**16. Adherence**

Adherence of a microorganism to mucosal or epithelial cells is an important step in the pathogenesis of infections. Host-related factors may influence this adherence. For example, women with recurrent urinary tract infections have a greater adherence of *E. coli* to their vaginal and buccal cells compared to controls [41].

*C. albicans* infection is frequently found in diabetic patients. Since infection mostly is preceded by colonisation, Aly et al. investigated which risk factors increased the risk of *Candida* carriage in diabetic patients [42]. Risk factors for oral *Candida* carriage in patients with DM type 1 were a lower age and a higher HbA1c level (poor regulation of DM). Continuous wearing of dentures and the presence of glucosuria (also an indication of a poor DM regulation) increased the risk of *Candida* carriage in DM type 2 patients, the mean number of cigarettes smoked per day was correlated with *Candida* carriage in DM type 1 and type 2 grouped together [42]. Cameron et al. extracted lipids from human buccal epithelial cells and found, using chromatogram overlay assays, that some *C. albicans* strains bind to fucose-containing and other *C. albicans* strains to *N*-acetylgalactosamine-containing lipids extracted from human buccal cells. The authors conclude that the existence of several adhesin-receptor systems contributes to the virulence of *C. albicans* [43]. The carbohydrate composition of receptors probably plays an important role in the susceptibility to infections. It has been shown that severely ill patients have a decreased amount of galactose and sialic acid on their buccal cells, compared with minimally ill patients and healthy controls. The investigators mentioned that these receptor changes possibly lead to an increased adherence of microorganisms and play a role in the high prevalence of Gram-negative bacterial colonisation in the respiratory tract of these patients [44]. This mechanism of increased adherence, due to an altered receptor carbohydrate composition, is possibly also present in diabetic patients. Buccal cells from 50 diabetic patients (DM type 1 and type 2) showed an increased in vitro adherence of *C. albicans* compared to buccal cells from controls [45]. A significantly higher incidence of *Candida* infection, but not *Candida* carriage, was also found in this patient group (12% versus 0%) [45]. No relationships, however, were found between the frequency or quantity of *Candida* and age, duration, regulation or type of DM [45]. This increased adherence to diabetic cells might also play a role for other microorganisms, for example the adherence of *E. coli* to uroepithelial cells, which would explain the increased prevalence of infections in patients with DM.

In conclusion, disturbances in cellular innate immunity play a role in the pathogenesis of the increased prevalence of infections in DM patients. In general, a better regulation of the DM leads to an improvement of cellular function. A second important mechanism is the increased adherence of the microorganism to diabetic cells. Furthermore, some microorganisms become more virulent in a high-glucose environment.
