Taxonomic studies of micrococci and staphylococci

Todd, Ewen Cameron David (1968) Taxonomic studies of micrococci and staphylococci. PhD thesis, University of Glasgow.

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In the course of 3 years, 274 strains of micrococci and staphylococci were isolated from a variety of habitats, and 132 strains were obtained as pure cultures, mainly from culture collections; this gave a total of 406 strains for taxonomic studies. All 406 strains were examined for a total of 49 morphological and physiological characters, and the strains were compared for characters in common. It would found that strains with practically all combinations of characters existed, from the coagulase positive, biochemically active staphylococci, through many intermediate groupings to the biochemically weak yellow and red micrococci; a classification scheme based on a few arbitrarily ohosen main characters, as is the tradition in this group of bacteria, would be entirely artificial. After discussing some of these main characters, and finding practically all of them unsuitable as important criteria for classifying the 406 strains of micrococci and staphylococci, I decided to adopt the Adansonian approach to classification, and treated 49 morphological and physiological character as being equal. As I expected, the results of this Adansonian classification demonstrated that there was no clear division of the 406 strains into 2 main groups, equivalent to the genera Microcccus and Staphylococous, but there was a division into very many small groupings, the majority of which contained only one strain. The most important conclusion drawn from this scheme was that all micrococcus and staphylococci should be placed into one genus - Micrococcus, and it seemed unlikely that further division of this genus into natural groupings by morphological and physiological characters was possible. Consequently, other characters, in particular those demonstrated by electrophoretic methods, were examined for their suitability in classification. I studied the isozyme bands, detected by specific colour reactions in acrylamide gol slices, which contained electrophoresed cell contents of the 406 micrococcal and staphylococcal bacterial strains, and I found that only 3 types of isozymes - esterase isozymes, used in classifications of other bacteria, and 2 previously unreported isozyme systems, blood band isozymes and starch hydrolysing isozymes - were of use in classifying' my strains. These strains showed great variety in the number and mobility of the isozyme bands; the strains produced between 0 and 6 of 87 esterase bands between 0 and 7 of 40 blood bands, and between 0 and 3 of 12 starch hydrolysing isozyme bands. With the 139 electrophoretic characters of these 3 isozyme systems, the 406 strains were classified by Adansonian means, and it was found that all but 2 of the strains fell into a large group, the genus Micrococcus and within this genus it was possible to detect natural groupings - 28 Micrococcus Groups. In addition, there were 2 other Electrophoretic Groups (25 and 30), which possessed electrophoretic characters, completely unrelated to the other Electrophoretic Groups, and these were excluded from the genus Micrococcus. The electrophoretic grouping does not compare well with my own Scheme 1, and published morphological and physiological classifications, but it does fit in closely with DAN base ratio analysis groupings. The classification scheme of micrococci and staphylococci, based on eleotrophoretic characters, seems to have certain advantages over schemes based on morphological and physiological characters, since electrophoretic analysis clearly shows the existence of natural groupings within one large group. Taxonomists have not been previously aware of the existence of Groups like Micrococcus Group 3, which, apart from a unique electrophoretic pattern of characters, contains strains which oxidise and ferment mannitol, and yet are coagulase negative. An important contribution to the taxonomy of micrococci and staphylococci has been made by the creation of the electrophoretic classification scheme since 1) coagulaso positive staphylococci have been shown to be closely related to certain coagulase negative strains (strains of Micrococcus Group 1). In addition, strains of Micrococci and staphylococci, other than those producing coagulase, have been shown to cause disease. The character of coagulase production, therefore, can no longer be regarded as the sole criterion for classifying, a unique group of pathogenic staphylococci, although it is a useful identification character. 2) the yellow and red pigmented biochemically weak micrococci - Electrophoretic Micrococcus Groups 24 and 27 respectively - have been classified on positive characters i.e. on electrophoretic characters which the strains possess, instead of the almost complete lack of physiological characters, except pigmentation, which have been previously used to classify these organisms. An identification scheme, based on the electrophoretic classification scheme, is proposed which would identify any unknown micrococcus or staphylococcus.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: J W Howie
Keywords: Microbiology
Date of Award: 1968
Depositing User: Enlighten Team
Unique ID: glathesis:1968-72775
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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