Virulence determinants in Klebsiella pneumoniae associated with septicaemia outbreaks in neonatal pigs

Klebsiella pneumoniae is recognized as an opportunistic pathogen in pigs causing pneumonia, mastitis and diarrhoea, but can also cause mortalities due to septicaemia and meningitis in previously healthy piglets. This study aimed to identify virulence genes present in K. pneumoniae that caused outbreaks of septicaemia in neonatal pigs. The genomes of thirty-eight Australian K. pneumoniae isolates from pigs with septicaemia, meningitis, myocarditis, pneumonia, enteritis and healthy cohorts were sequenced. The presence of antimicrobial resistance, siderophore and enhanced capsule production genes were identified by sequence analysis and verified by either PCR or phenotypic tests. An additional 52 international K. pneumoniae genomes from healthy and clinically affected pigs (28), humans (16), birds (3), one rodent and environmental isolates (4) were included in a pangenome analysis. Porcine septicaemic K. pneumoniae genomes from the UK and Australia clustered together and had higher virulence scores than all other clinical and non-clinical isolates. Septicaemic isolates were predominantly ST25, had enhanced capsule polysaccharide production with K2 capsule type and contained genes for the siderophores aerobactin, salmochelin and yersiniabactin. Septicaemic K. pneumoniae were more likely to have genes encoding the assembly of LPS, fimbriae and adhesins, and enzymes needed for the integration of mobile genetic elements. No single virulence gene was solely associated with isolates causing septicaemia. These findings indicate that there may be genotypes associated with clinical disease outcomes for K. pneumoniae. In the absence of some virulence genes, K. pneumoniae was still able to cause significant disease if the pig’s immune system was immature or compromised.