Prevalence and patterns of antimicrobial resistance in salmonella enterica serovar Typhi and Salmonella enterica serovar Paratyphi, Bangladesh

Abstract

Salmonella enterica serovar Typhi (S. Typhi) and Salmonella enterica serovar Paratyphi (S. Paratyphi) are two gram negative bacilli, responsible for enteric fever (typhoid and paratyphoid, respectively). Both of the fever, mainly typhoid caused by S. Typhi sometimes takes place in epidemic form in developing countries like Bangladesh. The morbidity and mortality rates of this disease can be reduced by effective antimicrobial therapy. But resistance to antibiotic is a never ending process that generate severe problem to treat this life threatening disease. The aim of our study was to assess the patterns of antimicrobial resistance and their changing trends in S. Typhi and S. Paratyphi that are endemic in Bangladesh. Blood and stool samples were cultured from the patients with high and continuous fever in icddr,b Dhaka hospital. One hundred S. Typhi, 21 S. Paratyphi A and 1 S. Paratyphi B were identified by biochemical and serological tests. Antimicrobial susceptibility test was carried out to observe the resistant patterns of these isolates against eight selected antibiotics. Minimal Inhibitory Concentration (MIC) of azithromycin, ciprofloxacin and nalidixic acid was determined using E-test and agar dilution technique. Seventy eight percent and 77% S. Typhi isolates were susceptible to ampicillin and chloramphenicol respectively where 100% S. Paratyphi was susceptible to those two antimicrobials. 77% isolates of S. Typhi were susceptible to trimethoprim-sulfamthoxazole where all S. Paratyphi isolates were susceptible to this antibiotic. All the S. Typhi and S. Paratyphi isolates were susceptible to cefixime and ceftriaxone. The majority of S. Typhi (87%) and S. Paratyphi (91%) were resistant to nalidixic acid and moderately susceptible to ciprofloxacin (83% of S. Typhi and 91% of S. Paratyphi). S. Typhi (83.84%) isolates were susceptible to azithromycin where as 91% S. Paratyphi were resistant to azithromycin determined by both disc diffusion and E-test. The findings suggested that multidrug resistant (resistant to ampicillin, chloramphenicol and trimethoprim-sulfamethoxazole) S. Typhi and S. Paratyphi were still a problem in Bangladesh. In this study, 18%, 5% and 4% of S. Typhi were resistant to four, three and two drugs respectively but multidrug resistant S. Paratyphi was not detected. Nalidixic acid resistant strains were susceptible to ciprofloxacin for the past few years but the susceptibility to ciprofloxacin was low (ciprofloxacin susceptible S. Typhi and S. Paratyphi were only 13 and 5%). In addition this study showed that azithromycin can be used for the treatment of typhoid fever but not paratyphoid fever. However, cefixime and ceftraixone showed the highest susceptibility to both bacteria for treating enteric fever at present circumstances in Bangladesh.