Enumerating Bacteria in Hamburger Meat from Various Sources in Flagstaff, AZ.
Ryan Kelly
October 18,2013
Section D

INTRODUCTION It is commonly known that bacteria can be found in places like bathrooms and sinks but they can also be found in unwanted places such as food. Over 70 million cases of food-borne illnesses are reported every year in the U.S. according to the Centers for Disease Control and Prevention (CDC) (Linscott, 2011). Although the government tries to regulate the amount of bacteria in meat that cause food borne illnesses, certain bacteria that cause illness don’t receive notice (Waters et al. 2011). Organizations, such as the National Antimicrobial Resistance Monitoring System (NARMS), that monitor the amounts of bacteria in food look at certain multidrug-resistant bacteria species like Escherichia coli, but neglect others like Staphylococcus aureus, which is one of the leading causes of clinical infections worldwide (Waters et al., 2011). Although, some bacteria found in meat can be less harmful than other.
Without lactic acid bacteria, sausage meats wouldn't be fermented safely. Although some strings can cause spoilage, most lactic acid bacteria prevent more harmful bacteria from growing. This makes the overall presence of lactic acid bacteria on meats more desirable than other bacteria (Egan, 1983). Steps of prevention are being taken to prevent food borne illnesses, such as pasteurization of dairy products, but more actions should be taken to further help the prevention of food-borne illnesses (Linscott, 2011).
The European Union has recently taken that step in furthering prevention. The fermentation of certain foods relies on starter cultures of bacteria when pasteurization is not desirable (Talon & Leroy, 2011). Aside from regulating the microorganisms in animal feeds and plant protection products, there is no other way microorganisms are formally recognized as harmful when used for human food preparation. The European Food Safety Authority, EFSA, have introduced a qualified presumption safety approach in order to assess the microorganisms throughout the food industry (Talon & Leroy, 2011). The assessment looks at qualifications like taxonomy and pathogenicity, along with the amount of bacteria found in meat. By enumerating bacteria and observing the concentration in meat, it can be determined if the governmental food regulation system is efficient.
For the experiment, samples of different hamburger meat from around the Flagstaff area were used to observe the amount of bacteria found in each sample. It can be determined how well the food contamination regulation system really is. It was hypothesized that if meat samples were handled correctly, the samples would have little to no bacteria on them. The experiment was done by distributing 1:10 serial dilutions of hamburger solution into four spread plates and four pour plates. After a week, the colonies on the plates were counted using a viable count assay on the pour and spread plates.
MATERIALS AND METHODS
All of the meat samples collected were from various locations in Flagstaff, Arizona. First a culture tube containing hamburger meat was made into 1:10 serial dilutions using .75% NaCl. Having different dilutions can ensure that there will be some plates with colonies between 30 and 300, otherwise the plate would be marked as NSS, not significant sample, or TCTC, too numerous to count.
For the five spread plates, 0.1 mL of the 10-2 dilution was placed onto the plate marked 10-3. A glass hockey stick was then dipped into ethanol and ignited using the Bunsen burner to sterilize it. Once the hockey stick cooled, the.1 mL of dilution was spread evenly over the surface of the plate. The stick was then flame sterilized again and the same procedure was repeated for the 10-3, 10-4, 10-5 tube dilutions. The last plate had .1mL of sterile diluents added to the plate for the control plate. The same process was repeated for the five pour plates except for after the dilution was added to each plate, molten NA was poured into the plate to cover bottom completely and gently mixed with the dilution and allowed to cool. Once cooled, the plates were incubated at room temperature for a week before each spread and pour plate were counted for colonies. Then the titer was determined by dividing the number of colonies found on each plate by the dilution.
All methods from Shand (2012).
RESULTS
The results show that each sample had at least 1.00X104 cfu/g. The sample with the highest amount of bacteria colonies was sample A with 8.04X10^7 cfu/g for the spread plate and 1.13X1068 cfu/gm for the pour plate. Sample B had the least amount of colonies on the pour plate. Sample D,C, and E had around the same amount of colony forming units for the spread plate and the pour plate.
Table 1: Average Concentration of Bacteria from Each Sample and Total Average of Spread/Pour Plates. | A | B | C | D | E | Average | Spread | 8.04X10^7 | 6.34X10^5 | 3.24X10^5 | 4.06X10^7 | 3.401X10^6 | 2.51X1-^7 | Pour | 1.13X10^8 | 8.4X10^4 | 1.88X10^5 | 9.15X10^7 | 1.02X10^6 | 4.1X10^7 |

DISCUSSION The objective of this experiment was to determine the amount of bacteria found in different samples from throughout Flagstaff, AZ. It was hypothesized that if meat samples were handled correctly, the samples would have little to no bacteria on them. The hypothesis was not supported by the data because the data showed bacteria colonies formed on all the pour and spread plates of each sample. The results showed majority of the meat samples were contaminated with bacteria. On average, the pour plates contained more colonies of bacteria than spread plates with 4.1X10^7cfu/g compared to 2.51X10^7cfu/g (Table 1). The sample with most bacteria for both pour and spread plates was sample A having 8.04 X107 cfu/g on the spread plate and 1.13 X108cfu/g on the pour plate (Table 1). Making sample A the most contaminated sample possibly from improper meat handling during processing. Sample B was the only sample that didn’t have a significant amount of bacteria growth. This could be the result of proper meat handling techniques performed or the result of improper dilution technique. It was concluded that almost all of the meat samples were contaminated with bacteria, which supports previous studies that have concluded that food contamination isn’t uncommon (Linscott, 2011). If less than 30 colonies were found on any plate, it was marked as not significant sample and considered to be the typical amount of bacteria found in meat. The samples would be seen as having exceeding amounts of bacteria if majority of the samples had an average of too numerous to count. It is hard to determine if the amount found was harmful because it depends more on the species of bacteria found in colonies (Egan, 1983). A way that the experiment could be improved is by using more samples of meat from different sources because the more data that is obtained, the more accurate the results will be. Other experiments similar to this one could be done in other areas in the U.S. to compare the amount of meat contaminated by the size of the populated area.
The enumeration of bacteria in food samples is very important in the detection of food-borne illnesses and prevention food-borne outbreaks (Linscott, 2011). Studies, along with the results found in the experiment, show that bacteria in different meats are commonly found. Better techniques of preventing food contamination should be taken by the FDA while NARMS has reason to invest more species of bacteria onto the list of monitored bacteria in food (Waters et al., 2011).

CITATIONS
Egan, A. F. (1983). Lactic Acid Bacteria of Meat and Meat Products. Antonie Van Leeuwenhoek, 49(3), 327-336.
Linscott, A. J. (2011). Food-Borne Illnesses. Clinical Microbiology Newsletter, 33(6): 41-45.
Shand, R. F. (2013). NAU Microbiology Lab Manual Bio 205. Englewood, CO. Morton Publishing Company.
Talon, R., Leroy, S. (2011). Diversity and safety hazards of bacteria involved in meat fementations. Meat Science 89(3): 303-309.
Waters, A. E., Cuomo, T. C., Bucchagen, J., Lui, C. M., Pearce, K., Foster, J. T., Bowers, J., Driebe, E. M., Engelthaler, D. M., Keim, P. S., Price, L. B. (2011). Multidrug-Resistant Staphylococcus aureus in U.S. Meat and Poultry. Northern Arizona University.