1. Microorganisms are classified based on their relationship with humans as commensals, pathogens, parasites, and opportunistic pathogens. 2. Pathogens have the ability to cause disease, known as pathogenicity, while virulence refers to the degree of pathogenicity. 3. Microbes can be transmitted via various routes including ingestion, inhalation, direct contact, sexual contact, bloodborne transmission, vectors, and vertical transmission. 4. For an infection to occur, a pathogen must first adhere to and invade host tissues, then survive the host's immune response through various mechanisms.

1. PRESENTED BY- DR. SARITA KUMARI SAHU
PG 1ST YEAR
Dept. of MICROBIOLOGY
SCB MCH,CUTTACK

2. Depending upon relationship of microbes with humans
microorganisms are of following types:-
Commensals:
 Harmless microorganisms living on the host and
causing no ill effect/injury to the host.
Pathogens:
 Microorganisms capable of causing disease.
Parasites:
 Microbes that live on living host, derieve nutrition,
cause harm to host.

3. Saprophyte:
 Free living microbes that live on dead or
decaying organic matter.
Opportunistic pathogens:
 Cause disease in immunocompromised people
(HIV, Solid organ transplant patient,
Chemotherapy)

4. Pathogenicity :
 It is the organism’s ability to produce disease in a
host.
Virulence :
 It refers to the measure of degree of pathogenicity of
the microorganism.
 Different strains of same species may exhibit varying
degree of virulence.
 Virulence of a strain may undergo spontaneous or
induced variation which can be;
 Exaltation- Enhancement of virulence.
 Attenuation- Reduction of virulence.

5. Ingestion : ( food or water )
 Salmonella typhi
 Shigella dysenteriae
 Vibrio cholerae
Inhalation: ( Respiratory Tract )
 Mycobacterium tuberculosis
 Streptococcus pneumonia
 Haemophilus influenza

6. Direct contact :
 Uncleaned hands: Common cold, skin and eye
infections.
 Break in the skin ( wounds): Staphylococcus aureus
 Burns: Pseudomonas aerugunosa
 Trauma (RTA) : Clostridium tetani
Sexual transmission :
 Neisseria gonorrhoeae ( gonorrhea )
 Treponema pallidum ( syphilis )
 Chlamydia trachomatis

7. Blood borne transmission:
 Needle stick injuries / Blood transfusion /
Intravenous drug abuse: HIV, HBV, HCV
Vector borne:
 Mechanical: Flies spreading bacteria to food
( Salmonella/ Shigella)
 Biological: Y. pestis multiplying in flea gut
Vertical transmission:
 Treponema pallidum ( syphilis )
 Toxoplasma gondii
 Cytomegalo virus

8. Infective dose of the organism is minimum inoculum
size that is capable of initiating an infection.
 Low infective dose :
Shigella ( Just 10 bacilli)
 Large infective dose:
Vibrio cholera (106 -108 bacilli)
Infective dose varies depending upon the factors
such as
 Virulence of the organism
 Host’s age and immune status
 Ability to resist gastric acid

9. .
1.Adhesion 2.Invasion 3.Survival
against
inflammation
4.Survival
against host
immune
system
5.Microbial toxins

10. Human body surfaces are colonized with a wide
variety of microorganisms which may lead to either
infection or colonization where as;
Colonization:
 Pathogen enters, multiplies at the site of
attachment, but does not invade, neither cause
disease nor elicit specific immune response.
Infection:
 Growth, multiplication and invasion of a
microorganism in the body with or without the
production of disease.

12.  Initial event of pathogenicity.
 Exception- organism are directly introduced by trauma or
other means into deeper tissues.
 Organisms which are not a part of normal human microbiota,
requires to outcompete the normal microbiota for a place on
body surface.

13. Non specific
 Hydrophobic and
electrostatic attractions
 Atomic and molecular
vibrations.
 Brownian movement
Specific
 Capsule
 Fimbriae
 Flagella
 Lipoteichoic acid
 Outer membrane
protein
 Bacterial biofilms.

14.  Commonly bacterial surface and the host cell surface
have a net negative charge so repulsive forces exist
between the two.
 This repulsive forces can be overcome by
hydrophobic forces.
 More hydrophobic the bacterial surface, greater will
be the adherence.

15.  Loose, relatively unstructured network of polymers that
covers the surface of an organism.
▪ Protects the bacterium from phagocytosis.
▪ Prevents complement mediated bacterial cell lysis.
▪ Prevents dessication.
▪ Protects the bacterium from action of lysozyme and
bacteriophages.
 eg- Pneumococcus, Meningococcus, H.influenzae,
Klebsiella, Pseudomonas, Bacillus etc.

17. Capsulated bacteria composition
Pneumococcus Polysaccharide
Meningococcus Polysaccharide
H.Influenzae Polysaccharide
Klebsiella pneumonia Polysaccharide
Pseudomonas aeruginosa Polysaccharide
Bacillus anthracis Polypeptide
Streptococcus pyogenes Hyaluronic acid

18. FIMBRIALADHESION MECHANISM EXAMPLES
•FIMBRIAE/PILI
A) Mannose sensitive
Fimbriae
B) Mannose-resistant
Fimbriae
These are the main
mechanism by which
bacteria adhere to host cell.
These are the fibers that
extends from bacterial
surface, mediate attachment
of bacteria to specific
receptor on host cell.
E . Coli ,
Neisseria gonorrhoea,
Vibro cholerae
NON-FIMBIAL ADHESION ORGANISMS INVOLVED
Haemaglutinin ( filamentous,mannose
resistant,fibrillar)
Biofilm
Curli (surface protein)
Fibronectin
Exopolysaccharide
Bordetella pertusis, Helicobacter pylori,
Salmonella typhimureum
CONS, Staphylococci, E.coli,Viridans group
of streptococci
E. coli, Salmonella, Shigella
Streptococcus pyogenes
Streptococcus mutans

19.  Gram negative and many gram positive bacteria has
numerous thin, rigid,rod-like structures called fimbriae or
pili.
 Mediate attachment of some bacteria to cell surface.
 Fimbriae are classified into:
1. Mannose sensitive fimbriae
2. Mannose resistant fimbriae

20.  Type I- (mannose sensitive):
hemagglutination of untreated RBCs.
Eg Escherichia ,klebsiella ,serratia ,salmonella spp.
 Type II - No adhesiveness.
 Type III- (mannose resistant):
adhesive to RBCs treated with tannic acid/heated to 70o C.
Eg. klebsiella, serratia
 Type IV- (mannose resistant):
adhesive to untreated RBCs.
Eg. proteus spp.
 Type VI-
no adhesiveness
Eg. Non fimbriated strains of K.ozaenae.

21.  Non fimbrial adhesions include protein or polysaccharide
structures that are surface exposed on bacterial cell or
secreted.
 Protein based adhesins include
▪ filamentous hemagglutinin of B.pertussis
▪ A mannose resistant hemagglutinin of salmonella
enterica serotype typhimurium
▪ A fibrillar hemagglutinin from H.pylori.
 Exopolysaccharides present on surface of gram positive
bacteria involved in adhesion.eg S.mutans

22.  Teichoic acid and surface proteins of Coagulase
negative staphylococcus aureus, mediate adherence
to prosthetic device and cathetors.
 Flagella acts as adhesins in V.cholera and C.jejuni.
 Bacterial motility helps in chemotaxis of V.cholera,
C.jejuni and H.pylori as well as in penetration through the
mucous layer during colonization

23. Outer membrane proteins-
 Gram negative cell wall contains certain proteins called
OMP.
 These are target sites for phages, antibiotics and
bacteriocins.
▪ Eg:- EPEC-OMP(EAF) helps in adherence of EPEC
to the mucosa of SI.
▪ Non pilated gonococci can still bind to the urethra
and other mucosal surfaces by OMPII/PII

24.  Biofilm is an aggregate of interactive bacteria
attached to a solid surface or to each other and
encased in an exopolysaccharide matrix.
 They form a slimy coat on solid surfaces, implants
and prosthetic devices.
 It may be single species (Monomicrobic aggregation)
or more than one (Polymicrobic aggregation).
 The bacteria in the exopolysaccharide matrix may be
protected from the host’s immune mechanisms.

25.  Matrix functions as a diffusion barrier for some
antimicrobials.
 They have complex antibiotic resistant profile indicating
failure of antibiotics to penetrate the polysaccharide matrix.
 Eg -: Pseudomonas aeruginosa
Staphylococcus aureus
Candida albicans
 After biofilm is formed quorum sensing molecules produced
by the bacteria in the biofilm accumulate resulting in a
modification of the metabolic activity of bacteria.

27.  Quorum sensing is the regulation of gene expression in
response to fluctuations in cell-population density.
 Gram-positive Bacteria:
 Gram-positive bacteria use autoinducing peptide (AIP)
(autoinducer).
 When Gram-positive bacteria detect high concentration of
AIP in their environment, AIP binds to a receptor to activate
a kinase that phosphorylates a transcription factor, which
regulates expression of virulence genes.
Gram-negative Bacteria:
 Gram-negative bacteria produce N-acyl homoserine lactones
(AHL) as their signaling molecule.
 AHL binds directly to the transcription factor (LuxR) to
regulate expression of virulence genes

30.  Cell to cell signalling is made possible by activation of two
genes.
 I gene codes for synthase responsible for synthesis of
autoinducer.
 Autoinducer is often N-acyl homoserine lactone .
 The autoinducer can diffuse freely through the cell membrane.
 The R-gene codes for a transcriptional regulator protein that
combines with the autoinducer to become an activator for
transcription of various virulence genes.

31.  IIN
AUTOINDUCER
SYNTHASE
I GENE
AUTOINDUCER
R GENE
REGULATOR
AUTOINDUCER
REGULATOR
COMPLEX
VIRULENCE GENE

32.  Ability of microorganism to enter host tissue.
 Once surface attachment is secured microbial invasion
into subsurface tissues and organs is accomplished by
disruption of the skin and mucosal surfaces by several
mechanisms such as;
 Disruption of skin and mucosal surface by-
 Trauma
 Inhalation of toxic gases / particulate matter / smoking
 Implantation of medical device

33.  Childbirth
 Overuse of antibiotics
 Diseases like Malignancy, Diabetes mellitus , previous
repeated infection
 By direct action of an organism’s virulence factors-
 Some microorganisms produce factors that force
mucosal surface phagocytes to ingest them and then
release them unharmed into the tissue below the
surface.

34.  In staphylococci and streptococci produce an array
of enzymes(Hyaluronidase, Nuclease, Collagenase)
that hydrolyse the host proteins and nucleic acids
destroying host cells and tissues.
 Destruction allows the pathogens to burrow through
minor openings in the outer surface of the skin and
into deeper tissues.
 Once a pathogen has penetrated the body, it uses a
variety of strategies to survive attack by host’s
inflammatory and immune responses.

35. Invasion of the tissue is enhanced by following
factors:
 (1) Invasin
 (2) Enzymes
 (3) Antiphagocytic factor
 (4) Intra-cellular survival

36.  INVASIN: Bacterial surface protein that affect physical
proportion of tissue matrices , intracellular spaces,
thereby promoting the spread of pathogens.
 ENZYMES: Many pathogens secrete enzymes that
enable them to:
1. Dissolve structural chemicals in the body.
2. Maintain an infection.
3. Invade further.
4. Avoid body defenses.
5. Inactivate antibiotic

37. 1. Hyaluronidase:
 “Spreading Factor”.
 Digests hyaluronic acid
 cement substance between cells.
2 .Collagenase:
 Breaks down collagen.
3. Neuraminidase:
 Produced by intestinal pathogens.
(Vibrio cholerae and Shigella dysentriae).
 Degrades neuraminic (sialic) acid; an
intercellular cement of the epithelial cells of
the intestinal mucosa

38. 4. Coagulase:
 Coagulates blood proteins.
 Providing a “hiding place” for bacteria
within a clot.
5. Kinases:
 Such as staphylokinase and streptokinase.
 Kinase enzymes convert inactive plasminogen
to plasmin which digests fibrin and prevents
clotting of the blood.

39. 6. Ig A Proteases:
 Split IgA at specific bonds.
 Inactivates Ab activity.

40.  7. Lecithinase:
 Produced by Clostridium perferingens.
 Destroys lecithin (phosphatidylcholine) in cell membranes.
 8. Phospholipases (alpha toxin).
 Produced by Clostridium perferingens.
 Hydrolyzes phospholipids in cell membranes by removal
of polar head groups.
 9. Hemolysins
 Produced by staphylococci (alpha toxin), streptococci
(streptolysins) and various Clostridia.
 May be phospholipases or lecithinases that destroy red
blood cells and other cells (phagocytes) by lysis.

41. Cell wall proteins :
 The cell wall proteins such as protein A and protein M
of S.aureus and S.pyogenes are antiphagocytic.
 eg protein A of S.aureus binds to IgG and prevents the
activation of complement.
Cytotoxins :
 Some bacteria produce cytotoxins that interfere with
chemotaxis or killing of phagocytes.
 Eg S.aureus produces hemolysin and leukocidin that
lyse and damage RBCs and WBCs.

42. Surface antigens :
 Surface antigens of bacteria like Vi antigen of S.typhi
and K antigen of E.coli make the bacteria resistant to
phagocytosis and lytic activity of complement.
Inhibition of the phagocytic “oxidative burst”:
 No formation of reactive o2 radicals in
phagocytes.
 eg- Legionella,salmonella

43.  Some bacteria grow inside PMNL, macrophages or in
monocytes.
 They survive by several mechanisms:-
 Avoid entry into phagosome.
 Prevent phago-lysososme fusion
(Mycobacterium tuberculosis).
 Acquire resistance to lysosomal activity.
 Examples: Mycobacterium tuberculosis, Brucella, Listeria

45. For a pathogen to survive action of phagocytes and the
complement , inflammation must be avoided or controlled.
 Avoidance of complement activation by-
1.By masking its activating molecules.
2.Produce enzymes disrupt crictical biochemical
components of complement pathway.
 Rapid invasion and multiplication resulting in damage
to the host before the immune response can be fully
activated.

46.  Invasion and destruction of cells involved in the
immune response.
 Avoiding detection by the immune system.
 Masking the organisms antigens with a capsule or
biofilm so that an immune response is not activated.
 Altering the expression and presentation of antigens
so that the immune system is constantly fighting a
primary encounter.
 Production enzymes to directly destroy or inactivate
antibodies .

47.  Mycobacterium tuberculosis, L.monocytogenes,brucella sp &
Legionella sp live and grow in the hostile environment within
PMN cells,macrophages or monocytes.
 They do so by
▪ avoiding entry into some phagolysosome and live within
the cytosol of phagocyte.
▪ Prevent phagosome lysosome fusion and live within
phagosome.
▪ May be resistant to lysosomal enzymes and survive
within the phagolysosome.

49.  Antigenic type of bacteria can be a marker of virulence.
 V.cholera O Ag type 1 and O Ag type139 produce cholera
toxin.
 Some group A streptococci M protein types are associated
with a high incidence of post streptococcal
glomerulonephritis.
 N.meningitides capsular polysaccharide types A &C are
associated with epidemic meningitis.
 Some bacteria make frequent shifts in the antigenic form of
their surface structures invitro and presumably
invivo.eg.Borrelia spp
 Gonococcus has 3 surface exposed Ags that switch forms
which allows it to evade the host immune system ,survive and
cause disease.

50.  Essential for the interaction of bacteria with the eukaryotic
cells of the host.
 It helps in transport of proteins that make pili or flagella and
secretion of enzymes or toxins into the extracellular
environment.
 Both gram positive and negative bacteria have general
secretion (Sec) pathway as major mechanism for protein
secretion.

51.  Type I- sec independent
 E.coli-α-hemolysin
 P.vulgaris-hemolysin
 Morganella morgagni-hemolysin
 B.pertussis-adenylate cyclase
 Ps.aeruginosa-alkaline protease
 Serratia marcescens-Zn protease
 Type II (utilize sec or tat)
 Ps.aeruginosa-elastase,exotoxin A,phospholipase C,others
 Legionella pneumophila-acid phosphatase, phospholipase,
lipase,protease
 V.cholera -cholera toxin
 Serratia marcescens –hemolysin

52.  Type III (sec independent)
 Yersinia species -ysc-yop system,toxins that block phagocytosis
Ps.aeruginosa -cytotoxin
 Shigella spp -controls host signalling,invasion&death
 Salmonella enterica -effectors from SP1 &SP2,which promote
attachment & invasion.
 Type IV (Sec dependant and independent)
▪ Protein substrates-Bordetella pertussis-PT
H.pylori-cytotoxin
▪ DNA substrates-N.gonorrhoea-DNA export system
H.pylori-DNA uptake and release system

53.  Type V
 N.gonorrhoea -IgA protease
 H.influenzae -IgA protease
 E.coli -serine protease,adhesins,type1 pili,P pili
 S.flexneri -serine protease
 Serratia marcescens –proteases
 Bordetella pertussis -filamentous hemagglutinin

55. • They are lipid A portion of lipopolysaccharide .
• Present as an integral part of the cell wall of gram
negative bacteria.

56.  They are heat labile proteins
 Secreted by certain species of both gram positive and
gram negative bacteria.

57. 1. Released from the cell before
or after lysis
2. Protein
3. Heat labile
4. Antigenic and immunogenic
5.Toxoids can be produced
6. Specific in effect on host
7. Produced by gram-positive and
gram-negative organism
8. No fever
1. Integral part of cell wall
2. Endotoxin is LPS; Lipid A is toxic
component
3. Heat stable
4. Antigenic immunogenicity
5.Toxoids cannot be produced
6. Many effects on host
7. Produced by gram-negative
organisms only
8. Fever present

58.  Iron is essential nutrient for growth and metabolism and cofactor of
numerous metabolic and enzymatic process.
 Iron availability affects the virulence of many pathogens.
Eg. P.aeruginosa.
 E.coli, klebsiella and some staphylococci produce extracellular iron
chelators called siderophores for scavenging iron.
 C.jejuni & N.meningitides obtain iron by siderophores produced by other
species.
 H.influenzae type B, H.parainfluenzae, N.meningitides ,S.aureus &
S.epidermidis have specific receptors for transferrin and lactoferrin on
their surface which bind these protein and remove bound iron.
 Bacteroid species remove iron by proteolytic cleavage of the chelator.
 L.monocytogenes reduce Fe3+ to Fe2+ which reduces the affinity for the
chelator.

60.  Large groups of genes that are associated with pathogenicity and
are located on the bacterial chromosome (PAIs).
 One or more virulence genes present.
 Occupy large chromosomal regions (10-200 Kbp).
 Present in genome of pathogenic member of a species but absent
in nonpathogenic member of same species.
 Often found with parts of genome associated with mobile genetic
elements.
 Genetic instability present.

61.  Different G+C content (lower) from host chromosome.
 Associated with tRNA genes, which act as sites for recombination into
the DNA.
 Carry functional genes (e.g- integrases), to enable insertion into host
DNA.
 Properties of PAIs suggest that they originate from gene transfer from
foreign species(lysogenic bacteriophage and plasmid).