Infectious Diseases

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Browsing Infectious Diseases by browse.metadata.advisor "Sampson, Samantha"

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    Survival and re-aerosolization in dust of mycobacterium smegmatis - a surrogate for mycobacterium tuberculosis
    (Stellenbosch : Stellenbosch University, 2017-03) Tshilombo, Kazadi Valéry; Warren, Rob; Sampson, Samantha; Mehtar, Shaheen; Stellenbosch University. Faculty of Medicine and Health Sciences. Centre for Infectious Diseases.
    ENGLISH SUMMARY : Background: Mycobacterium tuberculosis (M. tuberculosis) is essentially an airborne pathogen transmitted via aerosols. It remains viable in the soil and outside its hosts for extended periods of time. It has been suggested that M. tuberculosis cannot be re-aerosolized therefore it cannot cause disease once it has landed outside the body. This project aimed answering indirectly several questions relating to M. tuberculosis and the possibility of it being able to cause disease after re-aerosolization: Can M. tuberculosis be re-aerosolized? If it can, does M. tuberculosis remain viable? If it is viable, can it cause infection? Finally, can environmental bio-burden be reduced using copper surfaces? Methodology: This two-phased prospective in vitro study preceded by a pilot study used as surrogate for M. tuberculosis, Mycobacterium smegmatis (M. smegmatis), a fast growing, non-pathogenic mycobacterium. A completely sealed Plexiglas (Polymethyl methacrylate) cabinet was used as aerosol chamber where 125 mg of sterile dust was spread prior to nebulization of 20 ml of 106 CFU/ml of M. smegmatis pCHERRY3. The sampling was performed with a six stage Andersen cascade impactor (ACI) and settle plates before and after the dust lift-up using two small fans. Plates were incubated for three to ten days at 37 degrees Celsius. The numbers of CFU were estimated based on viable plate count. The first phase of the study, the Plexiglas phase, tested the survival of M. smegmatis in dust. The second phase evaluated the impact of copper surface on the survival of M. smegmatis in similar conditions. Results: M. smegmatis survived in dust for more than nineteen days on settle plates after re-aerosolization in the presence of Plexiglas. In copper presence, M. smegmatis survival rate was approximately fifteen days after nebulization in dust, almost 25% less than on Plexiglas. Starting with an inoculum of 106 cells/ml nebulized on Day 0, on Day 1 there were 44.01% lower numbers of M. smegmatis isolated in copper presence compared with Plexiglas surface 24 hours after nebulization. There was a significant decrease in the number of mycobacteria picked up from both copper (100%) and Plexiglas surfaces (35.02%) on Day 2; copper showed significantly lower levels of mycobacteria (p=<0.05). From Day 3 onwards there was no statistically significant difference in M. smegmatis survival between the two surfaces as determined by the ACI level A5 & A6 (0.6-2.1 micrometre) which equates to particle sizes that can reach the alveoli and terminal bronchi. Conclusion: M. smegmatis, the model for M. tuberculosis, survived in dust and remained viable after re-aerosolization more than 19 days on Plexiglas but 15 days on copper. This is particularly relevant in low to middle income countries with high M. tuberculosis burden, where dust is common and sweeping and the use of fans in health care facilities are frequent. It also illustrated that the anti-microbial property of copper surface remains effective in presence of dust. Copper can be used as a touch surface to reduce the bioburden of microbes including mycobacteria that could be re-aerosolized.