Gale B. Hill

Fusobacterium nucleatum Induces Premature and Term Stillbirths in Pregnant Mice: Implication of Oral Bacteria in Preterm Birth

ABSTRACT Fusobacterium nucleatum is a gram-negative anaerobe ubiquitous to the oral cavity. It is associated with periodontal disease. It is also associated with preterm birth and has been isolated from the amniotic fluid, placenta, and chorioamnionic membranes of women delivering prematurely. Periodontal disease is a newly recognized risk factor for preterm birth. This study examined the possible mechanism underlying the link between these two diseases. F. nucleatum strains isolated from amniotic fluids and placentas along with those isolated from orally related sources invaded both epithelial and endothelial cells. The invasive ability may enable F. nucleatum to colonize and infect the pregnant uterus. Transient bacteremia caused by periodontal infection may facilitate bacterial transmission from the oral cavity to the uterus. To test this hypothesis, we intravenously injected F. nucleatum into pregnant CF-1 mice. The injection resulted in premature delivery, stillbirths, and nonsustained live births. The bacterial infection was restricted inside the uterus, without spreading systemically. F. nucleatum was first detected in the blood vessels in murine placentas. Invasion of the endothelial cells lining the blood vessels was observed. The bacteria then crossed the endothelium, proliferated in surrounding tissues, and finally spread to the amniotic fluid. The pattern of infection paralleled that in humans. This study represents the first evidence that F. nucleatum may be transmitted hematogenously to the placenta and cause adverse pregnancy outcomes. The results strengthen the link between periodontal disease and preterm birth. Our study also indicates that invasion may be an important virulence mechanism for F. nucleatum to infect the placenta.

The microbiology of bacterial vaginosis

A group of microorganisms are present concurrently in high concentrations in the vaginas of women with bacterial vaginosis. The major members of the group are Gardnerella vaginalis, anaerobic gram-negative rods belonging to the genera Prevotella, Porphyromonas and Bacteroides, Peptostreptococcus species, Mycoplasma hominis, Ureaplasma urealyticum, and often Mobiluncus species. Facultative species of Lactobacillus are present in lower concentrations and are less prevalent in bacterial vaginosis than in women with a normal vaginal examination. The exact microbe(s) responsible for bacterial vaginosis is unknown whether among the organisms listed above or an unknown agent. The high concentrations of anaerobic gram-negative rods, peptostreptococci, and other opportunistic pathogens in the lower genital tract place women with bacterial vaginosis at increased risk for genital infections and adverse pregnancy outcomes.

Susceptibility of the Bacteroides fragilis group in the United States: analysis by site of isolation.

An ongoing survey of the susceptibility of the Bacteroides fragilis group of bacteria was continued at New England Medical Center in 1984 and 1985. A total of 1,229 strains were obtained from eight centers in the United States. These results were compared with those for 1,847 isolates tested in 1981 through 1983. The most active beta-lactam drugs were imipenem and ticarcillin-clavulanic acid (Timentin), which had a less than 1% resistance rate. No metronidazole- or chloramphenicol-resistant isolates were found during the 5 years of the study. Isolates obtained from blood, perinatal, and bone sites of infection were more resistant to a variety of antimicrobial agents. Susceptibility patterns of the members of the B. fragilis group varied at the eight hospitals and among species. These data indicate the need for determining the susceptibility patterns for the B. fragilis group of organisms at each hospital.

Intra-amniotic bacterial colonization in premature labor

Bacterial culturing was performed on amniotic fluid obtained by transabdominal amniocentesis from 33 patients with singleton pregnancies who were in idiopathic premature labor with intact membranes prior to the thirty-fifth week of gestation. Bacteria were isolated in seven patients (21.2%). The patients who were at highest risk for intra-amniotic colonization were those who had two or more clinical parameters suspicious for intra-amniotic infection in a pregnancy prior to the thirtieth week. Anaerobic bacteria were isolated from all seven patients. Only one patient had mixed aerotolerance isolates. Anaerobic that were classified as significant pathogens were isolated in four patients. Three patients had isolates that grew on primary plates, and the rest were recovered only from broth. The greatest impact of intra-amniotic bacterial colonization in premature labor with intact membranes on perinatal outcome is expressed in extreme prematurity and appears to be a function of the pathogenicity and concentration of the offending organism(s).

Nationwide study of the susceptibility of the Bacteroides fragilis group in the United States.

A nationwide susceptibility survey of the Bacteroides fragilis group was continued at New England Medical Center in 1983. A total of 555 strains were obtained from eight centers in the United States. In addition to the nine antimicrobial agents studied in the two previous years, three other agents were added to the evaluation: cefamandole, cefuroxime, and cefonicid. The results for the strains tested with the original nine drugs in 1983 were compared with those for 1,292 isolates tested in 1981 and 1982. The most active beta-lactam drug was piperacillin, which had an 8% resistance rate. Cefoxitin resistance increased from 10% in 1982 to 16% in 1983. High rates of resistance to cefotaxime, cefoperazone, cefamandole, cefonicid, and cefuroxime were encountered. No metronidazole- or chloramphenicol-resistant isolates were found during the 3 years of the study. Susceptibility patterns varied at the eight hospitals: the outbreak of cefoxitin resistance reported in 1982 at New England Medical Center remitted, while a high clindamycin resistance rate was documented at one hospital in 1983. These data indicate the need for determining the susceptibility patterns for the B. fragilis group of organisms at each hospital.

Susceptibility of the Bacteroides fragilis group in the United States in 1981.

The minimal inhibitory concentrations of nine antimicrobial agents was determined for over 750 clinical isolates of the Bacteroides fragilis group of anaerobic bacteria collected from nine centers in the United States during 1981. High resistance rates were documented for cefoperazone, cefotaxime, and tetracycline. Cefoxitin had the best activity of the beta-lactam antibiotics, whereas moxalactam and piperacillin had good activities. The resistance rate for clindamycin was 6%. There were no metronidazole- or chloramphenicol-resistant isolates encountered. There were significant differences in susceptibility among the various species of the B. fragilis group, particularly with moxalactam, cefoxitin, and clindamycin. Clustering of clindamycin-, piperacillin-, and cefoxitin-resistant isolates was observed at different hospitals. The variability of resistance rates with the beta-lactam antibiotics and clindamycin indicates that susceptibility testing of significant clinical isolates should be performed to define local resistance patterns.

Antimicrobial susceptibilities of 1,292 isolates of the Bacteroides fragilis group in the united states: comparison of 1981 with 1982

A susceptibility survey of 537 strains of the Bacteroides fragilis group from eight centers in the United States was continued at the Tufts New England Medical Center in 1982. The results were compared with those of 755 organisms analyzed in 1981. Nine antimicrobial agents were tested by an agar dilution method. The respective percentages of resistance for 1981 and 1982 were as follows (%): cefoxitin, 8 and 10; moxalactam, 22 and 12; cefotaxime, 54 and 48; cefoperazone, 57 and 54; piperacillin, 12 and 7; clindamycin, 6 and 3; metronidazole, 0 and 0; chloramphenicol, 0 and 0; and tetracycline, 63 and 59. Regional differences in resistance rates were found. Declines in resistance to moxalactam, piperacillin, and clindamycin were noted at the participating hospitals. An outbreak of cefoxitin resistance was noted at the Tufts New England Medical Center, where the rate increased from 14 to 30%. The various species of the B. fragilis group had differing patterns of resistance; B. fragilis was the most susceptible species. Significant cross resistance among the beta-lactam agents was found. These data indicate the need to determine the susceptibility patterns of the B. fragilis group organisms within each hospital.

Comparative activities of newer beta-lactam agents against members of the Bacteroides fragilis group.

A nationwide susceptibility survey of 557 isolates of the Bacteroides fragilis group was continued in 1986. The most active beta-lactam drugs were imipenem and ticarcillin-clavulanic acid, which had 0.2 and 1.7% resistance, respectively. The rank order of activity of beta-lactam drugs was imipenem, ticarcillin-clavulanic acid, cefoxitin, piperacillin, moxalactam, ceftizoxime, cefotetan, cefotaxime, cefoperazone, and ceftazadime.

Bacterial colonization of amniotic fluid in the presence of ruptured membranes

Amniotic fluid (AF) was collected from 37 selected patients by amniocentesis, aspiration through a pressure catheter, or aspiration at the time of cesarean section. The unspun AF was examined directly by Gram stain for bacteria and white blood cells (WBC) and was cultured. Thirteen AF cultures were positive, defined as growth on primary plating media which corresponded to greater than 10(2) colony-forming units (CFU) per milliliter. Almost equal numbers of aerobic and anaerobic bacteria were isolated. The presence of bacteria, but not WBC, on Gram stain of AF correlated significantly with a positive culture, which indicated that microscopic examination of AF would usually predict the culture result. Growth of greater than 10(2) CFU/ml from AF was significantly associated with clinical chorioamnionitis, but colonization also was observed in five afebrile patients, four of whom were in premature labor. In patients delivered by cesarean section, bacteria on Gram stain and a positive culture from AF each were significantly correlated with postpartum endometritis.

Bacterial vaginosis: Diagnostic and pathogenetic findings during topical clindamycin therapy

We examined subjective and objective correlates among 67 women with symptomatic bacterial vaginosis before and after treatment with intravaginal clindamycin or placebo. We found no preponderance of any sexual practices among these patients. Nine patients (13.4%) had had hysterectomy. Whereas odor and discharge were the most common symptoms, 30 patients (44.8%) also complained of vulvovaginal irritation. Symptoms correlated poorly with objective therapeutic outcome. On examination the diagnosis would have been missed in seven patients (10.4%) if the clinician relied on presence of an abnormal vaginal discharge to suggest bacterial vaginosis. Vaginal pH greater than 4.5 was found immediately after curative therapy in 59.6% of patients. Mobiluncus spp. morphotypes were 99.0% specific and 52.1% sensitive and proline aminopeptidase activity in vaginal fluid was 84.4% sensitive and 70.2% specific for diagnosis. Our Gram stain criteria yielded no false-negative results, 6.1% false-positive, and frequent indeterminate results after therapy. We found little evidence for sexual transmission of bacterial vaginosis. Recurrence after effective therapy was not predicted by vaginal pH elevation, positive or indeterminate Gram stain result, or positive proline aminopeptidase test.