HETEROGENEITY OF STAPHYLOCOCCI AND OTHER BACTERIA ISOLATED FROM 6-WEEK-OLD BROILER-CHICKENS

In broiler operations, various health problems develop during the fina l 2 wk of the growing period, resulting in increased mortality and con demnation losses. At this stage, sickly birds were found to be systemi cally infected by various bacteria regardless of varied clinical signs , and the purpose of this study was to carry out thorough microbiologi cal investigations on this problem. Thirty-one 6-wk-old broilers showi ng signs of illness were obtained from three farms, and bacterial isol ations were carried out from the blood, Liver, and hock joint. Bacteri a were isolated from 87, 90, and 71% of the blood, liver, and hock joi nt samples, respectively. Mean bacterial counts in log(10) of the bloo d (per milliliter) and liver (per gram) were 2.15 and 2.93, respective ly. Among 132 bacterial isolates, major species were Staphylococcus (6 0%), Corynebacterium (18%), Escherichia coli (5%), and Stomatococcus ( 4%). Among 79 Staphylococcus isolates, 77 were coagulase-negative. Maj or species of staphylococci were S. lentus (19%), S. simulans (18%), S , cohnii (13%), S. gallinarum (10%), and S. captis (7%). in addition, six species of Gram-positive and five species of Gram-negative organis ms were isolated. Thus, the apparent systemic infections were not caus ed by predominant pathogenic bacterial species, and adequately describ ed as mixed infections. There were some significant relationships betw een isolated bacterial species and sampling sites, suggesting that cer tain organisms were abundant in the environment of a particular poultr y house. These results indicate that systemic infections in market age broilers are caused by mixed bacterial species and suggest that they are caused by suppressed host antibacterial systems rather than pathog enic factors of microorganisms.