The genome sequence of the lactic acid bacterium, Carnobacterium maltaromaticum ATCC 35586 encodes potential virulence factors

Abstract

The genus Carnobacterium belongs to the lactic acid bacteria and Carnobacterium maltaromaticum is commonly found in modified atmosphere packed and vacuum packed fish and meat products as well as in live fish. This species has been described as a fish pathogenic organism but human clinical isolates have only been obtained at one occasion. To investigate the virulence potential we sequenced the entire genome of strain ATCC 35586, isolated from a diseased salmon. When comparing the translated gene products of ATCC 35586 to those of Gram positive bacterial pathogens and probiotics as well as the related Carnobacterium sp. AT7 we identified a range of putative virulence genes including genes encoding products involved in adhesion to fibronectin and collagen, capsule synthesis, cell wall modification, iron scavenging mechanisms, haemolysis, invasion and resistance to toxic compounds. Of particular interest was the presence of internalin encoding gene homologues to some of those found in Listeria spp. and Lactobacillus plantarum. Furthermore, the ATCC 35586 strain possesses a gene encoding a product similar to the central Listeria monocytogenes transcriptional regulator PrfA, that in this organism controls virulence gene expression by binding to conserved DNA binding sites. Based on the consensus DNA sequence of this binding site, we identified a total of 65 genes in the ATCC 35586 genome that in the upstream region carry a PrfA binding motif. Among these is one of the internalin encoding genes; two genes encoding products involved in capsule biosynthesis as well as various genes encoding products with metabolic functions. In contrast to L. monocytogenes, the ATCC 35586 strain did not encode other PrfA dependent virulence factors such as listeriolysin O, phospholipases A and B, ActA, listeriolysin O, zinc metallo protease and internalins A and B. In conclusion, C. maltaromaticum ATCC 35586 carries putative virulence genes that may explain its reported ability to infect fish. The findings of this study give no reason for concern regarding human health by the presence of this species in food products.