Comparison of nine brands of membrane filter and the most-probable-number methods for total coliform enumeration in sewage-contaminated drinking water

Analysis of Environmental and Pathogenic Bacteria Attached to Aerosol Particles Size-Separated with a Metal Mesh Device

Metal mesh devices (MMDs) are novel materials that enable the precise separation of particles by size. Structurally, MMDs consist of a periodic arrangement of square apertures of characteristic shapes and sizes on a thin nickel membrane. The present study describes the separation of aerosol particles using palm-top-size collection devices equipped with three types of MMDs differing in pore size. Aerosols were collected at a farm located in the suburbs of Nairobi, Kenya; aerosol particles were isolated, and pathogenic bacteria were identified in this microflora by next-generation sequencing analysis. The composition of the microflora in aerosol particles was found to depend on particle size. Gene fragments were obtained from the collected aerosols by PCR using primers specific for the genus Mycobacterium. This analysis showed that Mycobacterium obuense, a non-tuberculous species of mycobacteria that causes lung diseases, was present in these aerosols. These findings showed that application of this MMD analytical protocol to aerosol particles can facilitate the investigation of airborne pathogenic bacteria.

Atmospheric movement of microorganisms in clouds of desert dust and implications for human health

Billions of tons of desert dust move through the atmosphere each year. The primary source regions, which include the Sahara and Sahel regions of North Africa and the Gobi and Takla Makan regions of Asia, are capable of dispersing significant quantities of desert dust across the traditionally viewed oceanic barriers. While a considerable amount of research by scientists has addressed atmospheric pathways and aerosol chemistry, very few studies to determine the numbers and types of microorganisms transported within these desert dust clouds and the roles that they may play in human health have been conducted. This review is a summary of the current state of knowledge of desert dust microbiology and the health impact that desert dust and its microbial constituents may have in downwind environments both close to and far from their sources.

New screening test to determine the acceptability of 0.45-micron membrane filters for analysis of water

During routine membrane filter (MF) quality control testing, irregularities such as partial or complete inhibition of microbial growth at grid lines, abnormal spreading of colonies, growth in or along the grid lines, nonwetting areas, poor colony sheen and metallic sheen on the MF surface with mEndo agar, brittleness, decreased recovery, and severe wrinkling were observed with several lots of filters. To study these effects and to develop a more sensitive screening test for MF quality, we compared five different MFs with various types and degrees of defects by using five stock coliform cultures and five different media. Results showed that the Enterobacter aerogenes-tryptic soy agar test system detected more MF defects than any other combination did and was superior to the Escherichia coli-mFC agar American Society for Testing and Materials method for grid line inhibition. Filtered natural samples grown on the same media showed the same effects as were observed with the pure cultures. Poor colony sheen and sheen on the MF surface were best detected with Enterobacter aerogenes on mEndo agar. The use of tryptic soy agar and mEndo agar with this organism permitted the maximum detection of MF irregularities. Of the 142 MF lots tested by this method, 30% were acceptable, 10% were marginally acceptable, and 61% were unacceptable. This method provides a valuable screening test for determining the acceptability of 0.45-microm-pore-size MFs used for coliform and heterotroph analysis and may also be useful in conjunction with other methods.

[Growth kinetics of Escherichia coli and Saccharomyces cerevisiae cultured on membrane filters]

The growth kinetics of Escherichia coli and Saccharomyces cerevisiae cultivated on Millipore membrane filters (MF) was studied. Exponential growth kinetics was observed for both microorganisms, but in the case of E. coli cultivated on 0.8 micron and 1.2 micron MF, a decrease in the growth rate compared to that observed in liquid medium was noted. On the other hand, S. cerevisiae was unable to grow on a MF belonging to some batches, whereas E. coli showed normal behavior towards these MF. These data underline the importance of the effect upon growth kinetics of the relative cell size proportionally to the size of the MF pores.

Improved bacterial recovery by membrane filters in the presence of food debris

In the absence of food debris, m-FC agar counts of Escherichia coli on Oxoid Nuflow membrane filters (Oxoid Canada Inc., Nepean, Ontario, Canada) were lower than the corresponding surface plate counts. For seven food types tested, recovery of E. coli improved with increasing thickness of food debris on the membrane filter, and mats thicker than 0.5 micron protected the organism completely.

The enumeration of Bacteroides fragilis group organisms from sewage and natural waters

A membrane filtration technique has been developed for the enumeration of Bacteroides fragilis group (BFG) organisms from sewage and natural waters. The method uses the agar medium of Wilkins and Chalgren supplemented with gentamicin, penicillin, aesculin and ferric ammonium citrate. Membrane filters with 0.22 micron pores were significantly more efficient than those with 0.45 micron pores in the isolation of BFG. A preliminary incubation period of 4 h at 30 degrees C prior to 44 h at 37 degrees C yielded significantly higher numbers of BFG than direct incubation at 37 degrees C for 48 h.

Influence of diluents, media, and membrane filters on detection fo injured waterborne coliform bacteria

Pure cultures of Escherichia coli, Klebsiella pneumoniae, Enterobacter aerogenes, and Citrobacter freundii were injured ( greater than 90%) in water from a dead-end section of the Bozeman, Montana, distribution system. The effects of the following laboratory variables on the enumeration efficiency of injured and undamaged control cells were examined: (i) diluent composition, temperature, and time of exposure; (ii) media, using various formulations employed in enumerating gram-negative bacteria; and (iii) surface pore morphology of membrane filters. The addition of peptone or milk solids to diluents and low temperature (4 degrees C) maximized the recovery of injured cells, but had little effect on undamaged cells. Control cells were recovered with high efficiencies on most media tested, but recoveries of injured cells ranged from 0 to near 100%. Most of the media commonly used in water analysis recovered less than 30% of injured cells. This was explained in part by the sensitivity of injured bacteria to deoxycholate concentrations greater than 0.01%, whereas control cells were unaffected by 0.1%. Membrane filter surface pore morphology (at 35 degrees C) had a negligible effect on total coliform recoveries. Recommendations are made regarding procedures to improve the recovery of injured coliforms by routine laboratory practices.