Systemic Bacteriology 2

Question 1

What is colonisation ?

Answer 1

Establishment of microorganisms on or within a host without causing disease, which can lead to infections under certain conditions.

Question 2

What does virulence mean ?

Answer 2

The capacity of a microbe to cause damage to its host

Question 3

What is a comensal organism ?

Answer 3

Rrganism that is part of the normal flora
-Often a mutualistic relationship
-Endogenous

Question 4

What is an oppurtunistic pathogen ?

Answer 4

An organism that causes infection when opportunity/change in natural immunity arises

Question 5

What are coagulase tests used to differentitate between ?

Answer 5

Between Staph. aureus and coagulase negative Staph. (including Staph epidermis)

Question 6

What is haemolysis used to differentiate between ?

Answer 6

Used to differentiate between Streptococci

Question 7

What does sepsis cause ?

Answer 7

Patients with Gram-negative sepsis get very unwell very quickly due to endotoxin released when Gram-negative bacteria die
-Small blood vessels become ‘leaky’ and loose fluid into tissues; decreased blood volume so heart has to work harder
-Poor tissue perfusion means blood supply to less essential organs is shut down
-Blood clotting system activated; uses all clotting factors, increasing risk of haemorrhage

Question 8

How are fevers caused ?

Answer 8

1. Antigen/LPS interacts with macrophages
2. Macrophages release cytokines into bloodstream
3. Cytokines travel to anterior hypothalamus
4. Prostaglandin E released - increases body’s thermal set point
5. Body perceives it as cold - starts to ‘shiver’
6. FEVER

LPS = Lipopolysaccharides

Question 9

Give examples of gram negative cocci

Answer 9

Neisseria meningitidis: most common cause of bacterial meningitis
Neisseria gonorrhoeae: gonorrhea

Gram-negative aerobic cocci

Cocci = balls

Question 10

Give examples of Gram-negative bacilli associated with GI tract

Answer 10

Gut commensal coliforms
-Many are part of normal bowl flora
-Any coliform that gets into a normally sterile environment can cause infection e.g. UTI
-Gentamicin is the first line antibiotic for the treatment of infections caused by coliforms (when urosepsis; first line is generally nitro or trim)

Facultative anaerobies

Question 11

Give examples of gram-positive pathogens

Answer 11

All streptococci (facultative anaerobic)
Staphylococcus epidermis (facultative anaerobes)
Staphylococcus aureus (facultative anaerobes)
Enterococcus (faculttaive anaerobes)
Clostridium spp. (anaerobic)

spp. = species (several/various/many)

Question 12

Give examples of streptococci

Answer 12

Group A strep (GAS): numerous associated diseases e.g. Scarlet fever, impetigo, β-haemolytic (same thing as pyogenes)
Streptococcus pneumoniae: pneumonia, ⍺-haemolytic

Only streptococcus identified by haemolysis

Are all gram-positive, facultative-anaerobes

Question 13

What is Staphylococcus epidermis?

Answer 13

Nosocomial - associated with foreign devices e.g. catheters
Coagulase negative (coagulase produced to form clots around bacteria from fibrinogen into fibrin, helps avoid immune and protection from phagocytosis)
Gram pos, facultative anarobe

Nosocomial: originating in hospital

Question 14

What is Staphylococcus aureus

Answer 14

-Nosocomial and community
-Most common cause of skin, soft tissue and wound infection
-Sepsis
-Coagulase positive (appears golden); fibrinogen found in loads of places not just in blood e.g. tissue fluid, inflammation exudate, absesses,
-Clump forming - looks like grapes

Gram pos

Question 15

What is Enterococcus

Answer 15

-Enteric infections
-Part of normal bowel flora, can cause problems if they get into a normally sterile area
-𝛾-haemolytic (none)

Gram pos

Question 16

What are Clostridium spp. ?

Answer 16

-Part of normal bowel flora
-Produce endotoxins that can cause severe tissue damage
-Clostridium difficile: causes antibiotic-associated diarrhoea, especially in the elderly; Proliferates in the absence of normal flora

Gram pos anaerobic

Question 17

Give examples of gram negative and positive bacteria

Answer 17