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Microbiological Analysis of Raw Milk, Pasteurized Milk and Yogurt Samples Collected from Different Areas of Dhaka City, Bangladesh

TASMINA RAHMAN*
Department of Microbiology, Stamford University Bangladesh, Dhaka-1217, Bangladesh

TANZIA AKON
Department of Microbiology, Stamford University Bangladesh, Dhaka-1217, Bangladesh

IFTIKHARUN NESSA SHEULI AND
Department of Microbiology, Stamford University Bangladesh, Dhaka-1217, Bangladesh

NAIMA HOQUE
Department of Microbiology, Stamford University Bangladesh, Dhaka-1217, Bangladesh

Abstract/ Executive Summary:

A total of 300 different milk and yogurt samples were collected from Dhaka city and analyzed for total viable bacterial count (TVBC), total coliform count (TCC) and presence of several pathogens such as Escherichia coli, Salmonella spp., Shigella spp., Vibrio spp. and Listeria monocytogenes. Raw milk samples collected from Moghbazar area showed highest TVBC (4.2 × 106 cfu/ml) and samples from Mohammadpur area showed lowest count (3.5 × 103 cfu/ml). All the pasteurized milk samples showed TVBC of 1.9 × 102 to 2.8 × 103 cfu/ml, and TCC only in one sample Yogurt samples (open) collected from vendor showed TVBC of 9.1 × 103 to 8.2 × 107 cfu/ml, and TCC only in sample collected from Dhanmondi, Dhaka. The packed yogurt samples showed TVBC of 2.2 × 102 to 6.1 × 103 cfu/ml, and TCC only in one sample. All the milk and yogurt samples were found contaminated with E. coli and Shigella-like species. Listeria monocytogenes was not detected in any of the samples studied.

Keywords: Raw milk; Pasteurized milk; Yogurt; Listeria monocytogenes; Coliform

Location: Dhaka city

Start Date:

End Date:

Program Area: Pest Management

Non-commodity: Performance

Objectives:

The objectives of the present study were to assess the bacteriological quality of milk and several milk product samples giving priority to detect the presence of several pathogenic bacteria like E. coli, Salmonella, Shigella-like species, Vibrio and Listeria monocytogenes.

Methodology:

Twenty raw milk and 20 vendor’s yogurt samples were collected from each of five selected area (Moghbazar, Siddeswari, Lalmatia, Dhanmondi and Mohammadpur) of Dhaka Metropolitan city (total of 200 samples). These areas have been selected as they are densely populated and several schools and colleges have been located around. Furthermore, 10 samples each of pasteurized milk and packed yogurt were also collected from each of 5 commercially available brands. Samples were chosen randomly from different super shops and local markets. Raw samples were collected in sterile flask, however, packed milk and yogurt samples were purchased as sealed pack by checking the valid expiry dates. Samples were transferred to the laboratory for quality testing within 30 minutes it was collected. The samples were serially diluted up to 10-7 . Standard plate count (SPC) method recommended for dairy products (APHA 1960) was followed for quantitative analysis of bacteria. A volume of 10 ml raw sample was inoculated in buffered peptone broth, selenite cystine broth, alkaline peptone broth for enrichment of Escherichia coli, Salmonella spp., Shigella spp. and Vibrio spp., respectively and incubated for 6 hours. After that, 0.1 ml of enriched sample was spread over MacConkey agar, Salmonella-Shigella agar and Thiosulfate citrate bile Salt sucrose (TCBS) agar media and incubated at 37⁰C. On the otherhand, 0.1 ml raw sample was spread over Listeria identification media and incubated at 37⁰C. Following incubation for 24 hours, typical colonies for each genus were considered as positive growth and microscopic observation of the isolated bacteria was done by Gram staining. Confirmation of the organisms was performed by different biochemical tests, such as Triple Sugar Iron (TSI) agar, catalase test, citrate utilization test, indole test, motility test, methyl red test, Voges Proskaur test and urease production test (Cappuccino and Sherman 1996).

Source of Information: Journal of Bangladesh Academy of Sciences, Vol. 39, No. 1, 31-36, 2015

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The laboratory investigation confirms that most of the raw milk and open vendor yogurt samples that have been tested were contaminated with huge load of heterotropic bacteria. Bacterial contamination of these products assumed to be originated from poor hygiene sense of the handler and improper processing, preservation and marketing strategy. These products usually are found to be sold in an open condition with less sanitary measure which can introduce contaminants into these products. On the contrary, the pasteurized milk and packed yogurt are sold in sealed packs and in sufficient sanitary conditions. These physical barriers are useful to prevent microbial contamination. However, few products exceeded the acceptable limit of bacteria which indicate the inadequate processing and packaging of these goods. Therefore, proper guidance and education for the processor, handler and consumer are necessary to maintain a consistent healthy life of consumer body.

Knowledge Management: Journal