Characterization of Candida krusei strains from spontaneously fermented maize dough by profiles of assimilation, chromosome profile, polymerase chain reaction and restriction endonuclease analysis.

Abstract

Several isolates of Candida krusei from indigenous spontaneously fermented maize dough have been characterized for the purpose of selecting appropriate starter cultures and methods for their subspecifies typing. The present work describes the occurrence of C. krusei in Ghanaian fermented maize dough. For detailed pheno- and genotyping, 48 representative isolates were selected and comparison was made with clinical isolates of C. krusei and reference cultures. The techniques applied included the assimilation of carbon compounds by the API ID 32 C kit, determination of chromosome profile by pulse field gel electrophoresis, polymerase chain reaction (PCR) profiles, restriction endonuclease analysis (REA) and Southern blot hybridization. For the 48 isolates tested, 82% had the same assimilation profiles, being able to assimilate N-acetyl-glucosamine, DL-lactate, glycerol and to ferment glucose. Chromosome and PCR profiles, REA and Southern blot hybridization techniques all had a high discriminatory power and revealed DNA polymorphism, which allowed for discrimination among the strains and hence subspecific typing. On the basis of PCR and REA profiles, isolates were grouped into clusters. Southern blot hybridization appeared to be the most sensitive with respect to strain specificity. Our results demonstrated that the three methods, PCR, REA and Southern blot hybridization, were suitable tools, easy to analyse, fast (with regard to PCR) and reliable methods for the typing of C. krusei isolates to species and below species level. Based on the use of these techniques, we demonstrated that several strains of C. krusei were involved in the fermentation of maize dough from the onset and remain dominant throughout the fermentation.