Isolation of Gram-negative Bacteria

Three different areas -hospital, food-handling establishments and human dwellings, were surveyed for pathogenic gram-negative bacteria carried on the cuticles of cockroaches. Fifty species of bacteria were identified from all cockroaches. Escherichia coli, Klebsiella pneumoniae, Citrobacter freundii and Enterobacter cloacae were the most frequently found. Pathogenic and potentially pathogenic bacteria represented 58% of all bacteria identified. The numbers of pathogenic and potentially pathogenic bacteria were similar in hospital areas and food-handling establishments, while, human dwellings possessed a poorer bacterial flora. E. coli, K. pneumoniae and E. cloacae were dominant species in hospital areas, while in food-handling establishments and human dwellings, E. coli, K. pneumoniae and C. freundii predominated. Therefore, cockroaches can play a role in bacterial transmission, due to the bacteria carried on their cuticles. SOUTHEAST ASIAN J TROP MED PUBLIC HEALTH 682 Vol 35 No. 3 September 2004 three types of areas around the building of the Faculty of Allied Health Science, Chulalongkorn University, Bangkok, Thailand. The areas studied were as follows. Hospital. Cockroaches were caught around the patient building and canteens of Chulalongkorn Hospital. Food-handling establishments. Insects were trapped around several canteens and restaurants at Siam Square. Human dwellings. Insects were usually caught in kitchens, bathrooms and toilets. Cockroaches were caught in food-baited pitfall traps. Traps were deposited at night, collected the next morning, and transported to the laboratory for further processing. Bacterial isolation and identification of enterobacteriaceae from external surfaces Trapped cockroaches were frozen at 0oC for 10 minutes. Each cockroach was collected in a sterile test tube and identified using standard taxonomic keys (Herms, 1950). After identification, 2 ml of sterile 0.85% normal saline was added to the tube and the cockroach was thoroughly shaken for 2 minutes. 0.01 ml of the wash was cultured on blood agar and MacConkey agar and incubated overnight at 37oC. Identification of gram-negative bacteria was achieved by use of standard methods (API System, bioMerieux, France).