**1. Introduction**

*Candida albicans* is the most common pathogenic fungus and occurs frequently in the digestive tract (Bernhardt, 1998; Doskey, 2004). Vaginal candidiasis (Mohanty et al. 2007; Paulitsch et al., 2006; Sobel, 2007) is also a wide spread problem. This species can become invasive, causing infections on many different sites in patients with severe underlying diseases (Marol & Yükesoy, 2008; Odds et al., 2007).

Catheter or shunt related infections caused by *C. albicans* (Pierce 2005) were reported e.g. by Sánchez-Portocarrero et al. (1994), David et al. (2005) and Tumbarello et al. (2007).

The classical picture of yeast cells as unicellular life forms is based on the pure-culture model of growth. In their natural habitat microorganisms including yeasts are mostly organized in biofilm ecosystems which are often ´multicultural´, made not only of yeasts but also of bacteria (El-Aziz et al., 2004; López-Ribot, 2005; Ramage et al., 2005; Nobile et al., 2006). The possibility to adhere to a surface is a very important factor for the development of fungal (Hogan, 2006; Verstrepen & Klis, 2006) and bacterial biofilms (Dolan, 2001).

Microsatellites, which are also known as short tandem repeats, are repeated nucleotide sequences with a length from 2 up to 7 base pairs. These polymorphic DNA loci are variable within a population and in this way multiple alleles are created for a single microsatellite locus. These different multilocus genotypes are used to distinguish strains within a single species (Applied Biosystems [AB], 2005). Microsatellite markers provide the possibility to discriminate strains of the same species and to trace their epidemiological pathways (Botterel et al., 2001; Sampaio et al., 2005).

For this study, pairs for three loci (CDC3, EF3, and HIS3) on three different chromosomes developed by Botterel et al. (2001) were used to compare the *C. albicans* strains which were found to produce a biofilm, with those strains which did not produce a biofilm on the investigated catheter material. The differentiation of biofilm and non-biofilm forming

Microsatellite Typing of Catheter-Associated *Candida albicans* Strains 5

Typing of 123 *C. albicans* strains was done with the above mentioned three primer pairs. Only from strain number 85 (sample W60) no data from the EF3 locus was producible. Although the DNA was isolated a second time and several PCR reactions were done for this locus, no peaks could be generated. In table 1 detailed information of all three loci for each

**CDC3/CDC3R EF3/EF3R HIS3/HIS3R** 

**2.2 Results** 

strain is listed.

strains was based on scanning electron microscopical findings (Paulitsch et al., 2009). Different primer pairs and also different combinations of primer pairs for the subtyping of *C. albicans* were reported elsewhere, see e.g. the works of Sampaio et al. (2005) or Fan et al. (2007).

For each marker and for a given isolate one or two bands were observed, and each observed band was assigned to an allele. Because *C. albicans* is diploid each strain can be characterized by six alleles with the method used.

The discriminatory power (DP) is a numerical index to describe the probability that two unrelated samples of a test group are placed in two different typing groups. The DP of EF3 is 0.86, the DP of CDC3 is 0.77, and the DP of HIS3 is 0.91 (Botterel et al., 2001). The combined DP of all three markers was 0.97. In order to get reliable results, this index has to be greater than 0.90 (Botterel et al., 2001).
