Improve sponge sampling to accurately determine bacteria levels.

Beef processing plants are required to test their chilled carcasses to verify that their slaughter and dressing procedures are keeping E. coli contamination under control. Test results in a plant provide a base line that enables a company to determine how well it is doing when compared with national trends.

A problem that researchers at Kansas State University (Department of Animal Sciences and Industry, Manhattan, KS 66506) have encountered involves the loss of a substantial percentage of recovered E. coli cells placed in sponge bags that are transported to labs for analysis.

Beef carcasses are tested by using cellulose sponges to swab 300 square centimeters of the carcass surface to determine E. coli levels. These sponge samples are then placed in bags containing a diluent that hydrates the sampling sponges. Sponge samples stored in a lab awaiting analysis can lose some of the E. coli population that had been collected and provide an inaccurate picture of the actual contamination level. The key is to store the sponge samples in a diluent that maximizes the preservation of the bacterial population recovered from the carcass.

Scientists found that the organisms removed from the meat with sponges did not remain alive very long in the bag using certain types of diluent. Their studies have been directed at improving the method of sponge sampling so companies could better use the technique more accurately as an indicator of process control. The investigators examined different types of diluents, seeking to find one that would enable the organisms to maintain their viability. The most often-used commercial sponge diluent has been Butterfield's phosphate buffer. But virtually all of the E. coli collected by scientists as samples died within 24 hr. using this buffer.

A series of tests showed that buffered peptone water provided considerable improvement and offered the best survival for the E. coli samples. The KSU team concluded that standardized use of this diluent should be implemented to improve the value of sponge testing on carcasses. The USDA has begun making the same recommendation.

Scientists are still optimizing the technique. Preliminary data indicate that only a small percentage of E. coli cells physically attached to beef carcass surfaces are recovered by the sponge during sampling procedures. Researchers want to improve recovery of the E. coli cells from meat using the sponge. They are examining different types of sponges, surfactants that help detach organisms from the carcass and different types of diluents that might better meet transportation requirements.

Another advantage of buffered peptone water is that it serves as an acceptable medium for most Salmonella detection methods used on meat and poultry products. Many processors and the USDA use carcass sponge samples for Salmonella testing.

Further information. Randy Phebus; phone: [phone]; fax: [phone].