Sensitivity of bacterial coaggregation to chelating agents

Inhibition by EGTA of the formation of a biofilm by clinical strains of Staphylococcus aureus

The effect of EGTA on the adhesion and on the formation of a biofilm by two reference and eight clinical strains of Staphylococcus aureus was studied. All the clinical strains were isolated from patients from Kinshasa. Spa typing confirmed that these clinical strains were distinct. The Biofilm Ring Test (BFRT®) showed that EGTA (100 µM-10 mM) inhibited the adhesion of the four clinical methicillin-resistant (MRSA) strains and the crystal violet staining method that it inhibited the formation of a biofilm by all the strains. Divalent cations abolished the effect of EGTA on the formation of a biofilm, specially in the clinical MRSA strains. EGTA had no effect on established biofilms. Only concentrations of EGTA higher than 10 mM were toxic to eukaryotic cells. Our results establish the effectiveness and the safety of lock solutions with EGTA to prevent the formation in vitro of biofilms by S. aureus.

Physicochemical parameters influencing coaggregation between the freshwater bacteria Sphingomonas natatoria 2.1 and Micrococcus luteus 2.13

The aim of this study was to explore the physicochemical parameters that influence coaggregation between the freshwater bacteria Sphingomonas natatoria 2.1 and Micrococcus luteus 2.13. Using visual coaggregation assays, the effect of different buffers, solutions of differing ionic strength, pH, temperature, and viscosity on the degree of coaggregation was assessed. Coaggregation occurred maximally in distilled water but was inhibited when coaggregates were suspended in a commonly-used oral bacterial coaggregation buffer, saline solutions, and Tris-Cl buffers. Coaggregation was weakly expressed in standard laboratory buffers. The ionic strength of inorganic salt solutions required to inhibit coaggregation depended upon the inorganic salt being tested. Coaggregation occurred at a pH of 3-10, between 5 and 80°C and was inhibited in solutions with a viscosity of 22.5 centipoises at 20°C. Inhibition of coaggregation with NaCl impaired biofilm development. When developing buffers to test for coaggregation, the natural liquid environment should be considered. Coaggregation between S. natatoria 2.1 and M. luteus 2.13 is only affected by physicochemical conditions beyond those typically found in natural freshwater ecosystems. Such a robust ability to coaggregate may enhance the ability of S. natatoria 2.1 and M. luteus 2.13 to develop a niche in freshwater biofilms.

Biodegradation of nitrilotriacetic acid (NTA) and ferric-NTA complex by aerobic microbial granules

Development of mixed-culture microbial granules under aerobic conditions in a sequencing batch reactor (SBR), capable of completely degrading a recalcitrant metal chelating agent is reported. In laboratory-scale reactor studies, the microbial granules degraded 2mM of free nitrilotriacetic acid (NTA) and Fe(III)-NTA completely in 14 and 40 h, respectively. Free NTA was degraded at a specific rate of 0.7 mM (gMLSS)(-1)h(-1), while Fe(III)-NTA was degraded at a specific rate of 0.37 mM (gMLSS)(-1)h(-1). Achievement of significant degradation rates of NTA and ferric-NTA in double-distilled water suggests that the microbial metabolism is not constrained by lack of essential elements. Efficient degradation of recalcitrant synthetic chelating agents by aerobic microbial granules suggests their potential application in a variety of situations where heavy metals or radionuclides are to be co-disposed with metal chelating agents.

Preventive effect of sialylglycopeptide-nondigestive polysaccharide conjugates on salmonella infection

We have previously reported that sialylglycopeptide (SGP) and its derivatives isolated from egg yolk had a preventive effect on Salmonella infection in vivo; however, their retention time in the gut was rather short. To improve on this, SGP was conjugated with carboxymethyl cellulose (CMC) or carboxymethyl dextran (CMD). The conjugates inhibited the binding of Salmonella enteritidis and Escherichia coli to Caco-2 cells. Infection experiments with mice revealed that the SGP-CMD conjugate (SGP-CMD) had a strong protective effect against Salmonella infection. A turnover experiment in mice administered with radiolabeled SGP-CMD showed that SGP-CMD was more slowly absorbed into the blood and thus remained longer in the intestinal tract than SGP. SGP-CMD itself did not influence the production of tumor necrosis factor alpha (TNF-alpha), interleukin-1 beta, or nitrite ion (NO(2)(-)) by macrophages, although it suppressed that of TNF-alpha and NO(2)(-) in zymosan-treated macrophages, suggesting no causative effects of inflammation in SGP-CMD. SGP-CMD is potentially useful as a food ingredient with a preventive effect on Salmonella infection.

A continuum of anionic charge: structures and functions of D-alanyl-teichoic acids in gram-positive bacteria

Teichoic acids (TAs) are major wall and membrane components of most gram-positive bacteria. With few exceptions, they are polymers of glycerol-phosphate or ribitol-phosphate to which are attached glycosyl and D-alanyl ester residues. Wall TA is attached to peptidoglycan via a linkage unit, whereas lipoteichoic acid is attached to glycolipid intercalated in the membrane. Together with peptidoglycan, these polymers make up a polyanionic matrix that functions in (i) cation homeostasis; (ii) trafficking of ions, nutrients, proteins, and antibiotics; (iii) regulation of autolysins; and (iv) presentation of envelope proteins. The esterification of TAs with D-alanyl esters provides a means of modulating the net anionic charge, determining the cationic binding capacity, and displaying cations in the wall. This review addresses the structures and functions of D-alanyl-TAs, the D-alanylation system encoded by the dlt operon, and the roles of TAs in cell growth. The importance of dlt in the physiology of many organisms is illustrated by the variety of mutant phenotypes. In addition, advances in our understanding of D-alanyl ester function in virulence and host-mediated responses have been made possible through targeted mutagenesis of dlt. Studies of the mechanism of D-alanylation have identified two potential targets of antibacterial action and provided possible screening reactions for designing novel agents targeted to D-alanyl-TA synthesis.

Polycarboxylates inhibit the glucan-binding lectin of Streptococcus sobrinus

Polycarboxylates, such as carboxymethylcellulose and hyaluronan, were found to be reversible inhibitors of the glucan-binding lectin of Streptococcus sobrinus. When the carboxylate groups were coupled to ethylenediamine, or reduced with carbodiimide-borohydride, inhibitory powers were lost. Similarly, N-deacetylated hyaluronan had poor inhibitory powers, probably due to the introduction of positive charges into the polymer. Other polymers, such as chondroitin sulfates, dextran sulfate, fetuin, heparin were not inhibitors. It appears that inhibition is based on repeating carboxylates, free of influence from ammonium groups. Such polymers have the property of complexing with metals. Earlier studies had concluded that the streptococcal lectin depended on manganese for activity. It is likely the carboxymethylcellulose and hyaluronan perturb essential metal coordination centers in the lectin. Polycarboxylates may have value in oral health care by acting on glucan-dependent microbial adhesion and biofilm formation.