Bacterial Infections Flashcards
What are the causes of infectious diseases?
Ectoparasites (head lice) i.e. parasite outside the body
Helminths
Protozoa i.e. single cell complex organism = malaria
Bacteria
Viruses
Prions
What are sterile sites? Where are sterile sites of the body?
Areas of the body which do not contain any bacteria under normal conditions
Blood CSF Urine Peritoneal fluid Pleural fluid
How do bacteria cause disease?
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
How can you differentiate a bacterial infection from another type of infection?
Growing gram -ve rods
What is bacturia? Why is it important to consider in elderly?
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
Where do penicillins act? Why would penicillin not work for legionella?
Acts on the cell wall of bacteria
Legionella lacks a cell wall meaning there is no where for penicillin to act
What causes secretary diarrhoea in cholera?
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
How does tetanus present?
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
How does meningitis present? Why bacteria is commonly associated with meningitis?
Fever
Headache
Rash (test with glass i.e. if can see rash through glass then meningitis)
Stiff neck
Meningococcal meningitis
How is pathogenic activation of immune system involved in pathogenesis of meningitis?
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
Not all bacteria are pathogenic. Which bacteria are and what bacteria can be become pathogenic?
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
What are Kochs’ postulates and when are they used?
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
What process and tests can be done to determine if infection is bacterial?
Look at clinical condition of patient to see if matching with clinical syndrome
Diagnostic tests
Bacteriology
Bloods
Radiology
How does a thypoid infection present?
Headache
Fever
Lethargy
Gram -ve rods in blood culture
What are the possible pathological consequences of pseudomonas aeruginosa?
Can lead to hospital acquired pneumonia
Can colonise lungs with poor structure i.e. people who already have respiratory disease
What is the difference between colonisation and infection? Why is this important to consider when trying to determine whether infection is caused by bacteria?
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
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?
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
What is the difference between a gram -ve and gram +ve bacteria? How does this effect their staining?
+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
What are examples of gram -ve rods? Where are these bacteria normally found and what pathology can they cause?
E. coli Shigella Klebsiella Salmonella Thypoid
Gut organism (gut reservoir) which generally effect the biliary tree and urinary system
What is the difference between an endogenous infection and exogenous infection? Give examples of each for gram -ve rods.
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
Are gram negative rods or gram positive cocci more likely to have broad spectrum resistance? Why is this?
Gram negative rods
Plasmid exchange of resistance genes and virulence factors occurs leading to development of resistant population
Which antibiotics are used to treat gram negative rods?
Co-amox PTZ Cephalosporins Fluoroquinolones Carbapenems
What are examples of gram +ve cocci? Where are these bacteria normally found and what pathology can they cause?
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
Which antibiotics are used to treat gram +ve cocci?
Penicillin (Flucox)
Vancomycin
Linezolid
daptomycon
