Research Note: Bacterial composition of settled dust during growout of broiler chickens

Dust present in poultry houses can disseminate bacteria in air and deposit them on surfaces. This study evaluated bacteria in settled dust during growout of broilers from 2 flocks (Flocks A and B). Dust samples for bacteria analyses were obtained during 6 wk of growout (Flocks A and B) and 1 wk after flock termination (Flock B) by environmental swabbing and collecting dust in petri dishes from multiple locations inside the poultry house. For weekly swabbing, dust deposited during each wk of the sampling period (noncumulatively, n = 12/wk) and cumulatively (n = 12/wk) throughout the sampling period was collected. Swabbed dust samples were analyzed for counts (log₁₀ CFU/28 cm²) of aerobic bacteria, E. coli, coliforms, and Salmonella recovery. For petri dish dust collection, dust was collected in weekly and bi-weekly time spans during the sampling period and then analyzed for Salmonella recovery. Data were analyzed by one-way ANOVA and Fisher's Exact Test and means were separated using LSD. Only aerobic plate counts changed over time in dust during growout (Flocks A and B; P < 0.0001). In noncumulatively settled dust, aerobic bacteria (Flocks A and B; P < 0.0001), E. coli (Flock A; P = 0.0432), and coliforms (Flock B; P = 0.0303) varied during growout with peak counts on wk 5 or wk 6, wk 4, and wk 4, respectively, after bird placement. Salmonella recovery did not vary in cumulatively (3/72, 10/84) and noncumulatively (0/12, 10/84) settled dust during growout in both flocks. In dust sampled by bi-weekly collection in petri dishes, Salmonella recovery was highest (5/6) between wk 2 to wk 4 for Flock B (P = 0.0118). Overall, this study displayed that settled dust bacteria levels can fluctuate during broiler growout, and dust can contain Salmonella.