Human Normal Microbiota Lecture PDF

Human Normal Microbiota  Relationship Between Individuals Symbiosis -Permanent association between two different organisms. Types of symbiosis  Normal Flora Definition Normal flora is the mixture of microorganisms that regularly are found at an...

Human Normal Microbiota  Relationship Between Individuals Symbiosis -Permanent association between two different organisms. Types of symbiosis  Normal Flora Definition Normal flora is the mixture of microorganisms that regularly are found at any anatomical human body. site of The normal flora of human consist of: - a few eukaryotic fungi and -bacteria are the most and obvious numerous normal flora. component of the Viruses and parasites are usually not considered members of the normal flora, although they can be present in asymptomatic individuals.  Human Microbiome = Normal flora The term human microbiome is often used to describe the normal flora. Many new bacteria have been identified as members of the microbiome. The members of the normal flora vary in both number and kind from one site to another. Although the normal flora extensively populates many areas of the body, the internal organs usually are sterile.  Normal Flora A fetus is sterile when born (No Normal Flora), then newborn start having the normal flora from its mother, air, food and the environment. Our internal organs are sterile like the spleen, liver, pancreas, bladder, CSF, and blood unless during infection. Normal flora differ from one human to another depending on age, diet, and geographic habitat.  Colonization vs Infection Colonization - presence of microorganisms on skin or mucosa; no penetration into tissues. Typical of normal flora. Pathogenic microorganisms occasionally also show colonization behavior. Infection - Invasion of a host organism by microorganisms, proliferation of the invading organisms, and host reaction. Resident microbiota vs Transient microbiota The skin and mucous membranes always harbor a variety of microorganisms that can be arranged into two groups: Resident flora Microorganisms regularly found in a given area at a given age. If disturbed, it promptly reestablishes itself. Transient flora Nonpathogenic or potentially pathogenic microorganisms that inhabit the skin or mucous membranes for hours, or days.  Transient Normal Flora Normal flora that are temporarily living on and within humans. The transient microbes living in the external environment are attracted to moist, warm body areas. Why are these microbes temporary?? 1. They may be washed from external areas by bathing. 2. They may not be able to compete with resident normal flora. 3. They may be killed by substances produced by the resident normal flora. 4. They may not survive in the acidic or alkaline pH of the site. 5. They may be flushed away by bodily secretions like tears, sweat, oil, urine, feces,... If the resident flora is disturbed, transient microorganisms may colonize, proliferate, and produce disease. BENEFICIAL FUNCTIONS OF NORMAL FLORA (1) They are part of protective host defense mechanism. Prevent colonization by pathogens and possible disease by “bacterial interference”. The nonpathogenic resident bacteria occupy attachment sites on the skin and mucosa that can interfere with colonization by pathogenic bacteria. The ability of members of the normal flora to limit the growth of pathogens is called colonization resistance. If the normal flora is suppressed, pathogens may grow and cause disease.  BENEFICIAL FUNCTIONS OF NORMAL FLORA (2) They may serve a nutritional function. Bacteria of the gut provide important nutrients, such as vitamin K, and aid in digestion and absorption of nutrients. Poorly nourished people have vitamin deficiency. (3) Bacterial colonization of a newborn infant acts as a powerful stimulus for the development of the immune system.  HARMFUL EFFECTS OF NORMAL FLORA Members of the normal microbiota may themselves produce disease under certain circumstances. 1)When individuals are immunocompromised, normal flora can overgrow and become pathogenic. 2)When potential pathogens gain a competitive advantage due to diminished populations of harmless competitors C. difficile growing in the gut after antibiotic therapy. 3) Although these organisms are nonpathogens in their usual anatomic location, they can be pathogens in other parts of the body. For example, if large number of streptococci of the viridens group in the upper respiratory tract are introduced to the bloodstream (e.g. following tooth extraction), they can settle on the deformed or the prosthetic heart vessels and produce infective endocarditis.  When we get colonized with normal flora A human first become colonized by normal flora at the moment of birth and passage through the birth canal. Handing and feeding of the infant after birth leads to establishment of a stable normal flora of skin, oral cavity and intestinal tract in about 48 hour.  Microecosystem - Microecology Skin Staphy Mouth E. coli Nasopharynx Pseudomonas Ear Strepto Eye Nesseria Gastrointestine Corynebacteria Urinary tract …. Reproductive tract …. The Members of Normal Flora and Their Anatomic Locations Medically Importan t Members of the Normal Flora  SKIN Aerobic Bacteria: - Present in the outer layer of skin. - Staphylococcus epidermidis (accounts 90%) + Staphylococcus aureus. Anaerobic Bacteria: (More than Aerobic bacteria) - Present in the deeper skin layers, hair follicles, and sweat. - Propionibacterium acnes. Skin normal flora are generally harmless but it might cause bloodstream infections if skin was penetrated.  Important Members of the Normal Flora Skin Staphylococcus epidermidis Staphylococcus aureus Micrococcus species Streptococci Corynebacterium species Propionibacterium species Acinetobacter species Small numbers of other organisms (Candida species, Pseudomonas aeruginosa, etc).  EYES The conjunctiva of the eye has primarily S. epidermidis, followed by S. aureus, C. diphtheroids, and S. pneumoniae. Some skin normal flora are also present but at fewer amounts. Tears (Lysozyme enzyme), mucus, and oil will protect the conjunctiva of the eye from colonization by more bacteria. Normal Flora in the Eye  EARS The middle ear and inner ear: are usually sterile. The outer ear and the auditory canal: contain the same normal flora of the skin. When the person coughs, sneezes, or blows his nose, these microbes may move into the middle ear where they cause infection.  Respiratory Tract Upper Respiratory Tract: - Nose and throat have Many microorganisms. Some are normal flora, some are opportunistic, and others are carried like C. diphtheroids. - Nasopharynx: Streptococcus pneumoniae In immune compromised or elderly it might cause acute bacterial pneumonia. Lower Respiratory Tract: Is usually sterile because the mucous membranes of the lungs remove any microbes. Important Members of the Normal Flora The throat contains a mixture of viridans streptococci, Neisseria species, and S.epidermidis. These nonpathogens occupy attachment sites on the pharyngeal mucosa and inhibit the growth of the pathogens Streptococcus pyogenes, Neisseria meningitis, and S. aureus, respectively.  Oral Cavity (Mouth) They have both aerobic and anaerobic bacteria. The most common ones are: C. diphtheroides, S. aureus, and S. epidermidis. Also yeasts, molds, protozoa, and viruses can be living in the mouth. Teeth and Gingiva: S. mutans Poor dental hygiene help bacteria to grow and cause dental caries, gingivitis,... After dental surgeries, there might be a risk of bloodstream infection that might cause endocarditis.  The Role of the Normal Mouth Microbiota in Dental Plaque and Caries Dental plaque as a complex biofilm The initial colonizing organisms are mainly gram-positive bacteria Early colonizer is Streptococcus sanguis, but other streptococci (S. mutans, S. mitis, S. salivarius, S. oralis, S. gordonii), lactobacilli, and Actinomyces species are usually present. Late colonizers can appear in the biofilm in as little as 2–4 days and consist primarily of gram-negative anaerobes (eg, Porphyromonas, Prevotella, Fusobacterium, Veillonella species), including anaerobic spirochetes (eg, Treponema denticola), and more Actinomyces species. High-molecular-weight extracellular glucan polymers are synthesized, which act like a cement binding the plaque biofilm together. 300–400 bacterial species present in mature dental plaque.  Caries S. mutans is considered to be the dominant organism for the initiation of caries. Streptococci (S. salivarius, S. sanguis, S. sobrinus) Lactobacilli (L. acidophilus, L. casei) Actinomycetes (A. viscosis, A. naeslundii)  Control of Caries Physical removal of plaque Limitation of sucrose intake Good nutrition with adequate protein intake Limitation of carbohydrates Frequent cleansing  Gastrointestinal Tract Stomach: Only few bacteria are present in the stomach due to gastric enzymes and acidic pH. Small intestine: Only few normal flora are present in the upper part of small intestine because bile kills them. Lower parts have more no. of normal flora. Large intestine: - Has more bacteria than any other part of the body. 99% of normal flora in the large intestine are anaerobic Bacteroides spp. - Also many fungi, protozoa, and viruses can live there. - Many of the normal flora are opportunistic i.e. if they move to other areas e.g. E.coli cause urinary infection. Gastrointestinal tract  Urogenital Tract Urinary Tract Kidneys, Ureters and Urinary Bladder: are sterile. Lower Urethra and external opening: bacteria primarily S. epidermidis, yeast, and viruses has the same bacteria present on the skin. The female urethra can become colonized with fecal flora such as E. coli, which predisposes to urinary tract infections. Genital Organs Male and female genitals: are sterile except vagina. Vagina: Lactobacillus spp. keeps the pH acidic to protect the vagina from opportunistic infections e.g. fungal vaginitis (Candida albicans) or bacterial vaginosis (Bacteroides spp., Gardnerella vaginalis). Loss of this protective effect by antibiotic therapy can lead to infection by Candida ("yeast infection").  Summary Normal flora are those microorganisms that are the permanent residents of the body that everyone has. Some people can be colonized, either transiently or for long periods, with certain organisms, but those are not considered members of the normal flora. Carriers (also called chronic carriers) are those individuals in whom pathogenic organisms are present in significant numbers and therefore are a source of infection for others.  Summary The normal microbiota denotes the population of microorganism that inhabit the skin and mucous membranes of healthy normal persons. The normal microbiota provides a first line of defense against microbial pathogens, assists in digestion, and contributes to maturation of the immune system.  Summary Normal flora organisms are either bacteria or yeasts. Viruses, protozoa, and helminths are not considered to be members of thenormal flora (but humans can be carriers of some of these organisms).  Summary Normal flora organisms inhabit the body surfaces exposed to the environment, such as the Skin, Oropharynx, Intestinal tract, and vagina. Members of the normal flora differ in number and kind at various anatomic sites.  Summary Members of the normal flora are low-virulence organisms. In their usual anatomic site, they are nonpathogenic. However, if they leave their usual anatomic site, especially in an immunocompromised individual, they can cause disease. Colonization resistance occurs when members of the normal flora occupy receptor sites on the skin and mucosal surfaces, thereby preventing pathogens from binding to those receptors.  Summary The skin and mucous membranes always harbor a variety of microorganisms that can be divided into: (1) resident microbiota, which are fixed types of microorganisms regularly found in a given area at a given age that, if disturbed, promptly reestablish themselves, and (2) transient microbiota, which are nonpathogenic or potentially pathogenic microorganisms that inhabit the skin or mucous membranes for hours, days, or weeks. References Levinson, Review of Medical Microbiology and Immunology. Chapter 6