Except in the case of abscesses and certain skin infections, early studies of staphylococci furnished no definite information concerning their relation to disease. The term "skin cocci," used to designate albus varieties found in the skin, was in common use and even today persists in such trinomials as "Staphylococcus epidermidis albus." On the other hand, it was recognized early that cultures from pyogenic foci usually revealed pigmented types. This gave rise to a separation of the species into varieties based on their pigment production. It was generally considered that the white strains were not pathogenic. In this paper we will outline methods which we consider of value for the differentiation of pathogenic from non-pathogenic staphylococci. Many authors have shown that Staph. albus, and many of the intermediate-colored varieties, could be derived from Staph. aureus. Pinner and Voldrich (1932) also demonstrated that, of the strains which they examined, the yellow were more pathogenic than the white. Duran-Reynals (1933) showed that the albus variants differed from aureus parent strains in hemolysin production and the liquefaction of gelatin. He also found that all the very invasive strains were of the aureus variety while about 82 per cent of his non-invasive strains were of the albus variety. While a number of investigators have studied the pathogenicity of staphylococci, the results have been somewhat confusing as the following survey of the literature will demonstrate.
Rapid bacteriological study of food-poisoning outbreaks is essential for the prevention of recurrences. Direct application of the coagulase test, Chapman (1944a), to suspected foods and handlers has proved useful for rapid presumptive field investigation, Chapman and Domingo (1946), but the results must be confirmed by cultural methods. The in vivo demonstration of gastroenterotoxigenicity is desirable to add weight to the scientific evidence but it does not lend itself to routine testing of the numerous complaints of "food poisoning" received by health authorities and, because so many strains not associated with outbreaks also produce gastroenterotoxin, the results are not as conclusive as is generally thought [e.g., Fulton (1943) 1. For epidemiological purposes, therefore, a rapid, simple, highly reliable bacteriological procedure would be of inestimable value to the busy sanitarian. The development of such a method will be described here. No claim is made for identification of food-poisoning staphylococci "with certitude,'' indeed absolute accuracy is a biological rarity.Stone (1935) proposed a culture-medium technic by which food-poisoning staphylococci give a clear zone of gelatinolysis around the colonies on a special gelatin-agar medium. As originally applied the method proved to be nonspecific because many strains from outbreaks gave a negative reaction and many pathogenic and nonpathogenic strains from other sources produced considerable zoning. Later, Stone (1938) maintained that, if the test is applied promptly after isolation, nearly all implicated staphylococci show this zoning. Chapman, Lieb, and Cnrcio (1937) pointed out that the reaction is applicable only to pigmented strains. They found that, in addition to the Stone reaction, typical f ood-poisoning staphylococci produce pigment, coagulate plasma, and ferment mannitol and have other properties that are characteristic of pathogenic staphylococci. Other investigators claimed that many f ood-poisoning staphylococci do not give these reactions but a survey of the literature, Chapman (1942), showed that about 95 per cent of the published results of these tests were positive. Most of the organisms that were reported as negative were shown either to have had no established relation to the outbreak or t o have been tested by methods other than those specified. The more recent literature shows a similar high proportion of positive reactions to these tests, Chapman (1947a). I n a series of studies in which the Stone reaction was applied directly to an improved isolation medium [Chapman (1946a) and Chapman and Domingo (1946) ] all strains incriminated in local outbreaks showed considerable zoning in addition to producing pigment, coagulating blood, and 100
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