Contamination risk increases from multiple bacterial strains.Two genetically similar strains of L. monocytogenes, Scott-A and OSY-8578, differ in their sensitivity to high-pressure and pulsed electric field processing Pulsed electric field (PEF) processing is a method for processing cells by means of brief pulses of a strong electric field. PEF holds potential as a type of low temperature alternative pasteurization process for sterilizing food products. . Scott-A is processing-sensitive, while OSY-8578 is processing-resistant. It is likely that several of these strains are able to contaminate con·tam·i·nate v. 1. To make impure or unclean by contact or mixture. 2. To expose to or permeate with radioactivity. con·tam·i·nant n. food processing environments. It is of great interest for processors to determine how these two strains behave in mixed cultures when treated with alternative processes. Research at Ohio State University Ohio State University, main campus at Columbus; land-grant and state supported; coeducational; chartered 1870, opened 1873 as Ohio Agricultural and Mechanical College, renamed 1878. There are also campuses at Lima, Mansfield, Marion, and Newark. aimed to identify a way to isolate mixed cultures of L. monocytogenes and to evaluate how sensitive the pure and mixed cultures are to high-pressure and pulsed electric field treatments. Investigators developed mutant strains of L. monocytogenes: Scott-A and OSY-8578. Scott-A Str was developed with resistance to streptomycin streptomycin (strĕp'tōmī`sĭn), antibiotic produced by soil bacteria of the genus Streptomyces and active against both gram-positive and gram-negative bacteria (see Gram's stain), including species resistant to other , while OSY-8578 Rf,Nm was made resistant to both rifamycin rifamycin /rif·a·my·cin/ (rif?ah-mi´sin) any of a family of antibiotics biosynthesized by a strain of Streptomyces mediterranei, b and neomycin neomycin (nē'ōmī`sĭn), broad spectrum antibiotic effective against both gram positive and gram negative bacteria (see Gram's stain). . The strains were grown in tryptose broth before they were treated with either high pressure or pulsed electric fields. Inactivation inactivation /in·ac·ti·va·tion/ (in-ak?ti-va´shun) the destruction of biological activity, as of a virus, by the action of heat or other agent. of the two strains was determined in pure and mixed cultures. The researchers found that antibiotic-resistant strains of L. monocytogenes have an enhanced sensitivity to alternative processes, such as high-pressure processing and pulsed electric fields, compared to wild strains of the bacteria. Additionally, cultures containing Scott-A Str treated in the presence of OSY-8578 Rf,Nm gained a slight resistance to both high-pressure and electric field treatments. Closely related strains of L. monocytogenes may be more likely to interact during high-pressure or pulsed electric field treatments. Processing-resistant strains may be capable of inducing a protective effect against treatments toward processing-sensitive strains. This should alert processors to the risks of contamination from multiple strains in their processing facilities. Further information. Ahmed Yousef, Department of Food Science and Technology, Ohio State University, 2015 Fyffe Ct., 110 Parker Food Science Building, Columbus, OH 43210; phone: 614-292-2301; fax: 614-292-8120; email: yousef.1@osu.edu <mailto:yousef.1@osu.edu>. |
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