Miss Rashidah Hj Iberahim
MIC342 - Miss Rashidah Hj Iberahim
Types of Pathogens

 Primary Pathogens
 Cause disease upon infection, not normally associated with
host
1.
2.
Plague (Yersinia pestis),
influenza virus
 Opportunistic Pathogens
 Cause disease under some circumstances, sometime members
of normal flora
1.
2.
Pseudomonas,
Candida albicans
Progression of Disease

 Transmission: infectious dose from 10-10 organisms
6
 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
Proposed by Robert Koch
Conclude that a microbe causes a particular
disease

Must fulfill four postulates
1. Microorganism must be present in every case of
the disease
2. Organism must be grown in pure culture from
disease hosts
3. Produce the same disease from the pure culture
4. Organism recovered from experimentally infected
hosts
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

 1. Encounter:





fecal-oral (cholera)
human-human (tuberculosis)
animal-human (rabies)
vector-borne (plague, lyme disease)
environmental contact (anthrax)
Establishing an Infection

 2. Adherence
 Prevents early clearance
 Often bind host tissues via pili
 Specificity can determine host range of pathogen
Establishing an Infection
 3. Colonization: multiplication and maintainance
 Competition with normal
flora
 Resist:
1.
2.
3.
4.
5.
6.
bile
stomach acid
peristalsis
skin secretions
IgA (mucosal antibodies)
compete with host for iron
4.
Establishing an Infection

Molecule Delivery
 Affects target cell
structure and host
response
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

 m/org that normally found in particular area that do
not cause harm to host cell and body system
 Also known as microflora
Harmful

 *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

 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

Skin
Gram positive org:
1. Staphylococcus sp,
2. Micrococcus,
3. Coryneform bacteria/Demodex folliculorum (opening glands –
eyebrows)
Urogenital
1.
2.
3.
4.
5.
M. smegmatis,
Lactobacili,
Streptococci,
Staphylococcus,
E.coli
Body system w/out
normal flora

 Lower respiratory tract
 Systemic and cardiovascular
 Nervous system
Skin Flora

MIC342 - Miss Rashidah Hj Iberahim
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
Sweating

 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 Demodex folliculorum
MIC341 - Miss Rashidah Hj Iberahim
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 flora

Gram positive org.
1. Staphylococcus sp
2. Micrococcus
3. Coryneform bacteria
 Demodex folliculorum (opening glands – eyebrows)
MIC341 - Miss Rashidah Hj Iberahim
Urogenital Flora

MIC342 - Miss Rashidah Hj Iberahim
Urogenital

 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
Cont.

 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..

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