An accelerated method for the detection of extended-spectrum beta-lactamases in urinary isolates of Escherichia coli and Klebsiella pneumoniae.

We prospectively studied an accelerated phenotypic method by incorporating the double disk synergy test in the standard Kirby-Bauer disk diffusion susceptibility testing, to evaluate a protocol for the rapid detection of extended-spectrum beta-lactamases (ESBL) in urinary isolates of Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae). All ESBL-positive isolates were confirmed by the standard Clinical Laboratory Standards Institute (CLSI) confirmatory disk diffusion method. Between November 2004 and December 2005, a total of 6988 urine specimens were analyzed of which, 776 (11%) showed significant growth. They included E. coli in 577 cases (74%) and K. pneumoniae in 199 (25.6%). Of these, 63 E. coli (8%) and 15 K. pneumoniae (7.5%) were positive for ESBL by the accelerated and CLSI methods. Compared to the standard CLSI method, the accelerated method reduced the ESBL detection time from two days to one day. We conclude that the accelerated ESBL detection technique used by us in this study is a reliable and rapid method for detecting ESBL in urinary isolates of E. coli and K. pneumoniae.

Induction of clindamycin resistance in erythromycin-resistant, clindamycin susceptible and methicillin-resistant clinical Staphylococcal isolates.

OBJECTIVES: To demonstrate the in vitro ability of erythromycin to induce clindamycin in erythromycin resistant and clindamycin susceptible clinical isolates of Staphylococci. METHODS: We studied 291 clinical isolates of erythromycin-resistant (ER-R) clindamycin-susceptible Staphylococci (CL-S) at Almana General Hospitals, Al-Khobar, Dammam, Saudi Arabia during the period from June 2004 to May 2005. The isolates included 70 Staphylococcus aureus, 81 Methicillin Resistant Staphylococcus aureus (MRSA) and 140 coagulase-negative Staphylococci (CNS). We examined these isolates for inducible clindamycin resistance (ICR) by erythromycin induction test using double disc susceptibility test (D-test). Strains producing ICR show flattening of the clindamycin disc zone adjacent to the erythromycin disc. RESULTS: Of the 291 ER Staphylococci studied, 82 (28%) demonstrated constitutive clindamycin resistance [2 (2.9%) S. aureus, 43 (53%) MRSA and 37 (26%) CNS]. Inducible clindamycin resistance was demonstrated in 113 (38.8%) of Staphylococcal isolates, including 84 (28.9%) from adult patients and 29 (10%) from pediatric patients. The incidence of ICR was 49 (70%) for S. aureus, 35 (43%) for MRSA and 29 (20.7)% for CNS. Overall, 96 (33%) of the isolates remained susceptible to clindamycin and were negative for clindamycin induction [19 (27%) S. aureus, 3 (3.7%) MRSA and 74 (52.8%) CNS]. CONCLUSION: We conclude that a significant number of ER-R CL-S staphylococcal isolates studied were positive for ICR. These isolates should be reported as clindamycin resistant. Given the high rate of inducible resistance to clindamycin in the staphylococcal isolates, we recommend that microbiology laboratories perform erythromycin induction test on all ER-R CL-S staphylococcal isolates prior to reporting clindamycin susceptibility.

Extended-spectrum beta-lactamases in urinary isolates of Escherichia coli, Klebsiella pneumoniae and other gram-negative bacteria in a hospital in Eastern Province, Saudi Arabia.

OBJECTIVE: To evaluate the prevalence and antimicrobial susceptibility of extended spectrum beta-lactamase (ESBL) producing gram-negative organisms isolated from patients with urinary tract infection (UTI). METHODS: We carried out this study at Almana General Hospital, Eastern Province, Kingdom of Saudi Arabia, during the period August 2003 to October 2004. We studied urinary isolates of Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), Enterobacter spp and Pseudomonas aeruginosa (P. aeruginosa) for ESBL production and antimicrobial susceptibility. RESULTS: We studied a total of 2302 urinary gram-negative isolates for the presence of ceftazidime resistance and ESBL. The isolates included E. coli (1238), K. pneumoniae (522), Enterobacter spp (138) and P. aeruginosa (404). Of the 2302 isolates, 232 (10%) were ceftazidime resistant and 204 (8.9%) were ESBL producers. We detected ESBL in 119 (9.6%) E. coli, 59 (11.3%) K. pneumoniae, 14 (10.14%) Enterobacter species and 12 (2.97%) P. aeruginosa isolates. The ESBL-producing strains were most commonly isolated from patients with indwelling Foley s catheter [131 (64.2%)] and those in the long-term care ward [90 (44.2%)]. Only 26 (12.7%) ESBL-producing isolates were from outpatients. More than 89% of the ESBL producers were susceptible to imipenem and meropenem. Amikacin and piperacillin/tazobactam were active against 68% and 45% of the isolates. Susceptibility to gentamicin and ciprofloxacin was 22.5% and 14%. The least active antibiotic was cefepime (11.8%). CONCLUSION: This study shows the presence of ESBL producers in uropathogens from both inpatients and outpatients and demonstrates their high resistance to various classes of antimicrobial agents.

Prevalence of extended spectrum beta-lactamase among multidrug resistant gram-negative isolates from a general hospital in Saudi Arabia.

OBJECTIVE: To determine the prevalence of extended spectrum beta-lactamase (ESBL) among multidrug resistant isolates of enterobacteriaceae and non-fermenting gram-negative bacilli. METHODS: This study was carried out at the Almana General Hospital, Eastern Province, Kingdom of Saudi Arabia, during the period March 2002 through to June 2003. Multidrug resistant gram-negative isolates from patients admitted to the surgical, medical, pediatric, long-term care and intensive care units were studied for the presence of the ESBL enzyme. RESULTS: A total of 3231 gram-negative organisms were studied for the presence of multidrug resistance and ESBLs. Of these, 197 (6%) isolates were multidrug resistant (MDR), and 156 (4.8%) were positive for ESBL. Seventy nine percent of the MDR strains were positive for ESBL. The most frequent isolates were Escherichia coli (1116) and Klebsiella pneumoniae (687) and ESBL was detected in 72 (6.5%) and 37 (5.4%) of these isolates. The MDR strains that produced ESBL were most commonly isolated from surgical care patients with diabetic fascitis (83%) and patients with indwelling Foley's catheter (79%). Extended spectrum beta-lactamase producing strains showed the highest susceptibility to imipenem and meropenem (86%). The non-beta-lactam antibiotics with greatest activity against these ESBL strains in vitro were ciprofloxacin (72%), amikacin (70%), tobramycin (67%) and gentamicin (56%). CONCLUSION: The majority (79%) of the MDR enterobacteriaceae and non-fermenting gram-negative bacilli tested over 15-months were positive for ESBL. Imipenem, meropenem, ciprofloxacin and amikacin showed the highest activity against these ESBL-producing organisms. Due to the growing problem of infection with ESBL-producing bacteria, which are frequently resistant to many classes of antibiotics resulting in difficult-to-treat infections, clinicians need to be familiar with the clinical significance of these enzymes and potential strategies for dealing with them.