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Isolation and Quantification of Microorganisms from Some Common Milk Products Within Dhaka City, Bangladesh

Mushfia Malek
Department of Microbiology, Stamford University Bangladesh, 51 Siddeswari Road, Dhaka-1217, Bangladesh.

Jasmin Akter
Department of Microbiology, Stamford University Bangladesh, 51 Siddeswari Road, Dhaka-1217, Bangladesh.

Tasnia Ahmed
Department of Microbiology, Stamford University Bangladesh, 51 Siddeswari Road, Dhaka-1217, Bangladesh.

Md. Aftab Uddin
Department of Microbiology, Stamford University Bangladesh, 51 Siddeswari Road, Dhaka-1217, Bangladesh.

Abstract/ Executive Summary:

While milk is well known to be a balanced diet with its high nutritional values, conversely milk and milk products may serve as potential substrate for the growth and proliferation of a range of microorganisms which in turn fatally influences mass public health. Current study attempted to examine the likelihood of microbial contamination within some common milk products consumed by the locality of the city of Dhaka, Bangladesh. All samples exhibited the presence of bacterial and fungal contamination within a range of 10² -10⁴ cfu/mL and 10² -10³ cfu/mL, respectively. Among specific pathogens, Staphylococcus spp. was noticed to be the predominant ones and was recovered from 9 samples out of 20 samples in a range of 10² -10³ cfu/mL. Klebsiella spp. and Vibrio spp. were found within 6 and 9 samples, respectively. Products were also found to be contaminated with Vibrio spp. Study of antibiotic susceptibility test revealed that all the pathogenic bacteria were resistant against most of the commonly used antibiotics of which several isolates showed multi-drug resistant (MDR) trait. Therefore, the presence of pathogenic bacteria with the drug-resistance property in tested milk and milk products overall imparted the necessity of maintaining standardized hygienic handling and processing means for better management of public health.

Keywords: Milk, Bacteria,Fungi, Quality, Drug resistance

Location: Dhaka city

Start Date:

End Date:

Program Area: Food Safety and Security

Commodity: Milk

Objectives:

To examine the likelihood of microbial contamination within some common milk products consumed by the locality of the city of Dhaka, Bangladesh.

Methodology:

A total of 10 milk and milk products were collected aseptically from different shops within the city of Dhaka maintaining the standard procedure of sampling (1). Samples were transported immediately (approximately within 1 hour) to the laboratory for microbiological analysis. Prior to the estimation of bacterial and fungal load, samples were subjected serial dilutions up to 10^-2. For the enumeration of total viable bacteria and fungi, an aliquot of 0.1 mL of each suspension was introduced onto the nutrient agar (NA) plates and Sabouraud dextrose agar (SDA) plates by means of spreading in order to isolate and quantify the total viable bacterial count (TVBC) and fungi, respectively (1). The NA plates were incubated at 37 °C for 18 to 24 hours and the SDA plates were incubated at 25 °C for 48 to 72 hours, respectively. For the estimation of specific pathogenic bacteria, from the dilution of 10^-2 of each sample, 0.1 mL of suspension was spread onto MacConkey agar, mannitol salt agar (MSA) and cetrimide agar media for the enumeration of Escherichia coli, Staphylococcus spp. and Pseudomonas spp., consecutively. All the plates were incubated at 37 ºC for 24 hours. Appearance of the typical colonies such as pink colonies on MacConkey agar, yellow colonies on MSA and colonies with greenish pigmentation on cetrimide agar was analytical for the growth of E. coli or Klebsiella spp., Staphylococcus spp. and Pseudomonas spp., consecutively (29). For the detection of Salmonella spp. and Vibrio spp., samples were subjected enrichment for isolation and identification of these bacteria (30). One ml sample was added to selenite cystein broth (SCB) and alkaline peptone water (APW), respectively, and incubated at 37º C for 6 hours, and then 0.1 mL from each of the enriched broth was spread over Salmonella-Shigella agar (SSA) and thioglycollate citrate bile salt (TCBS). Appearance of small blackish colonies after incubation for 24 hours at 37 ºC was indicative of the presence of Salmonella spp., while the large (2-4 mm) and slightly flattened, yellow colonies on the TCBS agar denoted the presence of Vibrio spp. Finally the confirmative biochemical tests were conducted to ensure the identity of the isolates (29, 30). Isolated E. coli, Vibrio spp., Pseudomonas spp. and Staphylococcus aureus were subjected to antibiotic susceptibility assay against different groups of antibiotics in vitro by the Kirby-Bauer method (31). Drug resistance was observed against Penicillin (10 µg), amoxicillin (10 µg), Impenem (10 µg), cefixime (5 µg), Chloramphenicol (30 µg), gentamicin (10 µg); ciprofloxacin (5 µg), sulphamethoxazole-trimethoprim (25 µg), Vancomycin (30 µg), azithromycin (15 µg), Erythromycin (15 µg). From overnight culture plate, a small portion of a fresh colony was transferred to Muller-Hinton broth and incubated at 37 ºC for 4 to 5 hrs until the growth reached to the equivalent turbidity standard of McFarland (0.5 standards). Muller- Hinton agar plates were seeded properly by spreading the inocula using sterile cotton swab. Discs (OXOID, UK) were placed gently at a proportionate distance from each other using a sterile needle. The plates were then incubated overnight at 37ºC and zones of inhibition (if any) were measured and interpreted as susceptible, intermediate and resistant.

Source of Information: Stamford Journal of Microbiology, Vol.5(1) 2015: 13-17

Article Link (Online Journal): DOI: http://dx.doi.org/10.3329/sjm.v5i1.26913

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In cohort with the previous study findings on the microbiological analysis of milk and milk products carried out in the same laboratory, present study revealed the presence of a range of pathogenic bacteria which were of public health significance. Maintenance of proper hygiene during handling and processing of milk products as well as proper application of sterilization procedure such as pasteurization and UHT could ensure food quality and most importantly consumers’ safety.

Knowledge Management: Journal