RELATIONSHIP OF THE MICROBIOME AND THE HUMAN BODY: The great majority of these are commensals, defined as organisms that live symbiotically on or within the human host but rarely cause disease. Anatomic sites where bacteria are normally found include the skin (staphylococci and diphtheroids), oropharynx (streptococci, anaerobes), large intestine (enterococci, enteric bacilli), and vagina (lactobacilli). Enteric bacilli
DISEASES ASSOCIATED WITH THE MICROBIOME: Microbes do not exist in the human body in isolation but in complex communities and habitats. Imbalances in the composition of these habitats are associated with human infection and disease. One example of an infection that can result from a perturbed microbiota community is that caused by Clostridium difficile. C. difficile is an anaerobic gram-negative rod that causes intestinal disease in the setting of antibiotic administration. Antibiotics alter the structure and function of an individual’s gut microbiota, reducing the body’s innate resistance to colonization with C. difficile organisms (and other enteric pathogens) and providing them a niche to multiply and elaborate their enterotoxins. Innate immunity
ANTIBIOTIC INTERACTION AND THE MICROBIOME: Similarly, broad-spectrum antibiotics will destroy normal vaginal flora, such as lactobacilli, and allow overgrowth of Candida (yeast) species, resulting in Candida vaginitis. Determining when an isolate is a component of the normal flora rather than an invasive pathogen may be difficult. For example, culture of staphylococci from a blood sample may represent skin contamination at the time of phlebotomy or may indicate a potentially life-threatening bloodstream infection. Helpful clues include burden of organism (eg, number of positive blood cultures), symptoms and signs of infection (eg, cough, fever), and the presence of inflammatory cells (eg, polymorphonuclear cells in the sputum and an increased proportion of immature neutrophils in the blood).
Isolation of an obligate pathogen such as Mycobacterium tuberculosis from any anatomic site is diagnostic of infection. Fortunately, few microorganisms are absolute pathogens. For example, Neisseria meningitidis, a major bacterial cause of meningitis, can be cultured from the oropharynx of as many as 10% of asymptomatic individuals, in which case it represents transient normal flora. Even if asymptomatic, the host can serve as a carrier, transferring bacteria to susceptible individuals. Infections resulting from commensals that rarely cause disease (eg, Candida albicans) or organisms ubiquitous in the environment that are generally not considered human pathogens (eg, Aspergillus) are termed opportunistic infections. These infections occur almost exclusively in immunocompromised hosts, such as HIV-infected patients or transplant recipients. HIV/AIDS
The agents are opportunists in that they take advantage of impaired host immunity to cause infection but rarely cause disease in a healthy host. The presence of bacteria on a body surface without causing disease is called colonization, whereas invasion of the tissues by a microorganism that causes disease is termed infection. The site from which an organism is cultured is important in differentiating colonization from infection. Growth of any microorganism from a normally sterile site such as blood, cerebrospinal fluid,individuals are then at increased risk for life-threatening infections such as Pseudomonas pneumonia.
RELATED;
1. Bacteriology
2. Virology
3. Normal flora of the human body
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