United States from 2001 to 2002.

Newer beta-lactamases such as extended-spectrum beta-lactamases (ESBLs), transferable AmpC beta-lactamases, and carbapenemases are associated with laboratory testing problems of false susceptibility that can lead to inappropriate therapy for infected patients. Because there appears to be a lack of awareness of these enzymes, a study was conducted during 2001 to 2002 in which 6,421 consecutive, nonduplicate clinical isolates of aerobically growing gram-negative bacilli from patients at 42 intensive care unit (ICU) and 21 non-ICU sites across the United States were tested on-site for antibiotic susceptibility. From these isolates, 746 screen-positive isolates (11.6%) were referred to a research facility and investigated to determine the prevalence of ESBLs in all gram-negative isolates, transferable AmpC beta-lactamases in Klebsiella pneumoniae, and carbapenemases in Enterobacteriaceae. The investigations involved phenotypic tests, isoelectric focusing, beta-lactamase inhibitor studies, spectrophotometric assays, induction assays, and molecular analyses. ESBLs were detected only in Enterobacteriaceae (4.9% of all Enterobacteriaceae) and were found in species other than those currently recommended for ESBL testing by the CLSI (formerly NCCLS). These isolates occurred at 74% of the ICU sites and 43% of the non-ICU sites. Transferable AmpC beta-lactamases were detected in 3.3% of K. pneumoniae isolates and at 16 of the 63 sites (25%) with no difference between ICU and non-ICU sites. Three sites submitted isolates that produced class A carbapenemases. No class B or D carbapenemases were detected. In conclusion, organisms producing ESBLs and transferable AmpC beta-lactamases were widespread. Clinical laboratories must be able to detect important beta-lactamases to ensure optimal patient care and infection control.

Failure of cefepime therapy in treatment of Klebsiella pneumoniae bacteremia.

A case of failure of cefepime treatment of a bloodstream infection with AmpC-producing Klebsiella pneumoniae is reported. The failure was attributed to extended-spectrum beta-lactamase (ESBL) acquisition by the isolate, possibly during therapy. Problems encountered with ESBL detection in AmpC-producing isolates are discussed.

Community-onset disease caused by Citrobacter freundii producing a novel CTX-M beta-lactamase, CTX-M-30, in Canada.

Strains of Citrobacter freundii intermediate to cefotaxime but sensitive to ceftazidime were isolated from four different patients in Canada. Sequencing of PCR products by use of CTX-M-specific primers revealed a new combination of four amino acid substitutions. This new gene was designated bla(CTX-M-30) and was encoded on a 3-kb plasmid. The pI of CTX-M-30 was 8.0.

Unusual Salmonella enterica serotype Typhimurium isolate producing CMY-7, SHV-9 and OXA-30 beta-lactamases.

Beta-lactam resistance in Salmonella isolates is increasing. This paper describes the combination of three different beta-lactamases, OXA-30, SHV-9 and CMY-7, expressed by an isolate of Salmonella enterica serotype Typhimurium. This is the first report of an isolate of Salmonella having both an extended-spectrum beta-lactamase and an AmpC beta-lactamase.