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Beneficial Influence of Platelets on Antibiotic Efficacy in an In Vitro Model of Staphylococcus aureus-Induced Endocarditis. Renee-Claude Mercier, 2004.Platelets contribute to antimicrobial host defense against infective endocarditis (IE) by releasing platelet microbicidal proteins (PMPs) . We investigated the influence of thrombin-stimulated human platelets on the evolution of simulated IE in the presence and absence of vancomycin or nafcillin . Staphylococcus aureus strains differing in intrinsic susceptibility to PMPs or antibiotics were studied: ISP479C (thrombin-induced PMP-1 [tPMP-1] susceptible; nafcillin and vancomycin susceptible), ISP479R (tPMP-1 resistant; nafcillin and vancomycin susceptible), and GISA-NJ (tPMP-1 intermediate-susceptible; vancomycin intermediate-susceptible) . Platelets were introduced and thrombin activated within the in vitro IE model 30 min prior to inoculation with S . aureus . At 0 to 24 h postinoculation, bacterial densities in chamber fluid and simulated endocardial vegetations (SEVs) were quantified and compared among groups . Activated platelets alone, or in combination with antibiotics, inhibited the proliferation of ISP479C in chamber fluid or SEVs over the initial 4-h period (P < 0.05 versus controls) . Moreover, nafcillin-containing regimens exerted inhibitory effects beyond 4 h against ISP479C in both model phases . By comparison, activated platelets inhibited GISA-NJ proliferation in SEVs but not in chamber fluid . The combination of platelets plus nafcillin or vancomycin significantly inhibited proliferation of the GISA-NJ strain in SEVs compared to the effect of platelets or antibiotics alone (P < 0.05) . In contrast, platelets did not significantly alter the antistaphylococcal efficacies of nafcillin or vancomycin against ISP479R . These data support our hypothesis that a beneficial antimicrobial effect may result from the interaction among platelets, PMPs, and anti-infective agents against antibiotic-susceptible or -resistant staphylococci that exhibit a tPMP-1-susceptible or -intermediate-susceptible phenotype . Bacteriophage SP6 Is Closely Related to Phages K1-5, K5, and K1E but Encodes a Tail Protein Very Similar to That of the Distantly Related P22. Dean Scholl, 2002.The lytic salmonella phage SP6 encodes a tail protein with a high degree of sequence similarity to the tail protein of the biologically unrelated lysogenic salmonella phage P22 . The SP6 tail gene is flanked by an upstream region that contains a promoter and a downstream region that contains a putative Rho-independent transcription terminator, giving it a cassette or modular structure almost identical to the structure of the tail genes of coliphages K1E, K5, and K1-5 . It now appears that SP6, K1-5, K5, and K1E are very closely related but have different tail fiber proteins, giving them different host specificities . A Novel Cytology-Based, Two-Hybrid Screen for Bacteria Applied to Protein-Protein Interaction Studies of a Type IV Secretion System. Zhiyong Ding, 2002.DivIVA of Bacillus subtilis and FtsZ of Escherichia coli were used to target heterologous protein complexes to cell division sites of E . coli and Agrobacterium tumefaciens . DivIVA and FtsZ that were fused to the dimerizing leucine zipper (LZ) domain of the yeast transcription activator GCN4 directed the green fluorescent protein (GFP) that was fused to an LZ domain to E . coli division sites, resulting in fluorescence patterns identical to those observed with DivIVA::GFP and FtsZ::GFP . These cell division proteins also targeted the VirE1 chaperone and VirE2 secretion substrate complex to division sites of E . coli and A . tumefaciens . Coproduction of the native VirE1 or VirE2 proteins inhibited the dihybrid interaction in both species, as judged by loss of GFP targeting to division sites . The VirE1 chaperone bound independently to N- and C-terminal regions of VirE2, with a requirement for residues 84 to 147 and 331 to 405 for these interactions, as shown by dihybrid studies with VirE1::GFP and DivIVA fused to N- and C-terminal VirE2 fragments . DivIVA also targeted homo- and heterotypic complexes of VirB8 and VirB10, two bitopic inner membrane subunits of the A . tumefaciens T-DNA transfer system, in E . coli and homotypic complexes of VirB10 in A . tumefaciens. VirB10 self-association in bacteria was mediated by the C-terminal periplasmic domain, as shown by dihybrid studies with fusions to VirB10 truncation derivatives . Together, our findings establish a proof-of-concept for the use of cell-location-specific proteins for studies of interactions among cytosolic and membrane proteins in diverse bacterial species .
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