Evaluation of millipore HA and HC membrane filters for the enumeration of indicator bacteria

[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.

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.

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

Nine different brands of membrane filter were compared in the membrane filtration (MF) method, and those with the highest yields were compared against the most-probable-number (MPN) multiple-tube method for total coliform enumeration in simulated sewage-contaminated tap water. The water was chlorinated for 30 min to subject the organisms to stresses similar to those encountered during treatment and distribution of drinking water. Significant differences were observed among membranes in four of the six experiments, with two- to four-times-higher recoveries between the membranes at each extreme of recovery. When results from the membranes with the highest total coliform recovery rate were compared with the MPN results, the MF results were found significantly higher in one experiment and equivalent to the MPN results in the other five experiments. A comparison was made of the species enumerated by these methods; in general the two methods enumerated a similar spectrum of organisms, with some indication that the MF method was subject to greater interference by Aeromonas.

Comparison of the surface structure, metal binding, and fecal coliform recoveries of nine membrane filters

A comparative study was made of nine commonly used membrane filters from five manufacturers, all recommended for enumeration of coliform bacteria. Bacterial recoveries and flow rates were examined from three types of water and were found to correlate with the surface pore structure determined by scanning electron microscopy. The sorption of metals was also determined. The results of these studies indicate that the five best membranes for fecal coliform recovery could be placed in two groups: Millipore HC and Gelman, followed by Johns-Manville SG and AG and Sartorius 13806.