Molecular Typing of Salmonella Serotypes Isolated from Wildlife, Domesticated Animal Species and Humans in Zimbabwe

Abstract

Salmonella enterica serovar enteritidis (S. enteritidis) is one of the major causative agents of diarrhoea in humans and is associated with the ingestion of contaminated animal products such as meat, poultry and poultry products. In Europe, S. enteritidis is involved in 80% of Salmonella food poisoning cases. Traditional methods of typing have been used to identify Salmonella up to the species level. However the advent of molecular typing techniques has made it possible to type Salmonella beyond the species level. This study aimed at establishing epidemiological relationships of the Salmonella serotypes isolated from different geographical locations and from different host species using molecular typing techniques. The study also aimed at identifying and serotyping Salmonella strains isolated from wildlife, domestic animals and humans using culture on selective media, biochemical tests and serotyping using the slide agglutination method.

The Salmonella used in this study were first typed using the slide agglutination test method using Salmonella antisera, before being subjected to multiplex polymerase chain reaction (Multiplex PCR), Plasmid profiling and Pulsed Field Gel Electrophoresis (PFGE) as molecular typing schemes for sub-typing beyond species level to determine their differences at molecular.

The isolate subtypes used in this study were S. enteritidis, Group B and Group C Salmonella strains. These were analysed and compared in order to pick any strain differences in relation to geographical distribution and host origin in order to determine possible epidemiological relationships. Multiplex PCR was in a position to split S. enteritidis strains into those with and those without Salmonella Plasmid Virulence (spv) genes which was not possible with plasmid profiling. Spv genes carry virulence genes of bacteria.

No relationship of the plasmid profiles or pulsotypes to geographical location was, however, established in this study. The present study however, managed to place the S. enteritidis from the Salmonellosis outbreak into a single profile based on PFGE results.

Although Group B Salmonella were also from an outbreak, they produced more profiles, both by plasmid and PFGE profiling though PFGE produced the highest number of profiles. According to this study, PFGE could possibly be used for typing of Salmonella in Zimbabwe after confirming with multiplex PCR if one wishes to show epidemiological relationships of the Salmonella serotypes isolated from different geographical locations and from different host species. This conclusion is drawn from the fact that in this study PFGE produced more profiles after typing compared to the other tools used. This should be complemented by the traditional typing tools.

Group C produced the largest number of plasmid profiles compared to group D and Group B possibly as a result of more species in this group compared to group D and Group B. PFGE was, however, not performed on this group as a result of lack of reagents. In conclusion, no relationship to geographical location and host origin of isolates was established. There is need to carry out the study on a large scale to authenticate the findings.