Citrobacter braakii Isolated from Salami and Soft Cheese: An Emerging Food Safety Hazard?

<i>Citrobacter braakii</i> can colonize the intestinal tract of humans and animals and occasionally act as opportunistic pathogen. Although isolated from food and the environment, its potential as a foodborne pathogen remains uncertain. Twenty <i>C. braakii</i> isolates were previously collected from salami and soft cheese artisanal productions. In the present study, the potentialities of <i>C. braakii</i> as a food safety hazard were explored by a genomic comparison of <i>C. braakii</i> newly sequenced genomes with publicly available genomes, including those of clinical relevance, and a pathogenicity assessment in <i>Galleria mellonella</i> as an in vivo infection model. Phylogenomic reconstruction revealed that one salami clone and two <i>C. braakii</i> genomes of the soft cheese production were closely related (from 11 to 28 core SNP differences) to <i>C. braakii</i> publicly available clinical genomes. All genomes carried the chromosomally located <i>bla_CMY</i> and/or <i>qnrB</i> genes and were resistant to cephalosporins and/or had reduced susceptibility to ciprofloxacin. <i>G. mellonella</i> larvae showed 90% mortality after challenge with <i>C. braakii</i> strains carrying the <i>vex</i> and <i>tvi</i> operons coding for the capsular polysaccharide (Vi antigen), in comparison to 40% of strains lacking these two operons. The high mortality rate of <i>vex</i>- and <i>tvi</i>-positive <i>C. braakii</i> isolated from food processing plants suggests <i>C. braakii</i> to be a possible foodborne hazard.