Role of the Staphylococcus epidermidis slime layer in experimental tunnel tract infections.

An experimental animal model was used to assess the slime layer of Staphylococcus epidermidis as a pathogenic factor in tunnel tract infections. Mice were inoculated with high-slime-producing or non-slime-producing strains of S. epidermidis, either along the length of a subcutaneous catheter or in the area where a catheter had been placed and immediately removed (controls). Among the catheter-bearing mice, the phenotypically distinct staphylococci produced similar, high frequencies of abscess formation (72% [44 of 61] versus 81% [31 of 38]; P = 0.29). In controls, the non-slime-producing organisms were significantly more pathogenic (87% [40 of 46] versus 57% [25 of 44] abscess formation; P = 0.001). No consistent difference was detected between blood isolates obtained from patients with central venous catheter bacteremia and those from neonates with bacteremia in the absence of a prosthetic medical device. Quantitative culture of removed catheters showed greater adherence by the slime-producing isolates (P = 0.014). In this mouse model, slime production by S. epidermidis did not increase the risk of catheter tunnel tract infection, despite the greater catheter adherence of the slime-producing organisms. These findings suggest that traumatized tissue may be a sufficient condition for the development of S. epidermidis catheter-associated infections.

Identification of the innate human immune response to surface-exposed proteins of coagulase-negative staphylococci.

The presumed host defense against coagulase-negative staphylococci (ConS), recognized pathogens in hosts with compromised immunity or indwelling medical devices, is opsonophagocytosis. Targets for opsonization remain unclear. Using radiolabeling techniques, we identified the surface-exposed proteins of ConS and determined the innate humoral immune responses to them among healthy adults. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of surface proteins extrinsically labeled with 125I demonstrated 20 to 30 proteins with molecular weights of 15,000 to greater than 130,000. Five to ten of these proteins were immunogenic and recognized by normal human sera, including predominant 18-, 41-, 48-, and 51-kDa proteins. We also evaluated the humoral response of cancer patients with ConS bacteremia. Patients' sera obtained before bacteremic episodes demonstrated a pattern of reactivity similar to that of normal human sera. When patients' sera obtained after bacteremic episodes were used to determine whether an expanded immune response followed infection, only one of seven showed reactivity with more proteins than seen with the innate response. Western blot (immunoblot) analysis and whole-cell enzyme-linked immunosorbent assays were also evaluated. This study identifies (i) the surface-exposed proteins available for host interaction, (ii) the innate human antibody response to these proteins, and (iii) the immune response of cancer patients with ConS bacteremia.

Defining Staphylococcus epidermidis cell wall proteins.

Three Staphylococcus epidermidis isolates of differing bacteriophage types were studied to define proteins confined to the cell wall, which were surface exposed and thus available to interact with the host. Three major proteins of 37, 41, and 51 kDa were identified in all whole-cell lysates and cell wall extracts by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Two additional proteins of 18 and 25 kDa became evident by using 125I labeling to delineate surface-exposed proteins. A classification scheme using P1 to P5 to delineate the 51-, 41-, 37-, 25- and 18-kDa proteins is proposed. Additionally, murine immune sera were used to identify two immunodominant proteins of 51 and 25 kDa (P1 and P4, respectively).

Protein synthesis early in the developmental cycle of Chlamydia psittaci.

The incorporation of [35S]methionine into protein by intracellular and host-free Chlamydia psittaci 6BC was analyzed at intervals between 15 min and 28 h postinfection by autoradiography of sodium dodecyl sulfate-polyacrylamide gels. The profiles of proteins synthesized in the two systems were similar at all times, indicating that the host-free system can be used to monitor the temporal expression of genes in chlamydiae. The host-free system permitted detection of synthesis of chlamydial proteins as early as 15 min postinfection. Some of the proteins synthesized during the initial phases of reorganization of elementary bodies to reticulate bodies either were not synthesized or were synthesized in greatly reduced amounts during the other phases of the developmental cycle. The effects of rifampin and actinomycin D indicated that host-free protein synthesis was at least partially dependent on the initiation and continuation of RNA synthesis in the isolated organisms.