Inhibition of S. aureus by E. faecalis in flow biofilms and transfer of tetracycline resistance gene tetM from E. faecalis to S. typhimurium in mixed species biofilms

Enterococcus faecalis is a serious public health concern because it can cause multi-drug resistant opportunistic infections, spread antibiotic resistance to other bacteria and persist in hospital environments.;Static and flow biofilms were used to assess the role of amyloids in transfer of pCF10 from E. faecalis to Staphylococcus aureus. Transfer of tetM from E. faecalis to a clinical isolate of S. aureus, at a rate of 10-8 , was demonstrated by Ella Massie-Schuh using a static biofilm model. However, the recipient strain used in this model did not produce amyloids because the biofilms were grown in nutrient rich TH broth. This model was not successful when an amyloid producing strain of S. aureus was used as the recipient species because the low nutrient PNG medium, needed to induce S. aureus amyloid production, did not support growth of E. faecalis in static biofilms (Schwartz et al., 2012). A flow model presumably resolved nutrient insufficiency because both S. aureus and E. faecalis could be recovered from this model. However, counts of S. aureus were low when grown in mixed species biofilms with E. faecalis as compared to single species biofilms, which suggests that E. faecalis is inhibiting biofilm formation of S. aureus in this model. A mouse skin infection model was also used to examine transfer between E. faecalis and an amyloid producing strain of S. aureus . Unlike the flow biofilm model, E. faecalis did not inhibit the growth of S. aureus in a wound environment. However, no tetracycline resistant S. aureus colonies were recovered.;Conical tube biofilms were used to assess transfer of tetM from E. faecalis to E. coli MC4100, EPEC and S. Typhimurium. Mixed species biofilms were grown on glass slides, in conical tubes, for 5 days. In this model, transfer of pCF10 was induced by adding synthetic cCF10. Screening putative recipient colonies showed one transfer event of tetM from E. faecalis to S. Typhimurium. Transfer was confirmed by 16S rRNA sequencing and sequencing of the tetM gene. While this is interesting, it may not be useful as a transfer model because the spontaneous mutation rates approached 10-1 for E. coli, EPEC and S. Typhimurium. In a separate experiment, three mice were given either S. Typhimurium alone, S. Typhimurium with E. faecalis OG1RF(pCF10) or S. Typhimurium with E. faecalis OG1RF(pCF10) and E. faecalis lacking the plasmid. E. faecalis lacking pCF10 was used to provide cCF10 as synthetic cCF10 could not be used in this model. E. faecalis was not recovered from stool samples past day two. Chromosomal DNA was isolated from select S. Typhimurium isolates. None of the colonies tested were shown to be tetM recipients. In addition, the total number of tetracycline resistant S. Typhimurium was close to the total number of S. Typhimurium recovered. Therefore, similar to the conical tube model, this model may not be useful due to the high spontaneous mutation rate. While transfer was not detected using animal models, confirmation of transfer in the conical tube and static models may merit continuation of this project using improved wound and gastrointestinal models. (Abstract shortened by UMI.).