Methods of Detecting Injury in Bacillus Cereus

Presenter Information

Adeline Ngum, Minnesota State University, Mankato

Location

CSU 284A

Start Date

5-4-2010 1:00 PM

End Date

5-4-2010 3:00 PM

Student's Major

Biological Sciences

Student's College

Science, Engineering and Technology

Mentor's Name

Dorothy Wrigley

Mentor's Department

Biological Sciences

Mentor's College

Science, Engineering and Technology

Description

Bacillus cereus is a gram-positive, spore forming bacteria that survives in food and causes food poisoning in humans. Injured cells are more readily killed than uninjured cells. Knowing how to injure Bacillus cereus may provide ways to eliminate its growth in foods. Injury is typically detected when cells die in stressful conditions. The project developed media to detect injured cells. First, Bacillus cereus was frozen at two different temperatures -200C and -800C to check for survival. The survival of the cells was measured by counting viable colony forming units before and after freezing. More cells were killed at -200C than at -800C. A selective medium is needed to determine if surviving cells were injured. A selective media was prepared with polymixin B to which Bacillus cereus is usually resistant. It is hypothesized that freezing damage to cell walls would increase the sensitivity to polymixin B, a membrane disruptor. Polymixin B (antibiotic) mixed with Bacillus cereus yielded an unexpected result. The tested concentration of polymixin B killed Bacillus cereus. Lower concentration of polymixin B are being tested, results will be presented. Sub lethal concentration of polymixin B should not kill uninjured cells, but may kill injured cells. Development of this as a selective medium will allow testing of other potential sources of injury.