Infection X - Pathogens + Diseases (Part 1)

Question 1

What type of organism is staphylococcus aureus?
Where does it usually reside?
What virulence factor does it have?
What diseases does it cause?

Answer 1

• Gram positive cocci (grape-like)
• Part of microbiota in skin, nose + GIT
• Coagulase, converts fibrinogen (soluble) into fibrin (insoluble)
• Cellulitis, skin abscesses, implanted-device infections

Question 2

What organisms is cellulitis caused by?
How does it present?
How is the infection picked up?
What are the treatment options?

Answer 2

• Staphyloccocus aureus + streptococcus pyogenes
• Skin swollen, red, painful and warm to touch
• Anything that breaks skin, e.g.: eczema, insect bite, puncture wound etc.
• Flucloxacillin

Question 3

What other types of cellulitis is there?

Answer 3

1) Anaerobic cellulitis - causes skin necrosis and foul smelling wound
2) Necrotising fasciitis - life threatening infection of skin, subcutaneous tissue + multiple fascia layers. Due to rapid spread of cellulitis/sepsis infection.

Question 4

What kind of organism is candida albicans?
Where does it usually reside?
What disease does it cause + how?

Answer 4

• Fungi (yeast)
• Commensal to mouth + vagina
• Oral + vaginal candidiasis, when competing flora (e.g.: lactobacillus) is reduced (e.g.: by antibiotics), raising pH and numbers of the yeast

Question 5

How does oral/vaginal candidiasis present?

What is the treatment?

Answer 5

Oral = raised white plaques on tongue and gums
Vaginal = itchy, burning pain during sex, peeing etc

Oral = nystatin mouth wash
Vaginal = cotrimoxazole cream

Question 6

What type of organism is streptococcus pneumoniae?
Where does it usually reside?
What disease does it cause?

Answer 6

• Gram positive diplococci (viridans group)
• microbiota, skin, URT
• community acquired pneumonia

Question 7

What organisms cause pneumonia?
What is infected?
What are the symptoms?
What is the treatment?

Answer 7

• Streptococcus pneumoniae, haemophilus influenzae
• Infection of terminal bronchi, causing crackles
• SOB, coughing, chest pain upon breathing, coughing sputum, fever etc.
• Amoxicillin (+Doxycycline if severe)

Question 8

What type of organism are adenoviruses?
What kind of infections do they cause?
How are they diagnosed + treated?

Answer 8

• Non-enveloped double stranded DNA virus
• URT, GIT, UTI’s, viral pneumonia, bronchitis, common cold
• Antigen detection (ELISA), PCR - supportive treatments (no specific)

Question 9

What type of organism is Neisseria meningitidis?
What diseases can it cause?
Where does it usually reside?

Answer 9

• Gram negative diplococci w/polysaccharide capsule
• Meningitis + septicaemia (if together meningococcal sepsis)
• Commensal of oropharynx

Question 10

What is meningitis?

Answer 10

• Inflammation of the meninges
• Meninges are 3 layered membrane that surround and protect the brain and spinal cord (pia mater, arachnoid mater + dura mater - inside to out)
• CSF produced by choroid plexus is released into sub arachnoid space (in-between pia and arachnoid mater)

Question 11

What organisms cause meningitis?
How do the pathogens get into the blood stream?
What cell types increase in bacteria + viral meningitis?

Answer 11

• Neisseria meningitidis, haemophilus influenzae, enteroviruses, HSV 1+2, candida albicans + more
• Into blood stream from sinuses, ears, throat, across BBB into brain
• Bacterial = increase in neutrophils
• Viral = increase in lymphocytes

Question 12

What are the symptoms of meningitis?
How is diagnosis made?
What is the treatment?

Answer 12

• Headache, photophobia (difficulty looking at lights), vomiting, neck stiffness, irritable, non-blanching purple rash
• Diagnosis by lumbar puncture, look for neutrophils/lymphocytes
• I.V ceftriaxone (cephalosporin) as can cross BBB and intensive care as it causes multiple organ dysfunction + bacteria can cause DIC. Vaccinations also available.

Question 13

What is disseminated intravascular coagulation? (DIC)
What are the signs/symptoms?
What is it caused by?

Answer 13

• Widespread intravascular activation of coagulation. Lots of small blood clots form. Clotting factors and platelets used up so bleeding may also occur at same time.
• Petchiae (non-blanching) + necrosis (due to vascular damage and lack of blood/oxygen to skin and periphery), haemorrhage.
• Infections (such as meningococcal sepsis), cancers, allergic/toxic reactions etc

Question 14

What kind of pathogens cause UTI’s?
Why are women more susceptible?
What are the typical symptoms?
How is it treated?

Answer 14

• E.coli (most commonly), adenovirus, candida etc.
• Shorter urethra, therefore less distance to bladder/kidney
• Burning pain while urinating, polyuria, polydipsia, haematuria
• For E.coli - trimethoprim + painkillers and fluids