Event Title

The Effect of Sub-Lethal Concentrations on Bacillus cereus

Location

CSU 253/4/5

Start Date

4-4-2011 11:00 AM

End Date

4-4-2011 12:30 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

Nisin is a biopreservative that is produced by Lactococcus lactis. It can be used to inhibit Gram positive bacteria in foods. Other Gram positive bacteria in foods are not killed by the concentrations used in foods but may be affected by sublethal concentrations. The purpose of the study was to investigate the effects sublethal concentrations of nisin have on Bacillus cereus and to determine if stress increases nisin resistance.

B. cereus was conditioned to nisin by culture in 100 µg/ml nisin in Tryptic Soy broth. Conditioning with sublethal nisin concentration increases tolerance to nisin from 200 µg/ml unconditioned B. cereus to 300

µg/ml conditioned B. cereus. The percentage of cells surviving in nisinwas determined by plating ~500 colony forming units on to tryptic soy agar containing 0, 50, and 100 µg/ml nisin. Control B. cereus did not grow on the plates with nisin. However, 83 colonies of the nisin conditioned B. cereus grew on the 50 µg/ml plate. No colonies were formed on the 100 µg/ml plate. When removed from maintenance cultures with nisin Conditioned B. cereus rapidly reverted to the more sensitive phenotype of the control. Heat shock at 45°C did not increase nisin tolerance instead the heat shock bacteria were more sensitive to nisin. Sublethal concentrations of nisin induce a more resistant phenotype in B. cereus. Induction of increased resistance appears to be specific for nisin.

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Apr 4th, 11:00 AM Apr 4th, 12:30 PM

The Effect of Sub-Lethal Concentrations on Bacillus cereus

CSU 253/4/5

Nisin is a biopreservative that is produced by Lactococcus lactis. It can be used to inhibit Gram positive bacteria in foods. Other Gram positive bacteria in foods are not killed by the concentrations used in foods but may be affected by sublethal concentrations. The purpose of the study was to investigate the effects sublethal concentrations of nisin have on Bacillus cereus and to determine if stress increases nisin resistance.

B. cereus was conditioned to nisin by culture in 100 µg/ml nisin in Tryptic Soy broth. Conditioning with sublethal nisin concentration increases tolerance to nisin from 200 µg/ml unconditioned B. cereus to 300

µg/ml conditioned B. cereus. The percentage of cells surviving in nisinwas determined by plating ~500 colony forming units on to tryptic soy agar containing 0, 50, and 100 µg/ml nisin. Control B. cereus did not grow on the plates with nisin. However, 83 colonies of the nisin conditioned B. cereus grew on the 50 µg/ml plate. No colonies were formed on the 100 µg/ml plate. When removed from maintenance cultures with nisin Conditioned B. cereus rapidly reverted to the more sensitive phenotype of the control. Heat shock at 45°C did not increase nisin tolerance instead the heat shock bacteria were more sensitive to nisin. Sublethal concentrations of nisin induce a more resistant phenotype in B. cereus. Induction of increased resistance appears to be specific for nisin.

Recommended Citation

Ngum, Adeline. "The Effect of Sub-Lethal Concentrations on Bacillus cereus." Undergraduate Research Symposium, Mankato, MN, April 4, 2011.
http://cornerstone.lib.mnsu.edu/urs/2011/poster-session-B/5