Indian Journal of Medical Microbiology Home 

Year : 2001  |  Volume : 19  |  Issue : 4  |  Page : 224--226

Bacteriological study of Indian cheese (paneer) sold in Chandigarh

C Vaishnavi, S Singh, R Grover, K Singh 
 Department of Gastroenterology, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012, India

Correspondence Address:
C Vaishnavi
Department of Gastroenterology, Postgraduate Institute of Medical Education and Research, Chandigarh - 160 012


A study was conducted to isolate and identify bacterial pathogens/contaminants in paneer samples sold in Chandigarh. Fifty eight samples of paneer bought at random were cultured on several media. Bacterial colony counts were also done. The predominant organisms isolated were Staphylococcus species, aerobic spore bearers, Klebsiella pneumoniae, Campylobacter jejuni, Acinetobacter species and Streptococcus species. The viable bacterial counts obtained ranged from 3 x 102 to 9.7 x 1010 CFU/mL. Contamination of paneer by pathogenic bacteria could be an important factor of gastrointestinal illnesses in the consumers.

How to cite this article:
Vaishnavi C, Singh S, Grover R, Singh K. Bacteriological study of Indian cheese (paneer) sold in Chandigarh.Indian J Med Microbiol 2001;19:224-226

How to cite this URL:
Vaishnavi C, Singh S, Grover R, Singh K. Bacteriological study of Indian cheese (paneer) sold in Chandigarh. Indian J Med Microbiol [serial online] 2001 [cited 2020 Jul 5 ];19:224-226
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Full Text

In tropical countries like India, dairy products are responsible for many outbreaks of gastrointestinal infections. Dairy products prepared under unhygienic conditions pose a great threat to the health of consumers. The Indian cheese (paneer) is a regular dietary favourite among the North Indians. A study was carried out to isolate and identify bacterial pathogens/contaminants in paneer samples sold in Chandigarh with a view to assess the situation locally.

 Materials and Methods

A total of fifty eight (paneer) samples were purchased randomly from different shops and vendors of various sectors of the city, encompassing the whole of Chandigarh. They were collected in pre-sterilised containers and transported in ice-bucket to the Microbiology Section of the Department of Gastroenterology.

Each cheese sample was processed as follows under sterile conditions: In a 2 mL marked glass homogeniser, 1 mL of physiological saline was added and minced cheese was added upto the 2 mL mark. The material was then thoroughly homogenised to give a uniform mixture. Inoculation was carried out immediately on nutrient agar, MacConkey agar, selenite F broth, Xylose lysine deoxycholate (XLD) agar, Yersinia isolation agar and blood agar. The last media was incubated both aerobically and under microaerophilic conditions. After incubation for 24 hrs aerobically and for 48 hrs microaerophilically at 370C, the identification of the colonies grown was made. Subcultures were made from selenite F broth and both XLD and MacConkey agar plates to maximise the chances of isolation. Colonies obtained were identified by putting up various biochemical and immunological tests. Cultures for isolation of Mycobacterium tuberculosis were also done.

Samples were also subjected to standard methylene blue reduction test and for the presence of phosphatase enzyme.

To assess the bacterial colony counts, ten fold dilution of the homogenised samples were made in Ringer's salt solution. They were inoculated on plate count agar and incubated at 370C for 24 hrs. The colony forming units per mL (CFU/mL) of the original samples were obtained by multiplying the counts obtained with the dilution factor.


The bacterial isolates that were most commonly found are depicted in the [Table].

The total bacterial counts obtained from each sample are given in the [Figure]. All the 58 samples studied had bacteriological counts ranging from 3 x 102 to 9.7 x 1010 CFU/mL. Thirty-eight (65.5%) samples had a bacteriological count of > 106 CFU/mL.

Methylene blue reduction test was positive in 54 (93%) of the samples and phosphatase enzyme in 2 (3.4%) of the samples. Mycobacterium tuberculosis was not isolated in any of the samples.


In some countries, especially those with a warm climate, raw milk and its products such as cheese continue to be responsible for many outbreaks of gastroenteritis. Food borne bacterial infections in individuals with human immunodeficiency virus can be life-threatening.[1]

In the present study, a high degree of bacterial contamination has been seen. Bacterial colony counts assess the number of viable bacteria which will correlate with the quantum of cheese consumption. The positive methylene blue reduction test in 93% of the samples also confirms the degree of contamination. However the presence of phosphatase enzyme in 3.4% of the samples is intriguing because in India, cheese is usually prepared after thorough boiling of the milk. The most probable reason we envisage for the presence of phosphatase enzyme in Indian cheese could be the dipping of the products in unpasteurised milk to keep them soft for greater acceptability by the consumers.

Reports regarding several outbreaks of typhoid fever in Western Countries have been ascribed to consumption of unripened hard cheese made from raw milk handled by chronic carriers[2]. Enteric bacilli multiply in milk at ordinary atmospheric temperatures, so that even a trivial contamination may cause an explosive outbreak. Sporadic infections however may result if the dairy product is contaminated during the distribution process.[2] Industrial cattle breeding and food production facilitate the spread of non-typhoidal Salmonella spp., Campylobacter spp. and possibly Yersinia enterocolitica.[3] In the present study, even though Salmonella spp. (S. enteritidis 1; S. typhimurium 1) and Yersinia enterocolitica each were found in only 3.4% of the samples, Campylobacter jejuni was found in 17.2% of them. All these are potential gastrointestinal pathogens and fewer than a hundred microorganisms may be sufficient to cause disease.

Sims et al [4] reported the survival and growth of several food poisoning bacteria following inoculation into cottage cheese varieties. Ryser and Marth[5] have listed Listeria monocytogenes in two major cheese-related outbreaks of listeriosis. MacGowan et al[6] reported faecal carriage of L.monocytogenes in renal transplant patients consuming various types of cheese. Listeria spp. was however not isolated in our samples.

Staphylococcus spp. was the predominant organism isolated with the majority of them being S. aureus, the contamination presumably coming from the hands of the cheese-sellers. However, cows may excrete S. aureus from the udder, often without clinical evidence of mastitis.[7]

Although spores of B.cereus are ubiquitous, large numbers of toxin-producing organisms are required for illness to occur. Because it is a common contaminant, the isolation of B.cereus from our samples does not indicate whether it was a potential hazard or not. Bacteria are not uniformly distributed in food, and there are a number of confounding factors that make it difficult to quantitate the population present in a given lot. Moreover, physical attributes of the food matrix complicate detection and many of the processing steps, e.g. heating, chilling and dehydration can affect the dynamics of bacterial growth and development. Even with statistical significant sampling method, it is problematic to determine whether an entire lot is pathogen-free or contaminated.

The heavy bacterial contamination seen in all samples predominantly by S.aureus and faecal bacteria can be attributed to the practice of preparing large bulks far too in advance of requirement, which are being held for long periods at room temperature. It also indicates poor hygienic conditions and faults in manufacturing/handling during process of cheese production. Improvement in cheese preparation and storage has been recommended.


The authors are grateful to the Department of Science and Technology, Chandigarh for funding the project.


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2Topley and Wilson's Principles of Bacteriology, Virology and Immunity, Bacterial Diseases. 8th Edition 1990;3:433.
3Grundmann H. Differential therapy of infectious diarrhoea (Geruan) Schweiz Rundsch Med Prax 1994; 83: 76-78.
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