Bacterial Pathogenicity

Question 1

What is Koch’s postulates?

Answer 1

1) Micro-organism should be found only in diseased individuals
2) Must be cultured from diseased individual
3) Inoculation of micro-organism with healthy person must cause disease
4) Re-infection can be matched to the original organisms

Question 2

What are the sterile areas of the body?

Answer 2

Urine
CSF
Joint fluid
Pericardial fluid

Question 3

What is infective dose?

Question 4

What are overt pathogens?

Answer 4

Pathogens only associated with human disease. E.g Neisseria gonorrhoea.

Question 5

What are opportunistic pathogens?

Answer 5

Pathogens that cause disease only when the immune defences are compromised.
E.g pseudomonas aeuruginosa.

Question 6

What is facultative pathogen?

Answer 6

Grow and survive in both the environment and the host eg Baccillus anthracis.

Question 7

What are Type 3 molecules?

Answer 7

Pathogens like salmonella create a link to the host cell and secrete molecules which alter the host cell’s properties to benefit the pathogen.

Question 8

What is a non-obligate pathogen?

Answer 8

Intracellular acting pathogens.

Question 9

What is pneumolysins?

Answer 9

Virulence factor found in streptococcus pneumoniae which forms pores in the target cells

Question 10

What is streptococcus pneumonia?

Answer 10

Gram positive cocci which is spread by aerosols and causes MOPS (meningitis, otitis media, pneumonia, sinusitis.) It is alpha haemolytic and contains virulence factors like a capsule and secretory IgA protease, neuroaminidase and pneumolysins. It is highly invasive in lung tissue.

It is the most common cause of pneumonia, with a higher risk in cerebral insult, respiratory or heart dysfunction. It forms a part of the natural flora of the URT.

Question 11

What is the role of neuroaminidase?

Answer 11

Cleaves neuroaminic acid from sugar residues on host cell surface.

Question 12

What is minimal infective dose?

Answer 12

Minimum number of infectious organisms that cause disease in half of those given the dose.

Question 13

What is an endotoxin?

Answer 13

Heat labile toxin found in the LPS of -ve bacteria which is released after its death, which are recognised by the TLR4 receptor.

Question 14

What is an exotoxin?

Answer 14

Toxin produced extracellularly by both -ve and +ve bacteria which is heat labile and highly toxic.

Question 15

What is an enterotoxin?

Answer 15

Toxins which act only in the small intestine and affect the intestinal permeability by acting on ion channels for more Cl- efflux to cause water diarrhoea.

Question 16

What is alpha-haemolytic?

Answer 16

Partial breakdown of RBC, by pneumolysins. E.g Streptococcus pneumoniae and streptococcus viridans.

Question 17

What is beta-haemolytic?

Answer 17

Complete breakdown of RBC by streptococcus pyogenes and agalactiae.

Question 18

What is clostridium botulinum?

Answer 18

Gram negative bacilli which produces the exotoxin botulinum that inhibits the acetylcholine release and causes muscle paralysis and respiratory arrest. It is transmitted through foods like honey or canned food that colonises the gut and survives due to being bound to non-toxic proteins, and the effects on axon terminals are irreversible.

It is used clinically to treat overactive bladder, excessive sweating and chronic migraine.

Question 19

What is vibrio cholerae?

Answer 19

Gram negative bacilli bacteria which produces the enterotoxin cholera that increases adenylate cyclase pump activity t Cl- efflux and leads to watery diarrhoea, targeting the small intestine.

Question 20

What are the features of salmonella?

Answer 20

Gram negative bacilli which produces enterotoxin and colonises the small intestines and causes gastroenteritis. It invades cells using Type 3 secretion to modify the phagosome maturation pathway until cell lysis.

Question 21

What is listeria monocytogenes?

Answer 21

Gram positive bacilli found in unpasteurised milk and deli meat, which is transmitted by faeco-oral route. It grows at cold temperatures and produces enterotoxins which affect the small intestine and cause gastroenteritis and watery diarrhoea. It can lead to spontaneous abortion and meningitis in immune compromised people like newborns.

Question 22

What is the virulence factor of listeria?

Answer 22

The haemolysin LLO which forms pores and allows escape from vacuoles by the pathogen.

Question 23

How do pathogens achieve immune evasion?

Answer 23

Molecular mimicry
Antigenic variation
Hide intracellularly
Modify cell response

Question 24

What is molecular mimicry?

Answer 24

Pathogens produce cell surface molecules of a similar morphology to the host. Examples of pathogens that do this are haemophilius influenzae and streptococcus pyogenes.

Question 25

What is haemophilius influenzae?

Answer 25

Gram negative coccobaccilus which forms part of the normal flora of the URT, and causes epiglottis, pneumonia and meningitis. It is the most common agent of septic arthritis in children. It acts via molecular mimicry to evade the host defence.

Question 26

What is streptococcus pyogenes?

Answer 26

Gram positive cocci bacteria which is a Group A Strep that contains an M protein that evades the complement system, and is similar in structure to myosin in heart cells. It can lead to infection of:
PIT
P: pyogenic.
I: immunogenicity
T: toxigenic

Question 27

What pyogenic effects does streptococcus pyogenes have?

Answer 27

It causes impetigo, cellulitis and pharyngitis.

Question 28

What immunogenic effects does streptococcus pyogenes have?

Answer 28

The M protein induces molecular mimicry against myosin in heart cells and causes rheumatic fever. It also causes type 3 hypersensitivity of glomerulonephritis.

Question 29

What toxigenic effects does streptococcus pyogenes have?

Answer 29

It causes Scarlett fever and toxic shock syndrome.