Intoxication by staphylococcal enterotoxins (SE) is among the most common causes of food-poisoning outbreaks resulting from the consumption of raw milk or products made thereof. The aim of our study was to analyze the thermal stability of SE and evaluate the inactivation of SE types A, B, and C (SEA, SEB, SEC) by autoclaving at 100°C, 110°C, and 121°C. Milk samples were inoculated with 38 Staphylococcus aureus strains that possessed the ability to produce SEA, SEB, or SEC and incubated at 37°C for 24 h. This incubation was followed by heat treatment at 100°C, 110°C, or 121°C for 3 min. Samples were analyzed by Staph. aureus plate count method on Baird-Parker agar and specifically for the presence of SE. An enzyme-linked immunofluorescent assay (ELFA) on a MiniVIDAS analyzer (bioMérieux, Marcy l'Étoile, France) was used to detect SE, which were determined semi-quantitatively based on test values. The obtained results were analyzed by means of nonparametric statistical methods. All samples (100%; 38/38) were SE-positive before heat treatment, and the positivity rates decreased after heat treatment at 100°C, 110°C, and 121°C to 36.8% (14/38), 34.2% (13/38), and 31.6% (12/38), respectively. The rates of positive samples differed between SEA, SEB, and SEC producers: SEA was detected in the highest amounts both before and after heat treatment. The amount of SE (expressed as test values) decreased significantly after heat treatment. Comparing amounts of SE in positive and negative samples before and after heat treatment, we can conclude that the success of SE inactivation depends on the amount present before heat treatment. The highest amount of SE and the highest rate of SE-positive samples after all heat treatments were found in samples with strains producing SEA. For SEB and SEC, lower amounts of enterotoxin were present and were inactivated at 100°C. Although temperatures of 100°C, 110°C, and 121°C may inactivate SE in milk, the key measures in prevention of staphylococcal enterotoxicosis are avoiding initial contamination of milk by Staph. aureus, promoting consumption of heat-treated milk, and preventing disruption of the cold chain during milk production and processing.

Our aim was to assess the effect of pasteurization temperature on inactivation of staphylococcal enterotoxins (SE). Milk samples were inoculated with log 4.38 to 5.18cfu/mL of 40 different Staphylococcus aureus strains having the ability to produce types A, B, or C SE and incubated at 37°C for 24h to develop SE. This incubation was followed by heat treatment for 15 s at 72, 85, and 92°C. Samples were analyzed for Staph. aureus count by plate method and, specifically, for SE presence. An enzyme-linked immunofluorescent assay on a MiniVIDAS analyzer (bioMérieux, Marcy l'Étoile, France) was used to detect SE, which were determined semiquantitatively based on test values. The Staph. aureus count in milk before pasteurization did not affect the amount of SE. Before pasteurization, SEB was detected in the lowest amount compared with other SE types. Staphylococcal enterotoxins were markedly reduced with pasteurization and inactivated at pasteurization temperatures to an extent depending on the amount in the sample before pasteurization. After pasteurization at 72°C, SE were detected in 87.5% of samples (35/40), after pasteurization at 85°C in 52.5% of samples (21/40), and after pasteurization at 92°C in 45.0% of samples (18/40). We determined that SE may still persist in milk even when Staph. aureus bacteria are inactivated through pasteurization. Although pasteurization may partially inactivate SE in milk, a key measure in the prevention of staphylococcal enterotoxicosis linked to pasteurized milk consumption is to avoid any cold chain disruption during milk production and processing.

This study evaluates the influence of inadequate transport conditions on the microbiological quality of chilled chicken meat packaged in plain and modified atmosphere packaging (MAP). The experiments simulated the temperature increase during sample transport to 8, 11, 14, 17, 20, and 25°C with exposure times of 1, 2, 3, and 4 h. Aerobic plate count (APC), psychrotrophic microorganisms count (PMC), β-D-glucuronidase-positive Escherichia coli, and Salmonella spp. were evaluated immediately after the exposure to the elevated temperature (0 h), 3 h, and 24 h after the return to the temperature of ≤4°C. The upper acceptable limits for APC and PMC were set for each combination of investigated chicken meat and packaging type, taking also the initial bacterial condition into account. Chilled chicken breast samples in plain packaging exceeded the APC limits in 16 cases and PMC limits in 20 cases when exposed to temperatures of >4°C, while only 2 MAP samples exceeded APC limits and 8 samples PMC limits, respectively. In chicken legs, 8 samples in plain packaging exceeded the APC limits and 15 the PMC limits, while 12 samples in MAP exceeded the APC limits and 19 the PMC limits. In 402 samples (31.9%) in which the presence of E. coli was detected, its amount ranged from 1.70 to 3.65 log CFU.g^-1. It was more commonly detected in chicken legs (255 of 630; 40.5%) than chicken breasts (147 of 630; 23.3%) but was not related to exposure temperature, exposure time, or time until examination. The presence of Salmonella spp. was not detected in any of the samples. Data acquired in the presented study will be used in the development of software helping the national supervisory authorities in the Czech Republic to evaluate whether inadequate transport of samples to analytical laboratories could have affected the microbiological profile of the sample.

The aim of this study was to evaluate the impact of internal factors (pH, NaCl) and external factors (temperature, incubation time) on the ability of Staphylococcus aureus to grow and to produce staphylococcal enterotoxins SEA, SEB, and SEC. The fresh cheese environment was modelled in Brain Heart Infusion Broth media and food matrices (pasteurized milk from retail outlets) by internal and external factors (pH = 4.5 and 5.5, 2% NaCl, and t = 8 °C and 15 °C). The counts of enterotoxigenic strains of S. aureus at baseline, i.e. at the time of inoculation of model samples, corresponded to those encountered in the production of fresh cheeses as a result of post-pasteurization contamination. Enumeration of S. aureus was performed in accordance with EN ISO 6888-1, using agar medium. Staphylococcal enterotoxins were detected by the enzyme-linked fluorescence assay. The pH (4.5) and refrigeration temperature (8 °C) used prevented S. aureus from achieving the critical count of 105 cfu·ml ^-1 specified in Commission Regulation (EC) No. 2073/2005. The highest rates of enterotoxin production were recorded for enterotoxin A. The growth curves of S. aureus derived from model experiments were compared with the growth curve generated by a predictive microbiology program - Pathogen Modelling Program. The results of this study proved the Pathogen Modelling Program to be suitable for use in the Hazard Analysis Critical Control Points system in the process of the fresh cheese production to help manufacturers prevent the growth of S. aureus and enterotoxin production.

The aim of this study was to compare Bacillus cereus growth rates and diarrhoeal enterotoxin production in raw and pasteurized goat, sheep, and cow milk in terms of storage conditions. Milk samples were inoculated with B . cereus (CCM 2010), which produces diarrhoeal enterotoxins. Enterotoxin production was tested by ELISA (Enzyme-Linked Immunosorbent Assay), and the count of B . cereus was determined by the plate method. With raw cow milk, B . cereus growth and enterotoxin production can be completely suppressed; in raw goat and sheep milk, enterotoxin was produced at 22 °C. In pasteurized cow, goat, and sheep milk, the B . cereus count increased under all storage conditions, with more rapid growth being observed at 15 °C (sheep milk) and 22 °C (cow and goat milk). Enterotoxin presence was detected at 15 °C and 22 °C, and with pasteurized cow milk also at 8 °C. Our model experiments have determined that B . cereus multiplication and subsequent enterotoxin production depend on storage temperature and milk type.

The present study aimed to evaluate the dependence of growth dynamics of toxigenic B. cereus on rice type, inoculum type, storage time, and temperature using appropriate mathematical models. Samples of cooked white (milled) and brown (husked) rice inoculated with vegetative cell/spore suspension of B. cereus were stored for 48 h at 4 °C (correct storage) and 24 °C (inappropriate storage method). No growth of B. cereus was observed during 48 hours of storage at 4 °C and was characterised by a linear model. To assess the growth of B. cereus in the cooked rice stored at 24 °C, the Baranyi-Roberts, Gompertz and Buchanan mathematical models were used. The Gompertz model characterized the growth of B. cereus best. The type of rice and the type of inoculum did not have a significant effect on the bacterial growth. After 48 h of storage at 24°C, the B. cereus counts were in the range of 8-9 log cfu.g-1, critical value of 5 log cfu.g-1 was reached in less than 10 hours of storage. The study results indicate that cooked rice stored at 24 °C quickly becomes a health risk for consumers due to the rapid multiplication of B. cereus within a few hours. In conclusion, it is crucial to cool cooked rice immediately to 4 °C if it is not to be consumed right after cooking.