C. Pérez-Giraldo

In vitro activity of allicin against Staphylococcus epidermidis and influence of subinhibitory concentrations on biofilm formation

Aims: The aim of this study is to determine the in vitro activity of allicin against Staphylococcus epidermidis and to evaluate the influence of allicin on biofilm formation.

Enzymatic activities of Candida tropicalis isolated from hospitalized patients

Secretion of hydrolytic enzymes is considered a virulence factor in Candida spp. Extracellular enzymatic activities in 29 clinical isolates of Candida tropicalis were analyzed by plate assays. C. tropicalis, similar to Candida albicans, showed elevated hemolytic and esterase activities. However, unlike C. albicans, low aspartyl protease and very low phospholipase activities were detected in C. tropicalis isolates.

Moxifloxacin and Biofilm Production by Coagulase-Negative Staphylococci

The in vitro activity of moxifloxacin against 41 strains of coagulase-negative staphylococci was determined. A relationship between the activity of moxifloxacin and biofilm formation was detected. Biofilm-producing strains were more resistant to moxifloxacin than biofilm-negative strains. Our global results obtained with six strains of Staphylococcus epidermidis showed that subinhibitory concentrations of moxifloxacin did not significantly modify biofilm formation. On the other hand, moxifloxacin concentrations of 2, 10, 50 and 100 × MIC produced a log decrease in viable count (included in a biofilm) of 0.20, 0.37, 1.10 and 1.69, respectively.

Exposure to Therapeutic Concentrations of Ritonavir, but Not Saquinavir, Reduces Secreted Aspartyl Proteinase of Candida parapsilosis

The effect of ritonavir and saquinavir, HIV proteinase inhibitors, on the secreted aspartyl proteinase (Sap) activity of Candida parapsilosis was studied. In a proteinase-inducing medium (yeast carbon base-bovine serum albumin), Sap activity in all clinical isolates of C. parapsilosis (n = 20) was observed at 37°C but not at 22°C. The presence of ritonavir at a concentration of 8 µg/ml produced an inhibition close to 50% albumin consumption and also delayed yeast growth; however, saquinavir did not have any effect on growth or on Sap activity. In Sabouraud broth, which does not induce Sap production, no effect was shown on yeast growth by either of the two HIV proteinase inhibitors studied.

Aspartyl proteinase, phospholipase, hemolytic activities and biofilm production of Candida albicans isolated from bronchial aspirates of ICU patients.

A correlation between mucosal colonization by Candida albicans and the subsequent development of invasive respiratory infection has been previously described. The aim of this study was to evaluate different enzymatic activities in vitro and to determine the capacity to form biofilms by 17 C. albicans isolates from bronchial aspirates of mechanically ventilated patients hospitalized in intensive care units. All the C. albicans clinical isolates tested were biofilm producers and displayed detectable levels of proteinase and hemolytic activities, although phospholipase activity was not detected in one strain. The correlation noted among the virulence factors studied suggests that the presence of more than one concurrent factor could facilitate the spread of infection.

La hidrofobicidad de la superficie celular como indicador de otros factores de virulencia en "Candida albicans"

OBJECTIVE To evaluate virulence factors involved in the adhesion process, such as cell surface hydrophobicity (CSH), adherence to plastic capacity, adherence capacity to buccal epithelial cells (BEC), and biofilm formation, in 17 strains of C. albicans isolated from bronchial aspirates of critically ill patients. METHOD The CSH of the strains of C. albicans was determined using the MATH method, a microbial adhesion to hydrocarbons test. The study of adherence to plastic was performed in microtitre plates in accordance with Christensens technique. Biofilm formation was studied in polystyrene microtitre plates, according to the method of Ramage. Adherence to BEC was evaluated by quantifying the percentage of adhered yeasts to cells. RESULTS All the strains studied showed factors directly involved in adhesion, with variability in the degree of expression among them. Medium-high levels of CSH were found in 52.9% of the strains. The percentage of strains with high values in adherence to plastic was 35.3%. The most hydrophobic strains were the most adherent to plastic, with a correlation coefficient of 0.76. Of the 12 biofilm-producing strains, 6 were high producers. These strains had also high levels of CSH and adherence to plastic, with significant results. All the strains studied adhered to BEC, with results ranging widely from 45 to 157 yeasts/100 BEC, with no significant correlation with the rest of the parameters studied, although CSH was seen to be an indispensable prior requisite for adherence to cells. CONCLUSION CSH is a variable characteristic in C. albicans and is directly related to adherence to plastic and biofilm formation. Ease in evaluating CSH permits its quantification, and could be used as an indicator of the presence of other determinants of pathogenicity.

Resistance to Vancomycin, LY333328, Ciprofloxacin and Trovafloxacin of Community-Acquired and Nosocomial Strains of Enterococcus faecalis Isolated in Badajoz (Spain) with and without High-Level Resistance to Streptomycin and Gentamicin

In vitro resistance of community-acquired and nosocomial strains of Enterococcus faecalis isolated in Badajoz (Spain) were determined by a microdilution method. The isolates were identified with conventional MicroScan Pos Combo 4 I dehydrated panels. No resistance to glycopeptides was found, but LY333328 was 2–4 times more active than vancomycin. In the nosocomial strains, high-level resistance to streptomycin (HLRS) was 54.7%, and high-level resistance to gentamicin (HLRG) was 38.1%. Resistance to ciprofloxacin and trovafloxacin was 45.3 and 38.9%, respectively. In the community-acquired isolates, HLRS, HLRG, resistance to ciprofloxacin and resistance to trovafloxacin were 44.2, 17.3, 15.4 and 13.5%, respectively. Trovafloxacin was 2–4 times more active than ciprofloxacin against both groups of strains. An association between high-level resistance to aminoglycosides and resistance to fluoroquinolones was noted. The resistance to aminoglycosides did not influence the activity of vancomycin and LY333328.

Zeta Potential Aspects of Dispersed Solvents Involved in the Determination of Microbial Cell Surface Hydrophobicity

Electrical forces are present in those microbiological adhesion‐based tests performed to obtain bacterial surface hydrophobicity. In this context, zeta potentials (ζ) and isoelectric points of n‐hexadecane, p‐xylene, xylene, and chloroform particles are obtained through electrophoresis in conditions of clinical interest. Droplet formation and particularities of the particle movement inside the electrophoresis chamber are also analyzed. All the solvents are negatively charged from pH 4 and have isoelectric points in the pH range studied. Temperature changes do not imply important changes in ζ. Zeta potential values are dependent on the stationary planes where electrophoretic mobilities are measured. The high or low density of solvents can be crucial in defining a concrete value of the particle surface zeta potential. We propose to measure in the stationary planes where accumulation of droplets can be avoided.

Changes on the physico-chemical surface properties and adhesion behaviour of Enterococcus faecalis by the addition of serum or urine to the growth medium

The initial microbial adhesion of bacteria to different surfaces seems to be mediated by physico-chemical forces and this is the reason why the physico-chemical surface characterisation of bacteria has recently gained interest. In this context, the adhesion of different microorganisms to biological substrata has been described from a physico-chemical point of view, aiming to simulate, as closely as possible, the conditions of interest. On this basis, the objective of this work is to characterise the surface of Enterococcus faecalis ATCC29212 through hydrophobicity, surface free energy and zeta potential at 37°C, when cells grow in Trypticase Soy Broth (TSB) and TSB supplemented with serum or urine. These variations are used to provide a theoretical description of the bacterial adhesion to glass by interaction free energy, which is verified with experimental results employing a parallel plate flow chamber set at 37°C, to simulate the conditions of flow inside the human body. The results show that the addition of serum to the growth medium increases the hydrophobicity and isoelectric point (i.e.p.) of the microorganisms, and this could indicate an increase in the protein content on the cell surface. However urine does not introduce a change in the above magnitudes. At short separation distances between the cells and the substratum, the interaction free energy predicts a favourable adhesion for serum-grown cells while non-favourable adhesion is expected for control (TSB-grown cells) and urine-grown cells. These results are in agreement with the experimental adhesion data, obtained with the flow chamber.

Phagocytic Activity of Polymorphonuclear Leukocytes on Escherichia coli Previously Exposed to Metronidazole

A study was made of the action of different concentrations of metronidazole of the viability of Escherichia coli under aerobic and anaerobic conditions. The viability of E. coli was reduced by 60 to 99% after 24 hours of anaerobic incubation, according to the concentration of metronidazole tested. In addition, there were significant morphological changes in the bacteria. Exposure of antibiotic-induced filaments of E. coli LP 136 to phagocytosis caused the cfu/ml value to drop by 60% after 120 minutes. Under identical conditions, using the mutant strain E. coli RYC 819, which did not become filamented by metronidazole although it did present similar ultrastructural changes, this reduction reached 83%. These results may explain the therapeutic success of metronidazole in polymicrobial infections.