Routine Screening For ESBL Production, A Necessity Of Today

摘要

Background: Extended spectrum beta lactamases (ESBL) are plasmid mediated enzymes capable of hydrolyzing broad spectrum cephalosporins and monobactams. ESBL producing organisms also show cross resistance to many other antibiotics, limiting therapeutic options. Aim: To study the frequency of ESBL producers among Enterobacteriaciae, their prevalence in the hospital and their susceptibility pattern to other antibiotics. Materials And Methods: Between July 2004 to Dec. 2004, a total of 1889 clinically significant Gram negative bacilli belonging to Enterobacteriaciae isolated from various clinical specimens were subjected to screening for ESBL production by standard techniques.Results: ESBL production was noted in 60.98% (n=1152/1889) of the isolates tested. Percentage of ESBL producers within a species was highest in Enterobacter species 70.9% (n=105/148) followed by Klebsiella species 67.4% (n=439/651) and E.coli 62.34% (n= 568/911). The most frequent ESBL producer was E.coli from ambulatory and ward samples, while from intensive care units it was Klebsiella species. Sensitivity of these isolates to Meropenem was 99.8%, piperacillin tazobactam 96.8%, cefoperazone sulbactam 93.3%.Conclusion: There is a high prevalence rate of ESBL producers among Enterobacteriaciae. E.coli and Klebsiella species pose a major concern among these. Routine detection of ESBL production in clinical laboratories gives valuable information to the clinician in appropriate selection of antibiotics. Introduction The extended spectrum beta lactamase (ESBL) enzymes are plasmid-mediated enzymes capable of hydrolyzing and inactivating a wide variety of beta lactams, including third generation cephalosporins, penicillins and aztreonam.(1) Plasmids responsible for ESBL production carry resistance to many antibiotics like aminoglycosides, fluoroquinolones, tetracyclines, chloramphenicol and co-trimoxazole.(2,3) The ESBL producing organisms are reported in increasing numbers worldwide.(4,5,6,7) National Committee for Clinical Laboratory Standards (NCCLS), now called Clinical Laboratory Standards Institute (CLSI) recommends screening for ESBL production among E.coli, K.pneumoniae and K.oxytoca.(8) However, other organisms reported to produce ESBL less frequently are Enterobacter species, Proteus species, Morganella morganii, Serratia marcescens and Pseudomonas aeruginosa.(9,10) Materials and Methods Between July 2004 to Dec 2004, a total of 1889 clinically significant Gram negative bacilli belonging to Enterobacteriaciae isolated from various clinical specimens were subjected to ESBL screening. The isolates were identified by standard techniques. Antimicrobial susceptibility testing was performed by Kirby-Bauer method and interpretation of results was as recommended by NCCLS.(8) ESBL production was tested by using ceftazidime (30mcg) and ceftazidime plus clavulanic acid (30/10mcg) discs on Mueller-Hinton agar. Organism was considered as an ESBL producer if there was a ≥5mm increase in zone diameter around ceftazidime/clavulanic acid disc compared to zone around ceftazidime disc alone. ESBL production was tested in parallel with the antibiotic susceptibility testing on a separate Mueller Hinton agar plate. As per NCCLS guidelines, an isolate was reported as resistant to all penicillins, cephalosporins and aztreonam, if it was an ESBL producer. Klebsiella pneumoniae ATCC 700603 strain was used as ESBL producing control strain, E.coli ATCC 25922 was used as ESBL negative control strain. Sample source, patient location and other relevant details were noted. Sample source distribution of ESBL producers is shown in Table 1.