Experimental evolution and genome data analysis ofCandida albicansreveals cryptic bacteria in single yeast colonies

Abstract

ABSTRACTAt least 25% of patients with positiveCandida albicansbloodstream infection also have one or more bacterial species associated with the infection. These polymicrobial infections are usually caused by coagulase-negative staphylococci, most commonlyStaphylococcus epidermidisand are associated with significantly worse clinical outcomes as compared to monomicrobial infections. Here we show bacteria are present inC. albicanscultures started from isolated single colony platting. These co-evolving bacteria can only be detected by the use of specific selective medium and/or long periods of incubation from 8 days up to 48 weeks (approximately 4,000 generations), used in experimental evolution methods. The detection of these co-evolving bacteria is highly dependent on the type of enzyme used for 16S rRNA gene amplification and is often missed in clinical laboratory analysis because of short incubation periods, media and temperatures, used in mycology clinical routine, that are unfavorable for bacterial growth. In this study, we identified bacteria in cultures of differentC. albicansisolates from long term, continuous growth by molecular analysis and microscopy. Also, we confirmed the presence of these co-evolving bacteria by identification ofS. epidermidisgenome segments in sequencing reads of theC. albicansreference strain SC5314 genome sequencing project raw data deposited in GenBank. This result rules out the possibility of laboratory specific contamination. Also, we show that the presence of associated bacteria correlates with antifungal resistance alterations observed in growth under hypoxia. Our findings show the intense interaction betweenC. albicansyeasts and bacteria and have direct implications in yeast clinical procedures, especially concerning patient treatment.