Identification of Legionella in the Hot Water Supply of a General Hospital in Isfahan

Abstract

Background: Legionella is a gram negative, aerobic, and sporeless bacterium which is readily found in ventilation systems, cooling towers, hot water distribution systems, bathrooms, swimming pools, and fountains. Legionella is implicated in the legionnaires’ and Pontiac fever diseases. Hospitals are common habitats for the bacterium, where the bacterial growths are amply found and that provide the most likely places for susceptible people to contract the diseases. Given the importance of hospitals in this regard, this survey was carried out in a General Hospital in Isfahan. Methods: For the purposes of this study, a total of 30 samples were taken according to standard methods from hot water distribution system at various points in the kitchen, the bathrooms, the internal distribution system, and the cooling towers (8, 8, 8, and 6 samples, respectively). After that temperature, pH, and residual chlorine of samples were determined, the samples were transferred to lab where they were inoculated on a base medium of BCYE-a and two selective media of GPVA and CCVC. The plates were then incubated at a temperature of 37 °C and a humidity of 90%. The colonies were then identified and counted. Results: The tests showed that 11 from the total 30 samples were contaminated with Legionella, accounting for 36.6% of the samples. The numbers of Legionella positive samples from the kitchens, bathrooms, internal distribution system, and cooling tower were 4, 3, 3, and 1, respectively. From the total 30 heat and acid pretreated samples inoculated on base and selective media, 36.6% were Legionella positive while from the untreated samples, 6% grew on the base medium and 23% on selective media. Total mean of residual chlorine was 0.25 mg/l, pH= 7.6 , and average temperature was 31.1 °C. The results of biochemical tests Blood agar, Catalz, Urea agar, Gelatin agar, Motility, and gram staining were −, +, −, +, +, and −, respectively. In addition to these tests, Legionella colonies were grown by Direct Fluorescent Antibody, confirming their presence. Conclusion: The results indicate that temperature is a critical factor in Legionella sp.’s proliferation. An average 0.25 mg/l of residual chlorine showed to have no effect on disinfecting the bacterium. Heat pretreatment proved to be more effective than the acidic one in removing nuisance factors and, finally, bacterial growth was higher on the selective media than on the base medium.
Keywords: Legionella, water supply, hospital hot water.