0022-534 7/90/1432-0386$02.00/0 THE JOURNAL OF UROLOGY Copyright© 1990 by AMERICAN UROLOGICAL ASSOCIATION, INC. Vol. 143, February Printed in U.S.A. OUTER MEMBRANE PROTEINS OF E.COLI IN THE HOST-PATHOGEN INTERACTION IN URINARY TRACT INFECTION JAIME A. ROBLEDO, ALIX SERRANO AND GERALD J. DOMINGUE* From the Department of Urology and Department of Microbiology and Immunology, Tulane University School of Medicine, New Orleans, Louisiana ABSTRACT Outer membrane protein patterns (Omp) of Escherichia coli obtained directly from the urine of bacteriuric patients without passage on artificial culture media (ACM) were studied by polyacryl- amide gel electrophoresis (SDS-PAGE) in an effort to determine whether in vivo conditions of growth affected the expression of these bacterial surface structures. Seventeen strains studied showed two distinct Omp patterns: one protein band appeared at the level of porin proteins ( 40 kDa) in both patterns, but Omp A protein was at the level of 36 kDa in the first pattern and a new protein was observed at 21.5 kDa in the second pattern suggesting that it is a fragment of Omp A. High molecular weight proteins were also observed in most of the strains and this finding was related to lack of free iron when the same strains were grown under iron restricted conditions in vitro. The same strains grown in pooled urine from normal females showed the first pattern mentioned above. Comparative growth on ACM of urinary strains and E. coli strains isolated from blood, feces and wounds showed an increase in the number of porins expressed (from 1 to 2 or 3, with some variability observed between strains). Differences in osmolality between pooled urine and ACM used, plus in vitro studies varying the osmolality of culture media, showed that osmolality accounted for differences in the number of porins expressed: porin expression decreased in urine and ACM of high osmolality, suggesting that the same phenomena occurred in vivo. It is concluded that host factors including low availability of iron and high osmolality present in the urinary tract influence the expression of several E. coli surface proteins. These proteins may relate to the ability of E. coli to colonize and invade the urinary tract by regulating the physiologic and/or metabolic state of the bacterial cell favoring survival of the organism in a hostile environment. Specific immune responses directed against porins could influence the outcome of this host-parasite inter- action. (J. Ural., 143: 386-391, 1990) E. coli is the most frequent cause of urinary tract infection in humans. 1 Several bacterial virulence factors have been im- plicated in the host-pathogen interation, yet despite extensive research, no single virulence factor has completely accounted for the urovirulence of E. coli in pyelonephritis. Most of the recent efforts have been devoted to the role of adhesins (fimbriae) of E. coli recognizing specific receptors on the mucosal epithelium. Strains having P fimbriae adhesin have been linked to major inflammatory changes in the urinary tract, 2 and are more often isolated from patients with pyelo- nephritis, 3·4 suggesting that P fimbriae are important in the pathogenesis of the disease. Additionally, bacterial capsules and hemolysin have been reported to be significant as virulence factors. 5 ' 6 Recent data, however, from our laboratory, utilizing an ex- perimental murine model of pyelonephritis indicated that wild type E. coli strains devoid of fimbriae, hemolysin, acidic cap- sules and sensitive to human serumcidal activity were capable of causing incipient and acute pyelonephritis. 7 Furthermore, even among identical serotypes and biotypes, the presence of fimbriae did not appear to be critical factors in urovirulence, nor did the presence of several other positive characteristics (hemolysin, K capsule, flagella, serum resistance) in a given strain enhance uorpathogenicity. These phenotypic character- istics may simply represent associated or serologic markers with the host serving as the dominant determinant of bacterial virulence and susceptibility to urinary infection. Accepted for publication September 14, 1989. * Requests for reprints: Dept. of Urology, Tulane University School of Medicine, 1430 Tulane Ave., New Orleans LA 70112. Presented at the 88th Annual Meeting of the American Society for Microbiology, Abstract Number B205, May 8, 1988, Miami, Florida. 386 Bacterial virulence, therefore, should be examined in the context of the relationship of both microorganism and host: bacterial survival in a hostile environment, and host factors which intervene to overcome initiation of bacterial colonization and further infection of the urinary tract. This complex rela- tionship must involve not only the above mentioned virulence factors but the entire bacterial cell structure. In fact, bacteria growing in vivo may be different metabolically and structurally from organisms traditionally studied by in vitro conditions on artificial culture medium. 8 Urine is a complex body fluid containing a variety of excreted products. 9 It does support bacterial growth although several urine factors have been implicated as inhibitory. For example, the lack of free iron has been related to the expression of iron regulated membrane proteins (IRMP) on bacteria isolated from the human urinary tract, 10 • 11 indicating a restrictive condition for bacterial growth and a consequent adaptational change. Although other factors (pH, concentration of urea in urine and urine osmolality) have been demonstrated as inhibitory for bacterial growth under certain conditions, 12 • 13 the nature of the structural changes which bacteria undergo while growing in the urinary tract is mostly unknown. Major outer membrane proteins are part of the external surface of the bacterial cell. Porins belong to a particular group of outer membrane proteins that have been termed peptidogly- can-associated general diffusion pore proteins, which besides serving as receptors for certain bacteriophages also act as non- specific pores that allow the entrance of molecules smaller than 600 M.W. into the bacterial cell. 14 Since the expression in vitro of this group of proteins is related to the composition of the culture medium or environmental conditions, 15 - 17 it appears