Enterococcus spp. produces slime and survives in rat peritoneal macrophages

Abstract

Enterococcal clinical isolates were investigated for the ability to form bio®lm on inert surfaces, as a measure of slime production, in an attempt to ®nd new possible virulence factors for these microorganisms. This property was commonly found among Enterococcus faecalis. Also E. faecium isolates were able to form bio®lm, although to a lesser extent; for this species, however, bio®lm formation seemed more frequently associated with isolates from infection rather than with environmental strains or isolates from healthy individuals. Bio®lm formation was strongly aected by the presence of an additional carbohydrate source in the medium, or by iron deprivation, indicating a role of slime for survival in stressful conditions. Slime-producing E. faecalis were able to survive inside peritoneal macrophages for extended periods compared to slimenegative strains or to slime-positive bacteria grown in conditions depressing slime production. In particular, slime-producing and slime-negative cells showed a decrease of 1 and 2 log units, respectively, at 1 h after infection; slime-negative cells were then rapidly killed, with clearance of bacterial cells at 24 h. Slime-producing bacteria persisted up to 48 h, which was the last time point examined, as after that time viability of both infected and non-infected macrophages started to decline. Scanning electron microscopy observations showed the presence of abundant amorphous extracellular material, of possible polysaccharide nature, embedding bacterial cells to form a multilayered bio®lm. Even in conditions not supporting bio®lm formation, bacterial cells appeared capsulated, suggesting that capsule and slime might represent dierent structures. Genes belonging to the epa locus or to a putative icaA homolog did not seem to be involved in synthesis and export of slime.

What drives bacteria to produce a biofilm?

“…Certain bacterial species may have evolved to switch on transcription of genes required for EPS synthesis in response to certain environmental stimuli that are encountered upon host entry, before the immune system mounts a specific attack [9]. For example, certain stimuli that mirror the physiology of the human body, such as iron deprivation and osmotic stress, induce the expression of genes encoding proteins that synthesize EPS in staphylococci and enterococci [10,11].…”

Glycolipids are involved in biofilm accumulation and prolonged bacteraemia in Enterococcus faecalis

“…Enterococci were tested for production of biofilm using the protocol described by Baldassarri et al (2001). Briefly, bacteria were grown at 37°C in TSB for 18 h. Polystyrene tissueculture plates (Greiner, Nürtingen, Germany) were filled with 180 ml of TSBG and 20 ml of this culture, and the plates were then incubated at 37°C for 18 h. The plates were read in an ELISA reader (Bio-Rad Microplate reader) at an optical density of 630 nm.…”

Genotypic characterization of hospitalEnterococcus faecalisstrains using multiple-locus variable-number tandem-repeat analysis

“…All isolates were identified to the species level by the API ID32-Strep system (bioMerieux, France). Each strain was identified by PCR with E. faecalis-specific primers (Baldassarri et al 2001). The isolates from carriers were collected from throat and nose (n = 15), sputum (n = 6) and rectum (n = 7).…”