Antibiotic susceptibility of extended-spectrum ß-lactamase-producing Enterobacteriaceae
Antibiotic Reference Laboratory, Communicable Disease Group, Institute of Environmental Science and Research (ESR), PO Box 50-348, Porirua. Email: ARL@esr.cri.nz
Introduction •
Extended-spectrum ß-lactamases (ESBLs) confer resistance to all
• The plasmids may also carry other resistance genes.
• Overseas studies have reported that ESBL-producing bacteria are usually
• ESBLs are most commonly found in Klebsiella and Escherichia coli, but are
multiresistant to several classes of antibiotics, especially fluoroquinolones and
now also being identified in other Enterobacteriaceae, such as Enterobacter.
• ESBL-producing organisms are being isolated with increasing frequency in
• Little has been published about antimicrobial resistance among ESBL-
• The ESBL genes are carried on plasmids and therefore can be readily
Therefore, we determined the susceptibility of ESBL-producing
transferred within and between species.
Enterobacteriaceae, recently isolated from throughout NZ, to a range of antibiotics. Methods As part of a survey of methods to detect ESBLs, we tested the susceptibility of
Multiresistance was defined as, in addition to cephalosporin and monobactam
a representative sample of 137 isolates of ESBL-producing Enterobacteriaceae
resistance, resistance to >3 of the following antibiotic classes: co-amoxiclav,
to amikacin, ciprofloxacin, co-amoxiclav, co-trimoxazole, gentamicin,
meropenem, ciprofloxacin, aminoglycosides (gentamicin, tobramycin and/or
meropenem, nitrofurantoin, tetracycline, tobramycin and trimethoprim, by agar
amikacin), folate pathway inhibitors (co-trimoxazole and/or trimethoprim),
dilution according to CLSI/NCCLS methodology and interpretive standards.1
The isolates tested had been referred to ESR from throughout NZ. Duplicateisolates from a patient were excluded and only one isolate of any recognisedoutbreak strain was included. Results Table 1 and Chart 1 show resistance to the individual antibiotics and antibiotic Chart 1. Rates of resistance
classes. The rates of resistance are similar to those found in overseas studiesand a recent NZ study.2,3
% resistant
Table 2 shows the frequency of multiresistance.
Chart 2 shows the resistance patterns that were observed in >5% of isolates. Table 1. Rates of resistance among ESBL-positive Enterobacteriaceae Percent resistance Antibiotic E. coli Klebsiella Enterobacteriaceae Other Enterobacteriaceae Tetracycline amoxiclav E.coli ofurantoin trimoxazole Klebsiella species Gentamicin Tobramycin Amikacin Chart 2. Resistance patterns with each E. coli tetracycline ciprofloxacin folate pathway inhibitor aminoglycoside tetracycline ciprofloxacin folate pathway inhibitor aminoglycoside co-amoxiclav tetracycline ciprofloxacin aminoglycoside tetracycline ciprofloxacin aminoglycoside co-amoxiclav tetracycline folate pathway inhibitor aminoglycoside tetracycline ciprofloxacin folate pathway inhibitor folate pathway inhibitor Table 2. Multiresistance rates Klebsiella species aminoglycoside folate pathway inhibitor tetracycline Resistant to aminoglycoside folate pathway inhibitor (number of E. coli Klebsiella aminoglycoside tetracycline folate pathway inhibitor tetracycline nitrofurantoin ciprofloxacin antibiotic species Enterobacteriaceae aminoglycoside folate pathway inhibitor tetracycline ciprofloxacin aminoglycoside folate pathway inhibitor co-amoxiclav classes): Other Enterobacteriaceae folate pathway inhibitor co-amoxiclav aminoglycoside tetracycline folate pathway inhibitor co-amoxiclav aminoglycoside folate pathway inhibitor co-amoxiclav aminoglycoside tetracycline nitrofurantoin folate pathway inhibitor co-amoxiclav aminoglycoside tetracycline ciprofloxacin Conclusions References 1. National Committee for Clinical Laboratory Standards. Methods for dilution antimicrobial susceptibility tests for
• The majority of ESBL-producing Enterobacteriaceae in NZ are multiresistant to
bacteria that grow aerobically; approved standard - sixth edition. Pennsylvania: NCCLS; 2003. M7-A6.
2. Bell JM, Turnidge JD, Gales AC, Pfaller MA, Jones RN. Prevalence of extended spectrum beta-lactamase (ESBL)-
producing clinical isolates in the Asia-Pacific region and South Africa: regional results from SENTRY Antimicrobial
• Resistance to gentamicin, tobramycin, co-trimoxazole, trimethoprim and
Surveillance Program (1998-99). Diagn Microbiol Infect Dis 2002; 42: 193-8.
3. Briggs S, Ussher J, Taylor S. Extended-spectrum beta-lactamase-producing Enterobacteriaceae at Middlemore
• In addition, most ESBL-positive E. coli are resistant to fluoroquinolones.
Hospital. NZ Med J 2005; 118 (1218). Available at http://www.nzma.org.nz/journal/118-1218/1563/
• All ESBL-producing Enterobacteriaceae were susceptible to the carbapenem
These results are part of a report on ESBLs to be published on the ESR
We thank the microbiology laboratories throughout New Zealand whoreferred ESBL-producing organisms to ESR for our surveillance
Surveillance Website: http://www.surv.esr.cri.nz/antimicrobial/esbl.php
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