What are the routes of entry for Group B Streptococcus (Streptococcus agalactiae)?

Medical Advisory BoardAll articles are reviewed for accuracy by our Medical Advisory Board
Educational purpose only • Exercise caution as content is pending human review
Article Review Status
Submitted
Under Review
Approved

Last updated: September 29, 2026 • View editorial policy

Have a follow-up question?

Our Medical A.I. is used by practicing medical doctors at top research institutions around the world. Ask any follow up question and get world-class guideline-backed answers instantly.

Ask Question

B群溶連菌の侵入経路

B群溶連菌(GBS)の新生児への主要な侵入経路は、母体の膣からの垂直感染であり、具体的には膣から羊水への上行性感染と産道通過時の曝露の2つの経路がある。1

新生児早期発症感染における侵入経路

主要な感染メカニズム

新生児の早期発症感染は、GBSに定着している母体の膣からの垂直感染により獲得される1。感染は以下の2つの主要な経路で起こる:

  • 上行性感染経路: GBSは陣痛開始後または破水後に膣から羊水へ上行する。重要な点として、GBSは無傷の膜を通過して侵入することも可能である1
  • 産道通過時の曝露: 新生児は産道通過中にGBSに曝露され、消化管や気道の粘膜部位に定着する可能性がある1

感染の進行過程

上行性感染経路では、GBSが羊水に到達した後、胎児の肺に吸引され、その結果菌血症を引き起こす1。この経路が最も重篤な早期発症疾患(生後24-48時間以内に発症)につながる。

母体における一次的な定着部位

消化管がGBSの主要なリザーバーであり、膣への定着の供給源となっている1。妊婦の約10-30%が膣または直腸にGBSを保菌している1。

腸管上皮への侵入メカニズム(研究知見)

最近の研究により、特に高病原性CC17株における腸管上皮バリアの侵入メカニズムが明らかになっている:

  • 傍細胞経路: GBSは細胞間接合部を一過性に開放させることで、上皮細胞層を通過する2
  • インテグリン媒介侵入: α3β1およびα2β1インテグリンを介して、分極した腸管上皮細胞の側面から侵入する3, 4
  • エンドサイトーシス経路: カベオラおよび脂質ラフト依存性のエンドサイトーシスとアクチン再構成を伴う4

臨床的重要性

妊娠中のGBS保菌は早期発症疾患の最も重要な危険因子であり、GBS陽性妊婦は陰性妊婦と比較して25倍以上のリスクがある1。予防措置を講じない場合、保菌母体から出生した新生児の1-2%が早期発症GBS感染症を発症する1。

注意すべき点

  • 膜の早期破水や長時間の破水(12時間以上)は、上行性感染のリスクを増加させる1
  • 妊娠37週未満の早産もリスク因子である1
  • 尿中のGBS検出は重度の母体定着を示し、より高い感染リスクと関連する1

References

Related Questions

What are the routes of entry for Group B Streptococcus in adult patients?
Is Streptococcus agalactiae (Group B Streptococcus, GBS) considered a culture contaminant in blood cultures?
Is Streptococcus agalactiae the same as Group B Streptococcus?
In a 65-year-old patient with a urine culture growing Group B beta‑hemolytic Streptococcus (10,000–25,000 CFU/mL) but no urinary symptoms after treatment for a yeast infection, should I treat the organism with penicillin‑based therapy?
In an 87‑year‑old patient with Streptococcus agalactiae isolated from urine, should antibiotics be administered and what is the recommended regimen if treatment is indicated?
Which SGLT2 inhibitor and dosing regimen is recommended for a diabetic patient without coronary artery disease, based on renal function (eGFR) and absence of contraindications?
In irritable bowel syndrome, does abdominal pain typically improve markedly after a bowel movement?
What are the roles and recommended doses of N‑acetylcysteine, taurine, enalapril, telmisartan, and alpha‑ketoanalogues in a patient with stage 1 chronic kidney disease?
What are the routes of entry for Group B Streptococcus in adult patients?
In a 52-year-old obese man with hypertension, hyperlipidemia, atrial fibrillation on apixaban, an angiotensin receptor blocker (ARB), and atorvastatin, who has daytime sleepiness (Epworth Sleepiness Scale 16), loud snoring, witnessed breathing pauses, and an in‑home sleep test showing fewer than three events per hour, what is the next best step in management?
In a 66-year-old male (88.6 kg, creatinine 1.29 mg/dL, eGFR 61 mL/min/1.73 m²) on continuous tube feeding (232 g carbohydrate per 24 h) who received 30 units of NPH insulin at 2100 h with an insulin‑sensitivity factor of 25 mg/dL per unit and blood glucose readings of 146 mg/dL at 2100 h, 97 mg/dL at midnight, and 70 mg/dL at 0320 h, what should his morning NPH insulin dose be at 8 am and what should his insulin‑sensitivity factor be?

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.