# Resistance, virulence and genetic diversity of Salmonella Typhimurium in South Africa (1999–2021)

## TL;DR

This study analyzed antibiotic resistance, virulence genes, and genetic diversity of Salmonella Typhimurium in South Africa from 1999 to 2021, revealing high resistance and diverse genetic profiles.

## Contribution

The study provides a comprehensive analysis of resistance patterns, virulence genes, and plasmid diversity in S. Typhimurium isolates from multiple sources in South Africa.

## Key findings

- High resistance levels to antibiotics like ciprofloxacin, ceftriaxone, and piperacillin were observed in S. Typhimurium isolates.
- Class 1 integrons and resistance genes such as blaPSE, blaCMY-2, tetA, and qnrB were commonly detected.
- Genetic diversity was identified through ERIC-PCR, revealing 44 clusters with six major ones.

## Abstract

Salmonella Typhimurium is a major cause of human and animal salmonellosis, impacting global socioeconomic factors. This study examined antibiotic resistance patterns, virulence genes and plasmids in S. Typhimurium isolates from nine South African provinces (1999–2021). Among 180 randomly selected isolates, 129 were confirmed as S. Typhimurium from animal (n = 94), food (n = 16), environment (n = 7) and feed (n = 12) sources using polymerase chain reaction (PCR). Phenotypic resistance was assessed against 13 antibiotics, revealing high resistance levels: 86.8% to ciprofloxacin, 69.0% to ceftriaxone and 65.1% to piperacillin. Multidrug resistance (up to 11 antibiotics) was observed. Genetic analysis identified resistance genes, including blaPSE (32.6%), blaCMY-2 (21.7%), tetA (24.0%), tetB (22.5%), qnrB (21.7%) and qnrA (20.2%). Class 1 integrons were found in 47.4% of isolates. Virulence genes were prevalent, including sopB (95.3%), sspH1 (82.9%), sifA (82.9%), pefA (79.8%), spvC (79.1%), sspH2 (77.5%), srgA (71.3%) and invA (100%). Plasmid analysis detected 2 kb, 8 kb and 90 kb plasmids, with the 90 kb plasmid being most common (71.3%). Enterobacterial Repetitive Intergenic Consensus (ERIC) PCR identified 44 clusters (A–RR), including 6 major clusters.

These findings highlight the urgent need for enhanced surveillance and intervention strategies to curb antibiotic resistance and virulence in S. Typhimurium populations in South Africa, stressing the importance of monitoring and control measures to address this public health threat.