In vitro activity of azithromycin, newer quinolones and cephalosporins in ciprofloxacin-resistant Salmonella causing enteric fever

1 Department of Microbiology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi, India 2 Department of Microbiology, Majeedia Hospital, Hamdard University, New Delhi, India Correspondence Deepthi Nair deepthinair2{at}gmail.com Received 18 April 2007 Accepted 6 July 2007 The therapeutic alternatives available for use against ciprofloxacin-resistant enteric fever isolates in an endemic area are limited. The antibiotics currently available are the quinolones, third-generation cephalosporins and conventional first-line drugs. In this study, the MICs of various newer drugs were determined for 31 ciprofloxacin-resistant enteric fever isolates (26 Salmonella enterica serovar Typhi and 5 S. enterica serovar Paratyphi A). MICs for ciprofloxacin, ofloxacin, gatifloxacin, levofloxacin, cefotaxime, cefixime, cefepime and azithromycin were determined using Etest strips and the agar dilution method. By Etest, all of the ciprofloxacin-resistant isolates had ciprofloxacin MICs 32 µg ml –1 . S. Typhi showed MIC 90 values of 0.50, 0.25 and 0.38 µg ml –1 for cefixime, cefotaxime and cefepime, respectively. For the cephalosporins, a negligible difference in MIC 90 and MIC 50 values for S. Typhi and S. Paratyphi A was observed. A single isolate of S. Typhi showed a high azithromycin MIC of 64 µg ml –1 . The MIC 90 value for azithromycin in S. Typhi and S. Paratyphi was 24 µg ml –1 . Gatifloxacin demonstrated lower resistance (80.8 %) compared with the other quinolones (92–100 %) in S. Typhi. The rise in MIC levels of these antimicrobials is a matter for serious concern.