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Microbial Contamination of Street Vended Foods from a University Campus in Bangladesh

Sufia Islam
Department of Pharmacy, East West University (EWU), Aftabnagar, Dhaka

Nishat Nasrin
Department of Pharmacy, East West University (EWU), Aftabnagar, Dhaka

Farhana Rizwan
Department of Pharmacy, East West University (EWU), Aftabnagar, Dhaka

Lutfun Nahar
Department of Social Relations, East West University (EWU), Aftabnagar, Dhaka

Adity Bhowmik
Department of Pharmacy, East West University (EWU), Aftabnagar, Dhaka

Sayma Afrin Esha
Department of Pharmacy, East West University (EWU), Aftabnagar, Dhaka

Kaisar Ali Talukder
Enteric and Food Microbiology Laboratory, icddr,b, Mohakhali, Dhaka, Bangladesh

Mahmuda Akter
Enteric and Food Microbiology Laboratory, icddr,b, Mohakhali, Dhaka, Bangladesh

Ajoy Roy
Department of Pharmacy, East West University (EWU), Aftabnagar, Dhaka

Muniruddin Ahmed
Department of Pharmacy, East West University (EWU), Aftabnagar, Dhaka

Abstract/ Executive Summary:

The microbiological quality of street vended food samples from Dhaka, Bangladesh was evaluated. The objective of the study was to identify the presence of common pathogens (Escherichia coli, Shigella spp, Salmonella and Vibrio spp) and to describe the molecular characterization of E coli, a commonly found pathogen in various street foods. Fifty food samples were collected from fixed and mobile vendors from two sampling locations (Mohakhali and Aftabnagar) in Dhaka city, Bangladesh. The tested samples included deep fried and fried snacks; quick lunch items; pickles; fruit chutney; baked items; spicy, sour and hot snacks etc. Juices, tamarind water and plain drinking water were also tested. Sterile polythene bags were used for collecting 200 g of each category of samples. They were tested for the presence of microorganisms following conventional microbiological processes. Biochemical tests followed by serology were done for the confirmation of Shigella and Salmonella. Serological reaction was carried out for confirmation of Vibrio spp. DNA was isolated for the molecular characterization to detect the pathogenic E. coli by polymerase chain reaction (PCR). Out of 50 food samples, six (12%) were confirmed to contain different species of E. coli and Shigella. Molecular characterization of E. coli revealed that three samples were contaminated with enteroaggregative E. coli (EAEC) and one was contaminated with enterotoxigenic E. coli (ETEC). Shigella flexneri X variant was detected in one food item and Shigella flexneri 2a was found in drinking water. All these enteric pathogens could be the potential cause for food-borne illnesses.

Keywords: Street food, Shigella, Salmonella, Escherichia coli, Vibrio spp, Bangladesh

Location: Mohakhali and Aftabnagar, Dhaka, Bangladesh

Start Date:

End Date:

Program Area: Food Safety and Security

Commodity: Quality

Objectives:

To identify the presence of common pathogens (viz, E coli, Shigella, Salmonella and Vibrio spp) and to describe the molecular characteristics of E coli.

Methodology:

Sample collection Food samples (200 g of each category), namely, different types of fried and deep fried snacks, quick lunch items, pickled native fruits, baked items, spicy and sour items, different types of liquids including plain drinking water, and other snack items, were collected from mobile and fixed vendors in two areas of Dhaka, Mohakhali and Aftabnagar. The food samples were collected in sterile plastic bags, which were sealed and transported to the laboratory and processed within 2-3 hours of collection. Isolation and molecular characterization of E. coli Five grams (solid and semi-solid items) or 5 ml (liquids) of food samples were homogenized/mixed with 45 ml of trypticase soy broth (TSB) and 0.3% yeast extract (YE) and incubated under aerobic condition at 37ºC for 18-24 hours. The enriched broths were then inoculated onto MacConkey agar plates and incubated as described above. DNA was isolated for detection of pathogenic E. coli spp by PCR according to the standard procedures (Lüscher and Altwegg, 1994; Nguyen et al, 2005) using primers sequences listed. Isolation of Shigella, Salmonella and Vibrio spp For isolation of Shigella spp, 5 g or 5 ml of food samples were homogenized/ mixed with 45 ml of TSB containing 0.3% YE and 0.3 µg/ml novobiocin and incubated as described above. The enriched broths were inoculated onto MacConkey and Salmonella-Shigella (SS) agar plates and incubated as described. For Salmonella spp isolation, food samples were homogenized/mixed with 45 ml of buffered peptone water (BPW) broth and incubated as described. Enriched broths were inoculated onto brilliant green agar (BGA) and xylose-lysine-deoxycholate (XLD) agar plates and incubated as described for selective growth of the organism. For detection of Vibrio spp, homogenized/mixed samples were mixed with 45 ml of alkaline peptone water (APW) and incubated. Enriched broths were then inoculated onto taurocholate-tellurite-gelatin agar (TTGA) and incubated as described. Typical colonies identified on the selective agar plates were confirmed using standard biochemical tests (WHO, 1987). All biochemically-positive isolates were serologically confirmed using commercially available antisera kits specific for all groups and type-factor antigens (Denka Seiken, Tokyo, Japan). Isolates were sub-cultured onto MacConkey agar (Difco; Becton Dickinson, Sparks, MD) plates and after about 18 hours of incubation serological tests were performed using a glass slide agglutination method for identification of Shigella spp and the Manual of Clinical Microbiology for identification of Vibrio and Salmonella spp (Murray, 2007).

Source of Information: Southeast Asian J …, 2015 - tm.mahidol.ac.th, Vol 46 No. 3 May 2015

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The majority of 50 food samples tested were found to contain the presence of different species of pathogenic microorganisms indicating poor bacteriological quality of the food samples. Using culture and biochemical assay techniques, bacteria identified as being present in the food samples included Salmonella spp (50% of the samples), E. coli (46%), Shigella spp (20%), and Vibrio spp (2%). However, the single putative Vibrio isolate and all of the putative Salmonella isolates were negative when tested serologically. Only two samples showed contamination with S. flexneri X-variant and S. flexneri 2a. Among the 23 E. coli isolates, PCR-based assay revealed the presence of EAEC gene in singara, cake and buttered bun (13%) (Fig 1) and ETEC gene in lemon juice (4%).

Knowledge Management: Journal