Counting Bacteria in Rendered Products

By Annel K. Greene, PhD, Center Director, Clemson University, Animal Co-Products Research and Education Center


Microbiologist Dr. Thomas A. Hughes, a member of the Clemson University Animal Co-Products Research and Education Center (ACREC) team, is working to improve bacterial enumeration methods in rendered animal products. A native of Mullins, SC, Hughes earned his bachelor of science in biology from South Carolina State University.

After teaching junior high school for a year, he decided to continue his education at North Carolina State University where he obtained a master of science in microbiology with a minor in biochemistry and then a PhD in microbiology with a minor in plant physiology. His graduate work involved study of the symbiotic nitrogen fixation mechanisms of the Rhizobium bacteria with soybeans. He earned a National Institutes of Health fellowship and completed a post-doctoral study in molecular genetics of oral pathogens at the University of Alabama Birmingham Dental School.

Hughes joined Clemson University in 1983 and currently is a professor in the Department of Biological Sciences. He also has conducted studies on bacteriocins, which are small proteins that act as antimicrobial substances against other bacteria. He also has expertise in anaerobic digestion and antibiotic resistance.

Hughes currently teaches Bacterial Physiology, Advanced Microbial Molecular Genetics, and a graduate level Microbial Physiology course. In addition, he teaches the introductory Microbiology 101 course titled “Microbes and Human Affairs.” Hughes’ vast experience in numerous aspects of microbiology, molecular genetics, and microbial physiology are of great benefit in ACREC microbial projects.

Hughes is working on a significant issue for the rendering industry – the ability to accurately count bacteria in the high-fat matrix of rendered animal products. The universal standard method for enumerating bacteria involves diluting the sample in a precisely measured water-based sterile buffer in a dilution bottle. This dilution method requires that the sample be evenly mixed throughout the buffer so that bacteria are evenly distributed. A subsample of the diluted sample is transferred to another dilution bottle and the process repeated until the sample is sufficiently diluted. A subsample is then placed into a petri dish and mixed with an appropriate agar medium. However, a mistake in measurement or the inability to evenly distribute bacteria in any one of the dilution bottles can lead to extreme error in bacterial counts. The case of high-fat samples presents a particularly difficult challenge to microbiologists.

Fat causes bacteria to adhere and not distribute evenly in dilution buffers. Since dilution buffers are water based, and since fat and water are not miscible, this leads to even more difficulties in accurately enumerating bacteria. If equal distribution of the bacteria is not provided throughout the dilution series, extreme errors in bacterial counts occur. Hughes, in a joint project with this author, is working on new methods to overcome the problems associated with bacterial enumeration in high-fat materials. Unless accurate methodology can be created to ensure accuracy in bacterial counts, all microbiological studies on rendered animal products become suspect.

Thermal death time studies to establish a calculated process are dependent on the ability to accurately enumerate bacteria in rendering samples. Previous studies in this laboratory indicated huge variations in bacterial counts among replicates when plating both raw materials and finished rendered products. The results of previous bacterial enumeration trials had extremely high, and unacceptable, standard errors that were attributed to problems in evenly distributing high-fat samples. The current project is designed to investigate a number of techniques for improving accuracy of bacterial counts in high-fat rendered animal products. Hughes is working on new methods of resolving this bacterial enumeration dilemma.

Hughes is a member of Alpha Kappa Mu, Beta Kappa Chi, and has been listed in Who’s Who in American Colleges and Universities. His other studies have involved development of fluorescent techniques for identifying bacteria, nucleotide sequencing, cloning, and enzymology. In his other current research, Hughes is working on the bioremediation of polycyclic aromatic hydrocarbons using the unique bacterium Sphingomonas paucimobilis. This work has great application for reducing and/or eliminating hazardous compounds from contaminated environments.

ACREC is proud to have Hughes working on creating an accurate method of enumerating bacteria in rendered animal products. All microbial studies on rendered animal products require the ability to accurately enumerate bacteria. Without an accurate procedure, all microbiological data is suspect and all attempts to develop a calculated process remain impossible. With accurate methods of enumerating bacteria in rendered animal products, microbiologists can work to assist the industry with bacterial studies. The results of Hughes’ project will provide renderers with a powerful tool in their bacterial control efforts.


ACREC Solutions – December 2008 RENDER | back