The relationships between Brucella melitensis predilection sites, bacterial loads in vivo, and the agglutinating antibody response in experimentally infected sheep

Abstract

For exploring Brucella melitensis survival in in vivo predilection sites and the relationship between bacterial loads and the detection of antibody titers in experimentally subcutaneously infected sheep with B. melitensis 16M, ten rams and ten ewes were used. One ram and one ewe were euthanized at 7, 15, 30, 60, 90, 120, and 180 days post inoculation (dpi). Bacteriological results showed that tissue isolation rates and bacterial loads peaked from 7 dpi to 30 dpi and then cleared until 120 dpi. In in situ hybridization trials the strongest signals for B. melitensis were detected at 7 dpi and 15 dpi, and then they gradually cleared. Monitoring results of agglutinating antibodies showed that anti-Brucella antibodies began to be produced at 7 dpi, peaked at 15 dpi, and gradually declined until lower detection levels than the threshold were being detected at 180 dpi. Thus, we found that the more Brucella bacterial loads there were in vivo, the higher the antibody titers were in sera, which suggested that detection of the agglutinating antibody titers might be used as an indicator of a Brucella carrier in infected animals.