Colonisation and interaction between S. epidermidis and S. aureus in the nose and throat of healthy adolescents.

Nasal colonisation with Staphylococcus aureus is a risk factor for developing nosocomial infections. It has been reported that S. epidermidis may produce a serine protease (Esp) inhibiting S. aureus biofilm formation and nasal colonisation. We aimed to analyse the correlation between S. aureus nasal and/or throat carriage and co-colonisation with S. epidermidis strains carrying esp, and the inhibitory effects of S. epidermidis culture supernatants on S. aureus biofilm formation and growth. We obtained 114 S. epidermidis isolates from the nose and 74 S. aureus from the nose and/or throat of healthy adolescents. S. aureus biofilm formation was analysed in a microtitre plate assay and the prevalence of ica, encoding biofilm formation, and esp was analysed with polymerase chain reaction (PCR). Inhibitory effects of S. epidermidis culture supernatants on S. aureus biofilm formation and growth was analysed in vitro. esp prevalence and expression was correlated with inhibitory effects. We detected biofilm formation in 45/74 (61%) S. aureus strains. The ica operon was more prevalent in isolates colonising the nose (12/15; 80%) versus isolates colonising the throat only (8/46; 17%). Almost two-thirds of S. epidermidis culture supernatants displayed high (≥ 50%) S. aureus biofilm inhibitory activity, without affecting growth. We found no correlation between the level of inhibitory activity and S. aureus colonisation. esp was ubiquitous in S. epidermidis, but esp expression did not correlate with biofilm inhibitory activity. S. epidermidis culture supernatants inhibit S. aureus biofilm formation, but do not affect bacterial growth. esp expression was not correlated with the inhibitory effects observed.

Enterococcus faecium produces membrane vesicles containing virulence factors and antimicrobial resistance related proteins.

Enterococcus faecium is a commensal but also a bacteremia causing pathogen, which is inherently resistant to several antimicrobials and has a great ability to acquire new traits. Bacterial membrane vesicles (MVs) are increasingly recognized as a mode of cell-free communication and a way to deliver virulence factors and/or antimicrobial resistance determinants. These features make MVs interesting research targets in research on critical hospital pathogens. This study describes for the first time that E. faecium strains produce MVs. It presents a morphological as well as a proteomic analysis of MVs isolated from four different, clinically relevant E. faecium strains grown under two different conditions and identifies MV-associated proteins in all of them. Interestingly, 11 virulence factors are found among the MV-associated proteins, including biofilm-promoting proteins and extracellular matrix-binding proteins, which may aid in enterococcal colonization. Additionally, 11 antimicrobial resistance-related proteins were MV-associated. Among those, all proteins encoded by the vanA-cluster of a vancomycin resistant strain were found to be MV-associated. This implies that E. faecium MVs may be utilized by the bacterium to release proteins promoting virulence, pathogenicity and antimicrobial resistance. SIGNIFICANCE: Enterococcal infections, especially bacteremia and endocarditis, are challenging to treat because E. faecium have acquired resistance to multiple classes of antimicrobials, including ampicillin, aminoglycosides, and glycopeptides. Thus, research on different modes of enterococcal pathogenicity is warranted. This study utilized a proteomic approach to identify MV-associated proteins of different nosocomial E. faecium strains representing four clinically relevant sequence types (STs), namely ST17, ST18, ST78, and ST192. The presented data suggest that E. faecium MVs are involved in virulence and antimicrobial resistance.

Characterisation and identification of enzyme-producing autochthonous bacteria from the gastrointestinal tract of two Indian air-breathing fish.

Characterisation and identification of autochthonous enzyme-producing bacteria isolated from the proximal intestine and distal intestine of two species of Indian air-breathing fish, murrel (Channa punctatus) and stinging catfish (Heteropneustes fossilis), were investigated using conventional culture technique. Population levels of proteolytic strains were highest in the digestive tract of stinging catfish. In both species, the viable counts of amylase-producing bacteria were somewhat higher than cellulase-producing bacteria. Among the gut bacteria isolated, 8 strains (4 from murrel and 4 from stinging catfish) were selected as potent enzyme-producers on the basis of quantitative enzyme assays. All these strains were Gram-positive rods, but only four isolates (CPF4, CPH6, CPH7 and HFH4) were capable of forming endospores. The tested bacteria grew in wide range of temperatures and pH. The strains were further identified by 16S rRNA gene sequence analysis. Two strains, CPF3 (isolated from murrel) and HFH4 (isolated from stinging catfish) showed high similarity to Bacillus sp., strain HFH7 (isolated from the stinging catfish) was most closely related to Bacillus subtilis, while five strains belonged to Bacillus licheniformis. Based on the results of the present study, we suggest that incorporation of autochthonous enzyme-producing bacteria in aquafeeds merits further investigations.