Eliminating Harmful Hydrogen Sulfide Bacteria

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

Dr. Xiuping Jiang and her team of graduate students Chao Gong and Spencer Heringa are working to find new ways to reduce or eliminate bacterial production of harmful hydrogen sulfide within rendering plant environments. A food microbiologist, Jiang is an associate professor in the Department of Food Science and Human Nutrition as well as in the Department of Biological Sciences (Microbiology). She has conducted several studies for the Animal Co-Products Research and Education Center involving bacterial antibiotic resistance and reduction of Salmonella in rendered animal products.

In this study, Jiang is exploring a unique method of bacterial control via use of bacterial viruses. As in her Salmonella control study, Jiang is seeking bacteriophages that are virus particles specific only to a very narrow range of bacterial species. Bacterial species are very diverse and often as different as a cat is from an elephant or a bird is from a snake. Each bacterial species has its own unique characteristics and its own unique growth conditions. The hydrogen sulfide-producing bacteria are one type of bacteria that are capable of breaking proteins under oxygen starved conditions (anaerobic) and releasing hydrogen sulfide gas. In the rendering industry, with its protein-rich raw products, the incidence of deadly hydrogen sulfide production can lead to tragedies.

Bacteriophages are small viruses that can affect only specific bacteria. These viral particles cannot harm humans, animals, or plants. The estimated 10 million trillion trillion bacteriophages found on Earth are ubiquitous and are found in air, water, food, and thousands of other environments. Each bacteriophage can affect only a specific type of bacteria. They completely lack any mechanism to be able to affect humans, animals, or plants, and cannot be converted into a virus that harms anything other than a bacterium. Upon finding a suitable host bacterium, the bacteriophage attaches to the bacterial cell wall and injects its viral material into the bacterium. This viral material commandeers the machinery of the bacterium such that the bacterium produces multiple copies of the bacteriophage. The bacterial cell dies and bursts to release the newly formed bacteriophages that can seek out new bacterial host cells to commandeer and destroy. Via this infection process, bacteriophages can quickly destroy populations of target bacteria.

The usefulness of bacteriophage technology has long been recognized. As early as the 1930s, bacteriophages were used as therapeutic agents in the treatment of bacterial infections. The technology was growing rapidly until the discovery of antibiotics overshadowed it and most bacteriophage research was terminated. However, bacteriophage research has recently found a resurgence, mainly due to problems with antibiotic resistance and applications where antimicrobial activities are needed but antibiotics are not suitable (such as foods). In 2006, the U.S. Food and Drug Administration approved use of bacteriophages for bacterial control in foods (Listeria monocytogenes in ready-to-eat foods).

In animal co-products, micro-organisms from the gut, hide, and environment contaminate the raw materials. Under ambient conditions, certain hydrogen sulfide-producing bacteria can multiply very quickly and utilize the sulfur-containing amino acids (cysteine and methionine) as a terminal electron acceptor in the anaerobic environment. As a result, harmful hydrogen sulfide gas is generated. The most predominant of these sulfide-producing bacteria are species of Pseudomonas and Aeromonas. Not only are these bacteria problematic in the production of hydrogen sulfide from animal co-products and meat processing wastewater, but these also can spoil the meat products by causing development of off-flavors and odors. These are common microorganisms, found not only in animal co-products but also in almost all pre-packaged meats.

In her most recent project, Jiang has initiated work by isolating, purifying, and characterizing hydrogen sulfide-producing bacteria and bacteriophages. She has already had success in isolation of bacteriophages that prevent the growth of the hydrogen sulfide bacteria. The eventual goal is to have a product that could be mixed into animal co-products to prevent the growth of these bacteria and thus prevent the production of hydrogen sulfide gas. This bacteriophage technology could have application in the rendering environment to prevent hydrogen sulfide production and improve worker safety. It also would have potential application in the improvement of shelf-life of meat products for human consumption.

The Clemson University Animal Co-Products Research and Education Center is very proud to have Dr. Xiuping Jiang and her team working to create new control methods for preventing releases of hydrogen sulfide gas in the rendering industry. We look forward to the results from this vital project.

ACREC Solutions – June 2009 RENDER | back