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S L Welkos

Publications and source records attributed to S L Welkos.

45 records · Page 3Linked to original sources
PubMed1981

Regulation of toxinogenesis in Corynebacterium diphtheriae. I. Mutations in bacteriophage beta that alter the effects of iron on toxin production.

Diphtherial toxin is produced in maximal yields by Corynebacterium diphtheriae (C7(beta tox+) only when iron is present in growth-limiting amounts. Toxin production is markedly decreased under high-iron conditions. We studied the role of the bacteriophage beta genome in this apparent regulation of toxin production by iron. Using a passive immune hemolysis assay to detect toxin antigen production in individual plaques, we identified rare phage mutants that were toxinogenic in high-iron medium. Lysogenic derivatives of C. diphtheriae C7 harboring such phage mutants were constructed. The lysogens were compared with wild-type strain C7(beta) for their ability to produce toxin in deferrated liquid medium containing varying amounts of added iron. Quantitative tests for extracellular toxin were performed by competitive-binding radioimmunoassays. We identified phenotypically distinct mutant strains that produced slightly, moderately, or greatly increased yields of toxin antigen under high-iron conditions. The toxin produced by the mutant lysogens was biologically active and immunochemically indistinguishable from wild-type toxin. Complementation experiments demonstrated that the phage mutation designated tox-201 had a cis-dominant effect on the expression of the toxin structural gene of phage beta. The characteristics of the tox-201 mutation suggest that it defines a regulatory locus of phage beta that is involved in control of toxinogenesis by iron in C. diphtheriae.

Bacteriophages↗
PubMed1981

Regulation of toxinogenesis in Corynebacterium diphtheriae. II. Genetic mapping of a tox regulatory mutation in bacteriophage beta.

The structural gene for diphtherial toxin is present in corynebacteriophage beta. Previous studies located several point mutations within the tox locus and determined the orientation of transcription of the toxin structural gene. The production of maximal quantities of toxin by Corynebacterium diphtheriae C7(beta) occurs only when the bacteria are iron deficient. Mutations in phage beta can affect this control of toxin production by iron. The tox-201 mutation regulates expression of the toxin structural gene in a cis-dominant manner and permits large amounts of toxin to be made under high-iron conditions when phage beta tox-201 infects C. diphtheriae C7. In this study tox-201 was found to be closely linked to the structural gene for toxin. We performed a series of multifactor matings to determine the relative positions of tox-201 and several point mutations within the toxin structural gene. The order of these markers on the vegetative genetic map of phage beta was tox-201-tox-4-tox-2-tox-30. These findings establish that the tox-201 regulatory site is closely linked to the end of the toxin structural gene corresponding to the origin of transcription. This location is consistent with our hypothesis that tox-201 defines a cis-dominant regulatory element, such as an operator, promoter, or attenuator, involved in control of toxinogenesis in C. diphtheriae C7(beta).

Bacteriophages↗
PubMed1980

Comparison of the one-gram d-[14C]xylose breath test to the [14C]bile acid breath test in patients with small-intestine bacterial overgrowth.

In twelve patients with culture-proven bacterial overgrowth of the small intestine, the ability of a newly-developed one-gram d-[14C]xylose breath test to detect bacterial overgrowth was compared to that of the [14C]bile acid breath test. All patients manifested excessive production of breath 14CO2 after the administration of one gram [14C]xylose, with 83% of the patients being abnormal within the first hour of testing. In contrast, during the [14C]bile acid breath test, four of the twelve patients had no period of excessive 14CO2 production (above the 95% confidence range of controls). Nutrient malabsorption (fat, cobalamin, xylose) was seen with both true-positive and false-negative bile acid breath tests. The one gram [14C]xylose breath test, utilizing a substrate with more predominant absorption in the proximal small intestine and which can be catabolized by Gram-negative aerobic bacteria, appears to have a greater degree of sensitivity and specificity than the bile acid breath test in detecting the presence of small-intestine bacterial overgrowth.

Bacterial Infections↗
PubMed1980

Immunochemical studies of diphtherial toxin and related nontoxic mutant proteins.

Competitive binding radioimmunoassays were used to analyze the immunochemistry of diphtherial toxin. Rabbit antisera obtained by immunization with formolized toxoid or fragment A were used to characterize purified toxin, toxoid, fragment A, and related nontoxic mutant proteins. Antitoxoid serum had a high titer of neutralizing activity. Most of the antibodies in antitoxoid bound to toxin but not to fragment A. The anti-fragment A antibodies that were present in antitoxoid recognized determinants of fragment A that were exposed on unnicked toxin. Formaldehyde treatment partially destroyed antibody-binding sites associated with the A and B domains of toxin. Anti-fragment A serum had a low titer of neutralizing activity. The specificities of the anti-fragment A antibodies in antitoxoid and anti-fragment A sera were different. Approximately half of the anti-fragment A antibodies in anti-fragment A serum recognized determinants of fragment A that were masked in toxin. Per unit of fragment A-binding activity, anti-fragment A serum was significantly more potent than antitoxoid serum as an inhibitor of the enzymatic activity of fragment A. By analyzing the antigenic structure of several nontoxic mutant proteins (cross-reacting materials) that cross-react with toxin, we distinguished three different subgroups of antigenic determinants associated with the B domain of toxin. Furthermore, the exposed antigenic determinants of the A domain of toxin were separated into two subgroups, both of which were distinct from the masked determinants of the A domain. The radioimmunoassays described here provide rapid, sensitive, quantitative, and versatile methods for immunochemical characterization of toxin or related cross-reacting proteins encoded by corynebacteriophages.

Antibodies, Bacterial↗
PubMed1979

Characterization of a screening test for diphtherial toxin antigen produced by individual plaques of corynebacteriophages.

A passive immune hemolysis assay has been developed to detect diphtherial toxin produced in individual plaques of tox+ corynebacteriophages. This assay permits rapid screening of large numbers of corynebacteriophages for their ability to code for diphtherial toxin or related antigens. The specificity of the assay and its potential usefulness for genetic studies of toxinogenesis have been demonstrated with well-characterized tox+ and tox- laboratory strains of corynebacteriophages.

Antigens, Bacterial↗
PubMed1977

Clinical response of patients with gonococcal endocervicitis and endometritis-salpingitis-peritonitis to doxycycline.

The clinical response to single-drug therapy with doxycycline was evaluated in 25 patients with gonococcal endoceruicitis and was correlated with the bacterial isolates present within the cul-de-sac. The 10 patients with gonococcal salpingitis salpingitis and the three patients with gonococcal peritonitis exhibited excellent clinical responses. When polymicrobial infection coexisted with gonococcal peritonitis or functioned without the concomitant presence of Neisseria gonorrhoeae, a significantly altered therapeutic response was observed in four of the 12 patients. Four patients in this grouping exhibited either secondary temperature elevations or lack of a significant alteration of the white blood cell count, two features which were not characteristic of the patients with either gonococcal salpingitis or peritonitis. In the cases of polymicrobial peritonitis, there was a poor correlation between ensuing clinical response and in vitro resistance of one or more cul-de-sac isolated to doxycycline. The presence of a resistant organism did not preclude a good or satisfactory clinical response. The absence of a resistant organism correlated well with a good clinical response.

Adolescent↗
PubMed1976

Cul-de-sac isolates from patients with endometritis-salpingitis-peritonitis and gonococcal endocervicitis.

Neisseria gonorrhoeae was cultured from the cul-de-sac in 11 of 17 patients with bacteriologically documented gonococcal endometritis-salpingitis and identified by Gram stain in one other instance. In five, N. gonorrhoeae was the only isolate. In six other patients, the presence of other aerobic (two) and anaerobic bacteria (three), as well as N. gonorrhoeae, was documented. In the remaining six patients, only aerobic and anaerobic organisms were isolated. The data are interpreted as supporting the concept of anaerobic superinfections following initial infection with N. gonorrhoeae late in the course of this disease entity.

Aerobiosis↗