Determining the Effectiveness of a Food Preservative (THIS IS A CASE STUDY) - Essay Example

Experiment on Cottage Cheese TEACHER                 Experiment on Cottage Cheese Direct microscopic counts are not only unreliable when it comes to providing estimates of bacterial viability (Roszak & Colwell, 1987). This means that it is not a good indicator of how bacteria undergo growth, metabolism, respiration or cell division. Information on these aspects of growth of bacteria is essential in determining how virulent they are when ingested in this cottage cheese. Due to the unreliability of direct microscopic counts in determining viability, the value of this method in indicating public health safety is indeed “doubtful” (Roszak & Colwell, 1987).

Direct microscopic counts cannot distinguish between dead and living bacteria. Dead bacteria result from the fact that the “natural environments [for bacteria] do not always resemble standard laboratory culture media” (Roszak & Colwell, 1987). Hence, death of some bacteria is expected. Standard plate counts may not be able to differentiate among the different types of bacteria but is reliable when it comes to giving information about disease-causing bacteria such as Pseudomonas aeruginosa (“Swimming Pool,” 2010).

Identifying the growth and metabolism of organisms such as P. aeruginosa in cottage cheese can give insights on how effective a preservative is or, more specifically, how long it will last in protecting the cheese from bacteria. Moreover, standard plate counts seem to be the method of choice when it comes to experiments with cottage cheese, as long as the laboratory environment and all other variables are properly regulated (Fedio et al., 1994). Another thing is that, P. aeruginosa forms three colony types – a small and rough one, one with a fried-egg appearance, and one with a mucoid appearance (Todar, 2011).

Due to such differences in colonies, the number of bacteria will therefore obviously be relatively hard to determine through a direct microscopic count and hence will require a standard plate count. Besides, a standard plate count is appropriate for counting colony-forming bacteria (Todar, 2009).Turbidity measurements, just like direct microscopic counts, may fail to give an accurate bacterial count because it “cannot detect cell densities less than 107 cells per ml” (Todar, 2009). This means that colonies must have approximately at least 10,000,000 cells before it can be detected through turbidity measurements.

Considering that colonies of P. aeruginosa are varied in many aspects like appearance, it is possible to obtain samples where colonies would have cells less than the minimum limit that can be detected through turbidity measurements. In fact, thickness of P. aeruginosa colonies would vary from 150 to 300 µm (Werner et al., 2004).ReferencesFedio, W. M., MacLeod, A. and Ozimek, L. (1994). “The Effect of Modified Atmosphere Packaging on the Growth of Microorganisms in Cottage Cheese.” Milchwissenschaft, 49(11), 622-629.

Retrieved Oct. 11, 2011 from CSA Illumina: http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=20070650260817MT&q=cottage+cheese+standard+plate+count&uid=791122688&setcookie=yesRoszak, D. B. and Colwell, R. R. (1987). “Survival Strategies of Bacteria in the Natural Environment.” Microbiological Reviews, 51(3), 365-379. Retrieved Oct. 11, 2011 from the National Institutes of Health: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC373117/pdf/microrev00050-0073.pdfSwimming Pool Microbiological Testing Frequency. (2010). Retrieved Oct.

11, 2011 from the NSW Government: http://www.health.nsw.gov.au/factsheets/environmental/microbiological_test.htmlTodar, K. (2009). Growth of Bacterial Populations. Retrieved Oct. 11, 2011 from the University of Wisonsin-Madison: http://textbookofbacteriology.net/themicrobialworld/growth.htmlTodar, K. (2011). Pseudomonas aeruginosa. Retrieved Oct. 11, 2011 from the University of Wisconsin-Madison: http://textbookofbacteriology.net/pseudomonas.htmlWerner, E., Roe, F., Bugnicourt, A., Franklin, M. J., Heydorn, A.

, Molin, S., Pitts, B. and Stewart, P. S. (2004). “Stratified Growth in Pseudomonas aeruginosa Biofilms.” Applied and Environmental Microbiology, 70(10), 6188-6196. Retrieved Oct. 11, 2011 from the American Society for Microbiology: http://aem.asm.org/cgi/content/full/70/10/6188