OBJECTIVE: Legionellae are free-living bacteria present in many types of water bodies. Legionella pneumophila can cause severe fatal pneumonia called Legionnaire’s disease. These bacteria are commonly transmitted through air coolers. To examine the distribution and characterization of pathogenic Legionellae isolates from different water sources.

MATERIALS AND METHODS: A sum of 500 water specimens (100 samples from each) was obtained from various water bodies in and around Jimma town, Ethiopia. Water specimens were treated with mild acidic solution, subsequently concentrated and cultured on Legionella selective BCYE agar medium. Criteria such as capacity of Legionellae to tolerate and produce growth in different pH optima, bactericidal effect of various levels of chlorine on Legionella isolates and lethal effects of divergent temperature conditions were framed. Legionella species distinctions were carried out using phenotypic (biotyping) tests. Legionella pathogenicity experiments on animal model and antibiotic susceptibility tests were performed on these bacterial isolates.

RESULTS: The prevalence and distribution of Legionellae in various types of water bodies were observed to be, wells (35%), lakes (30%), ponds (15%), water tanks (10%), and canals (10%). It was observed that many of the pathogenic Legionellae isolates can tolerate and multiply in a wide range of pH 5-9. Legionella can also withstand the usual concentration of chlorine in water bodies. Our experiments have also revealed that these bacteria can multiply at a variable range of temperature from 25 to 45˚C. The current study expressed that a total of 6 species of Legionella have been identified. Furthermore, it also suggested that L. pneumophila was identified more frequently than other species. Many isolated strains of Legionellae were also showing resistance to many commonly employed antibiotics. Instilling isolates of Legionella through intranasal route in guinea pigs proved that most of L. pneumophila strains were possessing high virulence followed by other species. Lethal and severe infections due to Legionellae can arise from the infection of these bacteria present in water bodies. These bacteria can tolerate and multiply in wide ranges of physicochemical conditions of water.

CONCLUSIONS: Among the isolated species, L. pneumophila was the dominant and highly pathogenic species. Moreover, many isolates of L. pneumophila expressed multiple resistances to antibiotics. In spite of rapid development of medical field, health officials face a huge task ahead to curb the morbidity and mortality due to Legionellae especially in developing countries.