Microbiology

Question 1

Which cocci are gram positive and which are negative?

Which basili are gram positive and which are negative?

Answer 1

Most cocci are gram positive EXCEPT

• n meningiditis
• n gonorrhoea
• m catarhalis

Most bacili gram negative EXCEPT

• clostridium spp
• bacillus spp
• listeria
• corynebacertium diptheriae
• proprionibacterium
• mycobacterium

Question 2

What cell type is this?

Answer 2

Eosinophil

Question 3

What cell type is this?

Answer 3

Basophil

Question 4

What cell type is this?

Answer 4

Lymphocyte

Question 5

What cell type is this?

Answer 5

Neutrophil

Question 6

What cell type is this?

Answer 6

Monocyte

Question 7

Which of the following vaccines is least likely to induce long term immunologic memory?
A) Bacille Calmette-Guérin (BCG).
B) Diphtheria-tetanus-pertussis.
C) Haemophilus influenzae type B conjugate.
D) Hepatitis B.
E) Pneumococcal polysaccharide.

Answer 7

Pneumococcal polysaccharide
Pneumococcal polysaccharide vaccine is available for children aged 2 years and older as younger children are unable to mount an appropriate immune response to the non-conjugated vaccine (or actual pneumococcal disease).
Most healthy older people respond well to the vaccine, but those in groups at high risk of invasive pneumococcal disease may exhibit a poor immune response. It is unclear how long the antibody response lasts and most people will require a second vaccination after 3-5 years depending on age.
High risk children less than 5 years of age would generally be given both the polysaccharide and the conjugated vaccine for maximum protection.

Question 8

What organism is most likely to cause purulent otitis media?

Answer 8

Strep Pneumoniae

Question 9

MOA aminoglycosides

Answer 9

Aminoglycasides - binding to the 30S ribosomal subunit – bacteriocidal to Gram Negatives – peak concentration killing.

Question 10

MOA macrolides

Answer 10

Macrolides - bind to the 50S subunit of bacterial ribosomes – Resistance (i) alteration in ribosomal proteins (ii) macrolide efflux pump

Question 11

MOA Quinolones

Answer 11

Quinolones - direct inhibitors of bacterial DNA synthesis (Fluoroquinolones inhibit DNA gyrases). Resistance - mutation in chromosomal genes

Question 12

MOA tetracyclines

Answer 12

Tetracyclines – binds 30S ribosomal subunit - bacteriostatic effect.

Question 13

MOA Vancomycin

Answer 13

Vancomycin - Inhibits bacterial cell wall synthesis by blocking glycopeptide polymerization – VRE Vancomycin resistance gene cluster – ALTERS vanc binding site to low affinity site.

Question 14

MOA Trimethoprim-sulfamethoxazole

Answer 14

Trimethoprim-sulfamethoxazole: Folate synthesis inhibition (Reduced availability of THF inhibits thymidine synthesis and subsequently DNA synthesis) Resitance – decreased perm and efflux.

Question 15

MOA Linezolid

Answer 15

Linezolid: Inhibits bacterial protein synthesis by binding to bacterial 23S ribosomal RNA of the 50S subunit.

Question 16

MOA Penicillins/Beta lactams

Answer 16

Penicillins/Beta Lactams – inactivating enzymes located in the bacterial cell membrane, which are involved in the third stage of cell wall synthesis.

Enzymes = penicillin binding proteins (PBPs).

Bactericidal by autolytic enzymes.

Resistance:

• Alterations in PBPs (Pneumococcus, MRSA, gonococci, enterococci, and Haemophilus influenzae)
• Production of beta-lactamase (Chromosomal: Gram negatives, Plasmid: Cephalosporin cleavage)

Carbapenems (ß-lactam, ie meropenem) – resist beta-lactamases; Beta-Lactamase Inhibitors