Fluoroquinolone Susceptibility Pattern of the Salmonella Isolates From Enteric Fever Patients Visiting to National Public Health Laboratory Nepal

Abstract

Enteric fever caused by Salmonella enterica serovar Typhi and Paratyphi A is the most common clinical diagnosis among febrile patients presenting to hospital in Nepal. The aim of this study was to evaluate the fluoroquinolone susceptibility pattern in S. Typhi and S. Paratyphi A Salmonella enterica serovar Typhi and Paratyphi A. During the study period, 41 isolates of S. enterica serovar Typhi (59.54%) and Paratyphi A (41.46%) were grown from 443 blood samples from clinically diagnosed enteric fever patients visiting to NPHL. All isolates were identified by conventional biochemical tests and serotyping with Salmonella antisera (Denka Seiken Co. Ltd., Japan). Antibiotic susceptibility testing to 8 antibiotics (Ampicillin, chloramphenicol, cotrimoxazole, tetracycline, nalidixic acid, ciprofloxacin, ofloxacin and ceftriaxone) was performed by Kirby Bauer disc diffusion method and CLSI recommended interpretive criteria. MIC to ciprofloxacin, ofloxacin and nalidixic acid were determined by agar dilution method. Thirty three (80.49%) isolates were resistant to nalidixic acid, with S. Paratyphi A showing higher rate (88.23%) of resistance compared to S. Typhi (75%). Two S. Typhi isolates (4.88%) were MDR (one showing resistance to ampicillin, chloramphenicol, cotrimoxazole and nalidixic acid and other to cotrimoxazole, tetracycline nalidixic acid, ciprofloxacin, ofloxacin) while none of S. Paratyphi A were MDR. The isolates with full resistance to ciprofloxacin and ofloxacin with additional resistance to cotrimoxazole and tetracycline has not previously been characterized from Nepal. Ceftriaxone was the most sensitive (100%) drug. Despite this, one encouraging trend reported is the re-emergence of strains sensitive to ampicillin, chloramphenicol, cotrimoxazole and tetracycline (95.12%). Difference in both MIC and inhibition zone diameter in nalidixic acid sensitive and nalidixic acid resistant isolates was statistically significant (P < 0.001). S. Paratyphi A with reduced susceptibility to fluoroquinolones had higher MIC value compared to that of S. Typhi (P < 0.001). The decreased susceptibility to fluoroquinolones of S. Typhi and S. Paratyphi A was strongly correlated (sensitivity and specificity of 100%) with resistance to nalidixic acid. Ciprofloxacin and ofloxacin can no longer be considered as the drug of choice in treating enteric fever due to the high level resistant in nalidixic acid and increasing report of full fluoroquinolone resistant. Due to the re-emergence of susceptibility, conventional drug may play important role in the treatment of enteric fever.