Bacterial Infections

Question 1

What are the causes of infectious diseases?

Answer 1

Ectoparasites (head lice) i.e. parasite outside the body

Helminths

Protozoa i.e. single cell complex organism = malaria

Bacteria

Viruses

Prions

Question 2

What are sterile sites? Where are sterile sites of the body?

Answer 2

Areas of the body which do not contain any bacteria under normal conditions

Blood
CSF
Urine 
Peritoneal fluid 
Pleural fluid

Question 3

How do bacteria cause disease?

Answer 3

Direct effect on body i.e. rupture, organ block, pressure, cell destruction
Eg TB lymphadenitis forms mass which can block trachea

Exotoxins which effect human tissue
Eg vibrio cholerae= causes severe watery diarrhoea

Pathogenic activation of immune system
Eg meningitis

Question 4

How can you differentiate a bacterial infection from another type of infection?

Answer 4

Growing gram -ve rods

Question 5

What is bacturia? Why is it important to consider in elderly?

Answer 5

Non-pathological growth of bacteria in urinary system in elderly people (50% of those over 80 have it)

Can mean that urine test will be positive for bacteria but bacteria may not be the cause of symptoms meaning treating with antibiotics will not have any effect

Question 6

Where do penicillins act? Why would penicillin not work for legionella?

Answer 6

Acts on the cell wall of bacteria

Legionella lacks a cell wall meaning there is no where for penicillin to act

Question 7

What causes secretary diarrhoea in cholera?

Answer 7

A subunit from cholera toxin enters epithelial cells and activates cAMP and secondary messengers to cause efflux of Cl- ions which leads to secretary diarrhoea

Question 8

How does tetanus present?

Answer 8

Opisthotonos= abnormal posture where back arches due to muscle spams associated with damage to CNS

Muscle rigidity in jaw i.e. jaw cramping

General muscle spasms

Trouble swallowing

Seizures

Headache

Question 9

How does meningitis present? Why bacteria is commonly associated with meningitis?

Answer 9

Fever
Headache
Rash (test with glass i.e. if can see rash through glass then meningitis)
Stiff neck

Meningococcal meningitis

Question 10

How is pathogenic activation of immune system involved in pathogenesis of meningitis?

Answer 10

Meningococcal endotoxin causes:
-neutrophil activation which leads to secretion of proteases which causes endothelial damage

• complement activiation
• dysregulation of coagulation
• organs dysfunction
• intravascular thrombosis
• capillary leakage
• cardiac dysfunction

Question 11

Not all bacteria are pathogenic. Which bacteria are and what bacteria can be become pathogenic?

Answer 11

TB= pathogenic

E. Coli and Staph aureus can acquire virulence factors that lead to transformation into pathogenic bacteria

Staph epidermidis when gains deep access to tissues

Acinetobacter infection associated with immunosuppressed patients
M. Chelonae can cause skin infections in immunosuppressed patients

Question 12

What are Kochs’ postulates and when are they used?

Answer 12

pathogen present in every case of disease

Pathogen must be isolated from disease host and grown in pure culture

Specific disease mist be reproduced when inoculated into healthy susceptible host

Pathogen must be recoverable from experimentally infected host

Used to determine if bacteria causing infection BUT not clinical important

Question 13

What process and tests can be done to determine if infection is bacterial?

Answer 13

Look at clinical condition of patient to see if matching with clinical syndrome

Diagnostic tests

Bacteriology

Bloods

Radiology

Question 14

How does a thypoid infection present?

Answer 14

Headache
Fever
Lethargy
Gram -ve rods in blood culture

Question 15

What are the possible pathological consequences of pseudomonas aeruginosa?

Answer 15

Can lead to hospital acquired pneumonia

Can colonise lungs with poor structure i.e. people who already have respiratory disease

Question 16

What is the difference between colonisation and infection? Why is this important to consider when trying to determine whether infection is caused by bacteria?

Answer 16

Colonisation= bacteria present in body but not causing any signs or symptoms

Infection= symptomatic bacterial infection

Patient may test positive for bacteria due to colonisation by this bacteria without this bacteria being the cause of the infection and symptoms
I.e. Bacturia in elderly patients

Question 17

What is a possible sign that a sample taken via a needle may be contaminated and falsely showing bacterial infection? What can help to differentiate infection from contamination?

Answer 17

Staph hominis growing in culture:
-common skin bacteria which can contaminate the needle

Look at clinical signs and see whether symptoms are congruent with bacterial infection or more pointing towards viral infection

Question 18

What is the difference between a gram -ve and gram +ve bacteria? How does this effect their staining?

Answer 18

+ve:
Thick peptidoglycan layer which no lipid membrane
Purple
I.e. positive purple

-ve:
Thin peptidoglycan layer with lipid membrane
Pink
I.e. don’t like pink so negative

Question 19

What are examples of gram -ve rods? Where are these bacteria normally found and what pathology can they cause?

Answer 19

E. coli 
Shigella 
Klebsiella 
Salmonella 
Thypoid 

Gut organism (gut reservoir) which generally effect the biliary tree and urinary system

Question 20

What is the difference between an endogenous infection and exogenous infection? Give examples of each for gram -ve rods.

Answer 20

endogenous= normal bacteria in wrong place
I.e. biliary sepsis/urinary sepsis/peritonitis

Exogenous= pathogenic bacteria entering body
I.e. Gastroenteritis due to shigella, salmonella, typhoid and ETEC

Question 21

Are gram negative rods or gram positive cocci more likely to have broad spectrum resistance? Why is this?

Answer 21

Gram negative rods

Plasmid exchange of resistance genes and virulence factors occurs leading to development of resistant population

Question 22

Which antibiotics are used to treat gram negative rods?

Answer 22

Co-amox
PTZ
Cephalosporins 
Fluoroquinolones 
Carbapenems

Question 23

What are examples of gram +ve cocci? Where are these bacteria normally found and what pathology can they cause?

Answer 23

Staphylococci aureus
Streptococci

Associated with skin and soft tissues and use the skin and GU system as a reservoir

Can cause:

• cellulitis
• osteomyelitis
• septic arthritis
• disciitis
• endocarditis

Question 24

Which antibiotics are used to treat gram +ve cocci?

Answer 24

Penicillin (Flucox)
Vancomycin
Linezolid
daptomycon