Unique gene structure and paralogy define the 7D-cadherin family.

Cadherins are Ca2+-dependent transmembrane glycoproteins crucial for cell-cell adhesion in vertebrates and invertebrates. Classification of this superfamily due to their phylogenetic relationship is currently restricted to three major subfamilies: classical, desmosomal and protocadherins. Here we report evidence for a common phylogenetic origin of the kidney-specific Ksp- (Cdh16) and the intestine-specific LI-cadherin (Cdh17). Both genes consist of 18 exons and the positions of their exon-intron boundaries as well as their intron phases are perfectly conserved. We found an extensive paralogy of more than 40 megabases in mammals as well as teleost fish species encompassing the Ksp- and LI-cadherin genes. A comparable paralogy was not detected for other cadherin gene loci. These findings suggest that the Ksp- and LI-cadherin genes originated by chromosomal duplication early during vertebrate evolution and support our assumption that both proteins are paralogues within a separate cadherin family that we have termed 7D-cadherins.

Phylogenetic origin of LI-cadherin revealed by protein and gene structure analysis.

The intestine specific LI-cadherin differs in its overall structure from classical and desmosomal cadherins by the presence of seven instead of five cadherin repeats and a short cytoplasmic domain. Despite the low sequence similarity, a comparative protein structure analysis revealed that LI-cadherin may have originated from a five-repeat predecessor cadherin by a duplication of the first two aminoterminal repeats. To test this hypothesis, we cloned the murine LI-cadherin gene and compared its structure to that of other cadherins. The intron-exon organization, including the intron positions and phases, is perfectly conserved between repeats 3-7 of LI-cadherin and 1-5 of classical cadherins. Moreover, the genomic structure of the repeats 1-2 and 3-4 is identical for LI-cadherin and highly similar to that of the repeats 1-2 of classical cadherins. These findings strengthen our assumption that LI-cadherin originated from an ancestral cadherin with five domains by a partial gene duplication event.

Ksp-cadherin is a functional cell-cell adhesion molecule related to LI-cadherin.

Ksp- and LI-cadherin are structurally homologous proteins coexpressed with E-cadherin in renal and intestinal epithelia, respectively. Whereas LI-cadherin has been shown to mediate Ca2+-dependent homotypic cell-cell adhesion independent of stable interactions with the cytoskeleton, little is known about the physiological role of Ksp-cadherin. To analyze its potential adhesive and morphoregulatory functions, we expressed murine Ksp-cadherin in CHO cells. In this report, we show that Ksp-cadherin induces homotypic and Ca2+-dependent cell-cell adhesion that can be specifically blocked with antibodies raised against the cadherin repeats EC1 and EC2. Ksp-cadherin mediates about the same quantitative adhesive effect (aggregation index) as LI- and E-cadherin. However, the cellular phenotype induced by Ksp-cadherin resembles more closely that of LI- than E-cadherin. This could reflect our observation, that Ksp-cadherin, as well as LI-cadherin, does not directly interact with beta-catenin. In conclusion, both cadherins are thus not only structurally but also functionally related and may share other functions within their respective epithelia.

Synergistic bactericidal activity of rat serum with vancomycin against enterococci.

Animal models of infectious diseases may not predict clinical efficacy when species-related factors come into play. Recently, unexpected bactericidal activity of vancomycin alone against enterococci was observed in a rat model of endocarditis. A factor or factors in rat serum, but not rabbit or human serum, enhanced in vitro killing by vancomycin in four of five clinical isolates of enterococci. Bactericidal activity was maintained on dilution of rat serum to 5.0% and after exposure of serum to 56 degrees C for 30 min. Activity was lost by heating at 60 degrees C for 2 h, ultrafiltration, or absorption with bentonite or heat-killed bacteria. Rat serum appears to contain a factor or factors that contribute bactericidal activity to vancomycin, a drug normally bacteriostatic for these enterococci. The mechanism by which this factor enhances killing of enterococci by vancomycin is unknown.

In vitro susceptibilities of oral pigmented Bacteroides species to trospectomycin and other selected antimicrobial agents.

The in vitro activity of trospectomycin against 97 clinical isolates of oral pigmented Bacteroides species was compared with the activities of five other antimicrobial agents. At 4 micrograms/ml, more than 90% of isolates were inhibited by trospectomycin. Overall, strains that produced beta-lactamase (n = 41) were more resistant to trospectomycin, penicillin G, cefoxitin, piperacillin, and tetracycline but not to clindamycin. In this study, trospectomycin had excellent in vitro activity against oral pigmented Bacteroides species.

In vitro postantibiotic effect of daptomycin (LY146032) against Enterococcus faecalis and methicillin-susceptible and methicillin-resistant Staphylococcus aureus strains.

The suppression of bacterial growth that persists after brief exposure to antimicrobial agents has been termed the postantibiotic effect (PAE). This pharmacodynamic interaction varies for each microorganism-antimicrobial agent combination. Daptomycin (LY146032) is a new lipopeptide antibiotic with activity against gram-positive organisms. We studied the in vitro bactericidal activities and PAEs of the following drugs: daptomycin compared with penicillin G and vancomycin, without and with gentamicin against Enterococcus faecalis strains; daptomycin compared with nafcillin and vancomycin against methicillin-susceptible Staphylococcus aureus strains; and daptomycin compared with vancomycin against methicillin-resistant S. aureus strains. Daptomycin, alone and when used in combination with gentamicin, exhibited greater bactericidal activity and in general produced a longer PAE than standard effective regimens against the organism strains studied.

High-level penicillin resistance among isolates of enterococci. Implications for treatment of enterococcal infections.

STUDY OBJECTIVE: To determine the extent and clinical significance of high-level penicillin-resistant Enterococcus faecium at our institution. DESIGN: Surveillance of clinical enterococcal isolates, in-vitro susceptibility and timed survival studies, and determination of antibiotic efficacy in an experimental model of enterococcal endocarditis. MEASUREMENTS AND MAIN RESULTS: For a 6-month period, 14% of enterococcal isolates (30 of 212) were identified as E. faecium. One third of the isolates were highly resistant to penicillin G (minimum inhibitory concentration [MIC], greater than or equal to 200 micrograms/mL) but did not produce beta-lactamase. The findings from in-vitro survival studies showed that this high-level resistance resulted in the loss of bactericidal activity normally observed when an aminoglycoside antibiotic agent is combined with penicillin. An experimental rat model of endocarditis provided in-vivo data that confirmed our in-vitro observations. After the rats received therapy for 72 hours, penicillin G either alone or in combination with gentamicin did not significantly decrease the numbers of enterococci in vegetations on heart valves compared with untreated controls (P = 0.62 and P = 0.58, respectively). CONCLUSIONS: Enterococcus faecium accounts for a notable proportion of clinical enterococcal isolates. Many strains from patients at our institution, as well as from patients at other institutions throughout the country, are highly resistant to penicillin. Because high-level penicillin resistance has important therapeutic implications, periodic surveillance and MIC testing of significant enterococcal isolates, especially E. faecium, are suggested.