Comparison of Molecular and Phenotypic Methods for the Detection and Characterization of Carbapenem Resistant Enterobacteriaceae.

In recent years, there has been a rapid dissemination of carbapenem resistant Enterobacteriaceae (CRE). This study aimed to compare phenotypic and molecular methods for detection and characterization of CRE isolates at a large tertiary care hospital in Saudi Arabia. This study was carried out between January 2011 and November 2013 at the King Khalid University Hospital (KKUH) in Saudi Arabia. Determination of presence of extended-spectrum beta-lactamases (ESBL) and carbapenem resistance was in accordance with Clinical and Laboratory Standards Institute (CLSI) guidelines. Phenotypic classification was done by the MASTDISCS(TM) ID inhibitor combination disk method. Genotypic characterization of ESBL and carbapenemase genes was performed by the Check-MDR CT102. Diversilab rep-PCR was used for the determination of clonal relationship. Of the 883 ESBL-positive Enterobacteriaceae detected during the study period, 14 (1.6%) isolates were carbapenem resistant. Both the molecular genotypic characterization and phenotypic testing were in agreement in the detection of all 8 metalo-beta-lactamases (MBL) producing isolates. Of these 8 MBL-producers, 5 were positive for blaNDM gene and 3 were positive for blaVIM gene. Molecular method identified additional blaOXA gene isolates while MASTDISCS(TM) ID detected one AmpC producer isolate. Both methods agreed in identifying 2 carbapenem resistant isolates which were negative for carbapenemase genes. Diversilab rep-PCR analysis of the 9 Klebsiella pneumoniae isolates revealed polyclonal distribution into eight clusters. MASTDISCS(TM) ID is a reliable simple cheap phenotypic method for detection of majority of carbapenemase genes with the exception of the blaOXA gene. We recommend to use such method in the clinical laboratory.

ESBL-producing Escherichia coli and Klebsiella pneumoniae at a tertiary care hospital in Saudi Arabia.

INTRODUCTION: The increasing frequency and antibiotic resistance among extended-spectrum ß-lactamases (ESBLs)-producing bacteria are posing a serious threat. This study sought to investigate the frequency and antibiotic susceptibility of ESBL-producing E. coli and K. pneumoniae at a tertiary care hospital. METHODOLOGY: Data were collected from samples sent to the microbiology laboratory between 2006 and 2010 at King Khalid University Hospital, Riyadh. ESBLs were confirmed using Etest strips of cefotaxime/cefotaxime + clavulanic acid, ceftazidime/ceftazidime + clavulanic acid, and cefepime/cefepime + clavulanate. RESULTS: Out of 17,105 samples, 1,076 (6.3%) ESBL-producing isolates of E. coli (808) and K. pneumoniae (268) were confirmed. Among these, 680 (63.2%) isolates were found in urine samples, followed by 287 (26.7%) in superficial swabs, deep wounds swabs, tissues and sterile body fluids, 71 (6.6%) in respiratory, and 38 (3.5%) in blood samples. The overall frequency rates of ESBL E. coli and K. pneumoniae were 6.6% and 5.5%, respectively. The frequency of ESBL-producing E. coli and K. pneumoniae increased significantly during the study period. E. coli resistance against cotrimoxazole was 71.1%, followed by ciprofloxacin (68.2%) and gentamicin (47%). Similarly, 62.7% of K. pneumoniae isolates were resistant to gentamicin, 59.5% to cotrimoxazole, and 49.8% to ciprofloxacin. There was no statistically significant change in antimicrobial resistance over the study period. CONCLUSIONS: Although the frequency rates of ESBL-producing E. coli and K. pneumoniae increased, no change in the anti-microbial susceptibility was observed over the study period.

Antimicrobial susceptibility patterns of multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii against carbapenems, colistin, and tigecycline.

OBJECTIVE: To examine susceptibility of Pseudomonas aeruginosa (P. aeruginosa) and Acinetobacter baumannii (A. baumannii ) against carbapenems along with colistin and tigecycline as alternative therapeutic options. METHODS: A total of 117 strains of multidrug-resistant (MDR) non-fermenting Gram negative bacteria isolated from non-duplicate samples were collected consecutively. We included one sample from each patient (84 isolates of A. baumannii and 33 isolates of P. aeruginosa isolated from patients seen at King Khalid University Hospital, Riyadh, Saudi Arabia, from June to December 2010). Isolates were identified by the MicroScan WalkAway 96 Plus system. The minimum inhibitory concentrations (MICs) were determined by E-test following the Clinical and Laboratory Standards Institute breakpoint recommendations. RESULTS: Most A. baumannii strains were resistant to imipenem (90.5%), meropenem (90.5%), and doripenem (77.4%). Whereas, a higher percentage of P. aeruginosa was resistant to imipenem (90.9%), and meropenem (81.8%), only 39.4% were resistant to doripenem. Colistin had excellent activity against both A. baumannii (100%) and P. aeruginosa (93.9%), while 89.3% of A. baumannii strains were susceptible to tigecycline. CONCLUSION: Among the carbapenems, doripenem was found to be the most potent antimicrobial agent against P. aeruginosa, whereas colistin proved to be an effective alternative antimicrobial agent for treatment of A. baumannii or P. aeruginosa. Tigecycline remains the best therapeutic option for MDR A. baumannii.