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Objectives: To determine the in vitro activity of antibiotics, including arbekacin, cefminox, fosfomycin and biapenem which are all still unavailable in India, against Gram-negative clinical isolates., Methods: We prospectively collected and tested all consecutive isolates of Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa and Acinetobacter spp. from blood, urine and sputum samples between March and November 2012. The minimum inhibition concentration (MIC) of 16 antibiotics was determined by the broth micro-dilution method., Results: Overall 925 isolates were included; 211 E. coli, 207 Klebsiella spp., 153 P. aeruginosa, and 354 Acinetobacter spp. The MIC50 and MIC90 were high for cefminox, biapenem and arbekacin for all pathogens but interpretative criteria were not available. The MIC50 was categorized as susceptible for a couple of antibiotics, including piperacillin/tazobactam, carbapenems and amikacin, for E. coli, Klebsiella spp. and P. aeruginosa. However, for Acinetobacter spp., the MIC50 was categorized as susceptible only for colistin. On the other hand, fosfomycin was the only antibiotic that inhibited 90% of E. coli and Klebsiella spp. isolates, while 90% of P. aeruginosa isolates were inhibited only by colistin. Finally, 90% of Acinetobacter spp. isolates were not inhibited by any antibiotic tested., Conclusion: Fosfomycin and colistin might be promising antibiotics for the treatment of infections due to E. coli or Klebsiella spp. and P. aeruginosa, respectively, in India; however, clinical trials should first corroborate the in vitro findings. The activity of tigecycline should be evaluated, as this is commonly used as last-resort option for the treatment of multidrug-resistant Acinetobacter infections.

AmpC enzymes can be differentiated from other extended-spectrum beta-lactamases by their ability to hydrolyse cephamycins as well as other extended-spectrum cephalosporins. The present study was designed to determine the occurrence of AmpC enzyme-harbouring Gram-negative clinical isolates in a tertiary care hospital in Delhi, India. Among the 135 clinical isolates of Gram-negative bacilli tested, 20.7% were found to harbour AmpC enzymes using a modified three-dimensional test. Inhibition of zone distortion in the presence of cloxacillin confirmed AmpC-harbouring isolates. Maximal incidence of AmpC producers was found among Acinetobacter spp. (42.8%) followed by Klebsiella pneumoniae isolates (33.3%). No AmpC-harbouring isolates revealed decreased susceptibility to cefoxitin. Therefore, Gram-negative bacilli showing resistance to any cephalosporin or aztreonam irrespective of cefoxitin susceptibility should be screened for the AmpC enzyme. The modified three-dimensional test is easy to carry out and can be applied as a phenotypic screening method for detection of AmpC-harbouring Gram-negative organisms. This is the first study to determine the occurrence of AmpC beta-lactamases from India.