Comparison of genomic differences between Streptococcus suis serotype 1 strains in pigs and humans

Authors : Dr. Marcelo Gottschalk and Nahuel Fittipaldi

Read the original article published on Aprl 3, 2023 in Scientific Reports : https://www.nature.com/articles/s41598-023-32724-z

Streptococcus suis is a well-known zoonotic pathogen in pigs, causing various invasive infections. However, it can also infect humans, posing a growing public health problem. Among the methods of prevention in pigsties, autovaccines are not all effective; otherwise prevention and treatment involves the use of antibiotics while the pork industry seeks to reduce their use. Within the different serotypes of S. suis, serotype 2 is most frequently associated with human infections, but other serotypes may also be involved, including serotype 1. Recently, two strains of Streptococcus suis serotype 1 belonging to the complex clonal 1, were isolated in Thailand, one from a human patient and the other from an asymptomatic pig. This discovery raises questions about a possible common origin of the two S. suis serotype 1 strains recovered from humans and pigs, as well as their pathogenic potential and antimicrobial resistance.

With our collaborators, we examined the genomes of these two strains to identify genetic differences that could influence their virulence and their ability to cause infections. The results revealed that the strains belonged to two distinct clonal groups, and differed only in a small fraction (55 of 1926) genes. Therefore, by their pathotype, their profile of genes associated with virulence, their typing of the central genome and their content of antimicrobial resistance genes, the two strains belonged to the classification of “virulent strains”. However, unlike the pig strain, the human strain had a virulence gene encoding a molecule produced on the surface of the bacteria, known as adhesin P, which could explain its ability to cause human infections. Not surprisingly, both strains were sensitive to penicillin and other antibiotics in the same family, but were resistant to tetracycline, macrolides and clindamycin. With our collaborators, we found that some of these resistances were encoded by genes carried by mobile genetic elements, which represents a danger of transmission to other strains of S. suis and even to other streptococci. In conclusion, this study highlights the importance of complete genomic analyzes to properly characterize the strains of this bacteria and target appropriate interventions in veterinary public health.

As researchers continue to explore the implications of these findings, they highlight the need to closely monitor the emergence of antimicrobial-resistant strains, which could compromise the effectiveness of antibiotic treatments. Ultimately, genetic diversity, virulence characteristics, and a better understanding of the epidemiology and pathogenesis of S. suis could help reduce the incidence of human and swine infections associated with this pathogen.