Quinolone and Multidrug Resistant Salmonella typhi in Ibadan, Nigeria

Typhoid fever remains prevalent worldwide especially in a developing country like Nigeria. Many first line drugs such as chloramphenicol were discontinued due to Multi-Drug Resistant (MDR) Salmonella Typhi (S. typhi). Quinolones are now the recommended therapy but in spite of their usefulness there are several reports of failure of therapy due to quinolone resistance. This study sought to find the prevalence of quinolone resistant and MDR S. typhi in this environment. About 146 (4.6%) out of the 3184 blood culture samples collected for the study yielded Salmonella typhi disk diffusion antibiotic susceptibility testing was carried out for the following antibiotics: chloramphenicol, ampicillin, amoxicillin, amoxicillin-clavulanic acid, nalidixic acid, ciprofloxacin, azithromycin and ceftriaxone. The minimum inhibitory concentration of ciprofloxacin was determined against the isolates using broth macrodilution technique. Of the Salmonella typhi isolates 37.7, 32.2, 38.4 and 50.7% were susceptible to chloramphenicol, cotrimoxazole, ampicillin and amoxicillin, respectively while susceptibility to amoxicillin-clavulanic acid, nalidixic acid, ciprofloxacin, azithromycin and ceftriaxone were 87.7, 91.1, 95.9, 99.3 and 100%, respectively. The MIC50 and MIC90 of ciprofloxacin were 0.06 and 0.125 μg mL-1, respectively. The prevalence of multidrug resistance was 56.2% while that of quinolone resistance was 8.9%. There is high prevalence of multidrug resistant Salmonella typhi therefore, the use of chloramphenicol and other previous first line antibiotics should be discouraged. Though, resistance appears to be emerging, quinolones remain useful in treating typhoid fever in this environment but surveillance should be continuous.