Genetic diversity and the presence of circular plasmids in Bacillus cereus isolates of clinical and environmental origin

Abstract

The diversity of 61 Bacillus cereus strains isolated from different clinical specimens, food including raw milk and milk products, and water was evaluated. PFGE analysis could discriminate 61 distinct pulsotypes with similarity levels from 25 to 82%, which were divided into 13 clonal complexes. The similarity between clonal complexes was at least 40%. Clinical strains were divided into 10 clonal complexes, while the strains, isolated from milk, food and water were included in 9, 6 and 6 clonal complexes, respectively. Three clonal complexes were dominated by clinical isolates, while they were absent in two complexes. Bacterial isolates from foods, being a probable source of alimentary toxoinfection, showed low similarity to isolates from stool specimens. The isolates from both sources were classi ed together in only 4 out of 13 clonal complexes. The large circular and linear plasmids with the sizes between 50 and 200 kb were detected in 24 (39.3%) and 14 (23%) B. cereus strains, respectively. Thirteen (21.3%) strains contained only one plasmid, two plasmids were found in 6 (9.8%) of strains, and three or more plasmids were obtained in 5 (8.2%) of tested strains. The plasmids were con rmed in 30.8% and 40% of isolates from clinical specimens and food and milk samples, respectively. No clear correlation between the PFGE pro les, the source as well as plasmid content among all tested strains was observed.

Get to Know Your Neighbors: Characterization of Close Bacillus anthracis Isolates and Toxin Profile Diversity in the Bacillus cereus Group

“…Sixty-five Bacillus isolates were kindly provided by Institute of Microbiology and Immunology, Faculty of Medicine, University of Ljubljana (Ljubljana, Slovenia) and were collected between 2007 and 2015 from multiple isolation sources: thirty isolates from clinical specimens, twenty-one from dairy products, nine from foods and five from water. Some isolates were previously investigated for their antimicrobial susceptibility and their pulsotype diversity [30,31]. Strains were purity-checked upon receipt on tryptic soy agar plates supplemented with 5% sheep blood (TSS-agar; BioMérieux, Marcy l'Etoile, France).…”