November 3, 2006

USDA introduces two new methods for counting pathogens in beef plants
 

As concerns about bacteria in meat mount amidst the absence of reliable ways to count pathogens, USDA reasearchers have developed two methods for counting bacterial pathogens in beef-processing plants.

Besides helping beef-porcessing plants assess their hygiene standards, the system also provides information that can be used for making risk assessments for public health, USDA researchers said.

One method uses a "spiral plater," a special instrument that is similar to a Petri dish on a turntable and is suitable for samples where a high pathogen load could be expected, such as fecal matter or hides.

The test uses a syringe to distribute the sample onto an agar plate. The plate rotates as the stylus distributes the sample from the centre to the edges.

Microbes are concentrated at the center and at the edges, the sample gets thinner, which allows counting bacteria over a very large range, Dr Terry Arthur, a researcher said.

The second method, which works better for carcass and ground beef samples with low numbers of pathogens, uses a hydrophobic grid printed on a membrane filter. A sample is placed on the filter where a vacuum draws the liquid from the sample, leaving the bacteria on the grid.

Both methods enable scientists to count bacterial colonies and identify the bacteria in the sample.

Enumeration costs approximately US$100 per sample if non-USMARC methods are used. With USMARC methods, the cost drops to about $2 per sample, the news release said.

Although tests currently apply to only Salmonella and E. coli, researchers hope to expand the range of bacteria it can detect soon.