In vitro antimicrobial susceptibility patterns of Salmonella enterica serovars and emergence of S. typhimurium phage type DT071 in a suspected community-associated outbreak in Lagos, Nigeria

Abstract

Background: The unprecedented upsurge of Salmonella-associated illness noticed in a community in Lagos within a three-month period necessitated the present work with the aim to determine antimicrobial resistance patterns and to generate epidemiological data on Salmonella phage types involved in the suspected outbreak.Methodology: Thirty-five Salmonella enterica isolates from human clinical samples (n=21), water (n=5), cattle (n=5), and sewage (n=4) were isolated, identified, serotyped, and subjected to in vitro antimicrobial susceptibility testing by standard methods. S. typhimurium (n=19) and S. enteritidis (n=13) strains were further phage-typed by standard procedure.Results: Eleven (68.8%) of the 16 outbreak-related S. Typhimurium strains belonged to the DT071 phage type, and were isolated from patients, sewage, and water samples and were resistant to at least chloramphenicol, tetracycline, gentamicin, or ampicillin. Most S. Enteritidis strains were multidrug resistant and did not belong to a definite phage type; however, only one strain from a water sample belonged to PT29.Conclusions: S. typhimurium phage type DT071 and S. enteritidis RDNC strains were the most identified phage types in this study. Antimicrobial resistance patterns exhibited among strains from different sources were diverse, which highlighted the relatively poor discriminatory power of antibiogram patterns, and made it difficult to trace the present upsurge in this community to a single origin. This study also identified, for the first time, multiple drug resistance in S. typhimurium phage type DT071 strains that pose a threat to public health.

Keywords

• Salmonella
• phage-typing
• antimicrobial resistance
• human
• environment.