PEPTIDE PERMEASES FROM STREPTOCOCCUS-PNEUMONIAE AFFECT ADHERENCE TO EUKARYOTIC CELLS

To gain access to tissues within the human host, Streptococcus pneumon iae initially colonizes the nasopharynx and then interacts with glycoc onjugates on the surfaces of target cells at various sites of infectio n. Although pneumococcal adhesins are currently unknown, exported prot eins on the bacterial surface are potential candidates, To identify ba cterial elements involved in this process, mutants of S. pneumoniae wi th defects in exported proteins were screened for the inability to adh ere to cells representative of three in vivo niches: (i) agglutination of bovine erythrocytes, which reflects adherence to cells which resid e in the nasopharynx; (ii) human type II pneumocytes (lung cells [LC]) , representing the alveolar site of infection; and (iii) human vascula r endothelial cells (EC), representing the endovascular site. The capa city of the mutants to adhere during the course of pneumococcal diseas e was also assessed by using cytokine-activated LC and EC. All of the 30 mutants analyzed produced hemagglutination valles comparable with t hose of the parent strain, Four independent mutants demonstrated a gre ater than 50% decrease in adherence to both LC and EC. Sequence analys is of the altered alleles from these strains showed that mutations had occurred in two previously identified loci, plpA and ami, which belon g to the family of genes encoding protein-dependent peptide permeases. Mutations in the ami locus resulted in an inability to recognize the GalNAc beta 1-4Gal glycoconjugate receptor present on resting LC and E C, whereas mutations in plpA resulted in a failure to recognize a GalN Ac beta 1-3Gal glycoconjugate receptor also present on resting cells. Mutations in neither allele affected recognition of GlcNAc receptors p resent bn cytokine-activated LC and EC. These results suggest that pep tide permeases modulate pneumococcal adherence tb epithelial and endot helial dens either by acting directly as adhesins or by modulating the expression of adhesins on the pneumococcal surface during the initial stages of colonization of the lung or the vascular endothelium.