Microbial Flora of Human Body (Normal Flora)

NORMAL FLORA: These are mixture of micro-organisms regularly found at any anatomical site on or within the body of a healthy person.

Factors influencing normal flora: The makeup of the normal flora depends upon various factors, including: Genetics Age Sex Stress Nutrition Diet Antiobiotic & other drugs

Normal Microbial Flora: Resident Flora: Microbes that are always present on or within body Transient Flora: Microbes that live in or on the body for a period of time (hours, days, weeks, months) then move on or die off

Anatomical sites involved: Skin Eyes (i.e Conjunctiva) Nose (i.e Respiratory tract) Mouth (i.e Human Oral Cavity) Ears Genitourinary tract Alimentary canal

EXAMPLES OF TISSUE TROPISM OF SOME BACTERIA ASSOCIATED WITH HUMANS BACTERIUM TISSUE Corynebacterium diphtheriae Throat N.gonorrhoeae Urogenital epithelium S.mutans Tooth surfaces S.salivarius Tongue surfaces E.coli Small intestine epithelium S. aureus Nasal membranes S.epidermidis Skin

Normal flora of Skin: Important bacteria: 1. Staphylococcus epidermidis 2. Micrococcus sp. 3. Corynebacterium sp. 4. Mycobacterium smegmatis

Normal Flora of the Conjunctiva: 1. Staphylococcus epidermidis 2. Corynebacterium spp. 3. Propoinibacterium acnes 4. Staphylococcus aureus 5. Viridans streptococci 6. Neisseria spp. 7. Haemophilus influenzae

Normal Flora of the Respiratory Tract: A). The nares (nostrils) : 1. Staphylococcus epidermidis 2. Corynebacteria spp. 3. Staphylococcus aureus 4. Neisseria spp. 5. Haemophilus spp. 6. Streptococcus pneumoniae

Normal Flora of the Respiratory Tract: B) The upper respiratory tract (nasopharynx): 1. Non-hemolytic streptococci 2. Alpha-hemolytic streptococci 3. Neisseria spp. 4. Streptococcus pneumoniae 5. Streptococcus pyogenes 6. Haemophilus influenzae 7. Neisseria meningitidis

Normal Flora of the Respiratory Tract: C) The lower respiratory tract:(trachea, bronchi, and pulmonary tissues): Usually sterile. The individual may become susceptible to infection by pathogens descending from the nasopharynx: e.g. H. influenzae, S. pneumoniae

Sputum Sample

Normal Flora of the Human Oral Cavity: Oral bacteria include: 1. Viridans streptococci 2. Lactobacilli 3. Staphylococci (S. aureus and S. epidermidis) 4. Corynebacterium sp. 5. Bacteroides sp. 6. Streptococcus sanguis (dental plaque) 7. Streptococcus mutans (dental plaque) 8. Actinomyces sp.

The Normal Flora of The Ears (i.e. external ear) The external ears contains a variety of micro-organisms. These include: 1. Staphylococcus epidermidis 2. Staphylococcus aureus 3. Corynebacterium sp

Normal flora of the Urogenital Tract: a) The anterior urethra: 1. Staphylococcus epidermidis 2. Enterococcus faecalis 3. Alpha-hemolytic streptococci. 4. Some enteric bacteria (e.g. E. coli, Proteus sp.) 5. Corynebacteria sp. 6. Acinetobacter sp. 7. Mycoplasma sp. 8. Candida sp. 9. Mycobacterium smegmatis

Normal flora of the Urogenital Tract: b) The vagina: 1. Corynebacterium sp. 2. Staphylococci 3. Non-pyogenic streptococci 4. Escherichia coli 5. Lactobacillus acidophilus* 6. Flavobacterium sp. 7. Clostridium sp. 8. Viridans streptococci 9. Other Enterobacteria

Vaginal Flora:

Urethritis:

Normal flora - Gastrointestinal tract Location (adult) Bacteria/gram contents Duodenum 103-106 Jejunum and ileum 105-108 Caecum and transverse colon 108-1010 Sigmoid colon and rectum 1011 In the normal adult colon, 96–99% of the resident bacterial flora consists of anaerobes: bacteroides species, especially B fragilis; fusobacterium species; anaerobic lactobacilli, e.g., bifidobacteria; clostridia (C perfringens); and anaerobic gram-positive cocci (Peptostreptococcus species).

Normal Flora of the Gastrointestinal Tract (GIT): In breast-fed infants : 1. Bifido bacteria account for more than 90% of the total intestinal bacteria. 2. Enterobacteriaceae 3. Enterococci 4. Bacteroides 5. Staphylococci 6. Lactobacilli 7. Clostridia

Normal Flora of the Gastrointestinal Tract (GIT): In bottle-fed infants: Bifidobacteria are not predominant. When breast-fed infants are switched to a diet of cow's milk or solid food, bifidobacteria are progressively joined by: 1. Enterics 2. Bacteroides 3. Enterococci 4. Lactobacilli 5. Clostridia

Normal Flora of the Gastrointestinal Tract (GIT): In the upper GIT of adult humans mainly acid-tolerant lactobacilli present: e.g. Helicobacter pylori

Normal Flora of the Gastrointestinal Tract (GIT): The proximal small intestine: 1. Lactobacilli 2. Enterococcus faecalis 3. Coliforms 4. Bacteroides

The flora of the large intestine (colon): Enterococci Clostridia Lactobacilli Bacteroides Bifidobacterium (Bifidobacterium bifidum) Escherichia coli Methanogenic bacteria Viridans streptococci Staphylococcus sp. Proteus sp. Candida albicans (Yeast) Mycoplama sp.

THE ROLE/ BENEFITS OF THE NORMAL FLORA: 1. The normal flora synthesize and excrete vitamins in excess of their own needs, which can be absorbed as nutrients by the host. For example, enteric bacteria secrete Vitamin K and Vitamin B12, and lactic acid bacteria produce certain B-vitamins.

THE ROLE/ BENEFITS OF THE NORMAL FLORA: 2. The normal flora prevent colonization by pathogens by competing for attachment sites or for essential nutrients.  This important beneficial effect, which has been demonstrated in the oral cavity, the intestine, the skin, and the vaginal epithelium. 

THE ROLE/ BENEFITS OF THE NORMAL FLORA: 3. The normal flora may antagonize other bacteria through the production of substances which inhibit or kill non-indigenous species. Intestinal bacteria produce a variety of substances like non-specific fatty acids, peroxides and highly specific bacteriocins, which inhibit or kill other bacteria.

THE ROLE/ BENEFITS OF THE NORMAL FLORA: 4. The normal flora stimulates the development of certain tissues, i.e., the caecum (in animals) and certain lymphatic tissues (Peyer's patches) in the GI tract. The caecum of germ-free animals is enlarged, thin-walled, and fluid-filled, compared to that organ in conventional animals.

THE ROLE/ BENEFITS OF THE NORMAL FLORA: 5. The normal flora stimulates the production of “cross-reactive antibodies’’. Since the normal flora behave as antigens in an animal, they induce an Ab mediated immune response.  Low levels of antibodies produced against components of the normal flora are known to cross react with certain related pathogens, and thereby prevent infection or invasion.

Sterile tissues: In a healthy human, the internal tissues such as: blood brain muscle Cerebrospinal fluid (CSF) are normally free of microorganisms.

Role of Microbiologist: Accurate diagnosis: by Rapid/ quick, meaningful reporting Role of Physician: Proper treatment with antimicrobial regimen/ standard guidelines by avoiding overuse*/ misuse of antimicrobials * by treating pathogen, NOT the normal flora!!

NATURAL MICROBIAL HABITATS Animals and Animal Products Soil Water Air Animals and Animal Products

HOST Host-Parasite Interactions DISEASE TRIAD PATHOGEN ENVIRONMENT Microbial Interactions OTHER MICROBES

Symbiotic Relationship: Mutualistic/ mutualism: Both organisms benefit – “mutually benefical” Commensalistic/ commensalism: One organism benefits, the other is neither helped nor harmed Opportunistic: Under normal conditions, microbe does not cause disease, but if conditions become conducive , it can cause disease. (Immuno-compromised or immuno-suppressed conditions)

Mutualistic Escherichia coli : Synthesizes Vitamin K & B complex Vitamins In return, we provide a warm, moist nutrient rich environment for Escherichia coli

Commensalistic We have no Commensalistic relationships with Bacteria If Bacteria are in or on our body, they are either helping us (Microbial Antagonism) or harming us.

Opportunistic: Escherichia coli - normally in our digestive tract where it causes no problems, but if it gets into the urinary tract it can become pathogenic. Staphylococcus aureus – commonly found in the upper respiratory tract, but if it gets into a wound or a burn it can become pathogenic

Probiotics/ Prebiotics: Oral administration of living organisms to promote health Species specific: adherence and growth (tropism) Prebiotic: Non-digestible food that stimulates growth or activity of GI microbiota, especially bifidobacteria and lactobacillus bacteria Typically a carbohydrate: soluble fiber

KEY QUESTIONS: 1. Define normal microbial flora. Mention the role/ benefits of normal flora in human body. 2. Normal flora of mouth and upper respiratory tract. 3. Normal flora of skin. 4. Normal flora of gastro-intestinal tract. 5. Normal flora of genitourinary tract.

Nocardia Morphologically resembles Actinomyces. They are acid fast up to 1% Sulphuric acid. Majority of them are saprophytes. Species: N. asteroides. N. brasiliensis. N. madurae

Culture: Readily grow on ordinary media. Requires incubation for 3 weeks, usually produce pigmented colonies. Pathogenesis: Mainly produces opportunistic infections in immuno-compromised persons. Causes mainly pulmonary disease like pneumonia, lung abscess or lesion resembling tubercolosis. May cause mycetoma.

Culture: Lab. Diagnosis: Specimen: Pus or sputum. Gram’s staining: Gram positive ZN Staining: Acid fast (1% Sulphuric acid) Culture:

Treatment: MEDICAL Rx- sulfa drugs like TMP-SMX (Cotrimoxazole) for three months. SURGICAL Rx- drainage of abscess

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