Abstract
Some strains of Listeria monocytogenes can persist in food-processing environments, increasing the likelihood of the contamination of foodstuffs. To identify traits that contribute to bacterial persistence, a selection of persistent and sporadic L. monocytogenes isolates from a poultry-processing facility was investigated for biofilm-forming ability (crystal violet assay). The susceptibility of sessile cells to treatments (five minutes) with sodium hypochlorite having 10% active chlorine (SHY: 10,000 ppm, 25,000 ppm, and 50,000 ppm) and benzalkonium chloride (BZK: 2500 ppm, 10,000 ppm, and 25,000 ppm) was also studied. All isolates exhibited biofilm formation on polystyrene. Persistent strains showed larger (p < 0.001) biofilm formation (OD580 = 0.301 ± 0.097) than sporadic strains (OD580 = 0.188 ± 0.082). A greater susceptibility to disinfectants was observed for biofilms of persistent strains than for those of sporadic strains. The application of SHY reduced biofilms only for persistent strains. BZK increased OD580 in persistent strains (2500 ppm) and in sporadic strains (all concentrations). These results indicate that the use of BZK at the concentrations tested could represent a public health risk. Findings in this work suggest a link between persistence and biofilm formation, but do not support a relationship between persistence and the resistance of sessile cells to disinfectants.
Highlights
Listeriosis is a food-borne disease responsible for 23,000 infections yearly worldwide [1].Its lethality rate may reach 30% [2]
Some of the serotypes of L. monocytogenes detected in samples taken from surfaces in the chicken-processing plant studied (1/2b, 1/2c, 3b, 4a, and 4b) are among those most often involved in human listeriosis
To the best of our knowledge, this is the first report where the greater susceptibility to biocides of the biofilms by L. monocytogenes was observed in the case of the group of persistent strains (Table 2). These findings suggest that resistance to disinfectants in L. monocytogenes sessile cells is strain-dependent, but not associated with persistence
Summary
Listeriosis is a food-borne disease responsible for 23,000 infections yearly worldwide [1]. Its lethality rate may reach 30% [2]. In the United States, approximately 1600 cases of severe forms of human listeriosis occur each year (the incidence rate is 0.26 cases per 100,000 population), and about 260 of these die [3]. As a consequence of demographic changes, the country expects an increase in the prevalence of the disease, such that it will reach a figure of 0.32 cases per 100,000 inhabitants in. As for the European Union, in 2017 there were 2480 confirmed cases of invasive listeriosis (0.48 cases per 100,000 population). The lethality rate was 13.8% of the 1633 confirmed cases with a known outcome, the highest among all food-borne illnesses [6]. Over the last ten years, there has Pathogens 2019, 8, 250; doi:10.3390/pathogens8040250 www.mdpi.com/journal/pathogens
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