Activity of Natural Polyether Ionophores: Monensin and Salinomycin against Clinical Staphylococcus epidermidis Strains

Staphylococcus epidermidis, a coagulase-negative Staphylococcus, is the most important pathogen responsible for chronic nosocomial infections. These bacteria produce extracellular slime and form biofilms on various biotic and abiotic surfaces. Bacterial biofilms are very resistant to standard antimicrobial therapy and difficult to eradicate, so it is important to search for new more effective anti-biofilm agents, for example in the group of natural substances. The aim of the study was to examine the activity of two ionophores-salinomycin and monensin against clinical S. epidermidis strains, using MIC/MBC method and biofilm formation inhibition assay. Bacterial strains were tested also for slime production using Congo Red Agar. Both tested ionophore antibiotics showed the highest activity against planktonic bacteria of clinical as well as standard S. epidermidis strains and effectively inhibited the formation of bacterial biofilm.

Enzymatic Detachment of Staphylococcus epidermidis Biofilms

ABSTRACT The gram-positive bacterium Staphylococcus epidermidis is the most common cause of infections associated with catheters and other indwelling medical devices. S. epidermidis produces an extracellular slime that enables it to form adherent biofilms on plastic surfaces. We found that a biofilm-releasing enzyme produced by the gram-negative periodontal pathogen Actinobacillus actinomycetemcomitans rapidly and efficiently removed S. epidermidis biofilms from plastic surfaces. The enzyme worked by releasing extracellular slime from S. epidermidis cells. Precoating surfaces with the enzyme prevented S. epidermidis biofilm formation. Our findings demonstrate that biofilm-releasing enzymes can exhibit broad-spectrum activity and that these enzymes may be useful as antibiofilm agents.

Effects of Growth Phase and Extracellular Slime on Photodynamic Inactivation of Gram-Positive Pathogenic Bacteria

ABSTRACT The emergence of antibiotic resistance among pathogenic bacteria has led to efforts to find alternative antimicrobial therapeutics to which bacteria will not be easily able to develop resistance. One of these may be the combination of nontoxic dyes (photosensitizers [PS]) and visible light, known as photodynamic therapy, and we have reported its use to treat localized infections in animal models. While it is known that gram-positive species are generally susceptible to photodynamic inactivation (PDI), the factors that govern variation in degrees of killing are unknown. We used isogenic pairs of wild-type and transposon mutants deficient in capsular polysaccharide and slime production generated from Staphylococcus epidermidis and Staphylococcus aureus to examine the effects of extracellular slime on susceptibility to PDI mediated by two cationic PS (a polylysine-chlorin e6 conjugate, pL-c e6 , and methylene blue [MB]) and an anionic molecule, free c e6 , and subsequent exposure to 665-nm light at 0 to 40 J/cm2. Free c e6 gave more killing of mutant strains than wild type, despite the latter taking up more PS. Log-phase cultures were killed more than stationary-phase cultures, and this correlated with increased uptake. The cationic pL-c e6 and MB gave similar uptakes and killing despite a 50-fold difference in incubation concentration. Differences in susceptibility between strains and between growth phases observed with free c e6 largely disappeared with the cationic compounds despite significant differences in uptake. These data suggest that slime production and stationary phase can be obstacles against PDI for gram-positive bacteria but that these obstacles can be overcome by using cationic PS.

Virulence ofStaphylococcus epidermidisin a mouse model: significance of extracellular slime

SummaryThe ability to produce large quantities of bioflim on solid surfacesin vitrois believed to distinguish potentially pathogenic strains ofStaphylococcus epidermidisfrom commensals. Bioflim consists of staphylococcal cells encased in a matrix of extracellular polysaccharide (also referred to as slime), firmly adherent to each other and to the underlying surface structure. The association of slime with colonization of catheter surfacesin vivohas been examined extensively. Less attention has been paid to the contribution of slime to infections that occur in the absence of an inserted device. In a mouse model of subcutaneous infection without an implanted device 10S. epidermidisstrains (5 slime-positive, 5 slime-negative) produced abscesses; thus a foreign body is not essential for the expression of virulence byS. epidermidis. Biofilm-positive strains produced significantly more abscesses, that persisted longer than biofilm-negative strains. In these chronic infections, large numbers of staphylococci were associated with macrophages and viable staphylococci were cultured from specimens of pus collected at autopsy. Thus slime or components of slime appear to delay the clearance ofS. epidermidisfrom host tissues, possibly by interfering with intracellular killing mechanisms. However, differences in the capacity to produce abscesses, within both the slime-positive and slime-negative groups, indicate that other factors also contribute to the virulence ofS. epidermidis.