T3-L5: Pathogen-Antibiotic Matching

Question 1

Give the 4 classes of antibiotics and examples within each.

Answer 1

Cell wall inhibitors: such as the beta lactams (penicillin, cephalosporin, carbapenem) and glycopeptides.

Protein synthesis inhibitors: such as tetracycline, macrocodes and gentamycin.

DNA replication inhibitors such as Trimethoprim

RNA synthesis inhibitors - Rifampin

Question 2

What type of bacteria is Staph. epidermdis and Staph aureus?

Answer 2

Gram positive cocci

Question 3

What type of bacteria is clostridium, neisseria and haemophilus?

Answer 3

Clostridum - Gram positive bacillus

Neisseria - Gram negative cocci

Haemophilus - Gram negative bacilli

Question 4

What are mechanisms of drug resistance?

Answer 4

1. Drug inactivation or modification
   = such as Staph aureus – penicillinase, E. Coli - carbapenemase
   
   2. Alteration of target- or binding site
      = Staph aureus - Alteration of Penicillin binding protein
   3. Alteration of metabolic pathway
      = Sulfa resistant bacteria can use pre-formed folic acid.
   4. Reduced drug accumulation
      = Here the Bacteria pumps out the antibiotic so that it does not accumulate in the cell
      = Efflux pump – quinolones

Question 5

How does co-amoxiclav work?

Answer 5

Most Beta-lactams have some gram positive and gram negative activity. Amoxicillin is a commonly used beta lactam for ENTs, respiratory infections and UTIs. A lot of bacteria have gained the ability to produced beta lactamase. We have developed clavulanic acid to inhibit the beta-lactamase. The combination of clavulanic acid and amoxicillin is co-amoxiclav. It is beta-lactase stable. It is a broad spectrum antibiotic. The same concept is used in Tozocin.

Question 6

What type of antibiotic cannot be used against MRSA?

Answer 6

MRSA - methicillin resistant Staphylococcus aureus.

It has a mutation in the PCP and so is resistant to flucloxacillin. We cannot use beta-lactams to treat MRSA. We ned to use other classes such as Vancomycin that target other parts.

Question 7

What drugs are used to treat community acquired pneumonia?

Answer 7

Co-amoxiclav and clarithromycin is a standard treatment in community acquired pneumonia in someone who is quite unwell. We use a CURB 65 score to give use an idea which antibiotic we should use. Low risk can get away with just amoxicillin.

Question 8

What are common causes of hospital acquired pneumonia?

Answer 8

Klebsiella pneumoniae and other gram negative bacteria.

Question 9

What drug is step. pneumoniae sensitive to?

Answer 9

Pencillin

Question 10

What antibiotics are usual causes of C. diff infection?

Answer 10

This is a common complication of broad spectrum antibiotic. Antibiotics will wipe out bacteria in the gut this means that C. diff can surge back and over grow. It is a toxin producer causing colitis.

Worst offenders to cause this is: Ciproflofloxacin, cefuroxime and co-amoxiclav. It is common in elderly patients.

Question 11

What drugs are used to treat Upper UTIs?

Answer 11

This can cause severe infection and a broad spectrum antibiotic is given before the organisms is known.

Patients present with fever, loin pain, tachycardia and hypotension.

Question 12

What drugs are used to treat Lower UTIs?

Answer 12

Nitrofurantonin, trimethoprim and pivmecillinam.

Patient present with dysuria and increased frequency of urination.

Question 13

What bacteria cause UTIs?

Answer 13

• Gram negative bacilli - most common is E. coli. Others include Proteus and Klebsiella.
  - Staphylococcus saprophyticus is also of note - associated with sexual intercourse but not an STI

Question 14

What is used to treat meningitis?

Answer 14

It is treated with IV broad spectrum antibiotic such as IV Ceftriaxone.

Question 15

What is sepsis?

Answer 15

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection - a body’s response to an infection injures its own tissues and organs.

Question 16

How is sepsis managed?

Answer 16

BUFALO

B- Blood cultures 
U- Urine output (catheterise to manage) 
F - Fluid resuscitation
A - Antibiotics 
L - Lacate 
O - Oxygen

Question 17

What are usual causes of cellulitis?

Answer 17

Cellulitis is a skin and soft tissue infection usually caused by gram positive cocci such as Staph aureus and Strep pyogenes.

Question 18

How do we treat cellulitis?

Answer 18

Flucloxacillin

Question 19

What is necrotising fasciitis?

Answer 19

A severe skin and soft tissue infection caused by a polymicrobial mix, but usually involving Streptococcus pyogenes.
Strep pyogenes is a very potent pathogen.

Treatment -

	- Debridement - remove all the dead tissue as no amount of antibiotics will sterilise dead flesh 
	- Meropenem + clindamycin (typically covers gram positive organisms and anaerobes- quite broad spectrum)

Question 20

What infection are PWID at risk of?

Answer 20

Infective endocarditis

There are many causes but the most common are:
- Staph aureus
- Streptococci
Any organism that makes you bacteraemia can stick on the heart valves. In those who are intravenous drug users, the most common causes are organisms on the skin.

Treatment:
~6 weeks IV antibiotics depending on bacteria. It is lengthy treatment but it depends on how the patient is doing and the organism.

Question 21

Which antibiotics are contraindicated in pregnancy?

Answer 21

Beta lactams are the most well tolerated antibiotics and safe in pregnancy: Penicillin & cephalosporins.

Avoid or limited use in pregnancy:
- Quinolones (ciprofloxacin) – damage to cartilage. DNA synthesis inhibitor.

• Trimethoprim – folic acid antagonist. It interferes with DNA synthesis. Typically avoided in the first trimester.
• Tetracyclines – deposits and stains bones/teeth. Works by inhibiting protein synthesis.