Abstract:
A study was performed to detect the human pathogenic bacteria and to estimate the
colony-forming units (CFU) and bacterial incidence from 3 selected leafy greens viz.
coriander, lettuce, and mint leaves. The study was conducted in the MS Laboratory of
the Department of Plant Pathology, Faculty of Agriculture, Sher-e-Bangla Agricultural
University during the period from July 2021 to June 2022. In total 27 samples were
collected from 9 different marketplaces in Dhaka city. The bacteria were isolated by
five-fold dilution from the stock solutions after being grown on NA media. Bacteria
were identified by performing cultural, morphological, biochemical, and molecular
studies. The biochemical tests were Gram-staining, KOH solubility, Oxidase, Catalase,
Motility, Simmon’s citrate utilization, Casein hydrolysis, Starch hydrolysis, Gelatin
liquefaction, Levan production tests, and the culture on selective and semi-selective
media were EMB agar, SS agar, Cetrimide agar, and Bacillus cereus agar. In molecular
analysis, the DNA samples were put through to PCR using universal primer 27F:
AGAGTTTGATCMTGGCTGAG and primer 1942R: CGGTTACCTTGTTACGAC
TT that targeted the 16s rRNA gene at 1465 bp. Initially, Nine different bacterial genera
viz. Bacillus, Escherichia, Pseudomonas, Neisseria, Klebsiella, Enterobacter,
Shigella, Vibrio, and Staphylococcus were detected, and the incidence was 93%, 67%,
44%, 30%, 26%, 26%, 11%, 7%, and 7% respectively. A total of twelve bacteria have
been identified from these nine genera viz, B. subtilis, B. velezensis, B. altitudinis, B.
cereus, E. coli, P. aeruginosa, Neisseria spp., K. pneumoniae, E. aerogenes, S. aureus,
Vibrio spp., and Shigella spp. Among them, B. cereus, E. coli, P. aeruginosa, K.
pneumoniae, E. aerogenes, S. aureus, and Shigella sp. were detected as human
pathogenic bacteria reported in several pieces of literature. The highest CFU was found
in mint (4.27×10
9
/g) followed by lettuce (2.87×10
9
/g) and the lowest in coriander
(2.43×10
9
/g). Considering marketplaces, the highest bacterial CFU was observed in
the samples of roadside stand bazaars (5×10
9
/g) followed by local markets (2.7×10
/g), and the lowest was in supermarkets (1.9×10
9
/g). However, further advanced
research is needed for the identification of undetected bacteria and to understand the
specific conditions that lead to bacterial contamination in leafy greens.
