Oogai, Y. | Search bioRxiv

bioRxiv2021

Complete sequences of epidermin and nukacin encoding plasmids from oral-derived Staphylococcus epidermidis and their antibacterial activity

Staphylococcus epidermidis is a commensal bacterium in humans. To persist in the bacterial flora of the host, some bacteria produce antibacterial factors such as the antimicrobial peptides known as bacteriocins. In this study, we tried to isolate bacteriocin-producing S. epidermidis strains. Among 150 S. epidermidis isolates from the oral cavities of 287 volunteers, we detected two bacteriocin-producing strains, KSE56 and KSE650. Complete genome sequences of the two strains confirmed that they carried the epidermin-harbouring plasmid pEpi56 and the nukacin IVK45-like- harbouring plasmid pNuk650. The amino acid sequence of epidermin from KSE56 was identical to the previously reported sequence, but the epidermin synthesis-related genes were partially different. The prepeptide amino acid sequences of nukacin KSE650 and nukacin IVK45 showed one mismatch, but both mature peptides were entirely similar. pNuk650 was larger and had an additional seven ORFs compared to pIVK45. We then investigated the antibacterial activity of the two strains against several skin and oral bacteria and found their different activity patterns. In conclusion, we report the complete sequences of 2 plasmids coding for bacteriocins from S. epidermidis, which were partially different from those previously reported. Furthermore, this is the first report to show the complete sequence of an epidermin-carrying plasmid, pEpi56.

microbiology↗

bioRxiv2019

An alternative nisin A resistance mechanism affects virulence in Staphylococcus aureus

Nisin A is a bacteriocin produced by Lactococcus lactis and is widely used as a food preservative. Staphylococcus aureus has the BraRS-VraDE system providing resistance against low concentrations of nisin A. The BraRS is one of a two-component system that senses nisin A by BraS and finally induces the expression of ABC transporter VraDE by phosphorylated BraR. Previously, we isolated a highly nisin A resistant strain with increased VraDE expression due to a mutation of braRS. In this study, we isolated a BraRS-VraDE-independent, nisin A resistant mutant from S. aureus MW2. These mutants, designated SAN2 (S. aureus nisin resistant) and SAN469, had a mutation in pmtR (MW1875) which encodes a transcriptional regulator responsible for the expression of the pmtA-D operon. As a result, this mutant exhibited a high level of constitutive production of PmtA-D, a transporter responsible for the export of phenol soluble modulin (PSM). We also obtained two pmtA-D overexpressing, nisin A resistant mutants which contained a point mutation in pmtR from other S. aureus strains.\n\nCharacterization of the mutants revealed that they have a decreased susceptibility to human beta defensin-3 and LL37, which are innate immune factors. Additionally, these mutants showed higher hemolytic activity than the MW2 original strain. Furthermore, in a mouse bacteremia model, the SAN2 strain exhibited a lower survival rate than the MW2 original strain. These results indicate that the over expression of pmtA-D due to the pmtR mutation is an alternative nisin A resistance, which also affects virulence in S. aureus.\n\nAuthor SummaryRecently, the emergence of antibiotic resistant bacteria such as MRSA, MDRP and CRE have brought serious problems for chemotherapy in the world. In addition, many antibacterial agents such as disinfectants and food additives are widely used. Therefore, it raises the possibility that bacteria are becoming resistant to all antibacterial agents. In this study, we investigated whether S. aureus become resistant against nisin A, one of the food additives. Finally, we isolated nisin A highly resistant S. aureus strains. Among these strains, we identified that one strain designated as SAN2 showed nisin A resistance by the overproduction of Pmts which were involved in the secretion of virulence factors called PSMs. We identified a mutation of pmtR gene encoding a regulator for pmt genes. SAN2 strain showed the decreased susceptibility to human antimicrobial peptides and the increased hemolytic activity. Finally, SAN2 showed higher lethal activity in mouse bacteremia model. Our study provides new insights into that S. aureus may cause resistance against various antibacterial food additives, together with the altering the virulence.

microbiology↗