Effect of attachment factors (pili plus Opa) on Neisseria gonorrhoeae invasion of human fallopian tube tissue in vitro: quantitation by computerized image analysis

Pili (P) and opacity-associated proteins (Opa) facilitate Neisseria gonorrhoeae attachment to human fallopian tube epithelium. Subsequent effects on invasion are unproven. Computerized image analysis was used to study the effects of attachment factors on invasion by comparing a P⁺Opa⁺ variant to a P^-Opa^- variant of strain R10 in the fallopian tube organ culture model. Gonococci in sections of infected fallopian tube tissue were identified with FITC-labelled monoclonal anti-gonococcal antibodies. Nomarski DIC microscopy was used to establish anatomic boundaries that excluded extracellular gonococci from invasion measurements. The area of intracellular fluorescence served as an index of gonococcal invasion. With conservative criteria to exclude extracellular gonococci, the per cent of the intracellular area occupied by fluorescent P⁺Opa⁺ gonococci was 18% compared to 4.7% for the P^-Opa^- variant (P <0.001). Data suggest that P⁺Opa⁺ organisms invaded deeper than P^-Opa^- microbes over the same time period (P = 0.029). Intra-observer variation in invasion measurements was not significant (P ≥ 0.85), and inter-observer correlation was high (correlation coefficient = 0.96). Computerized image analysis is a rapid, reliable means of quantifying gonococcal invasion of fallopian tube epithelium. We conclude that gonococcal attachment factors can facilitate events which enhance gonococcal invasion of fallopian tube epithelium.