A study of wall-defective variants of enterobacteriaceae and streptococci

Brogan, Oonagh (1987) A study of wall-defective variants of enterobacteriaceae and streptococci. MD thesis, University of Glasgow.

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The growth requirements of wall-defective microbial variants were studied to devise improved culture media for these interesting organisms The isolates from the new media were classified as vegetative bacteria or as microbial variants of the transitional or classical L-phase variant types on the basis of their morphological and cultural characteristics From a consideration of their nature and the clinical circumstances at the time of isolation, most of the variants were presumed to be significant pathogens Some of the more important features of these variants and the infections they caused may be summarised as follows Wall-defective Enterobacteriaceae variants Classical L-phase variants obtained from Escherichia coli by lysozyme induction in the laboratory were grown in osmotically stabilised agar-free broth without nutritional enrichment and maintained by subculture in soft agar, but attempts to isolate naturally occurring wall-defective microbial variants from blood cultures using the same methods were singularly unsuccessful However, wall-defective microbial variants were recovered quite readily from blood cultures by the use of an osmotically stabilised nutritionally enriched medium Despite the apparent success of this medium, it behaved somewhat erratically from batch to batch due to changes in its nutritional qualities These changes seemed to be related to a requirement for a folate metabolite supplied by a folic acid/pABA/cytosine mixture From a consideration of the laboratory characteristics of the above wall-defective Enterobacteriaceae variants and the antibiotic therapy of their associated infections, a number of interesting conclusions may be drawn First, reverted wall-defective variants were not only more often sulphonamide-resistant than vegetative bacteria, but there was a positive correlation between prior therapy with folic acid or the folic anologue sulphonamide and the development of infection These findings support the view that pABA or folic acid is a required metabolite Second, although the number of cases is small, the evidence suggests that infections with wall-defective variants may be more refractory to antibiotic therapy than vegetative infections This conclusion is based on the observation that such infections required treatment with additional antibiotics rather than with aminoglycoside alone Third, there is no evidence from the present studies that wall-defective microbial variants are induced in vivo by prior beta-lactam therapy Wall-defective streptococcal variants Wall-defective forms of viridans streptococcai are known to be auxotrophs with differing nutritional requirements but most are dependent on vitamin B6 (pyridoxine) and a sulphydryl moiety which may be supplied as thioglycollate or cysteine Two of the more outstanding features of the streptococcal variants are their diphtheroid morphology and growth in satellitism The latter is a symbiotic type of growth around colonies of another organism which supplies the required growth factor to the nutritionally defective streptococcus This phenomenon can make it possible to isolate variants of this type without the use of media containing specific nutritional supplements In this study the satellitism method was used for subcultures made from a simple primary culture medium and this was compared first, with the use of a freshly prepared, nutritionally rich primary culture medium and then with a biphasic medium Subcultures from these two media did not involve the use of the satellitism method Finally, a primary culture medium supplemented with vitamin B6 and cysteine was compared directly with sin osmotically stabilised primary culture medium supplemented with vitamin B6 and cysteine Subcultures from both of the latter were made to medium supplemented with pyridoxine and cysteine Pyridoxine-dependent variants of viridans streptococci were isolated from the blood of three patients who had bacterial endocarditis In each case, nutritional supplementation of the primary culture medium appeared to be as important as supplementation of the subculture medium Once again, there was no evidence to suggest that the wall-defective variants had been induced by prior beta-lactam therapy.

Item Type: Thesis (MD)
Qualification Level: Doctoral
Keywords: Medicine, Microbiology
Date of Award: 1987
Depositing User: Enlighten Team
Unique ID: glathesis:1987-76688
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 13:54
Last Modified: 19 Nov 2019 13:54
URI: https://theses.gla.ac.uk/id/eprint/76688

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