infections in microbiology

1. -Swathi K

3.  Introduction
 What is an infection?
 What is a disease?
 Classification of infection
 Sources of infection
 Methods of transmission of infection
 Factors of predisposing to microbial
pathogenecity
 Types of infectious disease

4.  Infection and immunity involve interaction
between the animal body (host) and the
infecting microorganism.
 Based on their relationship to their hosts,
microorganisms can be classified as
Saprophytes Parasites

5.  Greek word sapros; meaning decayed
 They are free-living microbes that subsist on
dead or decaying organic matter.
 Found in soil and water which plays an
important role in the degradation of organic
materials in nature.
 Little relevance in infectious disease because
they cannot multiply on living tissues.
 Exception- B.subtilis- infect
immunocompromised people.
(? Immunocompromised people)

6.  Greek pathos; suffering, gen; produce
 They are microbes that can establish
themselves and multiply in hosts.
 Parasitic microbes may be either pathogens
or commensals.
 (? Examples of other commensals)

7. Infection –
Is the invasion or colonization of the body by
pathogenic microorganisms.
 The presence of a particular type of
microorganism in a part of the body where it
is not normally found is also called an
infection—and may lead to disease.
 Ex- HepatitisA, influenza, Dengue etc.

8. Disease- occurs when an infection results in
any change from a state of health.
 Disease is an abnormal state in which part or
all of the body is not properly adjusted or
incapable of performing its normal functions.
 Ex- Common Cold, AIDS, Diabetes etc.

9. I) Infections may be divided in various ways-
1. Primary Infection- It is the initial infection
with a parasite in a host.
2. Secondary Infections- When a new parasite
sets up an infection in a host whose
resistance is lowered by a pre-existing
infectious disease.

10. 3. Re-infections- Subsequent infections by the
same parasite in the host
4. Focal Infection- a condition where, due to
infection or sepsis at localised sites such as
the appendix or tonsils.
5. Cross Infection- When in a patient already
suffering from a disease a new infection is set
up from another host or another external
source.
6. Cross-infections occurring in the hospitals
are called Nosocomial Infections.

11. 7. Iatrogenic infections- refers to physician-
induced infections resulting from
investigative, therapeutic or other producers.

12. Preventing direct contact transmission through
the use of gloves, masks, and face shields

13. II) Depending on whether the source of
infection is within or outside the host’s own
body, infection can be classified as
Endogenous Exogenous

14. III) Based on the clinical effects of infections, they
may be classified into
 Inapparent Infection- is one where the clinical
effects are not apparent. (Subclinical infection)
 Atypical Infection- is one in which the typical or
characteristic clinical manifestations of the
particular infectious disease are not present.
 Latent Infection- is one in which some
parasites, following infection, may remain in the
tissues in a latent or hidden form, proliferating
and producing clinical disease when the host
resistance is lowered.

15. 1. Humans- the commonest source of infection.
 Carrier- is a person who harbors the pathogenic
microorganism without suffering any ill effect
because of it.
 Convalescent Carrier- is one who has recovered
from the disease and continues to harbor the
pathogen in his body.
 Contact carrier- a person who acquires the
pathogen from a patient
 Paradoxical carrier- a carrier who acquires the
pathogen from another carrier.

16.  Depending on the duration of carriage,
carriers are classified as
Temporary carrier Chronic carrier
(a state lasts >6 months) (stage may last for several years)
 Human carriers play an important role in the spread of such
diseases as AIDS, diphtheria, typhoid fever, hepatitis,
gonorrhea, amebic dysentery, and streptococcal infections.

17. 2. Animals- Both wild and domestic animals
are living reservoirs of microorganisms that
can cause human diseases.
 Animals serve to maintain the parasite in
nature and act as the reservoir of human
infection—animals being asymptomatic.
(Reservoir hosts)
 Infectious diseases transmitted from animals
to humans are called Zoonoses.
 Zoonotic diseases may be bacterial, viral,
protozoal, helminthic or fungal.

18. 3. Insects-
 blood sucking insects—Arthopod-borne
disease
 Insects such as mosquitoes, ticks, mites, flies,
fleas and lice that transmit disease-Vectors.
 Mechanical vectors- transmission is by
mechanical methods. Dysentery by domestic
fly
 BiologicalVectors- pathogen multiplies in
the body of an insect. Anopheles mosquito in
malaria

19. 4. Soil and Water- some pathogens survive in the
soil for a very long of time.
i. Spores of tetanus bacilli-TETANUS
ii. Fungi and parasites such as roundworm and
hookworm
Water may act as the source of infection either due
to contamination with pathogenic microbes
(cholera vibrio) or
Due to the presence of aquatic vectors (cyclops)
5. Food- Contaminated food may act as a source of
infection.
Presence of pathogens (food poisoning by
Staphylococcus), or pre-existent infection in
meat/animal product (salmonellosis).

20. 1. Contact- may be direct or indirect
 Direct contact transmission- (person-to-person
transmission)
is the direct transmission of an agent by physical
contact between its source and a susceptible
host; no intermediate object is involved.
 Indirect contact transmission- occurs when the
agent of disease is transmitted from its reservoir
to a susceptible host by means of a nonliving
object.
 The general term for any nonliving object
involved in the spread of an infection is a fomite.

21. Direct Contact
Ex- the common cold and influenza),
staphylococcal infections, hepatitis
A, measles, scarlet fever, and
sexually transmitted infections
Indirect Contact- (Fomites)
Contaminated syringes serve as
fomites in transmitting AIDS and
hepatitis B.

22. 2. Inhalation- respiratory infections such as
Influenza and tuberculosis are transmitted by
inhalation of the pathogen.
 Are shed by patients into environment by
coughing, sneezing or while talking.
Droplet nuclei- Small droplets, under 0.1mm in
diameter, evaporate immediately to become
minute particles.
 they are suspended in the air for long periods,
acting as sources of infection.

23. Droplet transmission

24.  3)VehicleTransmission- is the transmission of
disease agents by a medium, such as water, food, or
air. Other media include blood and other body
fluids, drugs, and intravenous fluids.
 Ex-An outbreak of Salmonella infections caused by
vehicle transmission
Water Food Air

26.  Infections may be transmitted during
administration of injections, lumbar puncture
and catheterisation when meticulous care is
lacking.
 Exchange transfusion, dialysis and organ
transplant surgery- high risk of infection.
 Laboratory personnel handling infectious
material are at risk and special care should be
taken to prevent laboratory infection.

29. What type of transmission?

30.  Bacteria should be able to enter the body.
 Organism should be able to multiply in the
tissue.
 They should be able to damage the tissue.
 They must be capable to resist the host
defense.

32.  Pathogenecity is referred to the ability of
microbial species to produce disease.
 Virulence is referred to the ability of
microbial strains to produce disease.

33.  Adhesion:The initial event in the pathogenesis of
many infections is the attachment of the bacteria to
body surfaces.This attachment is specific reaction
between surface receptors and adhesive structures
on the surface of bacteria (adhesins).

34.  Examples- 1)

35.  Invasiveness is the ability of organism to
spread in a host tissue after establishing
infection. Less invasive organisms cause
localized lesion. Highly invasive organisms
cause generalized infection (septicemia).
 Toxigenicity. Bacteria produce two types of
toxins – exotoxins & endotoxins

37.  Heat labile protein.
 Diffuse readily into the surrounding medium.
 Highly potent, e.g. 3 kg botulinum can kill all the
inhabitants of world.
 They are generally formed by Gr+ bacteria and also by
Gr- organisms like Shigella,V.cholerae, E.coli.
 Exotoxin is specifically neutralized antitoxin.
 Can be separated from culture by filtration.
 Action is enzymatic and it has specific tissue affinity.
 Specific pharmacological effects for each exotoxin.
 Cannot cause pyrexia in a host.
 Can be toxoided.

38.  Proteins polysaccharide lipid complex heat
stable.
 Forms part of cell wall (don’t diffuse into the
medium).
 Obtained only by cell lysis.
 They have no enzymatic action.
 Effect is non-specific action.
 No specific tissue affinity.
 Active only in large doses 5 to 25 mg.
 Weakly antigenic.
 Neutralization by antibody ineffective.
 Cannot be toxoided.
 Produce in Gram negative bacteria.

40.  Communicability is the ability of parasite to
spread from one host to another. It determines
the survival and distribution of organism in a
community.
 Other bacterial products-
1) Coagulase (S.aureus) which prevents
phagocytosis by forming fibrin barrier around
bacteria.
2) Fibrinolysin promotes the spread of infection by
breaking down the fibrin barrier in tissues.

41. 3) Hyaluronidase split hyaluronic acid
(component of connective tissue).
4) Leucocidins damage polymorphonuclear
leucocytes.
5) Ig A1 proteases: split IgA and inactivates its
antibody activity.
6) Hemolysin is produced by some organisms
capable of destroying erythrocytes.

43.  Capsulated bacteria like Pneumococcus,
K.pneumoniae and H.influenzae stand
phagocytosis
 Surface antigen, e.g.Vi-antigen of S. typhi
and K- antigen of E.coli resisted phagocytosis
and lytic activity of complement.

44. A pili on E.coli

45.  The minimum infection dose (MID) or
minimum lethal dose (MLD) is the minimum
number of organism required to produce
clinical evidence of infection or dearth of
susceptible animal.

46.  Vibrio cholerae is effective orally. No effect
when it is introduced subcutaneously.
 Streptococci can initiate infection whatever
be the mode of entry.

47.  Infectious diseases may be localized or
generalized. Localized infections may be
superficial or deep-seated.
 Circulation of bacteria in the blood is
known as bacteremia (viruses – virusemia

48.  Septicemia is the condition where bacteria
circulate and multiply in the blood, form
toxic products and cause swinging type of
fever.
 Pyemia is a condition where pyogenic
bacteria produce septicemia with multiple
abscesses in the internal organs such as the
spleen, liver and kidney.

49. Depending on the spread of infectious disease
in the community they may be classified into
different types.
 Endemic diseases are ones that are constantly
present in a particular area. Typhoid fever is
endemic in most parts of India. An epidemic
disease is one that spreads rapidly, involving
many persons in an area at the same time.
Influenza causes annual winter epidemics in
the cold countries.

50.  A pandemic is an epidemic that spreads
through many areas of the world involving
very large numbers of persons within a short
period (Influenza, cholera, plaque).
 Epidemics vary in the rapidity of spread.
Waterborne disease such as cholera and
hepatitis may cause explosive outbreaks,
while disease, which spreads by person-to-
person contact evolve more slowly

51.  Ananthanarayana and Paniker’s, Textbook of
Microbiology, 9th edition.
 Kuby’s Immunology.

54. 1) Adhesins can be found on
 A. host cells.
 B. viruses.
 C. bacterial pili and capsules.
 D. cells at the portal of entry.

55. 2)Which one of the following is NOT true of
exotoxins?
 A.They are proteins.
 B.They are part of cell wall structure.
 C.They are released from live bacterial cells.
 D.They trigger antibody production.

56. 3) A zoonosis is a disease
 A. transmitted from humans to animals.
 B. spread from animals to humans.
 C. transmitted between wild and domestic
animals.
 D. spread between wild animals.

57. 4)Which one of the following is an example of
an indirect method of disease transmission?
 A. Coughing
 B. Droplet transmission
 C. A mosquito bite
 D. An animal bite

58. 5) If a person has recovered from a disease but
continues to shed disease agents, that person
is a
 A. vector.
 B. fomite.
 C. vehicle.
 D. carrier.

59. 1) Summarize the differences between
exotoxins and endotoxins as virulence
factors associated with disease.
2) What is a nosocomial infection?
3) Define epidemic, endemic and pandemic
with examples.
4) Define carrier with example.
5) What are fomites? Give examples.