Chapter 4 normal flora host parasite relationship
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Chapter 4 – NORMAL FLORA & HOST PARASITE RELATIONSHIP. Miss Rashidah Hj Iberahim. Types of Pathogens. Primary Pathogens Cause disease upon infection, not normally associated with host Plague ( Yersinia pestis ), influenza virus Opportunistic Pathogens

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Chapter 4 normal flora host parasite relationship


Miss RashidahHjIberahim

MIC342 - Miss Rashidah Hj Iberahim

Types of pathogens
Types of Pathogens

  • Primary Pathogens

    • Cause disease upon infection, not normally associated with host

      • Plague (Yersiniapestis),

      • influenza virus

  • Opportunistic Pathogens

    • Cause disease under some circumstances, sometime members of normal flora

      • Pseudomonas,

      • Candida albicans

Progression of disease
Progression of Disease

  • Transmission: infectious dose from 10-106 organisms

  • Incubation period: few days (common cold)-weeks (hepatitis A)-months (rabies)

  • Convalescence:

    • Clearing (Strep throat, S. pyogenes)

    • Latency (Chicken pox, tuberculosis, cold sores)

Koch s postulates
Koch’s Postulates

  • Proposed by Robert Koch

  • Conclude that a microbe causes a particular disease

  • Must fulfill four postulates

    • Microorganism must be present in every case of the disease

    • Organism must be grown in pure culture from disease hosts

    • Produce the same disease from the pure culture

    • Organism recovered from experimentally infected hosts

Molecular postulates
Molecular Postulates

  • Describe virulence factors

  • Four postulates

  • 1. Virulence gene or its product must be present

  • 2. Virulence gene must transform a non-pathogen into a pathogen

  • 3. Virulence gene must be expressed during disease process

  • 4. Antibodies against gene products are protective

Establishing an infection
Establishing an Infection

  • 1. Encounter:

    • fecal-oral (cholera)

    • human-human (tuberculosis)

    • animal-human (rabies)

    • vector-borne (plague, lyme disease)

    • environmental contact (anthrax)

Establishing an infection1
Establishing an Infection

  • 2. Adherence

    • Prevents early clearance

    • Often bind host tissues via pili

    • Specificity can determine host range of pathogen

Establishing an infection2
Establishing an Infection

  • 3. Colonization: multiplication and maintainance

    • Competition with normal flora

    • Resist:

      • bile

      • stomach acid

      • peristalsis

      • skin secretions

      • IgA (mucosal antibodies)

      • compete with host for iron

Establishing an infection3
Establishing an Infection

4. Molecule Delivery

  • Affects target cell structure and host response

Invasion breaching anatomical barriers
Invasion:Breaching Anatomical Barriers

  • Find new niche with few competitors

  • Gain access to rich nutrient supply

    1. Skin: tough barrier, rely on wounds or insect vectors

    2. Crossing mucous membrane (e.g. intestinal epithelial cells)

Definition of normal flora
Definition of normal flora

  • m/org that normally found in particular area that do not cause harm to host cell and body system

  • Also known as microflora


  • *microorganism in perianal area enter the urinary tract (UT) causing infection in internal UT

    Can prevent infection by:

    • Medical asepsis – personnel and hospital environment should be clean from pathogens

    • Surgical asepsis – instrument used should be sterile and including the surgical room

    • What did you implement in daily life?

MIC341 - Miss Rashidah Hj Iberahim

Normal flora
Normal Flora

  • More bacterial than human cells in the body

    • provide some nutrients (vitamin K)

    • stimulate immune system, immunity can be cross-reactive against certain pathogens

    • Prevent colonization by potential pathogens

      (antibiotic-associated colitis, Clostridium difficile)

Normal flora of body system
Normal flora of body system


Gram positive org:

  • Staphylococcus sp,

  • Micrococcus,

  • Coryneform bacteria/Demodexfolliculorum (opening glands – eyebrows)


  • M. smegmatis,

  • Lactobacili,

  • Streptococci,

  • Staphylococcus,

  • E.coli

Body system w out normal flora
Body system w/out normal flora

  • Lower respiratory tract

  • Systemic and cardiovascular

  • Nervous system

Skin flora
Skin Flora

MIC342 - Miss Rashidah Hj Iberahim

Oils production
Oils production

  • Different area consist of different microflora. Example armpits vs forehead.

  • Moisture area will support larger populations; nutrients from oils and sweat

  • Those normal flora might have capability to produce oils that known as fatty acid providing an acidic condition of particular area

  • Initiating host defense against infection in the 1st line stage

  • But, excess of oils production might resulting an odour of unpleasant smell to the body

MIC341 - Miss Rashidah Hj Iberahim


  • Beside oils, the 2nd line of host defends is the sweat that are salty

  • However, in opposite situation, there are bacteria that able to live in salty area such as Staphylococcus sp.

  • Majority of the skin flora – Gram +ve : Staphylococcus, Micrococcus and Corynebacterium

  • Hair follicles inhabitants – mite Demodexfolliculorum

MIC341 - Miss Rashidah Hj Iberahim

Skin shedding
Skin shedding

  • 3rd line defends is regarding the keratin-degrading fungi

  • It helps in rapid and continuous shedding of skin cells replacing layer by layer

  • Removing of skin cell together with group of m/org on the skin

MIC341 - Miss Rashidah Hj Iberahim

Normal flora1
Normal flora

Gram positive org.

  • Staphylococcus sp

  • Micrococcus

  • Coryneform bacteria

  • Demodexfolliculorum (opening glands – eyebrows)

  • MIC341 - Miss Rashidah Hj Iberahim

    Urogenital flora
    Urogenital Flora

    MIC342 - Miss Rashidah Hj Iberahim


    • Al parts are sterile except urogenital opening

    • Urine collection should have ‘clean catch’ technique

    • E.coli and Lactobacillus are common flora = 100,000 bact/ml of urine

    • Collection during direct puncture (suprapubic) = sterile sample

    • Acid pH, high salt and urea concentration leads to high m/org growth

    • Urine sample should be refrigerated during transportation if delay – high multiplication if stir in RT

    MIC341 - Miss Rashidah Hj Iberahim


    • Mycobacterium smegmatis (acid fast staining bacili) live in external genitalia of female and male

    • Esp under penis of uncircumsized male – smegma

    • If included in the sample, might leads to confusion wt the tuberculosis patient which actually having M. tuberculosis

    • In male, 1/3 of deep are for genital area don’t have normal flora

    MIC341 - Miss Rashidah Hj Iberahim

    In female
    In female..

    Due to hormonal changes..

    • Child-bearing – lactobacili numerous in vagina (eating glycogen)

    • Glycogen in vaginal cell will be fermented become lactic acid and pH decrease to 4.7

    • Childhood and after menopause, lactobacili absent coz no glycogen –replaced by streptococci and staphylococci due to alkaline pH in vagina

    MIC341 - Miss Rashidah Hj Iberahim