JAC Advance Access originally published online on May 8, 2007
Journal of Antimicrobial Chemotherapy 2007 60(1):187-188; doi:10.1093/jac/dkm131
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Correspondence |
In vitro efficacy of ceftriaxone/sulbactam against Escherichia coli isolates producing CTX-M-15 extended-spectrum ß-lactamase
Department of Microbiology, Jawaharlal Nehru Medical College and Hospital, Aligarh Muslim University, Aligarh 202002, Uttar Pradesh, India
* Corresponding author. Tel: +91-571-2720382; Fax: +91-571-2721776; E-mail: shahidsahar{at}yahoo.co.in
Keywords: E. coli , disc synergy , piperacillin/tazobactam , ESBLs
Resistance to third- and fourth-generation cephalosporins has become a major concern worldwide. Even more alarming is the emergence of carbapenem resistance; the carbapenems are often considered to be a ‘drug of choice’ and are increasingly used in empirical therapy. Against this rising resistance, the role of ß-lactam/ß-lactamase inhibitor combinations needs to be considered. Sulbactam has been approved recently in many countries to be combined with ß-lactam antibiotics,1 including, recently, in India.
CTX-M enzymes are a recently emerged group of extended-spectrum ß-lactamases (ESBLs) and CTX-M-15 has emerged as the most prevalent ESBL in many parts of the world, including the UK and India.2,3 We have evaluated the in vitro efficacy of ceftriaxone/sulbactam, a combination recently launched in India, against Escherichia coli harbouring blaCTX-M-15. Moreover, we describe the phenotypic detection of ESBL production by the synergy observed between cephalosporin and piperacillin/tazobactam discs and compare it with conventional disc synergy tests with co-amoxiclav.
Thirty-two urinary E. coli isolates previously shown to carry blaCTX-M-15,3 and 22 CTX-M-producing E. coli isolates from bronchoalveolar lavage and pus samples obtained during 2006, from Jawaharlal Nehru Medical College and Hospital, Aligarh Muslim University, Aligarh, India, were studied. The latter isolates were shown to carry blaCTX-M of genogroup-1 by PCR with primers 5'-AAA AAT CAC TGC GCC AGT-3' and 5'-AGC TTA TTC ATC GCC ACG TT-3'. Cycling conditions were initial denaturation at 94°C for 5 min; 35 cycles of 94°C for 30 s, 52°C for 45 s and 72°C for 1 min; and a final elongation at 72°C for 8 min. Precise CTX-M types were not identified in these 22 isolates because of the lack of sequencing facilities, but CTX-M-15 is the only variant that has been described to date in India.3,4 To ensure that multiple representatives of particular strains were eliminated, all isolates were selected to have unique randomly amplified polymorphic DNA fingerprint patterns.
The antibiotic discs used (Table 1) were from HiMedia Lab. Ltd, India, except piperacillin, piperacillin/tazobactam, ceftriaxone/sulbactam (kindly provided by Ranbaxy Lab. Ltd, India) and imipenem, which were obtained from Oxoid, Basingstoke, UK. E. coli ATCC 25922, E. coli ATCC 35218 and Klebsiella pneumoniae ATCC 700603 were used as control strains. The results were interpreted as per the CLSI (formerly NCCLS) criteria, except for ceftriaxone/sulbactam. Because there are no published breakpoints for the latter combination, the susceptibility criterion used for this combination was >8 mm increase in zone diameter of ceftriaxone/sulbactam in comparison with that of ceftriaxone alone. Phenotypic ESBL detection by disc synergy tests was performed on all 54 isolates using co-amoxiclav and piperacillin/tazobactam discs as a source of inhibitors. Briefly, the test inoculum (equivalent in turbidity to that of a 0.5 McFarland standard) was streaked on Mueller–Hinton agar. Discs of co-amoxiclav (20/10 µg) or piperacillin/tazobactam were placed 20 and 30 mm, centre to centre, from discs containing cefotaxime (30 µg), ceftazidime (30 µg) and cefpirome (30 µg) and plates were incubated at 37°C overnight. Enhancements of zones of inhibition of cephalosporins towards piperacillin/tazobactam or co-amoxiclav were considered as positive ESBL results. All tests were performed in duplicate.
|
Comparative susceptibilities of the isolates against individual ß-lactam antibiotics and ß-lactam/ß-lactamase inhibitor combinations are shown in Table 1. A total of 96.3% of isolates were susceptible to ceftriaxone/sulbactam in comparison with only 12.9% susceptible to piperacillin/tazobactam. This contrasts with previous international1 and national5 studies, which reported that combinations of ß-lactam with tazobactam showed greater activity than ß-lactam/sulbactam combinations against E. coli isolates. This marked difference may reflect different mechanism(s) in the different bacterial collections. In the present study, we specifically looked at CTX-M group-1 and CTX-M-15 producers and found ceftriaxone/sulbactam to be a highly effective combination (activity being equal to that of imipenem) in contrast to piperacillin/tazobactam and ticarcillin/clavulanate. Two isolates that were resistant to ceftriaxone/sulbactam were also resistant to imipenem (Table 1); they carried blaCTX-M-15 and blaampC alleles (data not shown).
In disc synergy tests, none of the 54 ESBL producers was detected when co-amoxiclav discs were placed 30 mm from cephalosporin discs, and only 4 isolates (7.4%) were detected when this was reduced to 20 mm. It is known that optimal disc placement is an important issue in such tests.6 However, when piperacillin/tazobactam discs were used and the discs were placed 20 mm apart, we readily detected most ESBL-producing isolates; synergy with ceftriaxone, cefotaxime and ceftazidime allowed detection of 92.6% (50/54), 90.7% (49/54) and 74.1% (40/54) of ESBL producers, respectively. When the discs were placed at 30 mm, ESBL could still be detected in all the isolates; most (88.9% with ceftriaxone and 83.3% with cefotaxime) of the isolates still giving excellent synergistic patterns. On the basis of these findings, we feel that piperacillin/tazobactam (or tazobactam alone) could be a better indicator when combined with ceftriaxone and cefotaxime for the phenotypic detection of ESBLs, especially in CTX-M producers. This needs to be evaluated further and also against other classes of ß-lactamases.
To conclude, ceftriaxone/sulbactam proved to be effective in vitro against 54 diverse CTX-M-15-producing E. coli strains. This novel combination merits further investigation, as does the use of piperacillin/tazobactam discs for the phenotypic detection of ESBLs.
None to declare.
References
1 Frank U, Mutter J, Schmidt-Eisenlohr E, et al. Comparative in vitro activity of piperacillin, piperacillin–sulbactam and piperacillin–tazobactam against nosocomial pathogens isolated from intensive care patients. Clin Microbiol Infect (2003) 9:1128–32.[CrossRef][Web of Science][Medline]
2
Bonnet R. Growing group of extended-spectrum ß-lactamases: the CTX-M enzymes. Antimicrob Agents Chemother (2004) 48:1–14.
3
Ensor VM, Shahid M, Evans JT, et al. Occurrence, prevalence and genetic environment of CTX-M ß-lactamases in Enterobacteriaceae from Indian hospitals. J Antimicrob Chemother (2006) 58:1260–3.
4
Walsh TR, Toleman MA, Jones RN. Comment on: Occurrence, prevalence and genetic environment of CTX-M ß-lactamases in Enterobacteriaceae from Indian hospitals. J Antimicrob Chemother (2007) 59:799–800.
5 Gupta V, Dutta P, Agnihotri N, et al. Comparative in vitro activities of seven new ß-lactams, alone and in combination with ß-lactamase inhibitors, against clinical isolates resistant to third generation cephalosporins. Braz J Infect Dis (2006) 10:22–5.[Medline]
6 Thomson KS. Controversies about extended-spectrum and AmpC ß-lactamases. Emerg Infect Dis (2001) 7:333–6.[Web of Science][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||