Cultural, serotyping and plasmid profile of Salmonellae in Lagos, Nigeria

Problems associated with typhoid fever epidemic about its diagnosis in developing countries like Nigeria is a perennial healthcare challenge the healthcare sector grapples with. Improper diagnosis of clinical cases have also led to treatment failure and errors as diseases caused by other microorganisms are treated as typhoid fever especially as a result of inadequate reliable diagnostic laboratories. A total of 3,000 stool specimens from patients were analyzed using standard microbiological techniques. Of this, 1,391 Salmonella spp. were recovered, constituting 233 (88.14%) S. typhi while 158 (11.36%) were non-typhoidal Salmonella. S. typhi was recovered from more females, 685(55.6%), than males, 548 (44.4%). The 41 and above age group had the highest incidence of S. typhi of 220(17.8%) in females as against 280 (22.7%) in males within the 21-30 age group. Antibiotic susceptibility testing using the disc diffusion method by Kirby Bauer showed high multiple resistance to most of the 15 different antibiotics tested but susceptible to the first line typhoid fever drugs (chloramphenicol 85%, cotrimoxazole 86.7%, ampicillin 88.3% and amoxicillin 90%) and highly susceptible to third generation cephalosporins and fourth generation fluoroquinolones. The S. typhi tested showed four different resistance patterns. Plasmid profile analysis of 200 multiple antibiotic resistant Salmonella isolates identified culturally and biochemically as S. typhi but by serotyping showed Salmonella other than S. typhi were erroneously classified as S. typhi. Majority of the S. typhi harbored mostly small sized plasmids which ranged from 2.2 Kb to 55.5 Kb. It can be deduced from this study that multiple drug resistance in S. typhi is likely to be plasmid mediated. The eleven antibiotic resistance patterns were reduced to eight plasmid clones indicating the diagnostic efficacy of plasmid profiling over the former method.