Studies of safety, infectivity and immunogenicity of a new temperature-sensitive (ts) 51-1 strain of Salmonella typhi as a new live oral typhoid fever vaccine candidate.

This report describes the results of a phase 1 study evaluating the safety, infectivity, and immunogenicity of a new live oral Salmonella typhi temperature-sensitive (ts) 51-1 typhoid fever vaccine in the human. Three normal male subjects aged 23-32 years received three oral doses of S. typhi ts 51-1, each dose containing 10(9) organisms. Prior to and following immunization each subject was carefully monitored by clinical and laboratory parameters over a 2 week period during which serial specimens of blood and stool were analysed for the presence of the organism. Blood specimens were also obtained for the determination of serum antibody and cell-mediated immune responses and stool filtrates were analysed for the development of coproantibody. The results of these studies indicate that: (1) the vaccine is well tolerated with no clinical or laboratory evidence of adverse reactions; (2) ts 51-1 was detected in only one stool specimen from one volunteer; the organism recovered displayed characteristics of the ts 51-1 vaccine strain; and (3) although no significant humoral or cell-mediated lymphocytotoxic immune responses were detected in the blood, coproantibody was detected in stool specimens from all of the three immunized subjects and IgA-armed ADCC activity was detected in two of three subjects. These studies indicate that S. typhi ts 51-1 may be a suitable strain for the development of an improved oral typhoid fever vaccine. Studies are in progress to determine optimal methods of vaccine delivery preparatory to large phase 2 studies of efficacy.

Growth response of several Candida albicans strains to inhibitory concentrations of heavy metals.

Prolonged exposure of several Candida albicans strains to inhibitory concentrations of Cd, Cu, or Zn resulted in the appearance of resistant colonies at frequencies and with kinetics significantly different than expected based solely upon the predicted spontaneous mutation rate. Characteristics of the response included: (i) a delay usually of 4-10 days in the emergence of the first resistant colonies; (ii) continued accumulation of resistant colonies for a minimum of 21 days after initial exposure to selection; and (iii) final mutation frequencies ranging from 7.0 x 10(-6) to 9.8 x 10(-4). Further examination of the response of one of the strains to Cd, demonstrated that pretreatment with either ultraviolet irradiation or hydroxyurea resulted in approximately a 10-fold increase in the number of resistant colonies detected. While the distribution and identity of colony phenotypes was altered for all strains after exposure to the heavy metals, no specific morphologies could be correlated to development of resistance.

Phenotypic variation of a virulent Candida albicans strain and two spontaneous, relatively avirulent mutant strain derivatives.

The effect of media and temperature of incubation on colony phenotype of Candida albicans strain 4918, and two relatively avirulent mutant strains, designated 4918-2 and 4918-10, has been investigated. In addition, the strains were characterized on the basis of morphotyping pattern. Colony phenotypes were determined for cultures grown on either Lee's medium supplemented with arginine and zinc, or M63 medium supplemented with casamino acids. Incubation was at either 24 or 37 degrees C for 7 days. The results demonstrated that the predominant colony phenotype observed at 24 degrees C was different from that at 37 degrees C for all three strains, irrespective of the medium. While the growth medium influenced the specific colony phenotypes observed, as well as their categorical distribution, no significant medium effect on switching frequency was apparent. The switching repertoire of strain 4918-10 was consistently more varied than either the parental strain or 4918-2 under the conditions examined. However, categorization of the colony phenotypes shown by the three strains suggested that the pattern exhibited by strain 4918-2 was distinct from that of the other two strains. In addition, individual primary colonies of each phenotype observed were clonally plated in order to examine further the switching frequencies. The results established that all three strains were capable of high frequency switching. Other experiments demonstrated that morphotypes of all three strains were different from one another as expected from the differences in their virulence reported previously.

Complementary transcripts from two genes necessary for normal meiosis in the yeast Saccharomyces cerevisiae.

The SPO12 gene, which is required for meiosis I chromosome division during sporulation of the yeast Saccharomyces cerevisiae, has been isolated. DNA sequencing has identified an open reading frame of 173 codons that encodes the putative SPO12 protein and has no significant sequence similarities to known genes. The last 15 amino acids of this putative protein have a high negative charge, which appears to be required for function. A second sporulation-specific gene, designated SPO16, was found adjacent to SPO12 and shown to be necessary for efficient spore formation. The two genes are encoded on opposite DNA strands with only 103 nucleotides between the termination codons. Up to 700 nucleotides of the SPO12 and SPO16 transcripts are complementary, and the 3' untranslated region of the longest SPO16 transcript is complementary to all or nearly all of the SPO12 mRNA. A strain homozygous for an insertion which removes the complementarity between the SPO12 and SPO16 mRNAs has an efficiency of sporulation, number of spores per ascus, and spore viability identical to those of a wild-type strain. The complementarity therefore has either no function or only a subtle function in meiosis and sporulation.