Abstract
Non-typhoidal Salmonella enterica continues to be a significant pathogen of global relevance. However, there is limited available comparative experimental data on the virulence of S. enterica strains that are isolated from poultry and circulating in Central Asia. This study aimed to investigate the virulence of four poultry-derived S. enterica isolates recovered in Kazakhstan using a standardized murine model of systemic infection. Outbred mice were inoculated intraperitoneally with graded bacterial doses ranging from 103 to 106 CFU and the pathogenicity was assessed by determining the median infectious dose (ID50) and median lethal dose (LD50) according to the Reed-Muench method. Systemic infection was confirmed by bacteriological re-isolation and real-time PCR. Mortality occurred primarily within 18-72 h post-inoculation and followed a clear dose-dependent pattern. Two S. enterica serovar Infantis strains showed relatively low LD50 (3.16 × 105 CFU) compared to the other isolates (1.78 × 106 CFU). This indicates relatively high virulence potential of the two S. Infantis strains compared to the others. Similar results were seen in the case of the ID50, where the same strains showed relatively high infectivity potential compared to the others. It is noteworthy that the systemic infection was seen with doses that were not lethal to the host, indicating some dissociation between virulence and infectivity potential.