NEW YORK (Reuters Health) – In most cases of intra-amniotic inflammation leading to preterm birth, bacteria that are undetectable using standard cultures appear to play a causative role, according to a report in the January issue of the Journal of Clinical Microbiology.

Roughly 60% of the microbes present in cases of intra-amniotic inflammation are missed with traditional culture testing, the current gold standard for identifying infection.

“Because culturing is not finding all bacteria present in the amniotic fluid, this calls for new detection methods,” lead author Dr. Yiping W. Han, from Case Western Reserve University, Cleveland, said in a statement. “It is also important to identify which germ is causing the infection and inflammation leading to preterm birth so that antibiotics are initiated early in this pathophysiological chain of events.”

In the new study, Dr. Han’s team used 16S rRNA-based culture-independent methods, as well as standard culture testing, to examine the amniotic fluid from 46 pregnancies complicated by preterm birth and 16 unaffected pregnancies.

No bacterial DNA was found in the fluid of any of the unaffected pregnancies, the report indicates.

By contrast, fluid from 16 preterm pregnancies were culture positive, all of which also had bacterial DNA. However, bacterial DNA was also found in another 5 (17%) of the remaining 30 pregnancies that were culture negative. Mass spectrometry testing confirmed that intra-amniotic inflammation was present in all five cases.

In 9 of the 16 culture-positive cases, additional bacterial species were detected with the culture-independent methods.

Microbes missed by standard culture included uncultivated and hard-to-cultivate species, such as Leptotrichia/Sneathia spp, Bacteroides spp., and Clostridales sp.

Positivity by culture-independent methods correlated with increased amniotic fluid levels of interleukin-6, histological chorioamnionitis, funisitis, and delivery of neonates with early-onset sepsis.

“This study shows that the process of intra-amniotic infection is complex and suggests that the involvement of uncultivated or difficult-to-cultivate species has been underestimated,” the research team concludes.

J Clin Microbiol 2009.