Abstract
Limited data are available on susceptibilities of these organisms to some of the recently made accessible antimicrobial agents. The in vitro activities of newer antibiotics, such as, ceftolozane/tazobactam (C/T) and ceftazidime/avibactam (CZA) along with some “older” antibiotics, for example fosfomycin (FOS) and colistin (CL) were determined against selected strains (resistant to antimicrobial agents) of Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Minimum inhibitory concentrations (MIC) were determined by Clinical and Laboratory Standards Institute microbroth dilution. 133 isolates: 46 E. coli, 39 K. pneumoniae, and 48 P. aeruginosa were tested. Results showed that E. coli isolates with MIC50/90, 0.5/1 for CL; 4/32 for FOS; 0.25/32 for C/T; 0.25/8 for CZA, exhibited susceptibility rates of 95.7%, 97.8%, 76.1%, and 89.1%, respectively. On the other hand, K. pneumoniae strains with MIC50/90, 0.5/1 for CL; 256/512 for FOS; 2/128 for C/T; 0.5/128 for CZA showed susceptibility rates of 92.3%, 7.7%, 51.3%, and 64.1%, respectively. P. aeruginosa isolates with MIC50/90, 1/1 for CL; 128/128 for C/T; 32/64 for CZA presented susceptibility rates of 97.9%, 33.3%, and 39.6%, respectively. Higher MICs were demonstrated against most of the antibiotics. However, CL retained efficacy at low MICs against most of the isolates tested.
Highlights
It all began with an increase in the prevalence of Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs) in the 1980s and 1990s
Among E. coli strains, only one of them was found to be uniformly susceptible to all the antimicrobial agents tested
The present study demonstrates that older antimicrobial agents, such as CL and FOS, are still potent against selected Gram-negative bacilli (GNB) isolated from our hospital
Summary
It all began with an increase in the prevalence of Enterobacteriaceae producing extended-spectrum beta-lactamases (ESBLs) in the 1980s and 1990s. Earlier to that almost all Enterobacteriaceae were susceptible to broad-spectrum antibiotics, including beta-lactam/beta-lactamase inhibitor combinations, oxyimino-cephalosporins (e.g., cefotaxime, ceftriaxone, and ceftazidime), aztreonam, and carbapenems [1]. Infections due to ESBL-producing Enterobacteriaceae (ESBL-PE) reached unprecedented levels in Europe [2,3,4,5] as well as in Asia [6]. These Gram-negative bacilli (GNB) are increasingly resistant to several antibiotics broad-spectrum cephalosporins, because of global spread of ESBL-PE as well as AmpC cephalosporinase producing.
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