Abstract
The influence of the strain on the ability of Salmonella enterica to form biofilms on polystyrene was investigated by confocal laser scanning microscopy. The effects of sodium hypochlorite with 10% active chlorine (SHY; 25,000, 50,000, or 100,000 ppm), and benzalkonium chloride (BZK; 1000, 5000, or 10,000 ppm) on twenty-four-hour-old biofilms was also determined. The biofilms of ten Salmonella enterica isolates from poultry (S. Agona, S. Anatum, S. Enteritidis, S. Hadar, S. Infantis, S. Kentucky, S. Thompson, S. Typhimurium, monophasic variant of S. Typhimurium 1,4,(5),12:i:-, and S. Virchow) were studied. Biofilms produced by S. Anatum, S. Hadar, S. Kentucky, and S. Typhimurium showed a trend to have the largest biovolume and the greatest surface coverage and thickness. The smallest biofilms (P < 0.01) in the observation field (14.2 × 103 µm2) were produced by S. Enteritidis and S. 1,4,(5),12:i:- (average 12.9 × 103 ± 9.3 × 103 µm3) compared to the rest of the serotypes (44.4 × 103 ± 24.7 × 103 µm3). Biovolume and surface coverage decreased after exposure for ten minutes to SHY at 50,000 or 100,000 ppm and to BZK at 5000 or 10,000 ppm. However, the lowest concentrations of disinfectants increased biovolume and surface coverage in biofilms of several strains (markedly so in the case of BZK). The results from this study suggest that the use of biocides at low concentrations could represent a public health risk. Further research studies under practical field conditions should be appropriate to confirm these findings.
Highlights
IntroductionRegulation (EU) 2017/1273, active chlorine released from sodium hypochlorite is approved as an active substance for use in biocidal product-types 1, 2, 3, 4, and 5 when active chlorine concentration in aqueous solution is ≤ 1800 ppm (i.e., ≤ 18% w/w)
Salmonellosis is the zoonosis associated with the largest number of outbreaks of food-borne disease in the European Union
Quaternary ammonium compounds, such as benzalkonium chloride (BZK), are cationic surfactants that act by disrupting lipid membrane bilayers, being effective against a number of pathogenic microorganisms [9]
Summary
Regulation (EU) 2017/1273, active chlorine released from sodium hypochlorite is approved as an active substance for use in biocidal product-types 1, 2, 3, 4, and 5 when active chlorine concentration in aqueous solution is ≤ 1800 ppm (i.e., ≤ 18% w/w) Quaternary ammonium compounds, such as benzalkonium chloride (BZK), are cationic surfactants that act by disrupting lipid membrane bilayers, being effective against a number of pathogenic microorganisms [9]. The aim of this research work was to compare, by means of confocal laser scanning microscopy (CLSM) and quantitative image analysis, the structural parameters of biofilms formed by strains belonging to ten different serotypes of Salmonella and to determine the effectiveness of various concentrations of two food-grade biocides (sodium hypochlorite and benzalkonium chloride) on these structures. The ultimate objective was to identify the concentrations that were fittest for this purpose
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