INHIBITION OF BACTERIAL ADHERENCE TO HOST TISSUE DOES NOT MARKEDLY AFFECT DISEASE IN THE MURINE MODEL OF PSEUDOMONAS-AERUGINOSA CORNEAL INFECTION

The prevention of bacterial infections by the inhibition of binding to host tissues is an oft-touted approach, but few studies with appropri ate models of infection have tested its feasibility. Pseudomonas aerug inosa causes severe corneal infections in mice after inoculations with low doses, and infection is thought to depend upon an initial adheren ce of the bacteria to corneal cells, In vitro, adherence to corneal ce lls is mediated to a large degree by the complete-outer-core oligosacc haride of the bacterial lipopolysaccharide (LPS). However, bacteria ad hering to tissues in vivo are difficult to differentiate from nonadher ent bacteria, Since a direct correlate of P. aeruginosa adherence to c orneal epithelial cells is the degree to which these cells internalize P. aeruginosa, the level of adherence in vivo can be approximated by measuring P. aeruginosa ingestion by cells by using gentamicin exclusi on assays, To determine the degree to which inhibition of the corneal cell adherence affects the course of infection and disease in the muri ne model, we evaluated the ability of LPS-outer-fore oligosaccharide t o inhibit bacterial association and entry into corneal cells and to mo dulate the development of disease, Mice were anesthetized, and their c orneas were scratched and inoculated with virulent P, aeruginosa 6294 or PAO1, along with either 50 pg of oligosaccharide derived from LPS f rom P. aeruginosa PAC557 (complete outer core but no O side chains) or oligosaccharide derived from LPS of P. aeruginosa P. aeruginosa (inco mplete-core oligosaccharide). After 4 h, there were no differences bet ween groups in the counts of infecting and internalized bacteria, At 2 4 h, the complete-core oligosaccharide decreased the levels of bacteri a per eye by 70 to 99.7% compared with the levels achieved by includin g the incomplete-core oligosaccharide in the infectious inoculum, Epit helial cell ingestion of bacteria was comparably affected, However, th e effect on disease was modest and only evident at lower challenge dos es that elicited mild disease in controls and when the bacterial assoc iation and ingestion were inhibited by >99%, Overall, it appears that in the murine model of P, aeruginosa corneal infection at challenge do ses of bacteria 10-fold or greater than the minimal amount needed to c ause disease, the absolute level of inhibition of bacterial adherence is insufficient to reduce tile bacterial counts below that which elici ts disease.