The Genotyping Diversity and Hemolytic Activity of Cronobacter spp. Isolated from Plant-Based Food Products in Poland

The present study aimed to determine the genotyping diversity and hemolytic properties of 24 strains of Cronobacter spp. (15 Cronobacter sakazakii, 6 Cronobacter malonaticus, 2 Cronobacter turicensis, and 1 Cronobacter condimenti) isolated from commercial ready-to-eat leaf vegetables, sprouts, nuts, and dried fruits. The multilocus sequence typing (MLST) method was used to determine the sequence types (ST) and clonal complexes (CC) of these strains. The study demonstrated the high genotypic diversity of the Cronobacter genus bacteria isolated from plant-based foods. Five novel sequence types (804, 805, 806, 807, and 808) and the presence of novel alleles in the ppsA, gltB, gyrB, and infB loci were detected. In total, 16 of the 24 strains were assigned to the sequence types ST99, ST258, ST17, ST648, ST21, ST494, and ST98. One C. sakazakii strain (s12) isolated from alfalfa sprouts was assigned to the clonal complex CC4, which encompasses strains often associated with severe infections leading to meningitis in infants. In addition, 87.5% and 16.7% of the Cronobacter spp. strains showed β-hemolysis of equine and sheep red blood cells, respectively. The presence of the pathogenic species C. sakazakii, C. malonaticus, and C. turicensis in ready-to-eat plant-derived food products shows they are potential sources of infection, especially to those with compromised immunity, which substantiates their further multi-faceted characterization. The significance of this study may prove useful not only in epidemiological investigations, but also in assessing the risk of infections caused by the presence of Cronobacter.