Microbial load of drinking water reservoir tributaries during extreme rainfall and runoff.

Hygienic and microbiological examinations of watercourses are usually not carried out during heavy rainfall and runoff events. After rainfall or snowmelt, there are often massive increases in turbidity in flooding creeks in mountain ranges, which are frequently interpreted as an indication of microbial contamination. The aim of this study was to quantify the microbial loads of watercourses during such runoff events and to compare these loads with loads occurring during regular conditions. In a 14-month monitoring period we investigated the microbial loads of three tributaries of different drinking water reservoirs. A total of 99 water samples were taken under different runoff conditions and analyzed to determine physical, chemical, bacterial, and parasitic parameters. Thirty-two water samples were considered event samples during nine measuring series. The criteria for events, based on duration and intensity of precipitation, water depth gauge measurements, and dynamics, had been fixed before the investigation for each creek individually. Of the physical and chemical parameters examined, only the turbidity, pH, and nitrate values differed clearly from the values obtained for regular samples. Most of the bacteriological parameters investigated (colony, Escherichia coli, coliform, fecal streptococcal, and Clostridium perfringens counts) increased considerably during extreme runoff events. If relevant sources of parasitic contamination occurred in catchment areas, the concentrations of Giardia and Cryptosporidium rose significantly during events. The results show that substantial shares of the total microbial loads in watercourses and in drinking water reservoirs result from rainfall and extreme runoff events. Consequently, regular samples are considered inadequate for representing the microbial contamination of watercourse systems. The procedures for raw water surveillance in the context of multiple-barrier protection and risk assessment ought to include sampling during extreme runoff situations.

Dental units: an environmental study of sources of potentially pathogenic mycobacteria.

SETTING: Infections caused by non-tuberculous mycobacteria (NTM) are generally thought to be acquired from environmental sources. However, little is known about the situations in which transmission occurs. OBJECTIVE: In an attempt to identify situations of relevant contact with NTM we investigated the water to which patients are exposed during dental treatment. DESIGN: The concentration and species of NTM were determined in 43 cooling and spray water samples from 21 dental units in ten offices. In addition, mycobacterial colonization of 16 biofilm samples from the waterlines of two dental units was investigated. RESULTS: The mean NTM concentration in the water samples was 365 colony-forming units (cfu) per mL, exceeding the mean drinking water concentration by a factor of almost 400. In the biofilm samples the mean NTM density amounted to 1165 cfu/cm2. The species identified included Mycobacterium gordonae, M. flavescens, M. chelonae, 'M. chelonae-like organism' and M. simiae. CONCLUSION: High numbers of NTM may be swallowed, inhaled or inoculated into oral wounds during dental treatment, possibly resulting in colonization, sensitization or infection. Mycobacterial proliferation in biofilms forming within dental units may explain the extent of NTM contamination of dental spray and cooling water.

Occurrence of mycobacteria in biofilm samples.

The occurrence of mycobacteria was studied in 50 biofilm samples from water treatment plants, domestic water supply systems and aquaria. Mycobacteria were found in 90% of the samples and their densities usually ranged between 10(3) and 10(4) cfu/cm2 (maximum density 5.6 x 10(6) cfu/cm2). Organic substances such as plastics and rubber were usually colonized by larger numbers of mycobacteria than inorganic substances such as copper and glass. The highest mycobacterial densities were found on plastic surfaces which were continuously perfused with water at temperatures between 22 and 30 degrees C. The species identified include Mycobacterium chelonae, M. flavescens, M. fortuitum, M. gordonae, M. kansasii, and M. terrae/nonchromogenicum. The occurrence in microcolonies indicate that biofilms may be an important replication site of aquatic mycobacteria.

Occurrence of mycobacteria in drinking water samples.

33 ground water samples from three drinking water treatment plants and 72 samples from domestic drinking water distribution systems were studied for the occurrence of mycobacteria. 86 out of these samples tested positive for mycobacteria with concentrations generally ranging between 10(2) and 10(3) cfu/l. In one distribution system up to 4.5 x 10(5) cfu/l were found. Species identified by biochemical reactions and by thin layer chromatography of mycolic acids included: Mycobacterium gordonae (most water samples), M. flavescens, M. kansasii, M. chelonae (domestic water systems) and M. fortuitum (drinking water treatment plant). Most isolates did not show patterns of biochemical reactivity attributable to any known mycobacterial species.

Mycobacteria in biofilms.

The objective of this study was to elucidate the role of biofilms as the habitat of aquatic mycobacteria. Investigations were carried out on a biofilm which grew on the inner surface of a silicone tube constantly perfused by water of a distribution system known to be contaminated with Mycobacterium kansasii and M. flavescens. The biofilm yielded 2 x 10(5) cfu/cm2 of M. kansasii and 7 x 10(4) cfu/cm2 of M. flavescens after 10 months of perfusion. Microscopic examination revealed that approximately 1/4 to 1/3 of the biofilm organisms visualized by the Ziehl-Neelsen procedure were acid-fast bacteria, most of which occurred in densely packed microcolonies. These findings indicate that biofilms are an important habitat and site for proliferation of aquatic mycobacteria. Biofilms may be an explanation for the problems of controlling mycobacterial contamination of water distribution systems by means of chemical disinfection.