Survival of the biocontrol yeast Pichia anomala after long-term storage in liquid formulations at different temperatures, assessed by flow cytometry.

AIMS: Investigate the survival of liquid formulations of the biocontrol yeast Pichia anomala J121 at different temperatures, and develop a system for comparative studies of different storage conditions and formulations. METHODS AND RESULTS: The survival of P. anomala in liquid formulations with lactose, starch and trehalose amendments was measured during prolonged storage at temperatures ranging from -20 to +30 degrees C. The relative survival of the stored cells was rapidly estimated by flow cytometry. After 4 weeks incubation at 4 and 10 degrees C, 75-90% of the cells were viable, with no significant differences between the various formulations. Supplementing the storage buffer with lactose or trehalose increased the survival after longer incubations (8 and 12 weeks) at all temperatures (-20 to 30 degrees C). Trehalose was the most effective protectant at 20 and 30 degrees C (>20% viable cells after 12 weeks at 20 degrees C). The biocontrol activity was maintained after formulation and prolonged storage of P. anomala. CONCLUSIONS: The storage potential of liquid formulated P. anomala cells can be increased by supplementation with lactose or trehalose. The combination of a custom made incubation chamber and flow cytometry was suitable to evaluate stability of P. anomala formulations. SIGNIFICANCE AND IMPACT OF THE STUDY: Liquid formulated P. anomala have a long shelf life. The developed test system can be used to study different formulations of other biocontrol agents.

Mouse skin passage of a Streptococcus pyogenes Tn917 mutant of sagA/pel restores virulence, beta-hemolysis and sagA/pel expression without altering the position or sequence of the transposon.

BACKGROUND: Streptolysin S (SLS), the oxygen-stable hemolysin of Streptococcus pyogenes, has recently been shown to be encoded by the sagA/pel gene. Mutants lacking expression of this gene were less virulent in a dermonecrotic mouse infection model. Inactivation of the sagA/pel gene affect the expression of a variety of virulence factors in addition to the hemolysin. Insertion of a Tn917 transposon into the promoter region of the sagA/pel gene of S. pyogenes isolate CS101 eliminated expression of SLS, as well as decreased expression of the streptococcal pyrogenic exotoxin B, streptokinase and M protein. RESULTS: In this study a mouse skin air sac model was utilized to analyze the effect of biological pressures on expression of SLS and other sagA/pel regulated gene products. The insertion delayed the lethal effect of S. pyogenes in a mouse skin infection model. Despite this, bacteria could be cultured from the kidneys 72 hours post infection. These kidney-recovered isolates were beta-hemolytic despite the transposon being present in its original location and had equivalent virulence to the wild type isolate when re-injected into naive mice. Northern blot analysis of the kidney-recovered isolates confirmed that transcription of sagA/pel was restored; however the expression of all sagA/pel regulated genes was not restored to wild type levels. CONCLUSIONS: These results show that biological pressure present in the mouse can select for variants with altered expression of key virulence factor genes in S. pyogenes.

Antibody response to Candida and its use in clinical practice.

Reference values for specific IgM, IgA and IgG antibodies against three defined Candida antigens were determined in 280 healthy Swedish children aged 1 month to 15 years. The antibody response in 10 children with Candida infections was also determined. Precipitating IgG antibodies to a mannan-free Candida protein antigen were detected only in children with Candida infection. The haemagglutinating IgM antibody response in healthy children to a polysaccharide Candida antigen was weak. Adult levels of < or = 320 (95% confidence interval, CI) were not reached even in the oldest children (< or = 160). All children with Candida infections had elevated IgM titres. Adult levels of IgA antibodies to Candida mannan were reached at 10-12 years of age; at 13-15 years the titres were higher (< or = 1600) than in healthy adults (< or = 1000, 95% CI). All children with an acute Candida infection had elevated IgA titres. Our study shows that antibody testing may be used to diagnose systemic Candida infection in children and to follow the progression and resolution of systemic Candida infection with the rise and fall of antibody titres.

Does streptomycin cause an error catastrophe?

We have examined the interpretation that streptomycin kills a bacterial culture by initiating the so-called error catastrophe. In particular, we asked whether the increased translational error rate induced by the antibiotic gives rise to an autocatalytic loss of functional fidelity of the devices responsible for gene expression, which ultimately causes the death of the culture. We have analyzed the performance characteristics of one of these devices, namely the ribosome in streptomycin-treated bacteria. We find that, although the treated ribosomes are constructed from error-containing proteins, they are not significantly different in elongation rate and fidelity from those ribosomes taken from untreated bacteria. We conclude that the bacteriocidal effect of streptomycin is not due to the initiation of an error catastrophe.