Indoor air bacterial and fungi bioburden in an electronic factory, an office and a winery in Malaysia

Background: Microbial loads differ for different work environments and it is greatly influenced by the manufacturing processes involved. Objectives: This study aimed to assess microbial loads and other indoor air quality parameters in selected work environments in Malaysia. Methods: This is a cross-sectional survey carried out in an electronic factory, a winery and an office. Six sampling events were performed at all the study sites. Trypticase soy agar (TSA) (with ambient air incubation) and TSA supplemented with haemin and NADH (with CO 2 enhanced incubation) were used to isolate the non-fastidious and fastidious groups of bacteria respectively. The plates were incubated at 37C for 3 days. Sabouraud’s dextrose agar (SDA) and dichloran glycerol agar (DG-18) were used to isolate the non-xerophilic and xerophilic groups of fungi respectively. The colonies were counted and the concentrations of airborne micro-organisms were calculated as CFU/m (colony forming units per cubic meter). Results: Indoor microbial loads were generally greater indoors than outdoors at the three study sites. The electronic factory had the highest indoor microbial counts (in the order of 10 to 10 CFU/m of air). All readings at the office were below the recommended level of 500 CFU/m of air for offices by the Institute of Environmental Epidemiology, Singapore. The readings at the winery were also below 500 CFU/m of air except for the first sampling event which coincided with the peak of production winery. Furthermore, there were significant negative correlations (P < 0.05) between outdoor light intensity and microbial loads. Thus, substantiates the bactericidal effect of ultraviolet light. Conclusion: Indoor manufacturing processes are major contributors to microbial load in work environments. The presence of pathogenic micro-organisms might be potential hazard indoors; high microbial loads could therefore indicate a need for further screening. Hence, having standards for indoor microbial loads at different work environment is worthwhile.