Increased Resistance of Listeria monocytogenes and Escherichia coli O157:H7 after Exposure to Repetitive Cycles of Mild Bactericidal Treatments

Abstract

Mild bactericidal technologies are becoming increasingly important in modem food industry. While maintaining nutritional and sensorial attributes of fresh foods these technologies generally deliver microbiologically perishable food products. Currently little information exists on possible increase in the resistance of pathogens after exposure to repetitive cycles of these bactericidal treatments. Multi-strain cocktails of two of the most important foodborne pathogens, Listeria monocytogenes and attenuated Escherichia coli O157:H7, were exposed to 20 consecutive cycles of mild inactivation by three different techniques. Used techniques comprised inactivation with lactic acid, chlorine dioxide and intense light pulses. Results showed that development of resistant mutant and/or selection of resistant cells was both species and technique dependent. While repetitive cycles of chlorine dioxide treatment did not result in increased resistance with any of three tested pathogens, lactic acid treatment showed potential to create or pull out resistant cells of L. monocytogenes. Effect was determined as decreased level of reduction in bacterial counts. Even greater effect was observed for intense light pulses which showed clear trend in increased overall resistance of both L. monocytogenes and E. coli O157:H7 strains. Trend observations were confirmed through linear regression analysis. Current findings indicate ability of foodborne pathogens to adapt to mild bactericidal treatments creating new challenges in risk assessment and more specifically in hazard analysis.