Growth dynamics of lactic acid bacteria and dairy microscopic fungus Geotrichum candidum during their co-cultivation in milk.

Production of high-quality and microbiologically safe fermented dairy products requires controlled growth and microbial interactions between lactic acid bacteria and microscopic fungi. For this purpose, detailed knowledge of their growth characteristics is needed. Therefore, the objective of this study was to analyse the growth dynamics of lactic acid bacteria of commercial DVS® FRESCO® 1000NG culture and dairy isolate of microscopic fungus Geotrichum candidum during their co-cultivation in milk. The growth dynamics of microorganisms was studied in dependence on their initial counts at 12, 15, 18, 21 and 30 °C. Growth parameters were calculated by two primary predictive models, model of Baranyi and Roberts and Huang's model. Both models showed good ability to describe the growth dynamics of studied microorganisms, as it was confirmed by low values of RMSE index. Both microbial cultures, Fresco culture and Geotrichum candidum, showed good growth ability in milk since they reached the average maximum density of 9.50 ± 0.13 log CFU/mL and 5.85 ± 0.69 log CFU/mL (n = 45), in order. Maximum density of studied microorganisms was not affected by their initial counts or incubation temperature. On the other hand, effect of mutual ratio of microbial initial counts and increasing temperature had a significant impact on growth dynamics.

Evaluation of surface active and antimicrobial properties of alkyl D-lyxosides and alkyl L-rhamnosides as green surfactants.

The use of carbohydrates, as a part of surface-active compounds, has been studied due to their biodegradability and nontoxic profile. A series of alkyl glycosides containing d-lyxose and l-rhamnose with alkyl chains of 8-12 carbon atoms were investigated. The effects of structural variations on their physico-chemical and biological properties have been evaluated for a detailed understanding of their properties. Alkyl glycosides were tested on their toxicity against bacterial cells of the genus Pseudomonas (MTT assay), microbiological adhesion to hydrocarbons (MATH assay), cell surface hydrophobicity (Congo red assay), cell membrane permeability (crystal violet assay), and bacterial biofilm formation. Furthermore, their antifungal activity against two pathogenic microorganisms Candida albicans and Aspergillus niger was investigated using the disc diffusion method. Toxicological studies revealed that compounds could reduce the metabolic activity of bacterial cells only moderately but they increased the hydrophobicity of cell surface in Pseudomonas strains. In addition, alkyl glycosides changed the permeability of the cell membranes to the level of 30-40% for this strain. The compounds with an even number of carbon atoms in their alkyl chain promoted stronger bacterial biofilm formation on the glass surface. All studied derivatives demonstrated very strong antifungal activity against fungus A. niger but very small effect against C. albicans. Overall, the results showed that long-chain alkyl glycosides could be considered as inexpensive, biocompatible, nontoxic agents, and serve for the surface design to avoid bacterial adhesion as an alternative solution to antibiotic treatment.

Staphylococcus aureus 2064 growth as affected by temperature and reduced water activity.

Based on 247 growth data, the growth of S. aureus 2064 in dependence on temperatures (8-50°C) and aw values (0.999-0.83) was described. Optimal values of aw at all studied temperatures were determined by using Gibson model. Its compatibility was confirmed by several statistical indices, e.g. root mean square errors (RMSE 0.003-0.138), standard errors of prediction (%SEP 0.6-17.5). Cardinal values for S. aureus growth (Tmin =7.7°C, Topt =40.6°C, Tmax =46.7°C, awmin =0.808, awopt =0.994, µopt =1.97 1/h) were determined by using CM model with indices RMSE=0.071, SEP=17.5%. Our findings can provide relevant growth information that can be used in S. aureus exposure assessment or in validation of other data regarding the growth of this opportunistic pathogen in foods.

Hospital wastewaters treatment: Fenton reaction vs. BDDE vs. ferrate(VI).

Various types of micropollutants, e.g., pharmaceuticals and their metabolites and resistant strains of pathogenic microorganisms, are usually found in hospital wastewaters. The aim of this paper was to study the presence of 74 frequently used pharmaceuticals, legal and illegal drugs, and antibiotic-resistant bacteria in 5 hospital wastewaters in Slovakia and Czechia and to compare the efficiency of several advanced oxidations processes (AOPs) for sanitation and treatment of such highly polluted wastewaters. The occurrence of micropollutants and antibiotic-resistant bacteria was investigated by in-line SPE-LC-MS/MS technique and cultivation on antibiotic and antibiotic-free selective diagnostic media, respectively. The highest maximum concentrations were found for cotinine (6700 ng/L), bisoprolol (5200 ng/L), metoprolol (2600 ng/L), tramadol (2400 ng/L), sulfamethoxazole (1500 ng/L), and ranitidine (1400 ng/L). In the second part of the study, different advanced oxidation processes, modified Fenton reaction, ferrate(VI), and oxidation by boron-doped diamond electrode were tested in order to eliminate the abovementioned pollutants. Obtained results indicate that the modified Fenton reaction and application of boron-doped diamond electrode were able to eliminate almost the whole spectrum of selected micropollutants with efficiency higher than 90%. All studied methods achieved complete removal of the antibiotic-resistant bacteria present in hospital wastewaters.

Prevalence of antibiotic-resistant coliform bacteria, Enterococcus spp. and Staphylococcus spp. in wastewater sewerage biofilm.

OBJECTIVES: Urban wastewater contains various micropollutants and a high number of different micro-organisms. Some bacteria in wastewater can attach to surfaces and form biofilm, which gives bacteria an advantage in the fight against environmental stresses. This work focused on analysis of bacterial communities in biofilms isolated from influent and effluent sewerage of a wastewater treatment plant (WWTP) in Bratislava, Slovakia. METHODS: Detection of biofilm microbiota was performed by culture-independent and -dependent approaches. The composition of bacterial strains was detected by denaturing gradient gel electrophoresis fingerprinting coupled with construction of 16S rRNA clone libraries. Analysis of the concentration of antibiotics and the prevalence of antibiotic-resistant coliforms, Enterococcus spp. and Staphylococcus spp. in sewerage was also studied. RESULTS: Biofilm collected at the inlet point was characterised primarily by the presence of Pseudomonas spp., Acinetobacter spp. and Janthinobacterium spp. clones, whilst members of the genus Pseudomonas were largely detected in biofilm isolated in outflow of the WWTP. Predominant antibiotics such as azithromycin, clarithromycin and ciprofloxacin were found in influent wastewater. The removal efficiency of these antibiotics, notably azithromycin and clarithromycin, was 30% in most cases. CONCLUSION: The highest number of antibiotic-resistant bacteria, with a predominance of coliforms, was detected in samples of effluent biofilm. Multidrug-resistant strains in effluent biofilm showed very good biofilm-forming ability.