Abstract
The persistence of certain strains of Listeria monocytogenes, even after the food processing environment has been cleaned and disinfected, suggests that this may be related to phenomena that reduce the concentration of the disinfectants to subinhibitory levels. This includes (i) the existence of environmental niches or reservoirs that are difficult for disinfectants to reach, (ii) microorganisms that form biofilms and create microenvironments in which adequate concentrations of disinfectants cannot be attained, and (iii) the acquisition of resistance mechanisms in L. monocytogenes, including those that lead to a reduction in the intracellular concentration of the disinfectants. The only available data with regard to the resistance of L. monocytogenes to disinfectants applied in food production environments refer to genotypic resistance to quaternary ammonium compounds (QACs). Although there are several well-characterized efflux pumps that confer resistance to QACs, it is a low-level resistance that does not generate resistance to QACs at the concentrations applied in the food industry. However, dilution in the environment and biodegradation result in QAC concentration gradients. As a result, the microorganisms are frequently exposed to subinhibitory concentrations of QACs. Therefore, the low-level resistance to QACs in L. monocytogenes may contribute to its environmental adaptation and persistence. In fact, in certain cases, the relationship between low-level resistance and the environmental persistence of L. monocytogenes in different food production chains has been previously established. The resistant strains would have survival advantages in these environments over sensitive strains, such as the ability to form biofilms in the presence of increased biocide concentrations.
Highlights
Listeria monocytogenes is a Gram-positive foodborne pathogen that can cause listeriosis, a relatively uncommon illness with a 20–30% case fatality rate (Silk et al, 2012; CDC, 2014; de Noordhout et al, 2014; EFSA and ECDC, 2014)
The persistence of certain strains of Listeria monocytogenes, even after the food processing environment has been cleaned and disinfected, suggests that this may be related to phenomena that reduce the concentration of the disinfectants to subinhibitory levels. This includes (i) the existence of environmental niches or reservoirs that are difficult for disinfectants to reach, (ii) microorganisms that form biofilms and create microenvironments in which adequate concentrations of disinfectants cannot be attained, and (iii) the acquisition of resistance mechanisms in L. monocytogenes, including those that lead to a reduction in the intracellular concentration of the disinfectants
This includes: (i) local environmental conditions that can lead to the formation of niches or reservoirs that are difficult for disinfectants to reach; (ii) microorganisms that form biofilms and create microenvironments in which adequate concentrations of disinfectants cannot be attained; and (iii) the acquisition of resistance mechanisms in L. monocytogenes, including those that lead to a reduction in the intracellular concentration of the disinfectants
Summary
Listeria monocytogenes is a Gram-positive foodborne pathogen that can cause listeriosis, a relatively uncommon illness with a 20–30% case fatality rate (Silk et al, 2012; CDC, 2014; de Noordhout et al, 2014; EFSA and ECDC, 2014). The majority of cases of human listeriosis are caused by contaminated processed foods (McLauchlin et al, 2004; Lianou and Sofos, 2007). When listeriosis outbreaks have been investigated, contamination is usually traced to the processing environment and equipment (Orsi et al, 2008; Nakari et al, 2014). This suggests that the contamination mainly occurs during the processing of food and is primarily due to strains from the processing plant environment (Malley et al, 2015; Garner and Kathariou, 2016)
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