Virulence potential of Bacillus cereus sensu lato group bacteria isolated from green leafy vegetables.

In this study, the virulence potential-including hemolytic activity, toxin gene content, and antibiotic resistance patterns-of Bacillus cereus sensu lato (B. cereus s.l.) group bacteria isolated from green leafy vegetables (mint, parsley, purslane, dill, cress, arugula, lettuce, and baby spinach) was investigated. A total of 59 presumptive B. cereus s.l. bacteria were isolated from 40 vegetable samples. Fourty-six isolates were confirmed as members of the B. cereus s.l. group by polymerase chain reaction (PCR). Species-specific PCR identified 42 of the 46 isolates as B. cereus sensu stricto (B. cereus) and four as B. mycoides. All isolates showed β-hemolytic activity on Columbia sheep blood agar. Except for B. cereus 472 and B. mycoides 571, all isolates harbored between one and eight toxin genes. The most frequently detected toxin gene was entFM, found in 81.0% (34/42) of B. cereus and 75.0% (3/4) of B. mycoides strains. The hblACD and nheABC gene clusters were identified in only 19.1% (8/42) and 7.1% (3/42) of B. cereus strains, respectively. Similarly, the emetic toxin genes ces (9.5%, 4/42) and CER (4.8%, 2/42) were detected exclusively in B. cereus strains. In total, 31 distinct toxin gene profiles were observed. Linezolid and vancomycin were the most effective antibiotics against both B. cereus and B. mycoides strains. However, B. cereus strains exhibited varying degrees of resistance to all tested antibiotics. All B. mycoides strains were resistant to clindamycin, and 75.0% (3/4) were also resistant to ciprofloxacin, imipenem, levofloxacin, meropenem, and norfloxacin. The multiple antibiotic resistance (MAR) index was greater than 0.20 in 60.9% (28/46) of the B. cereus s.l. isolates, and 52.2% (24/46)-including 21 B. cereus and three B. mycoides isolates-exhibited multidrug resistance (MDR). In conclusion, these findings suggest that B. cereus s.l. group isolates from green leafy vegetables may pose a potential risk to public health.