Effects of Chlorine Stress on Pseudomonas aeruginosa Biofilm and Analysis of Related Gene Expressions.

Chlorine is deployed worldwide to clean waters and prevent water-originated illnesses. However, chlorine has a limited disinfection capacity against biofilms. Microorganisms form biofilms to protect themselves from biological threats such as disinfectant chemicals. Pseudomonas aeruginosa is an opportunistic pathogen and its biofilm form attaches to surfaces, living buried into exopolysaccharides, can be present in all watery environments including tap water and drinking water. This research aimed to study the biofilm trigger mechanism of the opportunistic pathogen P. aeruginosa PAO1 strain, which is known to form biofilm in water supply systems and human body, under chlorine stress levels. In addition to biofilm staining, certain genes that are relevant to the stress condition were selected for gene expression analysis. The bacteria cultures were grown under chlorine stress with concentrations of 0.5, 0.7 and 1 mg/l. Six gene regions were determined related to biofilm and stress response: rpoS, bifA, migA, katB, soxR, and algC. Biofilm formation was analyzed by basic fuchsin staining, and gene expressions were quantified by quantitative real-time PCR. According to the results, highest biofilm production was observed in P. aeruginosa PAO1 wild strain under no stress conditions. Higher biofilm amounts were observed for bacteria under 0.5 and 0.7 mg/l chlorine stress compared to 1 mg/l chlorine stress.

Inactivation of Escherichia coli and Staphylococcus aureus by ultrasound.

OBJECTIVES: The aim of this study was to obtain valuable information about the effect of ultrasonic irradiation with a frequency of 30 kHz frequency and power of 100 W on the inactivation capability of two bacterial groups, namely, Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923, in physiologic water samples. METHODS: Ultrasonic irradiation of bacterial samples with different populations of 5 × 10(3), 1.5 × 10(4), and 3 × 10(4) colony-forming units/mL was performed at a constant frequency with various treatment times. The specific energy (γ) values were calculated for these different concentrations of E coli and S aureus. The rate constant for ultrasonic inactivation was estimated in the linear region of a plot representing a survival ratio logarithm versus sonication time. RESULTS: Although a significant death rate for E coli was observed with ultrasound treatment, in contrary to expectations, an increase in S aureus populations was observed. CONCLUSIONS: Considering the widespread use of ultrasound for sterilization of tools and equipment used in hospitals, the results obtained in this study indicate that ultrasonic irradiation is not a suitable method for the elimination of the major hospital pathogen S aureus.

Effects of pulsed ultrasound on Escherichia coli and Staphylococcus aureus.

BACKGROUND: Common disinfection methods like biocides, ultraviolet light and heat treatment are not efficient enough to succeed in bacterial inactivation for some microorganisms have become resistant to them. The aim of this study was to obtain information about the effect of pulsed ultrasound sonication with 30 kHz frequency and 100 W power on the inactivation capability of two bacteria groups, namely Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923, in physiological water samples. METHODS: The ultrasonic irradiation of bacterial samples with different populations of 5×10(3), 1.5×10(4) and 3×10(4) cfu/ml was performed at constant frequency with various treatment times. The specific energies (γ) were calculated for these different concentrations of E. coli and S. aureus. The rate constant of ultrasonic inactivation was estimated in the linear region of the plot representing survival ratio logarithm vs sonication time. RESULTS: While a significant death rate for E. coli was observed by ultrasonic treatment, contrary to expectation, an increase in S. aureus populations was observed. CONCLUSIONS: Considering the widespread use of ultrasound for the sterilization of tools and equipment used in hospitals, the obtained results indicate that ultrasound sonication is not a suitable method for the elimination of S. aureus, a major hospital pathogen.