Christina Rohlik

Project title: Characterization of Bioaerosols and Bacterial Surface Contamination at a Large Washington Dairy Operation

Degree: MS | Program: Environmental Health (EH) | Project type: Thesis/Dissertation
Completed in: 2009 | Faculty advisor: John Meschke


Cattle are a source of potentially pathogenic bacteria including E.coli, Salmonella, and Campylobacter. These fecally shed bacteria may persist and be widely distributed in the CAFO environment. This project sampled and characterized the microbiology of bioaerosols and contaminated surfaces at a large dairy CAFO in eastern Washington. Bioaerosols were sampled in multiple freestall feeding barns using the swirling impingers and single- and multi-stage impactors. Andersen six-stage impactors were used with general and selective media to evaluate the distribution of culturable microorganisms based on the aerodynamic diameter of captured bioaerosols. Culturable aerobic bacteria were observed at each size fraction examined, ~ 10³ CFU/m³. Single-stage impactor results showed that median concentrations of total culturable aerobic bacteria and gram-negative bacteria were 1.24 X 10³ CFU/m³ and 70 CFU/m³, respectively. Bioaerosol samples collected using swirling impingers were extracted for PCR and metagenomic analysis. These swirling impinger samples were also tested for endotoxin levels and results showed a median concentration of 2.38 X 10³ EU/m³ over six sampling trips. Contamination on surfaces was widespread as detected by contact plate and swab methods. Various surfaces were sampled throughout the CAFO including gates and apparel. Results showed that the median concentration of culturable bacteria on apparel was 2.02 CFU/cm² using the contact plate method with nutrient agar, while swab sampling of apparel yielded median concentrations of 63 CFU/cm² on nutrient agar and 1.18 X 10² CFU/cm² on MacConkey agar. Bacterial counts from gate counts were to numerous to count for total aerobic bacteria and 0.229 CFU/cm² for MacConkey agar using the contact plates. Presumptive detection of E. coli and Salmonella was recurrent in both bioaerosol and surface samples, while Campylobacter was infrequently observed in bioaerosols.