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Antonie van Leeuwenhoek (2011) 99:559566 DOI 10.1007/s10482-010-9524-3
ORIGINAL PAPER
Williopsis saturnus yeast killer toxin does not kill Streptococcus pneumoniae
Irma Ochigava Phillip J. Collier
Graeme M. Walker Regine Hakenbeck
Received: 18 August 2010 / Accepted: 8 October 2010 / Published online: 22 October 2010 Springer Science+Business Media B.V. 2010
Abstract Streptococcus pneumoniae is an important human bacterial pathogen, and the increase in antibiotic resistance demands the development of new antimicrobial compounds. Several reports have suggested that yeast killer toxins show activity against bacteria and we therefore investigated the activity of K9 killer toxin from the yeast Williopsis saturnus var. mrakii NCYC 500 against S. pneumoniae. However, no inhibition of bacterial growth was observed with concentrated K9 preparations in agar diffusion assays and in liquid culture. Although cell morphology was slightly affected by K9 treatment, no effect on cellular viability was detectable, and K9 had no stimulatory effect on cell lysis induced by b-lactams or Triton
X-100. This indicated that K9 did not contribute to cell wall damage. Moreover, ow cytometry was used as a sensitive assessment of integrity of cells exposed to killer toxin. No signicant damage of S. pneumoniae cells was evident, although minor changes in
uorescence suggested that K9 killer toxin may interact with bacterial surface components.
Keywords Antibacterial activity Flow cytometry
Streptococcus pneumonia Williopsis saturnus var.
mrakii Yeast killer toxin
Introduction
The increase of drug-resistant bacterial strains represents a major global medical challenge. Antibiotic therapy is becoming ineffective against a signicant number of nosocomial infections and there is therefore a pressing need to identify and characterize new antibacterial agents. Although the antimicrobial effects of antibiotics, bacteriophages and bacteriocins have been known for a long time, the antimicrobial activity of yeast-derived metabolites has been demonstrated only relatively recently (Bevan and Makover 1963).
Killer-yeasts secrete proteinaceous toxins that have potential in medicine and biotechnology (Schmitt and Breinig 2002). They have potential in the biocontrol of contaminant microbes in fermentation processes (Palpacelli et al. 1991), and for intraspecic characterization of industrially and clinically interesting yeast cultures (Buzzini and Martini 2000). The use of selected toxins as antimycotic agents against pathogenic yeasts that cause systemic mycoses has also
I. Ochigava R. Hakenbeck
Department of Microbiology, University of Kaiserslautern, Paul-Ehrlich St 23, 67663 Kaiserslautern, Germany
P. J....