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To investigate the distribution of oligotrophic bacteria inhabiting hospital tap water, tap water samples were subjected to pour culture at 25℃ for 7 days using R2A agar medium. Bacteria were detected in 222 of 271 samples (81.9 %) collected nationwide, mainly in the Kanto district, revealing that oligotrophic bacteria are present at a very high frequency in hospital tap water. The distribution was investigated in relation to the geography or hospital management form, but no marked tendency was noted. The number of isolated oligotrophic bacteria varied from 1.0 × 10^0 CFU/ml to 2.8 × 10^4 CFU/ml among the samples, but the number was less than 1.0 × 10^1 CFU/ml in 54 samples accounting for the highest ratio (24.3 %). Of 538 oligotrophic isolates, 457 isolates (84.9 %) were gram-negative rods, and 108 isolates (23.6 %) were Methylobacterium, ranked the highest, followed by 71 isolates of Pseudomonas (15.5 %). However, identification of 274 isolates (60.0 %) was not possible. Gram-positive rods, Bacillus and Corynebacterium, and cocci, Micrococcus and Staphylococcus, were also isolated, although the frequencies were low. Based on these findings, the presence of oligotrophic bacteria which may cause opportunistic infections in tap water should be noted, when patients use tap water in hospitals, being susceptible to the infection. |
