Abstract
Background: Fresh animal feces and farm manure seem to be a reservoir of various Acinetobacter spp., but detailed studies on factors conditioning the presence and abundance of acinetobacters in such environments are missing. Here, we assessed Acinetobacter abundance in cattle feces in relation to the in-farm antibiotic use and other farm- and cow-specific factors. Methods: Cattle feces were sampled in 28 Czech farms (both dairy and beef) with contrasting antibiotic use. Either fresh fecal samples were taken from individual cows (from rectum or at the moment of defecation), or mixed fecal samples (~several hours old) were collected on the farm floor. Total DNA was extracted from feces using DNeasy PowerSoil kit and the abundance of Acinetobacter was measured using qPCR with Acinetobacter-genus specific primers, targeting the 16S rRNA genes.
Results: In fresh feces from individual cows (n=94), the maximum absolute abundance of Acinetobacter was 5.69E+09 16S rRNA copies/g dry weight, corresponding to approx. 2% of total bacteria. About half of the fresh fecal samples remained below the limit of detection (~ 1E+06 copies/g dry weight). In mixed fecal samples from farm floor (n=28), the maximum and average abundance of Acinetobacter were 3.47E+10 and 4.33E+09 16S copies/g dry weight (7 and 1% of total bacteria), respectively. Statistical comparisons showed significantly higher Acinetobacter abundance in floor samples when compared to per-farm mean values from individual cows. Further comparisons of Acinetobacter abundance between bio vs. conventional farms, dairy vs. beef farms, and indoor vs. outdoor stabling did not reveal any significant differences. Correlation tests did not indicate any relationship between Acinetobacter abundance and onfarm antibiotic use, size of herd, cow age, sample pH, and sampling temperature. Conclusions: Acinetobacters seem to proliferate in feces deposited on farm floor, perhaps due to their higher competitiveness at lower temperatures and higher oxygen levels, as compared to the intestine conditions. Other underlying factors behind Acinetobacter abundance in cattle feces remain unknown. Further analyses of chemical composition of cattle feces as other explanatory factors are ongoing.