Department of Clinical Bacteriology, Public Hospital No. 1, ul. Debinki 7, 80-211 Gdansk, Poland
Sir,
In a recent article, Gottlieb & Wolfson1 compared MICs of cefepime for extended-spectrum ß-lactamase (ESBL)- producing and non-ESBL-producing Enterobacter cloacae strains, and raised the issue of whether to use fourthgeneration cephalosporins in the treatment of infections caused by these organisms. At Public Hospital No. 1 we have experienced an increase in infections caused by multidrug-resistant E. cloacae, and wish to express our opinion concerning the in vitro activity of cefepime against ESBLproducing E. cloacae.
ESBL-producing, constitutively derepressed E. cloacae strains are resistant to aminoglycosides and fluoroquinolones, and are susceptible to carbapenems and sometimes cefepime in vitro. Since the Jarlier double-disc potentiation (DD) method2 does not detect derepressed Enterobacter spp., we have used a modified method with ceftazidime and cefepime discs placed adjacent to a co-amoxiclav disc (20 mm centre to centre). One hundred and eighty-nine E. cloacae isolates collected from January to July 2000 were evaluated with the standard DD method. Of these, 102 non-replicate stable derepressed isolates required the modified DD method to be performed.
Using this method, 23 ESBL-producing isolates were detected and of the remainder, 70 isolates were non-ESBL- producing and nine isolates could not be differentiated because there was only a slight increase in inhibition zone diameter between the cefepime and co-amoxiclav discs. The results of the susceptibility tests are shown in the Figure. According to the NCCLS guidelines,3 eight ESBL-producing isolates were categorized as resistant to cefepime (14 mm), five as intermediate (1517 mm) and 10 as susceptible (
18 mm). In the non-ESBL-producing group, the numbers were 2, 1 and 67, respectively. All strains with a 26 mm zone around cefepime were ESBL-negative.
The production of ESBLs in Enterobacter spp. is rarely reported and studies are scarce.4 The presence of ESBL in derepressed E. cloacae isolates would probably not change the antimicrobial therapy of infections caused by such strains, since carbapenems are the drugs of choice.5 However, cefepime, which is another agent active against derepressed AmpC producers, could be affected by coproducing ESBLs. Reporting of ESBL production is of great epidemiological value since Enterobacter spp. can serve as the ESBL source for other species.6
In this investigation, ESBLs were detected in derepressed E. cloacae isolates deemed susceptible, intermediate and resistant in vitro to cefepime according to the NCCLS guidelines, although a 26 mm zone around the cefepime disc appeared to be the boundary for ESBL production.
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Corresponding author. Tel: +48-58-3492596; Fax: +48-58-3461188; E-mail: lnaum{at}amedec.amg.gda.pl
References
1
.
Gottlieb, T. & Wolfson, C. (2000). Comparison of the MICs of cefepime for extended-spectrum ß-lactamase-producing and non-extended-spectrum ß-lactamase-producing strains of Enterobacter cloacae. Journal of Antimicrobial Chemotherapy 46, 3302.
2 . Jarlier, V., Nicolas, M. H., Fournier, G. & Philippon, A. (1998). Extended broad-spectrum ß-lactamases conferring transferable resistance to newer ß-lactam agents in Enterobacteriaceae: hospital prevalence and susceptibility patterns. Reviews of Infectious Diseases 10, 86778.
3 . National Committee for Clinical Laboratory Standards. (1999). MIC Interpretative Standards (Ìg/ml) for Enterobacteriaceae, Pseudomonas aeruginosa and other non-Enterobacteriaceae: Approved Standard M7-A4. NCCLS, Villanova, PA.
4
.
Tzelepi, E., Giakkoupi, P., Sofianou, D., Loukova, V., Kameroglou, A. & Tsarakis, A. (2000). Detection of extended-spectrum ß-lactamases in clinical isolates of Enterobacter cloacae and Enterobacter aerogenes. Journal of Clinical Microbiology 38, 5426.
5
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Tenover, F. C., Mohammed, M. J., Gorton, T. S. & Dembek, Z. F. (1999). Detection and reporting of organisms producing extended-spectrum ß-lactamases: survey of laboratories in Connecticut. Journal of Clinical Microbiology 37, 406570.
6 . Bush, K. (1996). Is it important to identify extended-spectrum-beta-lactamase-producing isolates? European Journal of Clinical Microbiology and Infectious Diseases 15, 3614.[ISI][Medline]