Plasmid DNA analysis of Staphylococcus epidermidis isolated from blood and colonization cultures in very low birth weight neonates.

We prospectively studied the course of colonization and sepsis with Staphylococcus epidermidis among 29 very low birth weight neonates undergoing prolonged umbilical catheterization. S. epidermidis bacteremia occurred in 7 patients. In 6 bacteremia was preceded by positive colonization cultures. Isolates obtained from nares, base of umbilicus, umbilical catheter entry sites, catheter tips and blood were examined for plasmid DNA profiles. In 4 patients the plasmid profiles of the catheter entry site isolates were identical with those of the blood isolates. In the other 3 bacteremic patients plasmid profiles of the catheter entry site and blood isolates were different. No correlation was observed in the plasmid DNA patterns of isolates obtained from catheter tip cultures as compared to the corresponding blood cultures. The blood isolates from bacteremic patients had different plasmid profiles.

Sensitivity of surveillance cultures for the detection of methicillin-resistant Staphylococcus aureus in a nursing-home-care unit.

This study compared the sensitivity of nasal culture alone versus multiple-site cultures and single versus duplicate sampling for the detection of methicillin-resistant Staphylococcus aureus (MRSA)-colonized individuals in a nursing-home population. Repeat culture of 68 specimens collected from 35 colonized subjects yielded identical results for 57 specimens, (84%), and 89% of the colonized residents (31 of 35) were identified by the first culture of multiple sites. A single nares culture detected 27 (77%) of 35 (first screen) and 29 (83%) of 35 (second screen) residents colonized with MRSA at any site. The most cost-effective screening would consist of a nasal culture only or combined with a gastrostomy tube site, if applicable. To identify all colonized individuals, however, it would be necessary to culture more than one specimen from multiple sites on each resident.

Iron-regulated outer membrane protein OM2 of Vibrio anguillarum is encoded by virulence plasmid pJM1.

Vibrio anguillarum 775 harboring the virulence plasmid pJM1 synthesized an outer membrane protein of 86 kilodaltons, OM2, that was inducible under conditions of iron limitation. pJM1 DNA fragments obtained by digestion with restriction endonucleases were cloned into cosmid vectors and transferred into Escherichia coli. The OM2 protein was synthesized in E. coli, demonstrating that it is actually encoded by the pJM1 plasmid. Mobilization of the recombinant plasmids to V. anguillarum was accomplished by using the transfer factor pRK2013. A V. anguillarum exconjugant harboring the recombinant derivative pJHC-T7 and synthesizing the OM2 protein took up 55Fe3+ and grew under iron-limiting conditions, only in presence of the pJM1-mediated siderophore. Exconjugants harboring recombinant plasmids, such as pJHC-T2 which did not encode the OM2 protein, were transport negative. Membrane protein iodination experiments, together with protease treatment of whole cells, indicated that the OM2 protein is exposed to the outside environment of the V. anguillarum cells.

Iron uptake system medicated by Vibrio anguillarum plasmid pJM1.

Plasmid pJM1 from an invasive strain of Vibrio anguillarum mediates an iron-sequestering system that is associated with the ability of this bacterium to cause septicemia in marine fishes. This plasmid-mediated iron uptake system was analyzed by using mutations caused by transposon Tnl. Restriction endonuclease analysis of iron uptake-deficient and -proficient derivatives generated by insertion of Tnl and molecular cloning experiments permitted us to localize the plasmid regions involved in the process of iron sequestration to a stretch of about 20 kilobase pairs. In addition, the existence of two plasmid-mediated components involved in the process of iron uptake in V. anguillarum was defined: a diffusible substance which functions as a siderophore and a nondiffusible receptor for complexes of iron-siderophore, which we have tentatively identified as the pJM1 plasmid-mediated outer membrane protein OM2 of V. anguillarum.

Antimicrobic susceptibility and plasmid profile analysis as identity tests for multiple blood isolates of coagulase-negative staphylococci.

We compared a disk diffusion antimicrobic susceptibility panel with plasmid DNA profiles as tests for identity of 106 isolates of coagulase-negative staphylococci cultured from the blood of 45 patients on multiple occasions. The antimicrobic panel included penicillin, oxacillin, clindamycin, trimethoprim-sulfamethoxazole, chloramphenicol, tetracycline, tobramycin, kanamycin, and gentamicin. Nineteen patterns of antimicrobic susceptibility were found. The most common pattern was present in 25% of the isolates, and at least one isolate from 31% of the patients had this pattern. Forty-seven distinct plasmid DNA profiles were found. The most common plasmid profile was present in 8.5% of the isolates, and at least one isolate from 15% of the patients had this profile. Twenty-eight patients had multiple isolates that were identical by plasmid profile analysis. Twenty-seven (96%) of these patients had isolates that were also identical by antimicrobic susceptibility. Nineteen patients had multiple isolates that were different by plasmid profile analysis. In 18 (95%) of these patients, the isolates were also different by antimicrobic susceptibility. Although plasmid DNA profile analysis is a more discriminating tool, these data confirm that a selected disk diffusion antimicrobic susceptibility panel may be used to screen multiple blood isolates of coagulase-negative staphylococci for identity or differences.

Molecular factors associated with virulence of marine vibrios isolated from striped bass in Chesapeake Bay.

On the basis of cultural and biochemical properties as well as DNA homology assays, 81 Vibrio strains isolated from diseased striped bass and from Chesapeake Bay water were assigned to eight distinct groups. All organisms belonging to two of the groups were pathogenic for striped bass and were identified as Vibrio anguillarum, whereas organisms classified in the other six groups were nonpathogenic and were designated as Vibrio spp. Unlike the pathogenic V. anguillarum strain 775 isolated in the Pacific Northwest, strains pathogenic for striped bass did not contain any plasmids; however, they were similar to the Northwest isolates in that virulence was correlated with their ability to grow in the presence of nonimmune striped bass serum or under conditions of iron limitation. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of outer membranes showed that additional proteins were induced in those organisms capable of growth under conditions of iron limitation. It was of interest that 22 of the nonpathogenic isolates harbored one or more plasmids which, by restriction endonuclease analyses, were shown to be clearly different from the virulence plasmid pJM1.