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Microbiology

25.2 Bacterial Infections of the Circulatory and Lymphatic Systems

3 min readLast Updated on June 18, 2024

Bacterial infections in the circulatory system can wreak havoc on our bodies. From sepsis to endocarditis, these infections trigger widespread inflammation and organ dysfunction. Understanding how bacteria spread and interact with our immune system is key to grasping their impact.

Zoonotic diseases add another layer of complexity to circulatory infections. Plague, tularemia, and Lyme disease can all be transmitted from animals to humans, causing a range of symptoms. Knowing their transmission routes and treatments is crucial for managing these potentially severe infections.

Pathogenesis and Clinical Manifestations

Pathogenesis of circulatory bacterial infections

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  • Sepsis
    • Pathogenesis: Systemic inflammatory response syndrome triggered by bacterial toxins or components (lipopolysaccharide) leads to widespread inflammation, endothelial damage, and coagulation abnormalities
    • Clinical manifestations: Fever, tachycardia, tachypnea, hypotension, organ dysfunction; severe cases may progress to septic shock and multi-organ failure (kidney failure, liver failure)
  • Endocarditis
  • Bacteremia
    • Pathogenesis: Presence of viable bacteria in the bloodstream resulting from primary infections, surgical procedures, or intravenous drug use; transient bacteremia can occur after dental procedures or manipulation of infected tissues
    • Clinical manifestations: Fever, chills, malaise; if untreated, can lead to sepsis; complications depend on the causative organism and host immune status

Host-Pathogen Interactions

Zoonotic Bacterial Diseases

Zoonotic diseases of circulatory system

  • Plague (Yersinia pestis)
    • Transmission: Bite from infected fleas or contact with infected animals (rodents, prairie dogs)
    • Symptoms depend on the form of the disease:
      1. Bubonic: Fever, chills, weakness, buboes (swollen, tender lymph nodes in groin, armpit, or neck)
      2. Pneumonic: Fever, chills, cough, chest pain, dyspnea
      3. Septicemic: Fever, chills, abdominal pain, shock, disseminated intravascular coagulation
    • Treatment: Antibiotics (streptomycin, gentamicin, doxycycline)
  • Tularemia (Francisella tularensis)
    • Transmission: Contact with infected animals (rabbits, hares), tick or deer fly bites, inhalation, ingestion of contaminated food or water
    • Symptoms: Fever, chills, headache, muscle aches, cutaneous ulcers, lymphadenopathy; pneumonic form presents with cough, chest pain, dyspnea
    • Treatment: Antibiotics (streptomycin, gentamicin, doxycycline)
  • Lyme disease (Borrelia burgdorferi)
    • Transmission: Bite from infected Ixodes ticks (deer ticks, black-legged ticks)
    • Symptoms: Erythema migrans rash (bull's-eye rash), fever, chills, fatigue, headache, muscle and joint pain; late-stage symptoms include arthritis, neurologic symptoms (meningitis, facial palsy), cardiac involvement (heart block, myocarditis)
    • Treatment: Antibiotics (doxycycline, amoxicillin, cefuroxime)

Virulence Factors and Diagnostics

Virulence factors in lymphatic infections

  • Adhesion molecules allow bacteria to adhere to host cells and tissues
  • Toxins damage host cells and tissues and modulate immune responses
  • Capsules protect bacteria from phagocytosis and complement-mediated lysis by preventing recognition by immune cells
  • Biofilm formation enables bacterial persistence and resistance to antibiotics and host defenses by creating a protective extracellular matrix

Diagnostic approaches for circulatory infections

  • Blood cultures: Gold standard for diagnosing bacteremia and sepsis
    • Automated systems (BACTEC, BacT/ALERT) detect bacterial growth by monitoring CO2 production
    • Gram staining and biochemical tests (API strips, VITEK) identify the causative organism
  • Serological tests detect antibodies against specific bacterial antigens
    • ELISA and indirect fluorescent antibody tests commonly used for Lyme disease diagnosis
  • Molecular methods detect bacterial DNA or RNA
  • Imaging techniques visualize infections and complications
    • Echocardiography detects vegetations in endocarditis
    • CT scans identify abscesses and other deep-seated infections (psoas abscess, epidural abscess)

Term 1 of 186

16S rRNA Sequencing
See definition

16S rRNA sequencing is a molecular technique used to identify and classify bacteria based on the genetic sequence of the 16S ribosomal RNA (rRNA) gene. This method provides insights into the composition and diversity of the microbial community in various environments, including the human body's urogenital tract and circulatory system.

Key Terms to Review (186)

Term 1 of 186

16S rRNA Sequencing
See definition

16S rRNA sequencing is a molecular technique used to identify and classify bacteria based on the genetic sequence of the 16S ribosomal RNA (rRNA) gene. This method provides insights into the composition and diversity of the microbial community in various environments, including the human body's urogenital tract and circulatory system.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

Term 1 of 186

16S rRNA Sequencing
See definition

16S rRNA sequencing is a molecular technique used to identify and classify bacteria based on the genetic sequence of the 16S ribosomal RNA (rRNA) gene. This method provides insights into the composition and diversity of the microbial community in various environments, including the human body's urogenital tract and circulatory system.



© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.

© 2025 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.