DETECTION AND ESTIMATION OF BACTERIAL LOAD IN SELECTED LEAFY GREENS COLLECTED FROM DIVERSE MARKETPLACES OF DHAKA CITY IN BANGLADESH

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.