Staphylococcus argenteus (SAR) has been isolated from chicken and slaughterhouse meat samples. Sequencing and phylogenetic analysis of S. argenteus isolates from both sources suggested bacterial contamination of chicken meat at the slaughterhouse. Credit: M. Miyake & Y. Wakabayashi

People need to eat enough healthy, nutritious food to stay alive and healthy. Eating unsafe foods contaminated with harmful bacteria, viruses, parasites or chemicals is responsible for more than 200 illnesses, ranging from diarrhea to cancer. Diarrheal diseases are the most common diseases caused by contaminated food, affecting 550 million people and killing 230,000 people every year worldwide. Even in developed countries, some foodborne bacterial pathogens threaten people’s lives through the ingestion of daily meals. Of concern is Staphylococcus argenteus, a bacterial organism that causes food poisoning. It was first discovered as a genetically distinct line in Aboriginal communities in Australia. Since then, Staphylococcus argenteus has been isolated on other continents, indicating its worldwide prevalence.

In a recent study, a team of scientists based at Osaka Prefectural University in Japan, sought to examine the prevalence of Staphylococcus argenteus in foods such as vegetables, fish, chicken, beef and pork in retail stores. They used molecular techniques to identify bacterial genetic material through polymerase chain reaction and whole genome sequencing. With the exception of chicken, none of the foods they sampled showed evidence of Staphylococcus argenteus contamination. Surprisingly, Staphylococcus argenteus genetic material was found in 13.9% of chicken samples tested.

The researchers further profiled Staphylococcus argenteus genotype, virulence factors and level of antibiotic resistance. Using multi-locus sequence typing (MLST), strain ST2854 was the most predominant, accounting for 33% of all isolates. The other predominant strains were ST1223, ST5961 and ST2250 at 28.6%, 23.8% and 14.3%, respectively. All isolates had staphylococcal enterotoxin (SE) gene repertoires. In particular, the selx gene, which codes for the SELX protein. Surprisingly, one of the 21 strains tested for antibiotic resistance was resistant to penicillin, tetracycline, and doxycycline, while another was resistant only to penicillin.

Additionally, the researchers examined chicken samples from two different slaughterhouses, one specializing in broiler processing and the other in hen processing. A total of 357 samples were tested, including chicken feathers, cooling water and installation swabs. Surprisingly, 14 strains of Staphylococcus argenteus were isolated from the same slaughterhouse. These isolates have been found in cooler water, knife handle swabs and cutting boards, as well as in chicken carcasses.

During genetic analysis of the slaughterhouse isolates, 13 isolates were assigned to the ST5961 genotype and one isolate to the ST5964 genotype. Toxin profiling and antibiotic sensitivity testing were also performed. Toxin profiling revealed the selx gene in all isolates. Additionally, additional sey genes, sel26 and sel27, were only found in ST5964, implying that these isolates from an abattoir can cause staphylococcal food poisoning (SFP). Surprisingly, all 14 isolates from the slaughterhouse were susceptible to antibiotics.

In further confirmatory studies, researchers used phylogenetics to analyze the sequences of all 35 Staphylococcus argenteus isolates to clarify the relationship between retail chicken and slaughterhouse-derived isolates. Curiously, some of the retail chicken isolates clustered phylogenetically with slaughterhouse isolates. Additionally, three chicken isolates and one slaughterhouse cooling water isolate clustered phylogenetically. Additionally, five retail chicken isolates and 13 slaughterhouse isolates clustered and were all classified as ST5961. These results indicate that the slaughterhouse environment is most likely a source of Staphylococcus argenteus contamination, suggesting continued bacterial spread in processed foods.

In an interview, Professor Masami Miyake, who supervised this research, said: “Basically, this investigation showed that chicken meat was heavily contaminated with Staphylococcus argenteus, the bacteria that can cause human disease. Our molecular phylogenetic approach further revealed that meat processing plants may also have a role in transmitting germs from the environment to food and vice versa.” The schematic illustration of their contamination dynamics proposal food by Staphylococcus argenteus is shown in Figure 1. When we took part in an interview with Dr. Yuki Wakabayashi, who was a doctoral student when he conducted this study, he added: “This is the first study that have demonstrated the presence of S. argenteus in a food processing facility and the possibility of bacterial contamination during food processing should be considered.”

The research was published in the International Journal of Food Microbiology.

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More information:
Yuki Wakabayashi et al, Isolation and characterization of Staphylococcus argenteus strains from retail food and slaughterhouses in Japan, International Journal of Food Microbiology (2021). DOI: 10.1016/j.ijfoodmicro.2021.109503

Provided by Osaka Metropolitan University

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