A B S T R A C T The abilities of 14 strains of aerobic gram-positive cocci and gram-negative bacilli to adhere in vitro to human or canine aortic valve leaflets were compared. 2-mm sections of excised valve leaflets were obtained by punch biopsy and were incubated under standardized conditions in suspensions of bacteria. Valve sections were subsequently waslhed and homiogeniized, and quantitative techniques were used to determine the proportions of bacteria from the initial suspensions that had adhered to the valve sections. Comparable results were obtained when these adherence ratios were determined by two independent methods based either on measurements of bacterial viability or of radioactivity in 5"Cr-labeled bacteria. For each bacterial strain, the adherence ratio was constant over a wide range of concentrations of bacteria in the incubation mediuiml. Strains of enterococci, viridans streptococci, coagulase-positive and coagulase-negative staphylococci and Pscudoim oinas aeruginosa (adherence ratios 0.003-0.017) were found to adhere more readily to valve sections than strains of Escherichia coli and Klbsiella pfeum;oniiac (adherence ratios 0.00002-0.00004). The organisms that most frequently cause bacterial endocarditis Nwere found to adhere best to heart valves in vitro, suggesting that the ability to adhere to valvular endothelium may be an important or essential characteristic of bacteria that cause endocarditis in man.

A B S T R A C T The adherence of 18 strains of streptococci to sections of normal canine and human aortic, mitral, and tricuspid valves and to canine interatrial septum was compared in an in vitro system. Quantitative measurements of adherence ratios were performed by two independent methods. Adherence ratios for Streptococcus mutans, S. sanguis, S. bovis, and Group D streptococci were higher (0.0058-0.0101) than for the other streptococcal strains studied (0.0025-0.0041). With the exception of Group D streptococci, adherence ratios for each bacterial strain were similar with the aortic, mitral, and tricuspid valve sections. Adherence ratios with normal human and canine valve leaflets were similar, but adherence ratios with interatrial septum were lower than with normal valve sections.Adherence ratios for glucan-positive and glucannegative strains of streptococci with normal and with damaged aortic valve leaflets were also compared. The adherence ratios of the glucan-positive streptococci (S. mutans, S. sanguis, and S. bovis) and one glucannegative enterococcal strain (KG-3) were approximately five times higher with damaged aortic valves (0.039-0.051) than with normal aortic valves (0.009-0.010). For glucan-positive strains, adherence ratios with normal aortic leaflets were similar when bacteria were grown in media which contains or lacks sucrose. In striking contrast, growth of the glucan-positive strains in medium which lacks sucrose, with resultant deficiency of glucan production, decreased the adherence ratios with damaged aortic valve leaflets to those found with normal aortic leaflets. Treatment of This work was presented in part at the 16th Interscience

A randomized controlled study was done to determine whether initial combination therapy with zidovudine and zalcitabine or zidovudine and didanosine would delay the emergence of zidovudine-resistant virus. Human immunodeficiency virus (HIV)-1-infected patients with <300 CD4 cells/mm3 and <4 weeks of prior zidovudine therapy were randomized to zidovudine, zidovudine plus zalcitabine, or zidovudine plus didanosine. Combination therapy did not delay the emergence of zidovudine-resistant virus isolates. However, combination therapy resulted in a significant increase in CD4 cells through 72 weeks compared with zidovudine monotherapy and a greater and more sustained decline in serum HIV-1 RNA. Although this trial was not designed as a clinical end-point study, patients assigned to zidovudine plus didanosine combination therapy experienced a significant delay in time to first AIDS-defining event or death compared with those assigned to zidovudine monotherapy.

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The oropharyngeal colonization by Staphylococcus aureus and Gram-negative bacilli (GNB) and its duration were studied in 89 house staff officers, with biweekly quantitative cultures for 11 months. Eighty-two episodes of upper respiratory tract infection were documented during the study period. The oropharyngeal colonization during illness-free periods ranged from 12% to 18% for GNB and from 5% to 14% for S aureus. During an episode of upper respiratory tract infection, the oropharyngeal colonization of GNB increased to 60%; S aureus colonization increased to 43%. The colonization with both GNB and S aureus was transient and lasted for approximately two weeks. The increased colonization by S aureus and GNB during a viral respiratory tract infection may be a factor contributing to the increased risk of pneumonia in patients with this condition.