Microbiology

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SAMPLE2RIC.docx

Microbiology in Health and Disease

SAMPLE (2)

Fecal contamination in fresh products from supermarket in Brooklyn

The purpose of the Research in the Classroom (RIC) project was to apply set of skills and techniques received during Microbiology class. This project created to identify pathogenic bacteria that is responsible for foodborne illnesses. Food borne illnesses are caused by consuming food contaminated with prions, pathogenic, bacteria, toxin, viruses or parasites. Three major species of the Enterobacteriaceae family: Escherichia coli (E-Coli), Salmonella sp are associated with the periodic outbreak of food-related infection.

For the Research in the Classroom three food samples were purchased in Stop and Shop supermarket located in the 1710 Avenue Y, Brooklyn, NY 11235 on June 22, 2019. Sample # 1 was fresh fish. Sample # 2 was dill and sample # 3 was broccoli. All this sample were brought to microbiology class and placed to EE Broth, Mossel, selective enrichment media for Enterobacteriaceae species, incubated at 35-37º C at least for 18-24 hours. Typical EE Broth, Mossel, contains peptic digest of animal tissue (10g/L), dextrose (5g/L), disodium phosphate (6.45 g/L), monopotassium phosphate (2 g/L), Ox bile, purified (20g/L), Brilliant green (0.0135g/L), final pH: 7.2± 0.2 at 25ºC. In the following lab session samples were inoculated to Nutrient Agar (NA) plate, MacConkey Agar plate, and Xylose Lysine Tergitol-4 (XLT) Agar plates using streak (fishtail) method explained in the lab manual. NA media typically contains peptone (5g/L), sodium chloride (5g/L), HM peptone B (1.5g/L), yeast extract (1.5g/L), agar (15g/L), final pH: 7.4±0.2 at 25ºC. MacConkey Agar media typically contains peptone (17g/L), proteose peptone (3g/L), lactose monohydrate (10g/L), bile salts (1.5g/L), sodium chloride (5g/L), neutral red (0.03g/L), crystal violet (0.001g/L), agar (13.5g/L), final pH: 7.1±0.2 at 25ºC. XLT-4 agar media typically contains lactose (7.5g/L), sucrose (7.5g/L), sodium thiosulfate (6.8g/L), sodium chloride (5g/L), xylose (3.75g/L), yeast extract (3g/L), proteose peptone (1.6g/L), ferric ammonium citrate (0.8g/L), phenol red (80g/L), tergitol 4 (4.6g/L), agar (18g/L), final pH: 7.4±0.2 at 25ºC.

Results: The pictures of MacConkey, NA and XLT-4 Agar plates with bacterial species obtained from three mentioned samples are presented in the Figure #1 and #2. (PLEASE JUST SKIP IT)

DISCUSSION: MacConkey Agar plate are both selective and differential. MacConkey contain bile salt and the dye crystal violet. These components inhibit the growth of gram- positive bacteria and select for gram-negative bacteria. This plate contains the carbohydrate lactose, which allow differential of gram-negative bacteria based on their ability to ferment lactose. Organism on MacConkey agar ferment lactose produce acid end-products which react with the pH indicator neutral red and produce a pink color. E-Coli can grow and ferment lactose on this media. In MacConkey agar plate are definitely certain gram-negative bacteria in all three samples, but only in broccoli pink colonies can be seen. So, it indicates possibility presence of E-Coli bacteria in this plate. In Nutrient Agar (NA) can grow a variety type of bacteria and fungi. This plate contains many nutrients needed for the bacterial growth. The presence of cultures on Nutrient Agar plate indicate that all three samples possess some bacteria. Xylose-Lysine-Tegretol 4 (XLT-4) media is selective and differential media was developing for the isolation of gram-negative enteric pathogen. This media highly selective for Salmonella species. Typically, Salmonella colonies appear black or black-centered with yellow periphery after 18-24 hours of incubation. Colonies of negative Salmonella strains appear pink-yellow. XLT-4 plate confirms no presence of Salmonella in all three samples.(SAME AS MINE)

Escherichia coli is a bacterium found in lower GI tract of many animals. It can be harmless or cause from mild to serious infection disease. It is probably the best known of all the bacterium. It not only helps us with digestion, but also a source of some vitamins K and B as a result of its metabolism. People who take a lot of antibiotics may cause to significantly reduce the Escherichia coli in our intestine that will cause a digestive upset. Whenever it is present in food supplement it indicates that food was contaminated. As long as the bacteria does not get to other parts of the organ system it will not do any harms.

(SAMPLE)References:

https://academic.oup.com/fqs/article/1/4/289/4735151

https://www.cnn.com/2013/06/28/health/e-coli-outbreaks-fast-facts/index.html