Delayed-incubation membrane-filter test for fecal coliforms.

A delayed-incubation membrane-filter technique for fecal coliforms was developed and compared with the immediate fecal coliform test described in Standard Methods for the Examination of Water and Wastewater (13th ed., 1971). Laboratory and field evaluations demonstrated that the delayed-incubation test, with the use of the proposed vitamin-free Casitone holding medium, produces fecal coliform counts which very closely approximate those from the immediate test, regardless of the source or type of fresh-water sample. Limited testing indicated that the method is not as effective when used with saline waters. The delayed-incubation membrane-filter test will be especially useful in survey monitoring or emergency situations when the standard immediate fecal coliform test cannot be performed at or near the sample site or when time and temperature limitations for water sample storage cannot be met. The procedure can also be used for analyzing the bacterial quality of water or waste discharges by a standardized procedure in a central examining laboratory remote from the sample source.

Comparison of the hydrophobic-grid membrane filter procedure and standard methods for coliform analysis of water.

The hydrophobic-grid membrane filter (HGMF) has been proposed as an alternate method to the standard membrane filter (MF) procedure for the detection and enumeration of coliforms from water. Eight samples of nonchlorinated wastewater effluents were analyzed by the HGMF, standard MF, and tube fermentation most-probable-number methods for fecal coliforms, and eight samples each of polluted surface and dosed drinking waters were analyzed by the same methods for total coliforms. The drinking waters were dosed with coliforms and other heterotrophs concentrated from nonchlorinated domestic wastewater and treated with chlorine to reduce the numbers of organisms and simulate stress caused by chlorination. Statistical analyses determined that recoveries of fecal coliforms were significantly higher by the filtration methods for the nonchlorinated domestic wastewaters but not for the other waters. The results also indicated that recoveries of fecal and total coliforms did not differ significantly when either MFs or HGMFs were used. Total coliform results obtained with HGMFs having greater than 100 positive grid cells were significantly more precise than estimates obtained by the standard MF method only for polluted surface waters.

Holding effects on coliform enumeration in drinking water samples.

Standard procedures for analyzing drinking water stress the need to adhere to the time and temperature conditions recommended for holding samples collected for microbiological testing. The National Drinking Water Laboratory Certification Program requires compliance with these holding limits, but some investigators have reported difficulties in meeting them. Research was conducted by standard analytical methods to determine if changes occurred when samples were held at 5 and 22 degrees C and analyzed at 0, 24, 30, and 48 h. Samples were analyzed for coliforms by the membrane filter and fermentation-tube procedures and for heterotrophs by the pour plate method. A total of 17 treated water samples were collected from a large municipal distribution system from August to December 1981, and 12 samples were collected from January to May 1983. The samples were dosed with coliforms previously isolated from the water system, Enterobacter cloacae in 1981 and Citrobacter freundii in 1983. The coliform counts declined linearly over time, and the rates of decline were significant at both 5 and 22 degrees C. Within 24 h at 22 degrees C, levels of E. cloacae and C. freundii decreased by 47 and 26%, respectively, and at 5 degrees C, E. cloacae numbers declined by 23%. Results from these representative laboratory-grown coliforms reinforced those previously obtained with naturally occurring coliforms under the same experimental conditions. Significantly, some samples with initially unacceptable counts (greater than 4/100 ml) met the safe drinking water limits after storage at 24 h at 5 and 22 degrees C and would have been classified as satisfactory.(ABSTRACT TRUNCATED AT 250 WORDS)