Microbial Evaluation of Two Food samples

The microbial evaluation of foods usually require that individually viable propagules are encouraged to multiply in liquid media or on the surface, or within the matrix, of a medium solidify with agar (Adams and Moss 2000). Different group of microorganisms will grow best on selected media. However the general purpose of a media is to provide the necessary nutrients needed for the growth of the organism(s) under study.

Two common methods used to culture microorganisms are: (a) pour plate and (b) spread plate. In the pour plate method, a sample (usually 1ml), is pipette directly into a sterile petri dish and mixed with an appropriate volume of molten agar. The medium is then allowed to solidify and then incubated. Colonies to be counted will subsequently develop embedded in the agar. In the spread plate method, a sterilized wire is usually dipped in the suitable diluted suspension of organisms and then used to streak the surface of the surface of an already solidified agar plate. The isolated colonies for enumeration will grow along the lines of the streaks.

Salmonella, Staphylococcus and E. coli (enterovirulent) are some of the most common and dangerous microbial food borne organisms. Salmonella frequently has been associated with food borne illnesses and cause salmonellosis. Symptoms may include nausea, fever vomiting and acute gastroenteritis. Staphylococcus species such as S. aureus is also another principal causative agent in food borne illnesses. It grows in food and produces toxins that, when ingested causes an inflammation of the lining of the stomach and intestinal tract, or gastroenteritis. E. coli is mostly found on the surface of meats. When ingested it causes infection characterized by severe abdominal cramps followed by watery and bloody diarrhea.

This laboratory exercise seeks to identify and count the different bacteria present in chicken and doubles (Salmonella, Staphylococcus, and E. coli, and total aerobic bacteria. Materials and Methods In this laboratory exercise, Plate Count Agar will be used for total aerobic bacterial count; Eosin Methyl Blue Agar for E. coli; Brilliant Green Agar for Salmonella; and Mannitol Salt Agar for Staphylococcus.

One litre of Plate Count Agar (PCA), Eosin Methyl Blue Agar (EMBA), Mannitol Salt Agar and Brilliant Green Agar (BGA) and 500 mls of Ringers Solution were prepared based on manufacturers guidelines. Testubes containing 9mL of Ringers Solution were capped and autoclaved along with the different agars at 121oC for 15 minutes. Ten (10) grams of the doubles and chicken and were weighed and each individually placed in 90 mL of Ringers solution.

They were then placed in individual sterile stomacher bags and homogenized in a stomacher. After removal from the autoclave, the testube samples were diluted to obtain 10-4 dilution for the doubles and 10-6 for the chicken. To enumerate the organisms, the pour plate method was used for EMBA and MSA and the spread plate method for PCA and BGA. The petri dishes prepared were then incubated at 37oC for forty- eight (48) hours. Subsequent counts were done to identify the different organisms present in the chicken and the doubles.  The Ringers solution was used was used in the lab exercise to revive any weak or stressed bacteria present in the chicken or doubles. The PCA medium was used to identify total bacterial count; MSA for Staphylococcus, BGA for Salmonella and EMBA for total and fecal coliforms.

From the results obtained, it was observed that the total bacterial count, Salmonella, Staphylococcus and total and fecal coliform was higher for the chicken than the doubles. This is understandable seeing that chicken was not cooked. It was observed that the doubles was relatively clean seeing that the fecal and total coliform was very low. The pink zone, indicative of the presence of Salmonella was present in the chicken and doubles BGA, however it was overcome by yeast in the chicken BGA, thus no count could be taken for the chicken.

The green metallic sheen indicative of E coli was present in both the chicken and the doubles agar. However, the E coli count was higher in the chicken than the doubles. Conclusion The high level of microbial contamination on the raw chicken is understandable. However, this indicates that proper handling and cooking of raw materials is very important in reducing these high levels of contamination. Food handlers must also bear in mind that a poor quality raw material being subjected to the best processing technique will not result in a good quality end product. The doubles investigated in this lab exercise was relatively clean. Vendors should practice good sanitation and proper personal hygiene in order to maintain a good quality, healthy end product.

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