Antibiotic Resistance of Shiga-Toxin Producing E.coli in Raw Milk and Traditional Dairy Products

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Question 1

Background of the Study

The study by Ranjbar, Dehkordi, Shahreza, and Rahimi (2018) was carried out with the aim of isolating certain virulent factors of O-serogroups, as well as of studying and carrying out tests to show various antibiotic resistant properties of Shiga-toxigenic Escherichia coli through the isolation of milk and various traditional dairy products. The study was mainly carried out on milk because of the high prevalence of milk and dairy products intake by people in the world due to its nutritious value in terms of vitamins and minerals (Rozenberg et al., 2016).

Popular milk products, such as Kashk and dough, are mainly consumed in Iran and other places of the world (Ranjbar et al., 2018). Due to the increased intake of milk and dairy products in the world, it is, therefore, crucial to make sure that the milk is free from microbial infection, mostly from Escherichia coli (E.coli) strains which usually cause different foodborne illnesses around the world (Ranjbar et al., 2018). Carrying out investigation of E.coli on this microbial strain on milk and dairy products is needed because it is the most common source of transmission of E.coli strain in human (Atapoor, Dehkordi, & Rahimi, 2014).

Question 2

Hypothesis under Investigation

There was a significant difference in the occurrence of E.coli strains separated from raw milk, and those isolated from sterilized dairy products and traditional dairy products. Other hypothesis that would have occurred from the study was that there was no significant difference in the E.coli isolated from raw milk and traditional dairy products. More so, the antibiotic resistance properties of Shiga-toxin producing Escherichia coli strains were significantly different in raw milk and traditional dairy products.

Question 3

To study the hypotheses, 600 samples of raw milk and traditional milk products were put under investigation after they were collected from Isfahan province, Iran. The milk samples were taken from different species such as bovine, ovine, caprine, camel, and buffalo. The traditional milk samples included cheese, dough, yogurt, butter, ice-cream, cream, and kashk. All the products were of normal physical character of color, odor, and compounding. Twenty-five millimeters of raw milk and 25mg of the blended dairy products were then added to the tube that contained 225ml of Buffered Peptone Water (BPW, Merck, Germany) and hatched aerobically at 37 °C for 24 hours (Ranjbar et al., 2018). The samples were then cultured on 5% sheep blood and MacConkey agar (Merk, Germany) media, and later incubated at 37 degrees for 24 hours (Ranjbar et al., 2018).

Those samples with the color and appearance of E.coli were picked and streaked on blood agar plates and then re-streaked on EMB agar (Merck, Germany), and then nurtured at 37 degrees for 24 hours. Other methods used included the PCR confirmation of E.coli isolates, the disk diffusion test that was used to assess the antibiotic resistance pattern of E.coli isolates. There was also the test carried out to detect virulence factors, O-serogroups, and antibiotic resistance genes.

All the data collected was then statistically analyzed through the Microsoft Excel Spreadsheet (Microsoft Corp., Redmond, WA), and then the data was subjected to Kolmogorov-Smirnov test to study the distribution of E.coli. Statistical analysis was then performed using SPSS version 20.0 software. The p-values were calculated using chi-square. Use of statistical analysis was mainly for finding the significant relationship on prevalence of E.coli and STEC strains between raw milk and traditional dairy products, the distribution of O-serogroups , virulence factors and antibiotic resistance, as well as significance in the seasonal distribution of bacteria.

The results showed that in 181 samples out of the 600 samples, a proportion of 30.16% of the examples tested positive for E.coli strains. According to the results, cheese and raw buffalo milk had the highest prevalence of E.coli, and camel milk had the lowest level (Ranjbar et al., 2018). Kashk and dough samples did not have any positive test for E.coli. The results proved the hypotheses correct since there was a significant difference in the test of E.coli strains in raw milk and traditional dairy products. There was also a significant difference between the types of samples and distribution of antibiotic resistance genes thus proving the above hypotheses true.

Question 4

The results were significantly different because they had a p-value of <0.05. There is a need for further studies in order to determine the importance of different types of food samples as a risk factor for the survival and transmission of pathogenic bacteria such as E.coli in the community (Atapoor et al., 2014). This is because according to the findings of the investigation carried out, bacteria such as E.coli are not just limited to healthcare centers but the community. More so, foods may contribute wholly to transmission of E.coli pathogenic bacteria in humans (Atapoor et al., 2014). It is important to note that raw milk and traditional dairy products are not exempted from the regulation and presence of E.coli strains have been reported in types of clinical infections due to food contamination (Dehkordi, Haghighi Borujeni, Rahimi, & Abdizadeh, 2013).

Question 5

The above article was quite informative and interesting owing to the fact that dairy products are prevalent in the market. It also helped in addressing the importance of having great quality assurance techniques in the milk processing industry, and in distinguishing the role of pasteurized milk in avoiding foodborne illness.


Atapoor, S., Dehkordi, F.S., & Rahimi, E. (2014). Detection of Helicobacter pylori in various types of vegetables and salads. Jundishapur J Microbiol., 7(5), e10013. doi: 10.5812/jjm.10013

Dehkordi, F.S., Haghighi Borujeni, M.R., Rahimi, E., & Abdizadeh, R. (2013). Detection of Toxoplasma gondii in raw caprine, ovine, buffalo, bovine, and camel milk using cell cultivation, cat bioassay, capture ELISA, and PCR methods in Iran. Foodborne Pathog. Dis., 10(2), 120-125. doi: 10.1089/fpd.2012.1311

Momtaz, H., Farzan, R., Rahimi, E., Safarpoor Dehkordi, F., & Souod, N. (2012). Molecular characterization of Shiga toxin-producing Escherichia coli isolated from ruminant and donkey raw milk samples and traditional dairy products in Iran. The Scientific World Journal. doi: 10.1100/2012/231342

Ranjbar, R., Dehkordi, F.S., Shahreza, M.H.S., & Rahimi, E. (2018). Prevalence, identification of virulence factors, O-serogroups and antibiotic resistance properties of Shiga-toxin producing Escherichia coli strains isolated from raw milk and traditional dairy products. Antimicrobial Resistance & Infection Control, 7(1), 53.

Ranjbar, R., Pezeshknejad, P., Khamesipour, F., Amini, K., & Kheiri, R. (2017). Genomic fingerprints of Escherichia coli strains isolated from surface water in Alborz province, Iran. BMC Research Notes, 10(1), 295.

Rozenberg, S., Body, J.J., Bruyere, O., Bergmann, P., Brandi, M.L., Cooper, C., ... Rizzoli, R. (2016). Effects of dairy products consumption on health: benefits and beliefs – a commentary from the Belgian Bone Club and the European Society for Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases. Calcified Tissue International, 98(1), 1-17.

August 09, 2023



Illness Medicine

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