16S rRNA gene sequencing and culture dependent analysis of bacterial diversity associated with commercially processed salads

The main objective of the present study was to evaluate the biosafety of the raw-eaten processed salads by exploring the general microbial diversity. For this purpose, more than hundred bacterial strains were isolated from the processed salads collected from street restaurants from different localities in Lahore, Pakistan. Sequencing analysis of 16S rRNA gene showed the presence of bacterial strains belonging to the genera of Bacillus, Staphylococcus, Proteus, Macrococcus, Haemophilus, Escherichia, Citrobacter, Enterobacter, Salmonella, Shigella, Klebsiella and Acinetobacter. Antibiotic susceptibility pattern against different antibiotics showed that majority of the strains were resistant against amoxicillin and ampicillin. Strains were also evaluated for biofilm formation, swarming motility and slime production. Maximum biofilm production in single or double cultures was shown by B. cereus C35 and M. caseolyticus C96. In the presence of carbon sources, B. cereus C35 (1% sucrose), B. pumilus C49 (1% fructose) and H. influenzae C410 (3% lactose) showed significant biofilm formation. For swarming motility, P. mirabilis L21 and P. mirabilis B33 were strongly positive. In conclusion, processed salads from different localities of Lahore were inhabited by different potentially pathogenic bacterial strains. E. coli a potential human pathogen was isolated from samples which indicated fecal contamination. Additionally, pathogenic bacteria such as En. cloacae, K. pneumoniae, B. cereus, S. dysentriae, H. influenzae, S. saprophyticus were also identified that make the biosafety of salad sources questionable.