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Staphylococcal Mastitis in Alberta Dairy Herds

出版	University of Alberta, 1960
URL	http://books.google.com.hk/books?id=uRep0AEACAAJ&hl=&source=gbs_api

註釋Staphylococci were found to be of increasing importance as agents of bovine mastitis in Alberta dairy herds. Statistics from the files of the Provincial Dairy Laboratory, Edmonton, showed that the relative importance of staphylococci in the etiology of bovine mastitis had increased rapidly. In the Province of Alberta these organisms have now gained an importance equal to that of streptococci. The final diagnosis of staphylococcal mastitis is established, in the laboratory, ITicroscopic smear examin tion was found to be of the greatest diagnostic value. A n abnormal!v hi^h leucocyte count associated with a large number of staphylococci was considered suggestive of staphylococcal mastitis. The diagnosis was held to be confirmed if many of these staphylococci were phagocytized. Observations on eighty strains of staphylococci isolated as agents of acute mastitis included colonial morphology, production of hemolysins, fermentation of mannite, production of coagulase, phage type, and sensitivity to various antibiotics. Colonial morphology and nigment formation were found to be subject to gross variation and cannot be accepted as reliable criteria for the classification of staphylococci. Fermentation of lannite was observed in seventy-seven of the eighty strains. Most mastitis staphylococci seemed to be mannitol fermenters, but numerous staphylococcal strains isolated from normal udders were also able to ferment mannitol. Therefore, this character was not considered a reliable indication of pathogenicity. Seventy-three strains produced hemolysin, seven strains in this seri *s r ' 'e i-he stains of this sort are not mco in .gents of lastiti : produce e eras "ounl to suggest that the ability of a strain to hemolysin rnav be suppressed by some factor present in mastitic quarters, and may be potentiated by a diffusable product of alpha-streptococci. Of the eighty strains, eleven did not produce coagulase. Although the ability to produce coagulase may increase the pathogenic potential of a strain, pathogenicity is certainly not dependent upon this character. Coagulase negative strains can cause mastitis. The ability to produce coagulase, however, was found to be a fairly stable character and therefore the division of staphylococci into coagulase positive and coagulase negative strains is acceptable. The strains were typed by the Rippon and Williams phage system. Types 4-2 d and Si were of the highest frequency in mastitis. Observations tended to confirm the belief that the pattern of phage susceptibility is a persistant and dependable character of the staphylococcus, in vivo as well as in vitro. Types L2 d and Si were found to include both coagulase positive and coagulase negative strains. In some instances at least the phage type seemed to be more significant than coagulase production as an indicator of pathogenicity. It was observed that many staphylococci isolated as agents of mastitis were resistant to one or more antibiotics. Evidence suggested that this phenomenon was due to the emergence of resistant mutants. Irregular use and regular abuse of antibiotics in treatment initiated and carried out by the herd management were suggested reasons for this development. A mastitis control program was designed and carried out in two Alberta dairy herds in which major outbreaks of stanhylococcal mastitis had occurred. It was shown that the outbreaks in herd A originated mainly from negligence in herd management while in herd B the continuous misuse of antibiotics was considered a principal cause. The main steps in this urogram were: Instruction of personnel including an explanation of the character of the disease and its ament; elimination of predisposing factors; prevention of transmission; selection of treatment based on laboratory findings; rules for establishment of permanent herd hygiene. Excellent results with some promise of permanence were obtained. Those results suggest that the control of bovine mastitis is mainly a matter of good and effective herd management. Treatment with antibiotics should be considered a last resort and should be administered only by competent persons. Possible reasons for the increased importance of staphylococci were considered. The ubiquity and the high degree of variability of staphylococci were suggested as principal factors. T n these respects staphylococci were more effective agents of mastitis than It.rymtocoecus •agalactiae._ Finally, the necessity of revising conventional ideas on the control of bovine mastitis is emphasized. This is particularly necessarv on account of the current general use of mechanical milking which results in a heavy stress on the animals and makes them pecuniarily'- liable to infections with organisms such as staphylococci.