Gerald Riddle

Susceptibility of female pelvic pathogens to oral antibiotic agents in patients who develop postpartum endometritis

Fifteen hundred patients were enrolled in a prospective, randomized study on the effect of antibiotic prophylaxis during cesarean section. Two hundred thirty-one patients developed postpartum endometritis, and the isolates obtained from the endometrium were tested for sensitivity to ampicillin, cefuroxime, ofloxacin, ciprofloxacin, and clindamycin. Minimum inhibitory concentrations of 50% and 90% of ampicillin, cefuroxime, and clindamycin were similar to previously reported values; however, slight differences were noted in the activity of the two quinolones to common pelvic isolates. The minimum inhibitory concentrations of 90% of ofloxacin and ciprofloxacin to 119 isolates of Enterococcus faecalis were 4.0 and 2.0, to 17 isolates of Staphylococcus aureus 1.0 and 0.5, to 39 isolates of Escherichia coli 0.5 and 1.0, to 46 isolates of Bacteroides bivius 4.0 and 8.0, to 57 isolates of Gardnerella vaginalis 1.0 and 2.0, to 71 isolates of Staphylococcus epidermidis 0.5 and 0.5, to 16 isolates of Proteus mirabilis 0.25 and 0.12, and to 50 isolates of Lactobacillus species 32.0 and 8.0 micrograms/ml, respectively. In summary, the quinolones have activity comparable with a variety of other oral agents versus female pelvic pathogens, with the quinolones ofloxacin and ciprofloxacin having better activity against most of the gram-negative isolates. Anaerobic activities were comparable with the beta-lactams, but inferior to clindamycin and metronidazole as expected.

Effectiveness of ofloxacin in the treatment of Chlamydia trachomatis and Neisseria gonorrhoeae cervical infection

Forty patients with cervical infection caused by Chlamydia trachomatis were treated with ofloxacin (20) or doxycycline (20). Ofloxacin was successful in eradicating C. trachomatis from all 20 (100%) patients. Doxycycline was effective in 18 of 20 (90%) patients. Three patients had a concomitant cervical gonococcal infection. All three were successfully treated: one with ofloxacin and two with doxycycline. Ofloxacin, 300 mg, taken twice daily for 7 days, is effective in eradicating endocervical C. trachomatis infection.

Rapid diagnostic test for identifying group B streptococcus.

Neonatal infection with Streptococcus agalactiae (group B streptococcus [GBS]) causes significant morbidity and mortality. A truly rapid diagnostic test for identifying GBS would allow for more timely initiation of antibiotic prophylaxis and also reduce the administration of antibiotics for the prevention of early onset neonatal GBS infection. A stock culture was formed from a laboratory reference strain of GBS and was diluted from 10 (7) to 10 (1) bacteria/mL. Specific concentrations were used to inoculate nitrocellulose membranes (NCMs) that had been coated previously with polyclonal rabbit antibody against GBS. After specific times, the NCMs were removed from the sheep blood agar medium, and horseradish-peroxidase conjugate polyclonal antibody against GBS was added. Bound antibody was detected with diaminobenzidine. After 6 hours of incubation, GBS was detected at concentrations from 10 (7) through 10 (4) bacterial/mL. After 4 hours of incubation, GBS was detected at concentrations from 10 (7) through 10 (5) bacteria/mL. GBS was not detected at 2 hours of incubation. Rapid growth and detection of GBS can be performed, and the results can be reliably attained as early as 4 hours. This is in marked contrast to the 48 to 72 hours required by current methods.

Accuracy of an Accelerated, Culture-Based Assay for Detection of Group B Streptococcus

Objective. To determine the validity of a novel Group B Streptococcus (GBS) diagnostic assay for the detection of GBS in antepartum patients. Study Design. Women were screened for GBS colonization at 35 to 37 weeks of gestation. Three vaginal-rectal swabs were collected per patient; two were processed by traditional culture (commercial laboratory versus in-house culture), and the third was processed by an immunoblot-based test, in which a sample is placed over an antibody-coated nitrocellulose membrane, and after a six-hour culture, bound GBS is detected with a secondary antibody. Results. 356 patients were evaluated. Commercial processing revealed a GBS prevalence rate of 85/356 (23.6%). In-house culture provided a prevalence rate of 105/356 (29.5%). When the accelerated GBS test result was compared to the in-house GBS culture, it demonstrated a sensitivity of 97.1% and a specificity of 88.4%. Interobserver reliability for the novel GBS test was 88.2%. Conclusions. The accelerated GBS test provides a high level of validity for the detection of GBS colonization in antepartum patients within 6.5 hours and demonstrates a substantial agreement between observers.

Optimization of a rapid diagnostic test for detection of group B streptococcus from antepartum patients

We analyzed the performance of a new rapid diagnostic test for use in determining group B streptococcus colonization in pregnancy. Vaginal-rectal specimens were compared by the rapid test, a commercial laboratory culture result, and an in-house culture. Of 150 patient samples, 72 were positive by the rapid test, giving a prevalence of 48.0% versus 24.7% by traditional culture. Characterization of these results showed cross-reactivity with Enterococcus. The addition of bacitracin reduced this interference, and when reanalyzed, a colonization rate of 31.3% was found (P = 0.3961, chi-square), as well as a sensitivity of 100% (95% confidence interval [CI] 89.1-100) and a specificity of 93.6% (95% CI 86.9-97.2). The addition of bacitracin greatly improves the reliability of this diagnostic test and demonstrates a novel approach to reduce interference. An accurate determination of the tests sensitivity and specificity, however, awaits enrollment of the remaining subjects.

In Vitro Susceptibility Testing of Clinical Isolates of Chlamydia trachomatis

Penicillin class antibiotics have demonstrated varying degrees of in vivo and in vitro success when tested against Chlamydia trachomatis. The activity of ampicillin-sulbactam, an agent commonly utilized in the treatment of pelvic infections, was tested to ascertain if any antichlamydial activity is present. Up to six endocervical isolates of C. trachomatis were tested against each of five antibiotics including doxycycline, erythromycin, clindamycin, ampicillin/sulbactam, and sulbactam alone. McCoy cell monolayers were inoculated with high inclusion counts of 10,000–30,000 inclusion-forming units (IFU) per coverslip, and exposed to each antibiotic. Up to nine subsequent antibiotic free culture passes were performed to assess the viability of abnormal inclusions. Doxycycline, erythromycin, and clindamycin achieved 100% eradication of inclusions at concentrations of 4.0, 2.0, and 1.0 µg/mL. Exposure to ampicillin/sulbactam resulted in a greater than 99% reduction in the inclusion count at 32.0 µg/mL, while sulbactam by itself demonstrated considerably less activity. Abnormal inclusions were noted only in the ampicillin/sulbactam exposed cells, and these, plus all inclusions remaining following sublethal exposure to the other antibiotics, resulted in regrowth to control levels in subsequent passes. Doxycycline and erythromycin demonstrated excellent activity. Clindamycin and ampicillin/sulbactam also significantly reduced inclusion formation, and therefore may provide adequate C. trachomatis coverage in patients receiving these antibiotics for pelvic infections.

Development of a Novel Test for Simultaneous Bacterial Identification and Antibiotic Susceptibility

Background. Elucidation of a pathogens antimicrobial susceptibility requires subculture after the organism is first isolated. This takes several days, requiring patients to be treated with broad-spectrum antibiotics. This approach contributes to the development of bacterial resistance. Methods. Microtiter wells were coated with a polyclonal antibody targeting the pathogen of interest. Bacterial suspensions were added in the presence/absence of selected antibiotics. After washing, captured bacteria were detected. Findings. Group B streptococcus (GBS), Enterococcus faecalis, and Neisseria gonorrhoeae were each detected at 105 bacteria/mL following a 20-minute incubation period. Susceptibility to select antibiotics was discernable following a 6-hour incubation period (GBS and Enterococcus). Sensitivity was increased to 10−2 bacteria/mL for GBS, 10−1 bacteria/mL for E. faecalis, and 101 bacteria/mL for N. gonorrhoeae following 18–24-hour culture. Conclusion. This novel assay allows for the highly sensitive and specific identification of a pathogen and simultaneous determination of its antimicrobial susceptibility in a reduced time.

Umbilical Cord and Maternal Serum Levels of Mezlocillin in Term and Preterm Deliveries in Mothers Diagnosed with Chorioamnionitis

Recent investigations have demonstrated decreased morbidity in the newborn following maternal administration of antibiotics to mothers with a diagnosis of chorioamnionitis. These benefits are based upon transplacental passage of antibiotics. Fifteen preterm and term women with the diagnosis of chorioamnionitis were given 3 or 4 g of mezlocillin intravenously every 4 to 6 h. Maternal serum and umbilical cord samples were collected at delivery and the concentrations of antibiotics were determined by high-pressure liquid chromatography. Peak serum levels of mezlocillin in the cord and mother occurred within 60 min, but were eliminated more rapidly in the mother. Umbilical cord levels, while initially lower with the 3 g dose, were present longer than 4 hr for both regimens. Placental transfer of antibiotics appeared to be affected by the aging placenta with decreased initial levels and slower fetal clearance at term.

Cefotetan susceptibility testing against anaerobic bacteria from obstetrical and gynecologic sources: comparison of five different methods.

Five different antibiotic susceptibility methods were utilized to test the effectiveness of cefotetan against 200 anaerobic bacteria recovered from patients with obstetrical or gynecological infections. The object of this study was to determine if a more economical and rapid method for anaerobic susceptibility testing was as acceptable as the reference agar dilution method. The five methods were: 1) broth disk elution, 2) microbroth technique, 3) a commercially available microbroth technique, 4) a commercially available spiral gradient technique, and 5) reference agar dilution. The minimal inhibitory concentrations (MICs) calculated from the spiral gradient technique were equal to or within one doubling dilution of the reference system in 99.5% of cases, while the percentage for the commercially available microbroth system was 96.8%, very similar to the microbroth technique used in our laboratory that yielded a percentage of 96.3. The disk elution method correlated to the reference agar dilution method in 95.3% cases. While the overall agreement between these techniques is good, especially for the spiral gradient system, clustering of certain organisms near the breakpoint of the antibiotic tested results in variability in the labeling of these organisms as susceptible or resistant. This problem appears to be particularly significant for the disk elution method. Therefore, further refinements in these methods of suscleptibility testing are needed in order to provide a more clinically useful assessment of the susceptibility or resistance of certain bacterial isolates.