Abstract
Background16S rRNA-based genomic analyses have revolutionized our understanding of infectious diseases. Many cases which were recognized as “idiopathic” are now known to have an infectious etiology. Here, we present a proof-of-concept study to examine the microbial link between intra-amniotic infection (IAI) and early-onset neonatal sepsis (EONS).ResultsUsing culture independent methods, we analyzed paired amniotic fluid (AF) and cord blood (CB) samples from 36 singleton pregnancies complicated by preterm birth (PTB), IAI, and/or EONS. PTB cases were grouped as 1) Group 1– neonatal blood culture-positive EONS (n = 6). 2) Group 2– neonatal blood culture-negative presumed EONS with positive IAI (n = 16). 3) Group 3– neonatal blood culture-negative presumed EONS with no IAI (n = 7); 4) Group 4– no EONS or IAI (n = 7). In addition, samples from term healthy deliveries (n = 8) served as technical controls. A total of 31 species (15 non-redundant) were identified in AF, of which only 1/3 were cultivated. Significantly fewer microorganisms were detected in CB, with a total of 18 species (7 non-redundant) identified, of which only 2 (Escherichia coli, Streptococcus agalactiae) were cultivated. Of those, Bergeyella, Fusobacterium nucleatum, and Sneathia sanguinegens had not been detected in EONS before. The novel species identified in AF by PCR include Peptoniphilus harei and Lachnospiraceae sp. The majority (72%) of CB species were also detected in the matching AF, with E. coli and F. nucleatum as the most prevalent. The 16S rRNA sequences of paired AF and CB were 99.9–100% identical, while no identical sequences were found between different pregnancies.ConclusionsPreviously unrecognized, uncultivated or difficult-to-cultivate species are implicated in EONS. Microbial species in paired AF and CB likely share the same infectious origin. Given its prevalence in EONS, F. nucleatum should be placed on the same importance scale as E. coli.
Highlights
Studies of microbes have traditionally focused on bacterial species isolated in culture
Given its prevalence in early-onset neonatal sepsis (EONS), F. nucleatum should be placed on the same importance scale as E. coli
We hypothesized that uncultivated and difficult-to-cultivate organisms in amniotic fluid (AF) carry the potential to breach the fetal barrier, translocating to CB of neonates causing EONS (EONS-I). To test this hypothesis we examined the presence of microbial species in paired AF and CB in pregnancies complicated by intra-amniotic infection (IAI) and/or EONS using culture-dependent and independent methods
Summary
Studies of microbes have traditionally focused on bacterial species isolated in culture. Metagenomic techniques and sequencing technology have revolutionized our understanding of the bacterial diversity [2]. Applications of 16S rRNA-gene sequencing suggested the existence of a far greater microbial diversity in AF than appreciated based on culturedependent methods. In pregnancies where there was evidence of an inflammatory host response, approximately two thirds of microbes detected by culture-independent methods were not isolated by cultures. These included both uncultivated and difficult-to-cultivate species, such as Fusobacterium nucleatum, Leptotrichia (Sneathia), Bergeyella, Peptostreptococcus, Bacteroides and a species of the order Clostridiales. We present a proof-of-concept study to examine the microbial link between intra-amniotic infection (IAI) and early-onset neonatal sepsis (EONS)
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