Growth of Generic E. coli and Aerobic Bacteria on Beef Muscle held at 50°F for 8 Hours

Larry Eubanks, Chad Carr, and Chris Pantaleo


Bacteria are everywhere in our environment. Relative to food safety and quality, the two primary kinds of bacteria which are of consequence are pathogenic bacteria and spoilage bacteria. Spoilage bacteria are generally not harmful, but they will cause food to deteriorate or lose quality by developing a bad odor or texture. Pathogenic bacteria are those such as Salmonella, E. coli O157:H7, Campylobacter jejuni, Listeria monocytogenes, and Staphylococcus aureus, all which cause food-borne illness and cannot be seen or smelled (International Commission on Microbiological Specification for Foods, 1996).

The safety of meat products is the most important parameter to consumers and the food industry alike. The two primary pathogens of concern with fresh beef are Salmonella and E. coli O157:H7. Multiple steps are taken to reduce the presence of pathogens on beef cattle at the farm (Loneragan and Brashears, 2005) at the processing plant (Koohmaraie et al., 2005; Beef Industry Food Safety Council, 2003a) and during further processing (Beef Industry Food Safety Council, 2003b; 2006). Heating beef products to 162°F for 16 seconds or to 135 °F for 45 seconds will eliminate Salmonella and E. coli O157:H7 (Venkitanarayanan and Doyle, 2007). Irradiation is an effective method of eliminating pathogens; however, U.S. consumers are fearful of irradiated products (Venkitanarayanan and Doyle, 2007). Therefore, there is always an element of risk for processors of raw, ground beef products, because of the lack of a cooking step.

USDA inspected meat processing facilities try to minimize microbial growth and microbiological risk by refrigerated temperature control. However, refrigeration costs increase when processing at lower ambient temperatures. Therefore, some processors fabricate fresh meat at ambient temperature as high as 50°F. Little documentation exists of how long fresh meat can be held at this temperature without experiencing growth of pathogenic bacteria, particularly E. coli O157:H7 and Salmonella.

The purpose of this study was to determine the growth of generic E. coli and aerobic bacteria as indicators of pathogenic bacteria on beef muscle held at 50°F for eight hours.

Experimental Procedure

No live pathogenic bacteria were used in this study as all processes were conducted in a USDA inspected processing facility. A vacuum packaged beef inside round roast was obtained at retail, brought to the UF Meat Laboratory and held at 34°F until the roast was cut into 25g cubes using a flame sterilized knife. After cutting, the cubes (n = 7) were placed on a tray and held at 50°F for 0, 2, 4, 5, 6, 7 or 8 hours until each sample was placed in a Stomacher bag with 225 ml of peptone water. The beef cube was massaged within the bag for one minute to incorporate the solution into the cube, then 1 ml of the liquid was transferred to a test tube containing 9 ml of peptone water. The tube was vortexed, and the procedure from the initial test tube repeated on the subsequent tubes four times, resulting in five tubes containing dilutions ranging from 10-1 to 10-5.

After diluting, 1 mL of each dilution from the seven samples was placed on an aerobic petrifilm plate to assess aerobic plate count (APC) and an E. coli petrifilm plate. Three samples of each plate were generated and all plates were placed in a 95°F incubator for 48 hours, prior to counting. Generally, APC measures bacteria that grow in the presence of oxygen, serving as an indicator of the presence of spoilage organisms, and generic E. coli are indicators of the presence of fecal bacteria contamination. Results were reported as a logarithmic function of the colony forming units (CFU) per g and analyzed using the repeated measures function of SAS (SAS Inst., Inc., Cary, NC), considering time of measurement as a fixed effect and triplicate replication as a random effect.

Results and Discussion

No E. coli was isolated from the initial product (Table 2). Accordingly, there was no difference in E. coli growth rate for beef held at 50°F up to 8 hours. For APC, 15.1 CFU were identified from the initial product (Table 2). However, the APC of beef products stored at 50°F did not increase (P > 0.10) for any length of storage up to 8 hours.

This work complements the findings of other authors. Ingham et al. (2007) incorporated live pathogenic E.coli and Salmonella with various fresh meat products prior to aerobic storage at 50°F. At that ambient temperature, pathogens were dormant or in the lag phase of growth for 22 hours (Table 3). In another study, Ingham et al. (2005) reported one lb ground beef packages thawed 9 hours at 72 or 86°F resulted in 0.2 and 0.5 logarithmic increases of pathogens on the product surface, respectively.


Most processors use 41°F as a critical control point for holding beef to prevent an increase in hazardous pathogen growth. This data and other supporting documentation sited in this report suggest the critical limit can be increased to 50°F without jeopardizing the consumer's health.

Literature Cited

Beef Industry Food Safety Council. 2003a. Best Practices for Beef Slaughter. Supported by National Meat Association, Southwest Meat Association, American Meat Institute and National Cattlemen's Beef Association. Centennial, Colo. Accessed August 4, 2009.

Beef Industry Food Safety Council. 2003b. Best Practices for Raw Ground Beef Products. Supported by National Meat Association, Southwest Meat Association, American Meat Institute and National Cattlemen's Beef Association. Centennial, Colo. Accessed August 4, 2009.

Beef Industry Food Safety Council. 2006. Best Practices for Non-Intact Beef Products. Supported by National Meat Association, Southwest Meat Association, American Meat Institute and National Cattlemen's Beef Association. Centennial, Colo. Accessed August 4, 2009.

FDA. 2001. Factors that influence microbial growth. Washington D.C. Accessed August 4, 2009.

Ingham, S.C., R.K. Wadhera, M.A. Fanslau, and D.R. Buege. 2005. Research Note: Growth of Salmonella serovars, Escherichia coli O157:H7, and Staphylococcus aureus during thawing of whole chicken and retail ground beef portions at 22 and 30°C. J. Food Protection 68:1457–1461.

Ingham S.C., B.H. Ingham, D. Borneman, E. Jaussaud, E.L. Schoeller, N. Hoftiezer, L. Schwartzburg, G.M. Burnham, and J.P. Norback. 2007. Predicting pathogen growth during short-term temperature abuse of raw pork, beef, and poultry products: use of an isothermal-based predictive tool. J. Food Protection 70:1445-1456.

International Commission on Microbiological Specification for Foods. 1996. Microorganisms in foods. Roberts, T. A., A.C. Baird-Parker, and R.B Tompkin, editors. Volume 5, Characteristics of microbial pathogens. London: Blackie Academic & Professional. p 513.

Koohmaraie, M., T.M. Arthur, J.M. Bosilevac, M. Guerini, S.D. Shackelford, and T.L. Wheeler. 2005. Post-harvest interventions to reduce/eliminate pathogens in beef. Meat Sci. 71: 79–91.

Loneragan, G.H. and M.M. Brashears. 2005. Pre-harvest interventions to reduce carriage of E. coli O157 by harvest-ready feedlot cattle. Meat Sci. 71: 72-78.

Venkitanarayanan, K.S. and M. P. Doyle 2007. Foods Handbook of Nutrition and Food- Chapter 2- Microbiological Safety of Food. pp 38-43.


Table 1. 

Minimum, optimum, and maximum ambient temperature for pathogenic growth.


Ambient temperature (°F)





Campylobacter jejuni




Staphylococcus aureus




E. coli O157:H7








Table 2. 

Growth of generic E. coli and aerobic bacteria as indicators of pathogenic bacteria on beef muscle held at 50oF for eight hours.


Colony Count for E. coli (CFU/g)

Colony count for aerobic bacteria (CFU/g)

Log Difference from Hour 0.










P > 0.10




+ 0.062

P > 0.10





P > 0.10





P > 0.10





P > 0.10





P > 0.10

Table 3. 

Lag Phase Duration (LPD) and Growth Rate (GR) for Various Meat Sources Stored at 50oF.


E. coli 0157:H7



LPD (hrs)

GR (log CFU/min)

LPD (hrs)

GR (log CFU/min)

Ground Pork





Ground Beef










Publication #AN222

Date: 2018-07-17
Carr, Chad
Eubanks, Larry F
Animal Sciences

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About this Publication

This document is AN222, one of a series of the Animal Sciences Department, UF/IFAS Extension. Original publication date October 2009. Visit the EDIS website at for the currently supported version of this publication.

About the Authors

Larry Eubanks, coordinator of research programs, Department of Animal Sciences; Chad Carr, assistant professor, Department of Animal Sciences; Chris Pantaleo, Smithfield Food; UF/IFAS Extension, Gainesville, FL 32611.


  • Charles Carr