A mutation in rpoS enhances biofilm formation in Escherichia coli during exponential phase of growth.

Biofilm formation in Escherichia coli is a process that involves slow growth and stress conditions where several molecular signals and growth phase regulated genes are involved. Here we show that rpoS mutant strains (defective in the stress regulator sigma(S)) exhibit an increased production of biofilm, especially in the exponential phase of growth. Our results indicate that rpoS mutants produce an extracellular factor that promotes the production of biofilm during the exponential phase of growth. Thus, RpoS plays an important role in the regulation of the amount and initiation of biofilm formation in E. coli.

Biofilm formation in Escherichia coli is affected by 3-(N-morpholino)propane sulfonate (MOPS).

In most natural environments, association with a surface in a structure known as a biofilm is the prevailing microbial life-style. Escherichia coli has been a useful model for the study of biofilm formation. Here we analyzed the amounts of biofilm formed when E. coli was cultured in the presence of MOPS [3-(N-morpholino)propane sulfonatel. We used the "O'Toole and Kolter" method, which consisted of growing cells in PVC microtiter dishes and staining the formed biofilm with crystal violet. Our results showed that: 1) the addition of 100 mM MOPS to the rich Luria-Bertani (LB) medium increased the capacity of biofilm formation of several E. coli strains; and 2) the biofilm formed by cells growing in the presence of MOPS was more evident and well defined than that of cells cultured in LB-only medium. The improved ability of forming biofilms was maintained even for 60 h after removing MOPS from the medium, indicating that this improvement was due to a change in the metabolism of E. coli growing in the presence of MOPS or that, under these conditions, biofilm formation was favored.

[Salivary pH and culture determinations in HIV infected and non-HIV infected patients with oral candidosis]. / Determinación de pH salival y cultivo en pacientes con candidosis bucal VIH positivos y VIH negativos.

The aim of the present study was to determine the salivary pH in HIV (Human Immunodeficiency Virus) positive(+) and negative(-) patients and in a control group, for assessing if variations or changes in pH are related to the development of oral candidosis and the species isolated. The sample comprised 120 patients from the Infectology Unit of the Mexico General Hospital, and from the School of Dentistry, UNAM. Three study groups were performed: with oral candidosis HIV+, with oral candidosis HIV-, and a control group. All patients filled out a clinical data questionnaire and signed an informed consent document. A 2 ml sample of non-stimulated saliva was obtained from each patient. The pH was measured and the sample was cultured on dextrose Sabouraud agar. The Candida species determinations were performed by the API 20 C AUX system and statistically analyzed. In the HIV+ group, the pH mean was 6.17, with most prevalence of Candida albicans type I and pseudomembranous candidosis. In the HIV- group prosthesis users, the pH mean was 6.29, with most prevalence of C. albicans type I, but with erythematous candidosis. The control group showed a mean pH of 6.78. A statistically significant difference among pH values was found (F= 15.45 p<0.01). The present study revealed that in HIV+ patients, the most significant predisposing factors are: immunosuppression, antibiotic therapy, bad hygiene, anemia, leucoplakia, and diabetes. The salivary pH with acidic values (more in HIV+ patients) significantly favors candidosis development, specially for C. albicans and C. glabrata species and primarily the pseudomembranous and erythematous clinic types. The pH is not a determinant for Candida growth, but could affect the adherence and invasiveness of the yeast.