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Table 2 Historical evidence against the female intrauterine microbiome

From: Maternal and early life exposures and their potential to influence development of the microbiome

Year Endometrium or decidua Placenta parenchyma Chorion Amnion Amniotic fluid Meconium or fetal intestine Culture-independent detection Culture-dependent detection a Ref.
Method Conclusion Method Conclusion
1958       n/a n/a Aerobic and anaerobic; Blood and Chocolate 1/10 patients yielded positive endometrial culture, suggests endometrium is usually sterile [251]
1962        n/a n/a Culture, unspecified Occasional diphtheroid colonies in 2/44 abdominal punctures, suggests contamination not intrauterine infection [252]
1966       n/a n/a Aerobic: serum broth, PPLO, cooked meat, thiol, blood. Anaerobic: chocolate, thioglycolate, Casman’s Positive endometrial culture decreases with time following intrauterine device insertion [253]
1967       n/a n/a Aerobic: blood, MacConkey. Anaerobic: blood, thioglycolate Pathogens were cultured in 6% of endometrial samples, suggests uterine cavity is usually sterile [271]
1969        n/a n/a Aerobic: blood, desoxycholate, chocolate. Anaerobic (with H2): blood H2 44/50 negative cultures, 2/50 grew Staphylococcus albus. 4/50 grew Mycoplasma hominis. Trauma of vaginal exams introduces microbiota to enter uterus [254]
1970        Histology (Gram) Unspecified Aerobic and anaerobic culture in blood, MacConkey 1/39 positive pre-labor amniotic fluid culture. 8/78 positive mid-labor amniotic fluid cultures [255]
1971        Histology (Gram) Unspecified Aerobic and anaerobic culture 11/140 positive mid-labor amniotic fluid cultures. No maternal or fetal morbidity supports that amniotic fluid has antibacterial activity [256]
1976        n/a n/a Aerobic: TSA, blood. Anaerobic: PRAS chopped-meat glucose, blood Postive amniotic culture in cases of obvious intraurterine infection. Amniotic fluid removed from the intact amniotic cavity appears to be sterile. [257]
1984        Histology (Gram) 6/46 uncomplicated vaginal deliveries was positive for Gram-positive rods Aerobic: blood, chocolate, MacConkey, thioglycolate. Anerobic: blood, KV 1/46 uncomplicated vaginal deliveries was positive (Group B Strep) [258]
1987       n/a n/a Aerobic: SP-4, 10-B, Thayer-Martin. Murine and primate tissue culture. Anaerobic: BHI All cultures were negative for tested microbes suggesting the nonpregnant endometrium is sterile. [259]
2015        PCR coupled with electrospray ionization mass spectrometry Microbes were identified in 29/231 amniotic fluid samples without the presence of intra-amniotic inflammation Aerobic and anaerobic culture 5/231 positive amniotic fluid samples without intra-amniotic inflammation. 24/231 negative AF samples with intra-amniotic inflammation. [260]
2016      16S rRNA sequencing of the V1-2 HVRs using Illumina MiSeq Could not distinguish placental samples from contamination controls n/a n/a [261]
2018      16S rRNA sequencing of the V1-2 HVRs using Illumina HiSeq Could not detect placenta microbiome in preterm or term births. DNA detection limited to contamination with vaginal fluids or contaminants shared with negative controls n/a n/a [262]
2018        16S rRNA sequencing of the V5-7 HVRs using Illumina MiSeq No evidence of reproducible preterm placental microbiome. Differences depend on placental delivery abdominally or vaginally (thus, delivery contamination) n/a n/a [263]
2018        16S rRNA sequencing of the V3-4 HVRs was quantified using digital droplet PCR then sequenced using Illumina MiSeq No differences seen between membrane-intact and negative control amniotic fluids. Ruptured membranes was associated with higher bacterial DNA levels Anaerobic and aerobic: BHI No bacteria detected from membrane-intact or negative control amniotic fluids. Bacteria were detected in ruptured membrane samples [264]
2018        16S rRNA sequencing of the V4 HVR using Illumina MiSeq Bacterial microbiota of amniotic fluid was indistinguishable from buffer extraction negative controls n/a n/a [265]
2018        18S rRNA sequencing of the V9 HVR using Illumina MiSeq Unable to detect eukaryotic pathogens in placental biopsies from adverse pregnancy outcomes or healthy controls n/a n/a [266]
2019        16S rRNA sequencing of the V1-2 HVRs using Illumina HiSeq Major source of bacterial DNA was contamination from lab reagents and equipment. Placental tissue samples become contaminated during labor and delivery. Only bacteria found before labor was S. agalactiae n/a n/a [273]
2019    16S rRNA sequencing of the V4 HVR using nested PCR followed by Illumina MiSeq with comparative qPCR. WGS metagenomic sequencing using Illumina HiSeq Could not detect microbes in Cesarean-delivered term placenta Anaerobic and aerobic: TSA, chocolate, MacConkey 28/29 placental cultures were negative. 1/29 cultures yielded aerobic Bacillus circulans, Bacillus pumilus, and Brevibacterium casei [267]
2020        PCR coupled with electrospray ionization mass spectrometry. Cell-free DNA sequencing by Illumina NextSeq 500 or HiSeq. Low-biomass background correction. Histology (Gram) Reports reduced false-positive rate, suggesting the amniotic fluid is sterile in normal pregnancy Traditional clinical culture including genital mycoplasma 10/40 cultures were positive, all with clinical chorioamnionitis [14]
2020    16S rRNA gene PCR amplification and visualization of the V2 and V4 HVRs. TaqMan qPCR of the 16S rRNA V3-5 HVRs and Erythromycin resistance methylase B gene. Histology (Gram, anti-lipoteichoic acid, anti-lipopolysaccharide). Scanning electron microscopy No bacterial amplicons were identified (human and mouse) TSA, chocolate, MacConkey, SDC, thioglycolate None of the placental or environmental controls were positive for bacterial growth [13]
2020       16S rRNA sequencing of the V4 HVR by Illumina MiSeq with quantification by 16S rRNA amplification of the V1-2 HVRs by qPCR Bacterial loads from murine placenta and fetal tissues did not exceed those of background technical controls. Samples from maternal sites did exceed controls TSA, chocolate, MacConkey, SP4 with urea and arginine (for Mycoplasma and Ureaplasma) 9/165 placental cultures were positive (5/9 from single mouse). 1/165 fetal intestine cultures grew Staphylococcus hominis [12]
2021        16S rRNA sequencing of the V6-8 HVRs by Illumina MiSeq with comparative qPCR Amniotic fluid and placenta have indistinguishable bacterial DNA from negative controls. No differences between elective Cesarean delivery and vaginal birth. Placenta has anti-microbial activity Aerobic: LB. Anaerobic: Neisseria gonorrhoeae targeted culture Cesarean delivery: 87/152 negative placental cultures, freq. human skin-associated genera. Vaginal delivery: 21/78 negative placental cultures, freq. human vaginal-associated genera [15]
2021       16S rRNA sequencing of the V3-4 HVRs by Illumina MiSeq Neonatal rectal swabs could not be distinguished from negative controls Anaerobic and Aerobic: Columbia, Chocolate, Schaedler, MacConkey, Sabouraud 3/20 meconium samples were positive for anaerobic and aerobic culture. 5/20 samples were positive for only one condition [272]
  1. a Culture Media Abbreviations: A-7 Shepard’s Differential Agar Base, BHI Brain Heart Infusion, BP Baird Parker, CNA Columbia Colistin-Nalidixic Acid, EMB Eosin Methylene Blue, K-V Kanamycin-Vancomycin, LB Luria-Bertani, MRS De Man, Rogosa, and Sharpe, PEA Phenylethyl Alcohol Agar, PPLO PleuroPneumonia-Like Organism, PRAS Pre-Reduced Anaerobically Sterilized, PYG Peptone Yeast Extract Glucose, SDC Sabouraud Dextrose Agar with Chloramphenicol, TSA Tryptic Soy Agar, VRB Violet Red Bile, WC Wilkins-Chalgren