Effect of Microcolony Formation on the Adherence ofPseudomonas aeruginosato Human Buccal Epithelial Cells

Abstract

Pseudomonas aeruginosa is thought to initiate respiratory infections in susceptible individuals by adhering to and colonising the respiratory epithelium. We have examined the binding properties of P. aeruginosa strain P1 to human buccal epithelial cell (BEC)s and found that it may bind as a single bacterium or as an alginate encased microcolony. Examination of the binding of P1 to BECs revealed that single bacteria bound to BECs via a single class of adhesinreceptor site interactions, where the apparent association constant of binding (K a ) was 4.6 x 10 -9 ml/CFU and the maximum number of bacteria that could bind per BEC (N) was 223 bacteria/BEC. Cultures that produced microcolonies bound to BECs via two classes of adhesin-receptor site interactions. The first was identical to the class employed by single bacteria and was due to the presence of single bacteria in the culture and did not represent microcolony binding to the BECs. The second class of adhesin-receptor site interactions had a K a of 4.7 x 10 -10 ml/ CFU and N of 3388 bacteria/BEC. This second class of interactions was due to the binding of microcolonies to BECs. These data indicated that single bacteria bound to the BEC with a higher affinity than microcolonies. While the adherence of microcolonies to BECs was not as efficient as single cells, substantially higher numbers of bacteria could attach to an epithelial cell. Keywords: Pseudomonas aeruginosa ; Bacterial colonisation; Bacterial binding; Microcolony.