The effect of doxycycline on the microbial composition of chicken manure

The use of antibiotics during treatment of infectious diseases of chickens causes the release of their residues with manure and entry into the environment, which creates a risk of antibiotic resistance pathogenic and conditionally pathogenic microorganisms and violates the microbiocenosis of the digestive system of chickens. The purpose of research was to determine the effect of doxycycline as one of the most common antibiotics used in poultry on the microbial composition of chicken manure. Ingestion of doxycycline solution to the laying hens in therapeutic doses for 7 days caused a decrease of the number of gram-negative rodshaped bacteria, which include most strains of E. coli, by 43.5 %. The use of an aqueous solution of doxycycline to laying hens at therapeutic concentrations caused a 5.2-fold decrease of the number of Citrobacter colonies and a 4.4-fold decrease in Proteus mirabilis colonies in the laying hens manure, indicating a certain sensitivity of these microorganisms to doxycycline. Doxycycline at therapeutic concentrations did not affect to the number of microorganisms of the enterobacteria family: Klebsiella, Enterobacter and E. Faecalis, which were not sensitive to doxycycline. The effect of doxycycline in therapeutic concentration on the number of Staphylococcus in the chickens manure, including the opportunistic S. epidermidis, and the pathogenic species S. aureus, has not been established either. After stopping the use of doxycycline in the therapeutic concentration to the chickens of industrial herd on day 10, it was found that the number of E. coli bacteria in the manure was restored almost to the level of the control group. Microorganisms belonging to the genus Klebsiella, their numbers in the chickens manure 10 days after cessation of use of doxycycline in therapeutic concentration, recovered 4 times slower than the control.