Antimicrobial Effect of Acetic Acid, Sodium Hypochlorite, and Thermal Treatments against Psychrotolerant Bacillus cereus Group Isolated from Lettuce (Lactuca sativa L.).

Kyung-Min Park,Minseon Koo,Hyun-Jung Kim,Ji-Yoen Choi

doi:10.3390/foods10092165

Abstract

Various food products distributed throughout the cold chain can present a health risk for consumers due to the presence of psychrotolerant B. cereus group species that possess enterotoxin genes and antibiotic resistance. As these bacteria can grow at the low temperatures used in the food industry, this study evaluated the antimicrobial efficacy of acetic acid, sodium hypochlorite, and thermal treatments for inhibition of psychrotolerant strains and the effect that differences in activation temperature (30 °C and 10 °C) have on their efficacy. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and bacterial growth assay of acetic acid and thermal treatment showed an equal or higher antimicrobial efficacy in isolates activated at 10 °C than in those activated at 30 °C. In particular, psychrotolerant strains from the B. cereus group were completely eliminated with 0.25% acetic acid, regardless of the activation temperature. The possibility of tolerance was determined by observing responses in cells activated at 10 and 30 °C when exposed to different concentrations of sodium hypochlorite. Five isolates activated at 10 °C exhibited enhanced survivability in sodium hypochlorite compared to isolates activated at 30 °C, and these isolates were able to grow in sodium hypochlorite at concentrations of 250 ppm or higher. Although a significant difference in antimicrobial efficacy was observed for psychrotolerant B. cereus group strains depending on the activation temperature, acetic acid may be the most effective antimicrobial agent against psychrotolerant B. cereus species isolated from food products distributed in a cold chain.

Highlights

Bacillus cereus, a common soil bacterium, is one of the human pathogens associated with gastroenteritis, which is the major cause of foodborne illness in Europe [1], and is an opportunistic pathogen related to lethal non-intestinal infections in humans [2]
The minimum bactericidal concentration (MBC) of acetic acid for psychrotolerant B. cereus group isolates showed similar trends for all isolates activated at 30 and 10 ◦C, where the MBC was increased to 0.25% and was twofold higher than the minimum inhibitory concentration (MIC) values
Antimicrobials currently used in the food processing industry were examined to determine whether they were effective at eliminating psychrotolerant B. cereus group strains when subsequently grown at different culture temperatures

Summary

Introduction

A common soil bacterium, is one of the human pathogens associated with gastroenteritis, which is the major cause of foodborne illness in Europe [1], and is an opportunistic pathogen related to lethal non-intestinal infections in humans [2]. Some species (B. weihenstephanensis or B. wiedmannii) in the B. cereus group can grow at 7 ◦C or below; cold-tolerant B. cereus group species are able to proliferate in refrigerated food products [3]. The B. cereus group comprised mostly mesophilic strains until the identification of B. weihenstephanensis, in 1991, as a psychrotolerant strain belonging to the B. cereus group [4]. One of the most recently identified psychrotolerant B. cereus group species, B. wiedmannii, is able to grow at 7 ◦C or below and produces hemolysin BL (HBL) toxin and nonhemolytic enterotoxin (NHE). Members of the psychrotolerant B. cereus group are virulent, as they produce enterotoxins or emetic toxin genes and exhibit cytotoxic activity under cold conditions [6,7]. Psychrotolerant B. cereus group species should be considered a food safety hazard during food processing, distribution, and storage [7]

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