Infection And Immunity Flashcards
Name three modes of horizontal transmission.
Direct/indirect contact (incl. vectors)
Inhalation of droplets or aerosols
Ingestion (faecal-oral)
What is the difference between an exotoxin and an endotoxin?
Exotoxins- chemicals produced by microbes into the local environment.
Endotoxins- parts of micro organisms recognised by the body e.g. A
antigens.
Name some disease determinants.
Virulence factors Inoculum size Antimicrobial resistance Site of infection Co-morbidities
Describe the main features of a virus.
Have nuclei can acid (RNA/DNA)
May have an envelope/capsule
Invade and multiply within host cells
What is a bacteriophage and what is its significance in antimicrobial resistance?
Viruses that can infect bacteria, thus permitting transfer of DNA between bacteria as a vector.
Name some virulence factors.
Host entry
Adherence
Invasiveness
Iron sequestration
Name some gram positive cocci.
Staphylococcus aureus
Streptococcus pneumoniae
Enterococcus faecalis
Name some gram positive bacilli.
Listeria monocytogenes
Bacillus anthracis
Name some gram negative cocci.
Neisseria meningitidis
Neisseria gonorrohoeae
Moraxella catarrhalis
Name some gram negative bacilli.
E. Coli Salmonella typhi Pseudomonas aeruginosa Haemophilus influenzae Kleibsella pneumoniae
What investigations might you carry out for a suspected infection?
Full blood count including neutrophils and lymphocytes C-reactive proteins Liver and kidney function Imaging e.g. CXR History theology
How can we classify antimicrobials?
They can be classified as bactericidal or bacteriostatic, by spectrum, target site or chemical structure.
What are the ideal features of an antimicrobial?
Selectively toxic Reach site of infection Have few adverse side effects Long half life (infrequent dosing) No cross-reactivity with other drugs
What is the action of beta-lactams?
Prevent cell wall synthesis by blocking bacterial cross-linking proteins.
Name four types of beta-lactams with examples of each.
Penicillins e.g. Amoxicillin
Cephalosporins e.g. Cefalexin, Ceftriaxone
Carbapenems e.g. Meropenem
Combination with a beta-lactamase inhibitor e.g. Co-amoxiclav
What is the action of glycopeptides?
Affect cell wall synthesis by preventing the binding of cross-linking proteins e.g. Vancomycin
Name the classes of antibiotics that affect protein synthesis.
Tetracyclines e.g. Doxycycline
Aminoglycosides e.g. Gentamicin
Macrolides e.g. Erythromycin
What is the mechanism of action of quinolones?
Bonds two nuclear enzymes thus inhibiting DNA replication and nucleic acid synthesis e.g. Ciprofloxacin
Name the two classes of antifungals and their action.
Azoles inhibit cell membrane synthesis e.g. Fluconazole
Polyenes inhibit cell membrane function e.g. Nystatin, Amphoteracin
What is the action of the antiviral Aciclovir?
Inhibits viral DNA polymerase when phosphorylated.
What is the mechanism of action of Oseltamivir (Tamiflu)?
Inhibits viral neuraminidase.
What classes of antibiotics may you use for a gram positive infection?
Beta-lactams
Glycopeptides
Macrolides
Tetracyclines
What classes of antibiotics might you use for a gram negative infection?
Beta-lactams
Aminoglycosides
Quinolones
What are the mechanisms of antimicrobial resistance?
Drug inactivation by enzymes
Altered target site
Altered drug uptake e.g. Decreased permeability or increased active reflux
What is SIRS?
Systemic Inflammatory Response Syndrome
Requires 2 or more of:
Temperature below 36 degrees or above 38
Heart rate greater than 90bpm
Respiratory rate greater than 20 breaths per minute
WBC count less than 4x109L or greater than 12
What is sepsis?
SIRS and a documented/presumed infection
What is severe sepsis?
SIRS + organ dysfunction/hypoperfusion
What is septic shock?
Severe sepsis and persistent low blood pressure despite IV fluid resuscitation
What is the mechanism that brings about septic shock?
Binding of endotoxins to macrophages activates cytokines that in turn activate the inflammatory response.
Failure to restore homeostasis and activation of humoral cascades leads to circulatory insult.
Why is there a risk of thrombosis in septic shock?
Cytokines also initiate production of thrombin and inhibit fibrinolysis, thus promoting coagulation
What are the sepsis six?
To be delivered in one hour:
High flow rate oxygen
Blood and other cultures to be taken
Empirical IV antibiotics e.g. Ceftriaxone
Measure serum lactate
IV fluid resuscitation
Urine output measurement (catheterisation)
What are complications of sepsis?
Irreversible hypotension Respiratory failure Renal failure Raised intercranial pressure Ischaemic necrosis
Define the immune system.
Cells and organs that contribute to immune defences against infectious and non-infectious conditions and organisms.
Roles of the immune system?
Pathogen recognition
Killing/clearance mechanisms
Regulating itself to minimise damage to host
Remembering pathogens to prevent recurrence
Give four examples of barriers that prevent entry and limit growth of pathogens?
Physical barriers e.g. Skin, mucus membranes
Physiological barriers e.g. Diarrhoea, vomiting
Chemical barriers e.g. Low pH, IgA
Biological e.g. Normal flora
What steps are involved in pathogen recognition?
Pathogen associated molecular patterns (PAMPs) detected by pathogen recognition receptors (PRRs) and opsonisation (enhanced attachment of phagocytes).
Give examples of opsonins.
Complement factors e.g. C3b
Antibodies e.g. IgG, IgM
Acute phase proteins e.g. CRP
Describe oxygen dependent and independent mechanisms of phagocytosis:
Oxygen dependent respiratory burst using hydrogen peroxide
Oxygen independent e.g. Lysozyme, lactoferrin and proteolytic enzymes
Define infection:
Invasion of host tissues by microbes and disease caused by multiplication, toxins or the host response.
Why do you get a fever with infection?
TNF-alpha, IL-1 and IL-6 act on the hypothalamus to increase body temperature
Why might an individual have reduced ability for phagocytosis?
Decreased splenic function
Decreased neutrophils
Decreased neutrophil function e.g. Chronic granulomatous disease (no resp burst) and Chediak-Higashi syndrome (no phagolysosomes)
Define a healthcare infection:
Neither present or incubating at time of admission, onset 48hrs post-admission e.g. Norovirus, MRSA, C. diff
How can we prevent healthcare related infections?
Activities of healthcare workers e.g. PPE
Virulence factors
Healthcare environment e.g. Sterile
General and specific risk factors
Interactions with healthcare workers and other patients e.g. Isolation
Name some APC in the adaptive immune system:
Dendritic cells, langerhans cells, macrophages, B cells
How are antigens presented to lymphocytes?
Presented by Major Histocompatibility Complex e.g. HLA
- class I on all nucleated cells present intracellular antigens
- class II on dendritic, macrophage and B cells present extracellular antigens
Describe the antigen processing pathways:
Endogenous: virus attaches to LMP2 with antigenic peptide which leads to presentation of MHC I
Exogenous: exogenous antigen undergoes phagocytosis and is then passed on to MHC II
Describe features of T lymphocytes:
T cell receptors have alpha and beta chains responsible for antigen recognition
Produced in bone marrow and mature in thymus
CD4+ activate helper cells and produce TNF-alpha/ILs
CD8+ activate cytotoxic T cells and T killer cells
Describe features of B lymphocytes:
Undergo isotope switching to produce IgG antibodies
Why are B cells crucial for the immune response?
IgGs produce a faster and longer response in future infections and produce a stronger and higher affinity response
Describe the function of each antibody type:
IgG- complement activation, opsonisation for phagocytosis, neonatal immunity, toxin neutralisation
IgE- mast cell degranulation, immunity against helminths
IgA- mucosal immunity
IgM- complement activation
What are the main features of malarial infection?
Plasmodium falciparum/vivax/ovale/malariae
Vector is the female anopheles mosquito
No case-to-case spread
Incubation period of 1-3 weeks
What are the symptoms of malaria?
Fever, chills, night sweats cycle, may have splenomegaly due to increased RBC lysis (malarial trophozoite infiltrates)
Sever malaria may cause CVS symptoms, ARDS, AKI, cerebral malaria etc.