Download The study of pathogenic Bacteria Lecture No

The study of pathogenic Bacteria
Lecture No. 2
Invasiveness: " Pathogens ability to enter, spread , and
multiply "
Many pathogens release chemical products function as enzymes and
enhance the pathogen's invasiveness.
Invasive factors:
Production of extracellular enzymes:
* Collagenase: enzyme able to hydrolyze the protein collagen found
in many connective tissues.
ex. Clostridium perfringens
Promotes the spread of bacilli in tissues.
* Coagulase: enzyme that hastens coagulation (causes clotting in
plasma) such clotting is an advantage to the pathogen because it
walls itself off from invading phagocytes.
ex. Staphylococcus aureus
* Hyaluronidase: "Spreading factor" Enzymes hydrolyzing
hyaluronic acid , a constituent of the ground substance of connective
tissue.
ex. Staphylococci ;Streptococci ; Pneumococci; ;Clostridia.
* Leukocidins are able to kill white blood cells. Produced by some
bacteria .
ex. Staphylococcus aureus ; Strptococcus
* Streptokinase(Fibrinolysin) / many hemolytic streptococci produce
a substance (streptokinase) that activates a proteolytic enzyme of the
plasma (Plasminogen → plasmin) . This enzyme (also called
fbrinolysin) is then able to dissolve coagulated plasma and probably
aids in the spread of streptococci through tissues.
Variation and Viruence:
* Loss of virulence "Attenuation":
Pathogen from diseased host →direct inoculation causes death of the
animal
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1- Pathogen from diseased host →
→
→
→
Inoculation
Successive transfer
in culture
Attenuated
Strain
Animal
remains
healthy
2- Loss of capsule:
ex. Pneumococcus
3- Smooth → Rough colony
Variation ex. Salmonella ; Shigella
4- Loss of temperate phage ex. Corynebacterium diphtheriae ;
Staphylococcus pyogenes
5- Heat and dessication
Enhancement of Virulence
→
→
→
Attenuated
Culture
→
Final animal
dies
1- Successive passage in laboratory animals
2- Using colloidon sacs
3- Presence with other bacteria
ex. Corynebacterium diphtheriae with Streptococcus.
Conserving virulence
123-
Lyophilization
Culture medium containing blood stored in dark and at low
temperatures.
Spore forming bacteria resists unfavorable conditions ,thereforehave
perminant virulence.
Host Factors
Bacterial virulence differs according to:
1- Age / Susceptiblity is greatest in the very old and in the very young.
2- Malnutrition ,drug addicts and alcoholics.
3- Metabolic diseases like diabetes and hormonal upsets including those
that accompany corticosteroid therapy.
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4- Haematological disorders such as leukemia and drug – induced
granulocytopenia.
5- Immunological deficiencies.
Host factors and the Disease process
Portal of entry / various sites of microorganisms
 Skin
Physiological barrier
secretions. From sweat
and sebaceous glands
Mechanical epidermis
Hair follicle
Phagocytic cells
Attack agents that
penetrate skin
sebaceous glands
Sweat gland
Cross section of the skin demonstrating the barriers to infectious agents
ex. Staphylococcus / Corynebacterium are not pathogenic unless →
Abraded skin
depressed immune mechanism
Rabies virus → Transmitted by Dogs bite → Human
Plague /Malaria → Transmitted by insect bites → Human
 Mucosal surfaces
One of the first surfaces on which microorganisms make contact
with the host.
Mucosal surfaces found in:
Gastrointestinal tract ; Respiratory tract ; Salivary and lacrimal
glands; Biliary system and in portions of the genitourinary tract.
Host defense mechanisms at the mucosal surfaces are to prevent:
- Parasite colonization
- Damage by microbial products (ex. Toxins)
Defense mechanisms are:
1- Immunological defense.
III
The presence of SIgA (Secretory IgA) prevent binding of certain
pathogenic microorganisms to the mucosal surfaces.
ex. Staphylococcus mutans
Neisseria gonorrhoae
Some species of Neissiria ;Haemophilus; Streptococcus
→
Produce
Protease
that cleaves
S IgA
2- Microflora
Skin, respiratory tract and digestive tract colonized by indigenous
population of microorganisms.
The antagonistic effect on invading microbial species due to:
 - Change in the pH or oxidation –reduction potential.
 Production of antagonistic product.
 Depletion of essential nutrients.
ex. Anaerobes(In intestinal tract)
→
Produce
ex. Streptococcus viridans(In pharynx)
Fatty acids which inhibits potential
pathogens ex. Shigella;Salmonella
→
Pneumococci
Inhibit growth
ex. Staphylococcus epidermidis
→
Retards
colonization
Staphylococcus aureus in nasal
cavity
3- Mucins /hydrophilic glycoproteins
Present in Intestinal tract and respiratory tract. Functions are:
*- lubrical and water proof of the mucosal surface.
*- Prevent adherence of some microorganisms and their toxic products.
Microorganisms bound by mucin removed via cilliary action or
peristalsis.
4- Lysozyme ,Lactoferrin ,and Peroxidase
Found on the mucosal surface , aid in defense against microbial
invasion.
Lysozyme/found in normal secretions (Effect cell wall):
Tears, nasal secretions, breast milk, genital fluids.
Lactoferrin / iron – binding protein.
Peroxidase / found in saliva ,in combination with thiocyanate and
hydrogen peroxide. Active against several bacteria, fungi, and viruses.
*- Respiratory tract
Inhaled air contains suspended particles of various sizes.
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Inhaled particles include : dust ,epithelial cells shed from the skin, molds,
bacterial spores, suspended aerosols from sneezing and coughing.
*- Oropharynx
Gingival fluid 1x10 microorganisms/ milliliter saliva contains microbial
inhibitors as lysozyme and secretory antibodies.
*- Intestinal tract
Microorganisms enter intestinal tract via food and drink. Organisms that
survive acid conditions of the stomach
→
intestinal tract (Acid,bile
enter
salts and enzymes).
*- Urogenital tract
In normal conditions urine in the bladder is sterile .when contains
microorganisms
→
infection.
In women normal acidity of vagina is due to the presence of lactic acid
which inhibits the growth of many microorganisms.
Bacterial degredation of glycogen (component of vaginal
epithelium)
→
Lactic acid.
Produce
*-Epithelial and Sub epithelial factors
Once the epithelial surface has been penetrated there are three host
antimicrobial defense mechanisms:
1- Tissue fluids / Contain antimicrobial factors:
- Antibodies
- Serum factors as properdin
2- Lymph system
3- Phagocytic cells
Resistance of the host
Microbial infection of the host depends on the immunlological state of the
host.
ex. First infection by small pox → Ravaged the population long – term
interaction reduced the morbidity and mortality of the disease.
Resistance to infections is also influenced by:
*- Species ex. Rabies virus cause disease in human ,dogs and cats.
*- Race
*- Age
*- Sex
*- Nutrition
Iron complexed with iron – binding glycoprotein (exhibit bacteriostatic
effect in the host). Bacterial iron transport systems associated with iron –
binding compound called Siderophores which were able to remove iron
from transferrin and other complexed host iron.
V
*- Occupation
Expect more infection of Brucellosis in persons who are exposed to animals
and animal hides, ex. Veterinarians
Hepatitis acquired through infected blood or blood products more
prevalent among surgeons, nurses and others who work in hospitals.
The disease caused by microbial agents are not always the same in terms
of location or host response.
The following terms explain the various types of disease:
Local : A disease that is restricted to a confined area.
Focal : A localized site of disease from which bacteria and their products
are spread to other parts of the body.
Systemic : A disease in which the microorganisms can spread thoughout
the body ,not necessarily from a localized site.
Primary: A disease cause by one microbial species.
Secondary : A primary disease complicated with a second pathogen (ex.
Pneumonia following primary influenza)
Mixed: A disease caused by two or more microorganisms
Inapparent or subclincal: A disease that does not give rise to any
detectable manifestation.
Latent: A disease that persists in the tissues in a dormant state and later
becomes manifest, usually when there is lowered host resistance.
Bacteremia: A transitory disease in which bacteria present in the blood
are usually cleared from the vascular system with no harmful effects.
Septicemia: A condition in which the blood serves as a site of bacterial
multiplication as well as a means of transfer of the infectious agent from
one site to another.
Pyemia: The presence of pyogenic (pus – forming as staphylococci and
Streptococci) bacteria in the blood as they are being spread from one site to
another in the body.
Toxemia: The presence of microbial toxins in the blood.
Epidemiology:
The name is from the Greek epidemios = "among the people"
The science of epidemiology may be involved with infectious as well as non
infectious diseases.
Epidemiology deals with:
How infectious disease are spread?
How they are controlled?
How they may be identified?
As well as their frequency and prevalence in a population.
VI
Clinical stages of Disease in the host:
Acute and chronic disease
*- Acute disease / Characterized by symptoms
ex: measles, Chicken pox
It is divided into various stages :
1- Incubation
2- Prodromal "Not feeling well" malaise
3- Acute
4- Convalescent
1- Incubation period/Begins from the moment the infectious agent
enters the host until the first symptoms of disease appear.
2- Prodromal period
Symptoms include headache ,upset stomach ,slight fever.
3- Acute period /the stage in which the symptoms of disease are at their
peak. Symptoms varied from disease to other:
 Fever /mediated by pyrogens secreted by special phagocytes in response
to stimuli.
 Skin or epithelial lesions results from:
- localization of the microorganisms near the body surface.
- Effect of a microbial toxin near the body surface.
- An inflammatory response (hypersensitivity )to a microbial antigen.
 Other symptoms of disease include: cough/associated with respiratory
diseases, vomiting, diarrhea or dysentery (Bloody diarrhea )associated
with intestinal diseases.
4- Convalescent period /convalescence refers to the recovery period
from a disease. It is associated with a sharp decline in symptoms,
which is correlated with maximum antibody levels.
Chronic disease and persistence:
Represent a form of microbial persistence in the host in which the
symptoms of the disease are expressed over a long period of time . the
infectious agent is intracellular parasite.
ex.: Tuberculosis and Brucellosis
Reservoirs and sources of disease
Pathogenic microorganisms must have a place where they can maintain
themselves and replicate . This place of survival and replication called
reservoir. Reservoirs can be animate or inanimate.
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Animate reservoirs:
 - human / represent the most important reservoirs and in many
instances they are the only reservoir.
ex. Disease where human is the only reservoir
- viral agents / measles ,rubella, mumps, influenza and poliomyelitis.
- Bacterial agents / sexually transmitted disease, whooping cough
and diphtheria.
Carriers /When humans are the source of infectious agent even though
they do not exhibit any symptoms of disease.
The Carriers can be:
* - Convalescent carriers/ those who are recovering from the disease
and in whom the infectious agent remains and multiplies without causing
overt symptoms.
* - Healthy carriers / those who do not have the disease but still carry
infectious microorganisms.
ex. Healthy carrier of S. aureus in nares but when food contaminated with
S. aureus, multiplies and produce toxins, when ingested it causes food
poisoning.
The carrier state may last: few weeks
Several months
Several years
Chronic carrier
‫حامل مزمن‬
Transient carrier
‫حامل عابر‬
 - Animal /Particularly domestic animals are the source of disease to
human.
Zoonosis / A disease occurs primarily in animals and is secondarily
transmitted to humans.
ex: Salmonella normally found in the intestinal tract of animals
,poultry or cattle . when contaminated food ingested by human
produces salmonellosis.
ex. Salmonella / Animal reservoir
→
Human→ human.
Brucellosis / Animal reservoir
→
Human
→ human.
(Dead end)
*- Insect / important in the transfer of infectious and invertebrate agents
(vectors).
ex. Flies, Mosquitoes, Fleas , Lice and true bugs.
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Class Arachnida/ Ticks and Mites
Insect vectors are of 2 types:
1 – Mechanical /Invertebrates carry infectious agents on their
appendages and are not involved in the life cycle .ex Flies → Salmonella
2 - Biological / Invertebrates that serve as host and reservoir of the
microbial agent .ex. Mosquitoes → malaria.
Inanimate reservoirs or sources of disease : Soil , Water and Food
ex. Clostridium /Indigenous to the soil pure water is unable to support the
growth of microorganisms.
Contaminated water → water born diseases some microorganisms live in
the fish → Humans.
Food / - Meat of infected animal → Human disease
ingested
-
Contaminated meat or milk
→
Human diseases
ingested
- Food accidentally contaminated or uncooked food ex. Oysters
harvested from waters polluted with human sewage, caused
hepatitis
- Carrier could contaminate food → Human diseases
Ingested
Food properly refrigerated , smoked , canned, pasteurized → safe to eat
and will not cause disease.
Transmission of infectious microorganisms:
 - Contact
1- Direct contact / transmission of microorganisms from person to
person by close personal association.
Hand shaking , kissing , sneezing , coughing and sexual contact.
Direct contact may be responsible for the transmission of the
disease caused by the patients own microbial flora ( Endogenous).
Infection encountered in hospital examination, treatment and
surgery (Exogenous).
2- Indirect contact / transmission occurs when infectious
microorganisims is carried from one person to another on various
intermediate objects:
water , food , dust , fomites (catheter , needle)
(Animate or inanimate sources).
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Horizontal and Vertical transmission
Microorganisms must spread from one individual to another if they are to
persist and cause disease
Microorganisms →
Horizental spread /transfer of disease by every
transmitted
day contact: air , water , food, contact and vectors
Verticals spreads / transfer of infectious agents
from parent to offspring via sperm , ovum,
placenta , milk or direct contact.
Patterns of disease in the community
Infectious diseases occur in a population with a particular frequency ,
which may be defined as :
*- Endemic disease
The disease continues in a specified population without interruption.
ex. Cholera is a disease endemic to southeast Asia.
May also be associated with animal population, Enzootic disease.
*- Epidemic disease
When the number of new cases of disease in a defined period of time
rises above its normal endemic level . Usually begins with a sudden
occurrence of disease in those who are susceptible and who come into
contact with an infected source.
Epidemics involve specific populations / single site hospital , city , large
geographic areas that may encompass the globe.
*- Pandemic disease
World wide epidemics
* - Sporadic disease
Those that occur in such an irregular pattern that their frequency can
not be calculated .ex. An individual develop disease after the fracture of a
limb.
Incidence and prevalence
The occurrence of disease in a population may be quantified by
determining :
*- Incidence
The number of new cases in a particular population within a
specifically defined time period .
ex. Incidence may be expressed as the number of new cases per
10.000 individuals in the population per year.
Incidence may be referred as Morbidity rate
X
*- Prevalence
Total number of cases of disease in a defined population within a
specified time.
*- Mortality rate
The number of individuals that have died as a result of disease in a
specific time.
Out breaks
‫اندالع المرض‬
Laboratory Techniques in Epidemiology
" Epidemiological markers"
1- Biotyping /laboratory techniques used to identify a biological
property , usually a biochemical property.
2- Serotyping /makes use of antigenic differences between strains ,
Differences may be in flagellar antigens, cell wall antigens , capsular
antigens
Commonly used for identifying Salmonells , Shigella and
enteropathogenic strains of Escherichia coli.
M – protein sertyping → useful in epidemiology of Streptococcus
pyogenes
glomerulonephritis
‫التهاب الكلية ا لحبيبي‬
- Capsular swelling (quellung reaction)
Useful in sertyping of Klebsiella spp.
3- Antibiograms
Tests used to determine a microorganisms susceptibility to
antibiotics or other antimicrobials particularly used in hospitals.
4- phage typing
Bacterial viruses are very specific in respect to the hosts they infect ,
and this specifity can be used as an epidemiological tool.
ex. Staphylococcu aureus 22 phages are routinely used to
characterize the different strains.
5- Bacteriocin typing
Bacteriocins are antimicrobial – like proteins produced primarily by
strains of Gram- negative enteric species.
The bacteriocins are active against strains of the same or closely
related species.
Used to identify : Serratia marcescens
E coli
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Shigella species
Proteus mirabilis
Bacteria may also be typed by their ability to inhibit indicator
strains.
This is used for typing Pseudomonas aeruginosa strains
6 - Other methods
Plasmid characterization techniques involving plasmids.
*- direct techniques /direct plasmid analysis involves
hybridization of plasmid DNA from different strains
*- indirect techniques
- Agarose gel electrophoresis
- Restriction endonuclease analysis.
How can one prove that a given microorganism really causes
a disease?
The causative relation ship between a microorganisms and a disease
is established by fulfilling "Koch's postulates"
1- The microorganism must regularly be isolated from cases of the
illness.
2- It must be grown in pure culture in vitro.
3- When such a pure culture is inoculated into susceptible animal
species ,the typical disease must result.
4- From the experimentally induced disease, the microorganism
must again be isolated.
These postulates were adequate to prove the causes of some
bacterial diseases, they had to be modified for other infectious,
particular by viruses.
Thank you …..
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