M.J. Devleeschouwer

Study of the formation of a biofilm by clinical strains of Staphylococcus aureus

A study on biofilm formation was carried out using five methicillin-sensitive [MSSA] and five methicillin-resistant [MRSA] strains of S. aureus. In each group, there were four strains isolated from patients from Kinshasa (Democratic Republic of Congo, DRC) and one reference strain. All of the strains were hydrophobic. The adherence of the bacteria to an abiotic surface was studied with the Biofilm Ring Test (BFRT®) and the crystal violet staining method (CVSM). Both techniques showed that eight of the strains formed biofilms within 2–3 h. The extent of the biofilm formed by one strain could only be observed with the CVSM. Periodate prevented the formation of biofilms and, in separate experiments, destroyed the biofilm pre-formed by the MSSA reference, but not those pre-formed by the clinical strains. Proteinase K destroyed all pre-formed biofilms. Six of the strains were icaA+; the clinical MSSA strains were not. The results also indicated different mechanisms of biofilm development between MSSA and MRSA clinical strains. The BFRT® and the CVSM are complementary techniques to study the adhesion of bacteria and the development of biofilms.

Relationship between slime production, antibiotic sensitivity and the phagetype of coagulase-negative staphylococci

Three hundred and three strains of coagulase–negative staphylococci (CNS) were collected from the fingers of healthy donors (289) and from blood cultures (14). Twelve different species were identified (5 5. auricularis, 45 S. capitis, 15 S. cohnii, 86 S. epidermidis, 23 S. haemolyticus, 37 S. hominis, 1 S. lentus, 5 S. saprophyticus, 7 S. sciuri, 6 S. simulans, 54 5. xylosus and 19 5. warneri). Amongst these CNS strains, 151 were slime producers, 112 were phage–typable and 188, 133, 126 and 91 were, respectively, resistant to penicillin, teicopiamn, erythromicin and kanamycin. Slime–producing strains were resistant to at least seven antibiotics with a probability of 001 < P < 005. Non–slime–producing strains were sensitive to all the tested antibiotics with a probability of 0001 < P < 001. There was no direct relationship between antibiotic sensitivity and phage type, although a non–typable strain was more often resistant to seven or more antibiotics than a typable one (005 < P <01).

Prevention of the adhesion of Pseudomonas aeruginosa to human buccal epithelial cells

Abstract The influence of protamine on the adhesion of Pseudomonas aeruginosa to human buccal cells was investigated using 2 collection strains and 5 other strains isolated from the hospital environment. The serotype and pyocin type of the strains was established and their antibiotic sensitivity determined. For concentrations lower than 100 μg/ml there was a decrease in adhesion correlating with protamine concentration. Maximum inhibition was reached at about 100 μg/ml.

Analytical determination of nicotinamide using bacterial electrodes

Abstract Two bacterial electrodes have been studied for the determination of nicotinamide (vitamin PP) with a linear range of 2.8 × 10 −4 M to 2 × 10 −2 M. The used strains, although taxonomicaly different and differently improved ( E. coli mutated and B. pumilus induced), present the same nicotinamide deaminase activity, able to be used for analytical assays. Their long-term stability (more than 100-fold higher than the purified enzyme) is realized by the regeneration of living cells on the electrode itself. The parameters involved in this type of electrode construction are discussed. This type of bacterial electrodes presents a very good selectivity for nicotinamide in multivitamin pharmaceutical formulations.

An in vitro test for the evaluation of the efficacy of disinfectants

Abstract The paper presents a method for the in vitro evaluation of the effectiveness of disinfectants. It is a capacity test performed in hard water with or without horse serum. Some results are presented showing the ability of growth in disinfectant solution.

Difference of Pseudomonas aeruginosa sensitivity to chloroxylenol according to the culture medium

The authors recorded notable difference of sensitivity of Pseudomonas aeruginosa to chloroxylenol according to the growth medium; the amount of magnesium of the culture medium and the growth phase were not major factors. This difference, which can be extended to various strains, is due to a difference of permeability of the outer membrane. It is suggested that adsorption of medium components on the surface of the bacteria could participate in the phenomenon. Similar results were obtained with phenol and crystal violet.

In vitro modification of antimicrobial efficacy by protamine

Abstract The influence of serum and protamine on the in vitro effectiveness of some preservatives has been studied. The products tested were formaldehyde, benzalkonium chloride, esters of parahydroxybenzoic acid, benzoic and sorbic acids. Serum only strongly depleted the activity of benzalkonium chloride. In the case of protamine, this basic protein markedly enhanced the bactericidal effect of benzoic and sorbic acids and allowed a reduction in the concentration by a factor of four while still maintaining the same bactericidal power on Pseudomonas aeruginosa .

Efficiency of bioconversion of steroids by Fusarium oxysporum into Δ1,4-androstadiene-3,17-dione using gas chromatography

Gas-liquid chromatography is suitable for the study of the bioconversion yield of dehydroisoandrosterone into Δ1,4-androstadiene-3, 17-dione. Fusarium oxysporum (a wild isolated strain) exhibits the greatest activity for this bioreaction. The optimalization of the bioconversion efficiency has been studied in culture media or in buffered solutions using free and immobilized cells. Microbiological (cell weight, choice of strains and substrate, induction) and physicochemical (pH, temperature, ionic strength and choice of buffers, organic solvents, artificial cofactors) factors influencing the reaction yield are discussed. The same operating conditions can be used for free and immobilized cells. For both techniques, about 90% of Δ1,4-androstadiene-3,17-dione is formed in 48 h with non-induced cells and in 24 h with induced cells. A simple prototype of a laboratory bioreactor is employed and tested in order to describe the advantages and limitations.

Comparison of the sensitivity of Pseudomonas aeruginosa to disinfectants according to the growth conditions

Abstract During the evaluation of the bactericidal effect of some disinfectants, the authors observed major differences of sensitivity in the case of Pseudomonas aeruginosa depending on the culture medium used for the preparation of the inoculum. In particular for chloroxylenol the results were much more favourable when the culture was made in brain heart infusion (Difco) than in tryptic soy broth (Difco).

Influence of protamine on the in vitro sensitivity of Pseudomonas aeruginosa to antibiotics

We have studied the influence of protamine on the sensitivity of three strains of Pseudomonas aeruginosa to various antibiotics: streptomycin, gentamicin, polymyxin B, and beta-lactams. While protamine enhanced the antibacterial action of beta-lactams towards P. aeruginosa, it did not alter the effect of aminoglycosides. The antibacterial power of polymyxin B, on the other hand, was drastically reduced. The observed changes in this strains sensitivity to antibiotics could be due to changes in the permeability of the outer membrane.