Proof of principle: Physiological transfer of small numbers of bacteria from mother to fetus in late-gestation pregnant sheep

Abstract

The fetus is thought to develop in a sterile environment in utero. Long standing dogma that “the uterus and the feto‐placental unit is “sterile” is based primarily on microbiological culture‐based techniques that were unsuccessful in growing “culture resistant” bacteria or intracellular bacteria. We have reported the presence of low numbers of bacteria in tissues from normal sheep fetuses in pregnancies not complicated by infection. The exposure of the fetus to bacteria might aid neonatal survival by informing fetal immune development. We propose that the fetus is not sterile and that bacteria or fragments of bacteria can be transferred from mother to fetus. We hypothesize that inoculation in the maternal mouth results in the appearance of bacteria in the fetus. We used S. aureus containing green (GFP), red (RFP), or far‐red (FRFP) fluorescent protein‐expressing plasmids to inoculate late‐gestation pregnant sheep (gestational age= 130–135 days, n=7) intravenously (GFP, 104 cfu), into maternal mouth (RFP, 104 cfu) and vagina (FRFP, 104 cfu). These were small doses of bacteria which did not cause physiological (no fever) or psychological (no anorexia) signs of infection. Five to seven days post maternal inoculation, animals were humanely sacrificed, and fetal tissues were collected, and DNA was extracted from placenta and fetal liver, spleen, and cerebral cortex. We probed for GFP plasmid using several primer pairs for endpoint PCR. While detection of whole‐length plasmids was not successful, PCR reactions probing for smaller fragments of plasmid were successful. We found GFP plasmid DNA in all tissues in 10/10 fetal livers and RFP in 10/10 livers. The appearance of GFP and RFP‐labelled bacteria in fetal liver (p=7.497e‐06) was statistically significant as tested by Chi‐Square analysis. We did not detect significant FRFP plasmid DNA in liver. Analysis of tissues by immunohistochemistry revealed GFP and RFP‐expressing bacteria in fetal tissues, although most appeared to be in aggregates. We conclude that S. aureus, introduced in small numbers in maternal mouth and bloodstream, appear in the fetus and placenta. We were unable to determine whether these bacteria were alive in the fetus. Support or Funding Information This work was supported by HD033053, AI120195, and HL083810 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Evolving Technologies in Gastrointestinal Microbiome Era and Their Potential Clinical Applications

“…Prior to its birth, it is presumed that the unborn is free of microbial flora, and that at birth, the infant first comes in contact with the resident microbial flora of the mothers’ vagina if birth was through the natural birth canal, or the microbial flora of the mothers’ skin if birth was through cesarean section [ 20 , 21 , 22 ]. Although some studies [ 23 , 24 , 25 ] have suggested the early inoculation of the fetus with bacteria and bacteria DNA through the placenta. The study by de Goffau et al [ 26 ] reported that the human placenta has no microbiome.…”

Potential hazardous effects of printing room PM2.5 exposure include promotion of lung inflammation and subsequent injury

“…The lungs have previously been considered a sterile environment, and assessment of pulmonary disease has been examined from a bacterial pathology perspective (41). recently, 16s ribosomal rna studies and metagenomics revealed the presence of a flexible microbiota in the upper and lower respiratory tract, blood, placenta and amniotic fluid (42). increasing evidence has shown that bacteria are present in the lungs and serve key roles in fatal pneumonia, which can be both beneficial and harmful (43,44).…”

Contamination Is Not Linked to the Gestational Microbiome

“…Seventeen pregnant ewes of known gestational age were sampled for this study; all ewes and their fetuses/lambs had undergone surgery to place fetal catheters and/or telemetry devices for study in other protocols (Table 4). Ewes were housed and euthanized, and tissues were sampled as described by Yu et al (12). For all animals, the tissues were collected from the fetus/lamb, including liver, lung, spleen, and stool.…”

“…We have recently reported evidence that bacterial cell components can be found in the late-gestation fetus after inoculation of the mother with live bacteria. In that study, intravenous inoculation of pregnant ewes with 100 CFU of green fluorescent protein (GFP)-expressing Staphylococcus aureus resulted in the detection of GFP plasmid DNA and GFP protein in placenta and fetal tissues 4 to 6 days later (12). The inoculation did not cause any clinical signs of infection or septicemia in the ewes (which maintained normal body temperature and food intake).…”