INTRACELLULAR SURVIVAL OF BRUCELLA-ABORTUS, MYCOBACTERIUM-BOVIS BCG, SALMONELLA-DUBLIN, AND SALMONELLA-TYPHIMURIUM IN MACROPHAGES FROM CATTLE GENETICALLY RESISTANT TO BRUCELLA-ABORTUS

Peripheral blood monocyte-derived macrophages were obtained from a her d of cows selected, bred, and confirmed as resistant or susceptible by in vivo challenge of Brucella abortus Strain 2308, The ability to con trol in vitro intracellular bacterial replication of B. abortus Strain 2308, Mycobacterium bovis Bacillus Calmette-Guerin (BCG) Montreal Str ain 9003, Salmonella dublin Strain 5631, and Salmonella typhimurium St rain 14028 was evaluated in a bactericidal assay. The macrophages from resistant cattle were significantly superior (P < 0.05) in controllin g intracellular growth of B. abortus, M. bovis BCG, S. dublin but not of S. typhimurium than macrophages from susceptible animals, Controls of all four pathogens correlated strongly with each other in resistant or susceptible macrophages. Data from resistant cattle had a tighter grouping than that of susceptible cattle, while data from susceptible cattle overlapped considerably with data from resistant animals, ?Ther efore, this assay was considered a phenotypic marker of the resistant trait. For each bacterial species a percent bacterial survival value w as used as a cut-off point to designate animals as resistant or suscep tible. These data were compared with the in vivo challenged resistant or susceptible classification by using the Chi-square analyses. A cut- off point of 70% bacterial survival for B. abortus designated 14 cattl e as susceptible and seven as resistant and this correlated 100% with the number of animals designated as to the relevant category by in viv o challenge. A value of 65% bacterial survival for M. bovis BCG, and 1 00% bacterial survival for S. dublin correlated highly with actual num bers of animals designated as susceptible or resistant.