>5 million cases of paratyphoid fever compared to. >21 million cases of typhoid fever1. Paratyphoid fever is a major clinical problem in India but large outbreaks ...
Indian J Med Res 124, November 2006, pp 585-587
Correspondence Fluoroquinolone resistance among Salmonella enterica serovar Paratyphi A in Pondicherry Sir,
Antibiotic susceptibility testing was done by the disc diffusion method7 for the following antibiotics (mg) ampicillin (10), chloramphenicol (30), cotrimoxazole (25), nalidixic acid (30), ciprofloxacin (5) and ceftriaxone (30) (Hi-Media Laboratories Ltd, Mumbai), in accordance with Clinical and Laboratory Standards Institute (CLSI) 8 . Nalidixic acid susceptibility has been validated as a screening test for reduced susceptibility to ciprofloxacin which in turn associated with treatment failure9,10.
The incidence of enteric fever caused by Salmonella enterica serovar Paratyphi A has been increasing in Asia. It is a major public health concern in the Indian subcontinent. The situation is worsened by the sharp increase in the number of isolates showing resistance to fluoroquinolones which are currently recommended as the first line of therapy. S. Paratyphi A is the second most common cause of enteric fever after S. Typhi. It is estimated to have >5 million cases of paratyphoid fever compared to >21 million cases of typhoid fever 1. Paratyphoid fever is a major clinical problem in India but large outbreaks have been reported only after 1996. Increasing isolation rates have been reported from India 2 . Since 1998 drug resistant isolates of S. Paratyphi A with reduced susceptibility to ciprofloxacin has caused concern3. There are reports of S. Paratyphi A, showing high level ciprofloxacin resistance in India (minimum inhibitory concentration MIC 8 mg/ml)4 and Japan (MIC>128 mg/ml)5. We report here the sudden increase in the enteric fever cases caused by S. Paratyphi A with increasingly high level fluoroquinolone resistance.
Nalidixic acid resistant isolates were further studied for MIC levels against ciprofloxacin, gatifloxacin and ofloxacin by E-test (AB-Biodisc, Sweden). These isolates were also tested for cyclohexane tolerance to elucidate the efflux pump mechanism 11 . Cyclohexane resistance was determined by the method of Asako et al12. Briefly, bacteria grown overnight at 30°C were inoculated onto duplicate solid agar media in glass petri dishes. Each plate was flooded to a depth of 3 mm with hexane (control) or cyclohexane, sealed with Nescofilm, and incubated overnight at 30°C. Isolates that did not grow in the presence of cyclohexane was deemed cyclohexane sensitive.
Blood culture was done for 629 suspected cases of enteric fever at Jawaharlal Institute of Postgraduate Medical Education and Research, (JIPMER) hospital and Government General Hospital, Pondicherry, during the period August 2004 to December 2005. A total of 51 isolates were obtained by blood culture from suspected cases of enteric fever. Isolates were identified biochemically6 and confirmed by agglutination with specific antiserum (Murex Biotech, England).
Of the 51 isolates obtained from blood culture from suspected cases of enteric fever, 27 (53%) were S. Typhi and 24 (47%) were S. Paratyphi A. Of the 27 isolates of S. Typhi, only 2 were sensitive to nalidixic acid and the rest were resistant. All 24 isolates of S. Paratyphi A were resistant to nalidixic acid. MIC levels against ciprofloxacin, gatifloxacin and ofloxacin by E-test (AB-Biodisc, Sweden) were 585
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INDIAN J MED RES, NOVEMBER 2006
determined for 25 isolates of S. Typhi and 24 isolates of S. Paratyphi A, which were nalidixic acid resistant (NAR). The 25 NAR isolates of S. Typhi had MICs of
