Bacterial colonization of human urethral mucosa. II. Adherence tests using tissue organ cultures.

Interaction between two urinary tract pathogens, viz. Staphylococcus saprophyticus and Escherichia coli, and the mucosal lining of the human urethra was studied in a tissue organ culture system utilizing 14C-labelled organisms and scanning electron microscopy. Reduction of pH from 7.5 to 5.5 of the medium in which the organisms were suspended, significantly increased the number of staphylococci that adhered to the urethral cover cells, while no such effect was found when testing E. coli. Increasing time of incubation from 1 to 8 hours did neither effect the numbers, nor the proportions of S. saprophyticus that were bound to the urethral mucosal lining. At pH 6.5 and 7.5 a minor increase of the proportion of E coli that adhered to the urethral organ culture was found when the incubation period exceeded 4 hours, no corresponding finding could be verified at SEM. Two possible modes of the microorganisms to overcome the mutual repellent forces between the invading organism and the urethral surface cover cell are suggested--reduction of surface charge in microorganisms with high isoelectric point (S. saprophyticus) (utilizing pH-shift towards increased acidity), and attachment by means of poorly or non-charged bacterial appendices (i.e. fimbriae) (E. coli).