We tested in vitro 49 isolates of Chlamydia pneumoniae obtained from 35 children with community-acquired pneumonia against clarithromycin and erythromycin. The children were part of a treatment study comparing the two drugs. Clarithromycin was 2-to 10-fold more active than erythromycin, with a MIC for 90%6 of strains tested and minimal chlamydiacidal concentration for 90%Yo of strains tested of 0.031 ,ig/ml compared with 0.125 ,ug/ml for erythromycin. Eight of these children, two of whom were treated with erythromycin and six of whom received clarithromycin, remained culture positive after treatment. We were able to test 21 isolates from these children. All were susceptible to both drugs, and the MICs did not change after therapy.Chlamydia pneumoniae is emerging as a frequent cause of community-acquired respiratory tract infection in adults and children, including pneumonia and bronchitis (3, 4, 7). There are limited data on the treatment of these infections, because most studies have used serology only, and thus microbiologic efficacy could not be assessed. As part of a nationwide, multicenter study comparing clarithromycin and erythromycin suspensions for the treatment of community-acquired pneumonia in children 3 through 12 years of age, we isolated C. pneumoniae from 42 (16%) of the 260 children enrolled (7). Although all of the children with C. pneumoniae infection improved clinically and radiographically, 9 (21%) of these children remained culture positive after treatment. C. pneumoniae was eradicated from 15 of 19 (79%) evaluable patients who were treated with clarithromycin and 12 of 14 (86%) of those treated with erythromycin. The dosages of clarithromycin and erythromycin suspensions were 15 and 40 mg/kg of body weight per day, respectively, both given in two divided doses for 10 days. We performed in vitro susceptibility testing against clarithromycin and erythromycin with isolates of C. pneumoniae from these children. MATERIALS AND METHODSClarithromycin (Abbott Laboratories, North Chicago, Ill.) and erythromycin (Eli Lilly and Co., Indianapolis, Ind.) were supplied as powders and solubilized according to the instructions of the manufacturers.The C. pneumoniae isolates were originally isolated from nasopharyngeal swab specimens cultured in cycloheximidetreated HEp-2 cells (1). Patient isolates were passed three to four times in tissue culture in antibiotic-free medium.Susceptibility testing of C. pneumoniae was performed with cell culture of HEp-2 cells grown in 96-well microtiter plates (6). Each well was inoculated with 0.2 ml of the organism diluted to yield 103 inclusion-forming units/ml and centrifuged at 2,000 x g for 1 h. The wells were then aspirated and overlayed with 0. and serial twofold dilutions of the test drug. After incubation at 35°C for 72 h, cultures were fixed and stained for inclusions with fluorescein-conjugated antibody to the lipopolysaccharide genus antigen (Pathfinder Chlamydia Culture Confirmation System; Kallestad Diagnostics, Chaska, Minn.).The MIC was the lowest antibioti...
The in vitro susceptibilities of 12 strains of Chlamydia pneumoniae to a new quinolone, OPC-17116; ofloxacin; and sparfloxacin were determined. OPC-17116 was slightly less active than sparfloxacin but more active than ofloxacin, with a MIC for 90% of strains tested and a minimal chiamydiacidal concentration for 90% of strains tested of 0.5 gg/ml.
We evaluated the performance of three commercially available monoclonal antibodies for confirmation of the presence of Chlamydia pneumoniae in cell culture by examining their abilities to stain inclusions of eight strains of C. pneumoniae. The antibodies tested were two unconjugated C. pneumoniae-specific monoclonal reagents and one conjugated genus-specific reagent. All three produced similar intensities of staining of C. pneumoniae, with some strain-to-strain variation. Methanol appeared to be a better choice of fixative than acetone, which greatly reduced the intensity of fluorescence with one of the species-specific antibodies.
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