Studies on strong and weak killer phenotypes of wine yeasts: production, activity of toxin in must, and its effect in mixed culture fermentation.

Two different killer phenotypes were detected among K+ (killer) yeasts isolated from spontaneous wine fermentations using a plate bioassay. The two phenotypes differed in their degree of killer activity, and were designated as SK+(strong killer) and WK+(weak killer). Strains showing either phenotype were assayed for expression of killer activity under different growth conditions. Growth in must negatively affected expression of the killer activity of both phenotypes. The supernatant fluids from must cultures showed a lower killing effect than those from yeast phosphate dextrose broth (YPDB) cultures. The ability of the two K+ phenotypes to prevail on K-sensitive yeasts was studied in mixed-culture fermentation experiments. Under these conditions, only strains showing SK+ phenotype were able to prevail on the K-sensitive yeasts. These results suggest that the K+ phenotype could play a relevant role in spontaneous fermentations provided that the strain exhibits an SK+ phenotype, and that the latter phenotype should be preferred when selected K + strains are to be used as fermentation starters.

In-vitro evaluation of cefpodoxime.

In-vitro antimicrobial activity of cefpodoxime was evaluated against several microbial species by both conventional tests and additional parameters which take into consideration some of the conditions likely to be encountered in infected tissues. MICs for 414 recent clinical isolates, including staphylococci, streptococci, Haemophilus influenzae, Moraxella catarrhalis, several Enterobacteriaceae, Aeromonas hydrophila and Campylobacter jejuni were determined. MIC values overall were similar to those observed for strains from other geographical areas. Inhibition of growth by cefpodoxime was virtually unaffected by the inoculum size, even using bacterial populations as large as 10(9) cfu of Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, H. influenzae, beta-lactamase-negative M. catarrhalis, Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis. Growth in the presence of human serum as the only source of nutrients did not significantly affect the inhibition exerted by cefpodoxime, even against large bacterial populations of S. aureus, S. pneumoniae, E. coli, and K. pneumoniae. For K. pneumoniae, E. coli, P. mirabilis and beta-lactamase-negative M. catarrhalis it was also found that sub-MIC concentrations of cefpodoxime were still able to inhibit the majority of cells in microbial populations as large as 10(9) cfu. Evaluation of bactericidal activity demonstrated that cefpodoxime concentrations comparable to those achievable in plasma or in the respiratory tract were able to kill rapidly large bacterial populations of S. pneumoniae and S. pyogenes. The bactericidal activity was apparently lower against M. catarrhalis, H. influenzae, S. aureus, E. coli, and K. pneumoniae.

Occurrence of killer yeasts in spontaneous wine fermentations from the tuscany region of Italy.

The occurrence of killer yeasts in an area of Tuscany (central Italy) was studied. Killer yeasts were found in 88% of spontaneous wine fermentations from 18 wineries. The incidence of killers varied with respect to fermentation stage and vintage period, increasing from the first vintage to successive ones and from the commencement to the end of fermentation. At the end of fermentation, the proportion of killer strains relative to total yeast population was below 25% in 15 cases, above 75% in 6 cases, from 25 to 50% in 5 cases, and from 50 to 75% in 3 cases. Karyotype analysis also showed a mixed killer population in the fermentations in which the killers dominated.

Novel immunoenzymatic assay for identification of coagulase- and protein A-negative Staphylococcus aureus strains.

A purified monoclonal antibody (MAb) which specifically reacts with Staphylococcus aureus glucosaminidase was obtained. This MAb was utilized to develop an immunoenzymatic assay for the identification of S. aureus strains. The sensitivity of this assay, based on the simultaneous detection of S. aureus glucosaminidase and protein A, was evaluated by analyzing a total of 196 strains, 26 of which did not exhibit one or more of the following properties: protein A, clumping factor, and staphylocoagulase. All strains yielded positive results by the MAb-based immunoenzymatic test. The assay's ability to differentiate between S. aureus and other staphylococci was then analyzed by testing a total of 277 non-S. aureus strains that yielded negative results. Our data demonstrate that this immunoenzymatic assay can be used as a single S. aureus identification criterion, particularly useful for those strains negative for clumping factor, staphylocoagulase, or protein A.

Investigation of the mutagenic activity in Salmonella typhimurium of the furochromone khellin, proposed as a therapeutic agent for skin diseases.

The photomutagenicity of the furochromone khellin was tested in Ames Salmonella strains using 8-methoxypsoralen (8-MOP) and 4,5', 8-trimethylpsoralen (TMP) as positive controls. When khellin was assayed with strain TA1537, mutation induction was not detectable; in the same strain, an equitoxic dose (52-56% level of survival) of TMP (used at a concentration 12-fold lower than khellin and with a UVA dose 83-fold lower than that used with khellin) yielded an increase in revertants/plate 3-fold above the spontaneous background. In strain TA102, khellin plus UVA treatment yielded a 2-fold increase in revertants/plate above the spontaneous background (79% survival). 8-MOP, however, used at a concentration 8-fold lower than khellin with a UVA dose 13-fold lower than khellin, yielded an increase in revertants/plate about 14-fold above background (66% survival) in the same strain. These data show that khellin has a weak photomutagenic potential and, along with the previously reported low photogenotoxic potential in eukaryotic cell systems, support the notion that khellin may be safer than bifunctional psoralens for clinical use.

Production of serum-opacity factor by Streptococcus pyogenes strains isolated from pharyngitis in children. Prevalence of "rheumatogenic" M types among OF-negative strains.

Two hundred ten S. pyogenes strains isolated in 1979, 1980 and 1984 from children with pharyngitis were here examined for properties which might be relevant to their rheumatogenic potential. Strains were first tested for the production of streptococcal serum-opacity factor and, among those scored as OF-negative, the presence was then verified of M types which have been epidemiologically related to rheumatic fever. Members of "rheumatogenic" M types are present among strains causing pharyngitis in children, which, however, also include a considerable proportion of OF-positive, probably non-rheumatogenic, strains. The results are discussed in the light of the low incidence of rheumatic fever in this country.

Properties of an E. coli O26 mutant with modified cell wall and improved efficiency as recipient in conjugation for an FII plasmid.

Among populations of an E. coli O26 strain two types of mutants have been found to be present which act as better recipients in conjugation for an FII plasmid. Some properties of one of these mutants, O26SMB9, are here described. They indicate that a defect in the cell-wall structure has occurred which corresponds to a smooth----semirough transition.

Two different types of conjugation-prone recipients for an FII plasmid in populations of an E. coli O26 strain.

In populations of an E. coli O26 strain three types of cells can be found which show different degrees of recipient ability in conjugation for an FII plasmid. In this paper the characterization of the plasmid used, pSMB35, is described and the conjugation-proficient mutants, O26SMB9 and O26SMB11, are compared for some of their properties.

Enhanced sensitivity to the photodynamic effect of 3,4-benzpyrene in ethylenediaminetetraacetate-treated Escherichia coli.

Ethylenediaminetetraacetate treatment of Escherichia coli B enhanced cell sensitivity to the lethal effect of the photodynamic action of 3,4-benzpyrene. The alteration of the shape of the survival curve suggests that such photodynamic action may be modified by membrane barriers to the drug.