Isolation of antibiotic-resistant bacteria from the air plume downwind of a swine confined or concentrated animal feeding operation

Abstract

Objective: In this study we evaluated the levels of antibiotic- and multidrug-resistant bacteria in bioaerosols upwind, within, and downwind at locations 25 m, 50 m, 100 m, and 150 m from a swine confined animal feeding operation.

Design: We used Andersen two-stage samplers to collect bacterial samples, the replicate plate method to isolate organisms, and the Kirby-Bauer disk diffusion method to determine antibiotic resistance.

Results: The percentage of organisms resistant to at least two antibiotic classes and all four classes evaluated were, respectively, 2.1 and 3.0 times higher inside (n = 69) than upwind (n = 59) of the facility. Staphylococcus aureus was the most prevalent organism recovered. Concentrations of antibiotic-resistant S. aureus decreased with increasing distance from the facility. Using Fisher's exact methods, the change in distribution of antibiotic resistance profiles for each antibiotic was statistically significant (oxytetracycline, p = 0.010; tetracycline, p = 0.014; ampicillin, p = 0.007; erythromycin, p = 0.035); however, this relationship was not seen with lincomycin and penicillin (p > 0.05) . In addition, the levels of antibiotic-resistant S.aureus 25 m downwind were significantly greater than the levels from samples taken upwind from the facility for the same four antibiotics (p < 0.05) . The percentage of resistant group A streptococci and fecal coliform increased within the facility compared with upwind values for all antibiotics evaluated,except for lincomycin. The percentage of resistant total coliform organisms increased within the facility compared with upwind values for oxytetracycline and tetracycline.

Conclusions: Bacterial concentrations with multiple antibiotic resistances or multidrug resistance were recovered inside and outside to (at least) 150 m downwind of this facility at higher percentages than upwind. Bacterial concentrations with multiple antibiotic resistances were found within and downwind of the facility even after subtherapeutic antibiotics were discontinued. This could pose a potential human health effect for those who work within or live in close proximity to these facilities.

Figure 1

Estimated number of culturable multidrug-resistant bacteria located downwind of the facility. Triangles, cfu/m³ resistant to at least two classes of antibiotics [y = –612.25ln(x) + 3171.8]; diamonds, cfu/m³ resistant to all four classes of antibiotics [y = –98.936ln(x) + 528.33].