Antibiogram of Salmonella Isolates from Blood with an Emphasis on Nalidixic Acid and Chloramphenicol Susceptibility in a Tertiary Care Hospital in Coastal Karnataka: A Prospective Study

BACKGROUND: Enteric fever is caused by the serotypes Salmonella Typhi, Salmonella Paratyphi A, Salmonella Paratyphi B and Salmonella Paratyphi C. After emergence of multidrug resistant Salmonellae Ciprofloxacin, a fluorquinolone antibiotic was the first-line therapy. Treatment failure was observed with Ciprofloxacin soon and such strains showed in-vitro resistance to Nalidixic acid. Recent reports suggest re-emergence of Chloramphenicol sensitive strains and increasing Nalidixic acid resistance. This study is aimed at detecting the current trend in the antibiogram of Salmonella isolates from blood culture in coastal Karnataka, with an emphasis on antibiotic susceptibility of Nalidixic acid and Chloramphenicol and evaluate, if there is a need to modify the strategies in the antibiotic therapy for enteric fever. MATERIALS AND METHODS: Blood samples received for culture in the laboratory between June 2009 and August 2011 was cultured in Brain Heart infusion broth, bile broth or in a commercial BACTEC culture media. The growth from blood cultures were processed for identification and antibiotic susceptibility as per standard methods. Antibiotic susceptibility for Ampicillin, Trimethoprim-sulphamethoxazole, Chloramphenicol, Ciprofloxacin, Ceftriaxone and Nalidixic acid were noted. RESULTS: Out of 9053 blood culture specimens received, Salmonella was isolated from 103 specimens. There were 85 Salmonella Typhi isolates, 16 Salmonella Paratyphi A and two Salmonella Paratyphi B. Salmonella Typhi and Salmonella Paratyphi A showed the highest resistance to Nalidixic acid. Salmonella Typhi showed highest susceptibility to Ceftriaxone and Salmonella Paratyphi A to trimethoprim-sulphamethoxazole and Chloramphenicol. Two isolates were multidrug resistant. One Salmonella Paratyphi A was resistant to Ceftriaxone. CONCLUSION: Routine screening of Nalidixic acid susceptibility is practical to predict fluorquinolone resistance in Salmonella and preventing therapeutic failure while treating with it. It is worthwhile to consider replacing fluorquinolones with Chloramphenicol or Ceftriaxone as the first line of therapy for enteric fever. Periodic analysis of Salmonella antibiogram should be done to formulate the best possible treatment strategies.