Extended-spectrum beta-lactamase production by Enterobacteriaceae isolates from urine cultures of outpatients: results of a 7-year follow-up

Abstract

The aim of the study was to evaluate the change of the frequency of extended-spectrum beta-lactamase (ESBL) producing Enterobacteriaceae isolates from urine samples of outpatients in years and to analyse the antibiotic resistance profiles for a rational drug use. The urine samples cultured in our laboratory from the patients who were admitted to outpatient clinics of our hospital between years 2007-2013 were included in this study. Enterobacteriaceae strains were isolated and identified by conventional methods and API 20E system (BioMérieux, France). The standard antimicrobial susceptibility tests were performed by Kirby Bauer disk diffusion method. ESBL production were screened by double-disk synergy method according to CLSI guidelines. E-test method (BioMérieux, France) were used for the verification of suspicious ESBL production. The identification and antimicrobial susceptibility testing were performed for a total of 12.535 isolates. Of the isolates 8716 were identified as Escherichia coli (69.3%), 1514 were Klebsiella pneumoniae/oxytoca (12.1%), 257 were Proteus mirabilis (2.1%), 345 were other Enterobacteriae members (8%), 411 were various non-fermentative gram-negative bacteria (3.3%) and 1292 were various gram-positive bacteria (10.3%). The total positivity rate of ESBL was found as 21.8% (2.283/10.487), and the ESBL positive rates for E.coli, K.pneumoniae/oxytoca and P.mirabilis were 21.2%, 28.2% and 4.7%, respectively. Other Enterobacteriaceae isolates were not evaluated because of the absence of standardized methods and breakpoint values. There was no statistically significant difference among ESBL producing isolates within seven years (p= 0.364). The antibiotic resistance rates of the ESBL-positive isolates were statistically higher than ESBL-negative isolates [amoxicillin-clavulanate (73.1%/11.3%), trimethoprim-sulfamethoxazole (63.1%/31.0%), nitrofurantoin (17.3%/8.6%), gentamicin (42.2%/10.1%), amikacin (3.5%/0.9%), tobramisin (56.8%/10.5%), imipenem (0.3%/0.1%), ofloxacin (66.8%/19.8%), ticarcillin-clavulanate (73.5%/19.8%), piperacillin-tazobactam (28.8%/5.0%)] (p< 0.05). Statistically significant variations were detected within the years for the resistance rates of amoxicillin-clavulanate (p= 0.001), tobramycin (p=0.003), ofloxacin (p= 0.001), ticarcillin-clavulanate (p= 0.001) and piperacillin-tazobactam (p= 0.001) were detected within the years. Although a quite high percentage of ESBL positivity in Enterobacteriaceae isolates was determined, there was a slight but not statistically significant increase of this value during the seven-year period. The stability of the percentage of ESBL positivity may indicate a positive change in the habit of the usage of beta-lactam antibiotics. According to the results of our study, the most effective drugs for ESBL-producing isolates were piperacillin-tazobactam among inhibitor combinations, amikacin among aminoglycosides and nitrofurantoin among orally-used drugs.