Sequence polymorphisms and evolutionary analysis of Staphylococcus aureus enterotoxin A, B, C and D

ObjectiveTo analyze the sequence polymorphism and evolution of Staphylococcal aureus enterotoxin (SE) A, B, C and D from different sources and provide theoretical basis for further understanding the variation in SE expression among different subtypes and food safety risk assessment.

MethodsA total of 90 strains which were positive for enterotoxin A, B, C or D from different sources were selected and sequenced, and the results were compared with the sequences of the representative subtypes of enterotoxins downloaded from GenBank, and the phylogenetic tree was constructed by MEGA 7.

ResultsThere were three mutation sites in the amino acid sequences of SEA, which were mainly located on both sides of the N-terminal and C-terminal, and there were three subtypes. The main subtype of the strains in this study was SEA1. The mutation sites of the amino acid sequences of SEB were mainly located in the middle of the sequence. There were 18 mutation sites and 11 subtypes. The main subtypes of the strains in this study were SEB1 and SEB2. There were 24 amino acid mutation sites in SEC, which were distributed in the whole sequence and divided into 8 subtypes. SEC3 was the main subtype in this study. The amino acid sequences of SED were relatively conserved, including 7 subtypes. The main subtype in this study was SED1. At the same time, two new subtypes, SEB9 and SEC5, were also found in this study.

ConclusionThe amino acid sequences of SEA and SED were relatively conservative compared with SEB and SEC. The phylogenetic trees of SEA, SEB, SEC and SED were all divided into two branches. The main subtypes of strains selected in this study were SEA1, SEB1, SEB2, SEC3 and SED1.