The Effect of Overnight Refrigeration on the Results of the Bacteriological Examination of Farm Water Supplies

Abstract

About 20% of water samples examined 20 hr. after sampling, this period including 18 hr. storage at 3-5', had coli-aerogenes and Bact. coli contents significantly lowerlthan those determined after 2 hr. at air temperature. Samples with over 50 such organisms/100 ml. at the earlier testing time seldom showed an increased content after refrigeration overnight. The results of statistical analysis of the data confirmed the findings of other workers that coli-aerogenes bacteria are less abundant in samples of water stored before analysis. Colony counts at 37" and 22' did not reflect this reduction in numbers.THE effect of storage of samples on the content of coli-aerogenes bacteria in water has been studied by many workers since Houston (1911, 1913) reported a reduction in numbers during storage. Clemesha (1912) and Rogers (1917) analysed polluted water or water artificially polluted with faeces. They, and Winslow & Cohen (1918), Gray (1932), and Burke-Gaffney (1933) reported Bact. coli to be more liable to reduction on storage than members of the aerogenes-cloacae and intermediate groups.Platt (1935) confirmed this using pure strains at 18", but reported that Bact. coli was the more resistant at 0" and 37". Ruchhoft, Coulter, Adams & Sotier (1933) found that Bact. coli and Bact. aerogenes types died out during storage at similar rates. Other workers who have reported a diminution of coli-aerogenes bacteria after icing samples of water include Caldwell & Parr (1933) and Webster & Raghavachari (1935), but later Raghavachari & Iyer (1939) did not confirm this.Owing to the importance of these organisms in water this investigation was undertaken with the object of surveying the frequency and extent of the significant changes in numbers of presumptive coli-aerogenes bacteria and Bact. coli which occurred in samples of farm water supplies kept overnight in the refrigerator. EXPERIMENT& METHODSTreatment of samples. Fifty-two samples from farm water which arrived at the laboratory during the afternoon were examined within 2 hr. of sampling. The unused portions of about 400 ml. each were kept overnight in the refrigerator at 3-5" and tested next morning when 20 hr. old. The temperature of the samples dropped fiom 17+5" to 5" in 5&1& hr.Bacteriological examination of samples. On each sample the determinations made were : the presumptive coli-aerogenes content, the direct presumptive Bact. coldThe eflect of refrigeration on water analyses I09 content at 44", and the colony counts at 22" and 37" (in duplicate). The techniques prescribed by the Ministry of Health (1939) were used, except that additional 0.01 ml. portions of water were inoculated into MacConkey broth tubes at 37" and 44", thus making possible the determination of up to 18 x lo3 organisms/lOO ml. RESULTS Presumptive coli-aerogenes contentBuchanan -Wollaston (1941, 1942) showed that it was preferable to record changes in the number offertile tubes rather than in the ' most probable number ' of organisms calculated from Tables. Accordingly, the numbers of fertile tubes...

The Suitability of Farm Water Supplies for Dairy Purposes

“…Jones, Franklin & Thomas (1950) found that even when samples were stored a t 3-5" quite appreciable bacterial changes took place. Jones, Franklin & Thomas (1950) found that even when samples were stored a t 3-5" quite appreciable bacterial changes took place.…”

“…Samples for bacteriological examination should reach the laboratory as quickly as possible and preferably in less than 6 hr. Jones, Franklin & Thomas (1950) found that even when samples were stored a t 3-5" quite appreciable bacterial changes took place. More detailed investigation by the Public Health Laboratory Service (1953) supported this finding and showed that storage a t room temperature brought about even greater variation.…”

The Effect of Flaming of Taps Before Sampling on the Bacteriological Examination of Farm Water Supplies

“…A statistical treatment similar to that of Jones, Franklin & Thomas (1950) has been applied to the results. Tables 3 and 4 show a summary of the changes observed in the coli-aerogenes (37") content.…”