Normal flora, also known as commensal bacteria or microbiota, can become pathogenic under certain conditions, including:
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Immunocompromised Host: When the immune system is weakened due to factors such as illness, malnutrition, stress, or immunosuppressive medications, normal flora can take advantage of the compromised state and cause infections.
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Disruption of Normal Flora: Antibiotic use can disrupt the balance of normal flora, allowing opportunistic pathogens to overgrow and potentially cause disease. This is commonly seen with infections like Clostridium difficile.
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Invasive Procedures: Surgical interventions or the introduction of foreign bodies (such as catheters, prosthetic devices, or implants) can provide a pathway for normal flora to enter normally sterile areas of the body, leading to infections.
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Changes in Host Environment: Factors such as hormonal changes, diabetes, or other metabolic conditions can create an environment that favors the growth of certain bacteria over others.
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Trauma or Breaks in Barrier: Any disruption in the skin or mucous membranes can provide an entry point for normal flora to enter tissues where they can cause disease.
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Nutritional Factors: Poor nutrition can alter the immune response and the composition of the microbiota, potentially leading to opportunistic infections.
Under these conditions, normally benign bacteria can turn into pathogens and contribute to disease.