Infectious diseases

Question 1

Difference between gram positive and gram negative bacteria? Give an example of each.

Answer 1

Gram positive: thick peptidoglycan cell wall, stains purple with crystal violet
Cocci - staphlycoccus, streptococcus, enterococcus, anaerobes
Gram negative: don’t stain with crystal violet but stains pink with safranin. Eg niesseria, haemophila, escherisca, klebsiella, moraxella

Question 2

What is an atypical bacteria? Give 3 examples.

Answer 2

One that cannot be stained or cultured in the normal way.
Legions – Legionella pneumophila
of Psittaci – Chlamydia psittaci
M – Mycoplasma pneumoniae
C – Chlamydydophila pneumoniae
Qs – Q fever (coxiella burneti)

Question 3

Give 3 gram +ve bacilli.

Answer 3

Bacillus, Mycobacteria, Corneybacteria, Listeria, Nocardia

Question 4

Give 3 gram positive anaerobes.

Answer 4

Clostridium, Lactobacillus, Antinomyces, Proprionibacterium

Question 5

Give 3 gram negative bacteria.

Answer 5

Neisseria meningitis
Neisseria gonorrhoea
Haemophilia influenza
E. coli
Klebsiella
Pseudomonas aeruginosa
Moraxella catarrhalis

Question 6

How is MRSA treated?

Answer 6

Trust guidelines.
Options: Doxycycline, clindamycin/vancomycin, teicoplanin, linezolid
Prevention in surgery with chlorhexidine body wash and antibacterial nasal creams

Question 7

What are ESBLs and how are they treated?

Answer 7

Extended Spectrum Beta Lactamase bacteria. Resistant to beta-lactam abx. E coli/klebsiella common –> UTIs. Treat with carbapenems eg meropenem/imipenem

Question 8

How do carbapenems work?

Answer 8

Inhibit cell wall synthesis.

Question 9

Give 2 antibiotics which interfere with folic acid metabolism.

Answer 9

Sulfamethoxazole blocks the conversion of PABA to DHFA
Trimethoprim blocks the conversion of DHFA to THFA
Co-trimoxazole is a combination of sulfamethoxazole and trimethoprim

Question 10

How does metronidazole work?

Answer 10

Reduced to active form in anaerobic cells only. Inhibits nucleic acid synthesis.

Question 11

How do macrolides work? Give 3 examples

Answer 11

Inhibit protein synthesis by targeting the ribosome.

Erythromycin, clarithromycin, azithromycin.

Question 12

Which antibiotics are contraindicated in penicillin allergy?

Answer 12

Penicillins - amox, fluclox, co-amox, tazocin;

1% of patients with pen allergy have reaction to cephalosporins (ceftriaxone) and carbapenems (meropenem).

Question 13

What does amoxicillin cover?

Answer 13

Streptococcus (eg strep pneumoniae in pneumonia), listeria, enterococcus

Question 14

What does co-amoxiclav cover?

Answer 14

Streptococcus (eg strep pneumoniae in pneumonia), listeria, enterococcus
+ staphylococcus, haemophilus, E. Coli.

Question 15

What does tazocin cover?

Answer 15

Streptococcus (eg strep pneumoniae in pneumonia), listeria, enterococcus
+ staphylococcus, haemophilus, E. Coli.
+ pseudomonas

Question 16

What does meropenem cover that tazocin doesn’t?

Answer 16

ESBLs and n. meningitides

Question 17

What does teicoplanin cover that co-amoxiclav doesn’t?

Answer 17

MRSA

Question 18

What does doxycycline cover which amoxicillin doesn’t?

Answer 18

Staph aureus, MRSA, h. influenzae, Atypicals, moraxella catarrhalis

Question 19

What is sepsis? How is it defined?

Answer 19

Major immune response to infection that causes systemic inflammation and organ dysfunction.
Hypoxia
Oliguria
Acute Kidney Injury
Thrombocytopenia
Coagulation dysfunction
Hypotension
Hyperlactaemia (> 2 mmol/L)

Question 20

Why is lactate raised in sepsis?

Answer 20

Hypoperfusion of tissues –> anaerobic perfusion –> raised lactate

Question 21

What is septic shock?

Answer 21

Arterial blood pressure drops and results in organ hypo-perfusion
Measured by BP <90 after fluid resuscitation or lactate >4
Give IV fluids, inotropes if that doesn’t work

Question 22

What is the pathophysiology of sepsis?

Answer 22

1. Macrophages, lymphocytes and mast cells release cytokines (IL, TNF).
2. These trigger immune system to release nitrous oxide –> vasodilation, and increases endothelial permability, leading to oedema, reduces oxygen supply to tissues
3. Activation of coagulation system leads to fibrin deposition compromising organ and tissue perfusion, and DIC as platelets/clotting factors are used up in clots so none left to stop bleeding.
4. Hypoperfusion of tissues –> anaerobic perfusion –> raised lactate

Question 23

Give 5 risk factors for sepsis.

Answer 23

Under 1 or over 75 years
Chronic conditions such as COPD and diabetes
Chemotherapy, immunosuppressants or steroids
Surgery or recent trauma or burns
Pregnancy or peripartum
Indwelling medical devices such as catheters or central lines

Question 24

How does sepsis present? Give 5 signs

Answer 24

Raised EWS

Signs of potential sources such as cellulitis, discharge from a wound, cough or dysuria
Non-blanching rash can indicate meningococcal septicaemia
Reduced urine output
Mottled skin
Cyanosis
Arrhythmias such as new onset atrial fibrillation

High respiratory rate (tachypnoea) is often the first sign
Elderly patients often present with confusion or drowsiness or simply “off legs”
Neutropenic or immunosuppressed patients may have normal observations and temperature despite being life threatening unwell

Question 25

Give 5 initial investigations you’d do for suspected sepsis and why.

Answer 25

FBC- wcc, neutrophils, thrombocytopenia
U&Es to assess kidney function and for acute kidney injury
LFTs to assess liver function and for possible source of infection
CRP to assess inflammation
Clotting (DIC)
Blood cultures
Blood gas - lactate, pH and glucose

Urine dipstick and culture
Chest xray
CT scan if intra-abdominal infection or abscess is suspected
Lumbar puncture for meningitis or encephalitis

Question 26

What is the management for sepsis?

Answer 26

Local guideline, escalate, assess risk - if low-moderate can manage in community with safety netting advice.
Sepsis 6 within 1 hour if high risk for sepsis:
Lactate, cultures, urine out
Oxygen, broad spec abx and IV fluids in

Question 27

What is neutropenic sepsis?

Answer 27

Sepsis in a patient with neutrophils <1 x 10^9/L
Emergency - High risk of death from sepsis.
Usually due to immunosuppression or chemotherapy. If fever >38 in such patients, admit to hosp.

Question 28

Give 5 medications that may cause neutropenia and what they are used for.

Answer 28

Chemotherapy
Clozapine (schizophrenia)
Hydroxychloroquine (rheumatoid arthritis)
Methotrexate (rheumatoid arthritis)
Sulfasalazine (rheumatoid arthritis)
Carbimazole (hyperthyroidism)
Quinine (malaria)
Infliximab (monoclonal antibody use for immunosuppression)
Rituximab (monoclonal antibody use for immunosuppression)

Question 29

What is the most common bacterial cause of chest infection and how is it treated?

Answer 29

Strep pneumoniae (50%)
Haemophilus influenzae (20%
Amoxicillin, doxycycline if allergic

Question 30

What bacteria cause chest infections in cystic fibrosis and how are these prevented?

Answer 30

Pseudomonas (also in bronchiectasis)

Staph aureus - prophylactic fluclox

Question 31

What causes UTIs?

Answer 31

Usually E. Coli from anus to urethra
Poor hygiene, catheters, sex
Other causes: klebsiella, enterococcus, pseudomonas, staph saprophyticus, candida albicans

Question 32

How does pyelonephritis present?

Answer 32

Initial UTI - dysuria, frequency, urgency

Fever, loin pain, vomiting, loss of appetite, haematuria, renal angle tenderness

Question 33

How are UTIs diagnosed?

Answer 33

Dipstick: nitrites = gram Negative bacteria; leukocyctes (not proof of UTI on their own), MSU sample for culture if either of these are raised

Question 34

What is the management of UTI?

Answer 34

Uncomplicated = non-pregnant women. 3 days trimethoprim/nitrofurantoin

Complicated = 7 days.
Men, catheter related -change the catheter. Pregnancy - UTIs increase risk of pyelonephritis, PROM and pre-term labour
Avoid trimethoprim in first tri/anti folate meds, avoid nitrofurantoin in third tri (Haemolytic anaemia)

Immunosuppressed, abnormal anatomy or impaired kidney function - 5-10 days