Infection And Immunity Flashcards
What is an infection?
An invasion of host tissues by micro-organisms
3 mechanisms pathogen cause disease
Microbe multiplication
Toxins
Host response
4 environmental sources for pathogen transfer
Food, air, water, surfaces
Microbiota?
Commensal, microbes normally carried by host on skin and mucosal surfaces.
Normally harmless
May cause harm if transfer or immunocompromised
How is legionella transferred?
Water droplets
Modes of horizontal pathogen transfer
Contact - direct, indirect, vector
Inhalation - droplets, aerosols
Ingestion - contaminated water, food, f-o
Vertical pathogen transfer
Mother to child, at or before birth
What do pathogens do once in ?
Exposure, adherence, invasion, multiplication, disemmination
Virulence factors
Exotoxins - superantigens, AB toxins, enzymes, cytolytic
Endotoxins - LPS
What factors determine severity of pt disease after exposure to a pathogen?
Pathogen - virulence, inoculum size, Ab resistance
Pt - site of infection, co-morbidities
E.g. UTI by commensal
E. coli
E.g Community acquired pneumonia
Streptococcus pneumoniae
Eukaryotes have 80s ribosome, what about prokaryotes?
70s
E.g. Gram neg, diplococcus
N. meningitidis
Grape like cluster of coccus?
Staph aureus
Difference in structure b/w gram positive and negative bacteria?
Positive- thick peptidoglycan wall with teichoic acid retains crystal violet stain
Negative - Thin peptidoglycan layer with no teichoic acid, outer layers of lipoprotein and lipopolysaccharide also present. This allows crystal violet colour to be washed out, and counterstain (safranin) is visible.
Example of unicellular fungi
Candida albicans
Example of multicellular fungi
Aspergillus, dermatophytes
What is a protozoa?
A single celled eukaryotic parasite
What mechanism of action - beta lactams?
Inhibit cell wall synthesis - binds to penicillin-binding protein, which is important in forming cross-links between chains in cell wall. Without these links, cell wall weak - unviable
What mechanism of action - glycopeptides?
Inhibits cell wall synthesis, sits on chains to be cross linked in cell wall- prevents PBP making the links. Unviable cell wall (too weak)
Example of glycopeptide?
Vancomycin
Example of beta-lactam?
Penicillin
Amoxicillin
Why can’t we use vancomycin to treat bacterial meningitis?
Often caused by Neisseria meningitidis, which is gram negative - vancomycin is too big to be taken up past the cell walls of gram negative bacteria
Two antibiotics that affect bacterial protein synthesis?
Tetracycline and doxycycline - NOT FOR KIDS
Pt has gram negative sepsis. You need to give a protein synthesis inhibitor - which one and what are the potential side effects?
Aminoglycosides - gentamycin
Potentially nephrotoxin
TDM (therapeutic dose monitoring required)
Erythromycin and clarithromycin are types of?
Macrolides, inhibitors of protein synthesis
Ciprofloxacin works by inhibiting nucleic acid synthesis. How?
Inhibits DNA gyrase and topoisomerase
V active against gram neg
C. dif association
Give one mechanism by which bacteria can be rsistant to penicillin
They may have a beta-lactamase enzyme that will inactivate the drug
What can be done to deal with a strain of bacteria that have beta lactamase activity?
Combine a beta lactam with a beta lactamase inhibitor. E.g. Co-amoxiclav
You suspect that a pt has an infection. What supportive investigations can you do?
Full blood count - neutrophils, lymphocytes CRP LFTs, KFTs Imaging - xray, ultrasound, MRI Histopathology
How would you check if a pt had a virus?
Virology
Antigen detection
Antibody detection
Nucleic Acid detection - DNA/RNA
Virus basic structure
Nucleic acid, protein coat
+/- LPS/lipid capsule, spikes
What is the baltimore classification of viruses?
Classes based on nucleic acid structure- i.e. dsDNA, ssDNA, ssRNA etc.
Example of dsDNA non-enveloped viruses
Adenovirus,
Human papilloma virus
DsDNA enveloped virus
Herpes virus
Hep B
Molluscum contagiosum
Example of RNA virus
Hep A, E
Influenza
Norovirus
Bacteria basic structure
Circular DNA,
Plasma membrane
Cell wall
Ribosome
+/- envelope, pili, flagellum, plasmid
2 example of gram positive bacilli
Listeria monocytogenes
Bacillus anthracis
Bacillus cereus
Examples of gram neg bacilli
Salmonella typhi
Escherichia coli
Haemophilus influenzae
Some bacteria have enzymes that increase their virulence, give an example
Collagenase
Helps invasiveness
What fungal infection is a hallmark of immunocompromised pts?
Pneumocystis jiroveci
2 Examples of protozoa
Plasmodium falciparum
Trypanosoma cruzi
An example of a fluke (helminth)
Schistosoma mansoni
3 Mechanisms of resistance to antibiotics
1) Drug inactivation (e.g. Beta lactamases)
2) alteredTarget site i.e. Target enzyme may have lower affinity for drug (e.g. Meticillin)
3) Decreased uptake or increased efflux (tetracycline)
3 methods of horizontal gene transfer between bacteria
1) conjugation - bacteria share plasmid via conjugation tube
2) transduction - bacteriophage introduces new genes from previous host
3) transformation- free dna comes in
How to test for antibiotic sensitivity?
Disc sensitivity testing
May also want to measure min inhib concen
5 betalactam examples in 5 seconds. Go!
1) penicillin
2) benzylpenicillin
3) amoxicillin
4) flucloxacillin
5) Co-amoxiclav (amoxicillin + clavulanate)
6) Tazocin (pipperacillin + tazobactam)
Example of cephalosporin
Ceftriaxone
Example of carbapenem
Meropenem
Pt had infection which was treated successfully with penicillin. What’s most likely family of bacteria?
Streptococcus
Staph now resistant
Pt suspected to have gram negative sepsis. What is your treatment of choice?
Ceftriaxone, because of CSF penetration, watch out c.dif
Ideal features of an antibiotic?
Selective toxicity Few adverse effects Reach site of infection Oral/IV formulation Long half life - infrequent dosing No interference with other drug
Amoxicillin main use
Gram positive, some gram neg.
Flucloxacillin,
Staph
Strep
Pseudomonas infection what antibiotic?
Tazacin
Pipperacillin and tazobactam
Does co-amoxiclav work on anaerobes?
Yup
Cephalosporins such as ceftriaxone do not work on anaerobes. True or false?
True
You have a pt who is allergic to penicillin. Last time she took penicillin she threw up and didn’t feel too well. You now suspect she has an infection and are thinking of prescribing meropenem, which is a carbapenem. Is it safe?
Yes, unless she had anaphylaxis
Facts about vancomycin, go.
1) G positive only
2) most staph
3) some enterococci resistant (VRE)
4) not absorbed, hence iv only - but oral for c dif
5) resistance in staph rare
6) TDM required (narrow therapeutic window)
A patient comes in with a red, swollen leg that is tender and throbbing.
He most probably has cellulitis, so you start treatment with AB.
The blood culture however, comes back negative.
Is it possible to have an infection without a possitive blood culture?
Yes
Not all infections travel to blood
Some, such as this one, may be localised so a negative blood culture does not rule out cellulitis
Carry on AB and see how he does
Pt sick after being admitted to hospital.
What is the criteria for healthcare infections?
Infections arising as consequence of providing healthcare
In hospital pts:
- Neither present nor incubating at time of admission
- Onset at least 48 hours post-admission
Also includes infections in hospital visitors and healthcare workers
Give some examples of healthcare acquired infections
Blood borne viruses e.g. Hep. B, C, HIV
Norovirus
MRSA
Cdif
Pseudomonas aeruginosa
TB
4 Ps of Infection Control
Patient
Pathogen
Practise
Place
Have you I-fives your patient today?
Identify (Abroad, bbinfections, colonised, diarrhoea/vomiting, expectorating, funny looking rash)
Isolate
Investigate
Inform
Initiate
