RESUMEN

Staphylococcus aureus is a common pathogen found in cheese whose Staphylococcal enterotoxins (SE) are the main pathogenic factors that cause food poisoning. The objective of this study was to construct two models to evaluate the safety of Kazak cheese products in terms of composition, changes in S. aureus inoculation amount, Aw, fermentation temperature during processing, and growth of S. aureus in the fermentation stage. A total of 66 experiments comprised of five levels of inoculation amount (2.7-4 log CFU/g), five levels of Aw (0.878-0.961), and six levels of fermentation temperature (32-44 °C) were performed to confirm the growth of S. aureus and the presence of SE limit conditions. Two artificial neural networks (ANN) successfully described the relationship between the assayed conditions and the growth kinetic parameters (maximum growth rates and lag times) of the strain. The good fitting accuracy (R2 values were 0.918 and 0.976, respectively) showed that the ANN was appropriate. Experimental results showed fermentation temperature had the greatest influence on the maximum growth rate and lag time, followed by the Aw and inoculation amount. Furthermore, a probability model was built to predict the production of SE by logistic regression and neural network under the assayed conditions, which proved to be concordant in 80.8-83.8% of the cases with the observed probabilities. The maximum total number of colonies predicted by the growth model in all combinations detected with SE exceeded 5 log CFU/g. Within the range of variables, the minimum Aw for predicting SE production was 0.938, and the minimum inoculation amount for predicting SE production was 3.22 log CFU/g. Additionally, as competition between S. aureus and lactic acid bacteria (LAB) occurs in the fermentation stage, higher fermentation temperatures are conducive to the growth of LAB, which can reduce the risk of S. aureus producing SE. This study can help manufacturers to make decisions on the most appropriate production parameters for Kazak cheese products and to prevent S. aureus growth and SE production.

Asunto(s)

Queso , Infecciones Estafilocócicas , Humanos , Enterotoxinas , Staphylococcus aureus , Queso/microbiología , Microbiología de Alimentos , China

RESUMEN

In this study, extended-spectrum ß-lactamase (ESBL) Escherichia coli were isolated from five dairy farms in three areas of northern Xinjiang, China. Molecular biological techniques were used to systematically analyze drug resistance phenotypes and genotypes, virulence genes, phylogenetics, biofilm formation (BF), and pulsed field gel electrophoresis (PFGE) typing of isolated ESBL E. coli strains. A total of 766 samples were collected from five dairy farms in Shihezi, Urumqi and Yili, from which 149 (19.5 %, 95 % CI: 16.65 %-22.25 %) ESBL E. coli strains were isolated. Their distribution and contamination levels varied from region to region, with 16.2 % (68/419) in Urumqi, 22.4 % (60/268) in Shihezi, and 26.6 % (21/79) in Yili. The majority of isolates (97.3 %, 145/149) harbored the ß-lactamase blaCTX-M gene; while blaCTX-M-1 was the dominant phylogenetic group. The analysis of 21 resistance genes and the susceptibility to 13 different antibiotics showed that 91.3 % (136/149) of strains were resistant to three or more antibiotics. Thirty-six strains (24.2 %) belonged to extraintestinal pathogenic E. coli (ExPEC), and phylogenetic typing results were mainly grouped A (50.3 %) and B1 (37.6 %). Also, the biofilm assay revealed that 112 strains (75.2 %) could form biofilms. PFGE results showed that the 49 isolates revealed 21 major pulsotypes (P1-P21) and 28 subtypes with 80 % similarity, indicating the overall genetic diversity in the distribution area and sources of the samples.

Asunto(s)

Infecciones por Escherichia coli , Escherichia coli , Animales , Antibacterianos/farmacología , China , Infecciones por Escherichia coli/epidemiología , Infecciones por Escherichia coli/veterinaria , Granjas , Humanos , Leche , Filogenia , Prevalencia , beta-Lactamasas/genética

RESUMEN

Staphylococcus aureus is one of the main pathogens causing mastitis in dairy animals worldwide. It is an important opportunistic pathogen of raw milk, and the enterotoxin causes significant food poisoning. Monitoring the antibiotic resistance of S. aureus in raw milk is helpful for a risk assessment of S. aureus. In this study, 62 strains (43.1%) of S. aureus were isolated from 144 retail raw milk samples of different varieties from four regions in northern Xinjiang, China. Among them, the isolation rates at Shihezi, Hami, Altay, and Tacheng were 58.1% (54/93), 12.9% (4/31), 18.2% (2/11), and 22.2% (2/9), respectively. The isolation rate of positive strains in cow milk samples was the highest (61.7%, 37/60), followed by camel milk (35.9%, 23/64), and horse milk (10.0%, 2/20). The results of the classical virulence genes test showed that 12.9% (8/62) of the isolates carried at least one virulence gene. The main genotype was see (6.5%, 4/62), followed by sea+sec (3.2%, 2/62), sea (1.6%, 1/62), and sec (1.6%, 1/62). The analysis of 13 resistance genes and the susceptibility to 12 different antibiotics of 62 isolates showed that 80.6% (50/62) of the strains were resistant to at least one antibiotic, and 46.8% (29/62) were resistant to three or more antibiotics. The isolated strains had the highest resistance rate to penicillin (72.6%, 45/62), and 25.8% (16/62) of the isolates carried the blaZ resistance gene. In addition, 32 strains (51.6%, 32/62) of methicillin-resistant S. aureus were detected. All isolates had the ability to form biofilms. The pulsed-field gel electrophoresis results showed that the 47 isolates revealed 13 major pulsotypes (P1-P13) and 26 subtypes with 80% similarity, indicating the overall genetic diversity in the distribution area and sources of the samples. These findings indicate that S. aureus causes serious pollution of raw milk in northern Xinjiang, which has a negative effect on public health. Therefore, control measures and continuous monitoring should be undertaken to ensure the quality and safety of raw milk.