Medical microbiology 1

Question 1

Gram +

Answer 1

thick peptidoglycan layer, teichoic acid + lipoteichoic acid

PAMPs:
peptidoglycan

Question 2

Gram -

Answer 2

lipopolysaccharide layer, 2 membranes with thin peptidoglycan sandwiched in between

lysozyme can only break cell wall not cell membrane
penicillin is ineffective on gram negative
phagocytosis is ineffective on gram negative

Question 3

peptidoglycan

Answer 3

NAG + NAM beta linked
NAG = N acetylglucosamine
NAM= N acetylmuramic acid

lysozyme will break down the bond between polymers , this is also how penicillin works

TLRs sensing peptidoglycan:
TLR2 + TLR1 + TLR6

Question 4

LPS

Answer 4

TLR4 (a PRR) recognises LPS

Question 5

TLR 7/8/13

Answer 5

in the endosome once engulfed will recognise RNA in virus

Question 6

recognition, recruitment, resolution

Answer 6

recognition = TLRs, NLRs, PRR and epithelial and phagocytes

recruitment = cytokines release and lymphocytes activated

Question 7

gram negative: bacilli (rods)

Answer 7

enterobacteriaceae (associated with enteric system)

the coliforms:
E coli
kliebsiella
enterobacter

the non coliforms:
salmonella
shigella

other types:
aerobic pseudomonas aeruginosa

Question 8

the coliforms: enterobacterial bacteraemia

lab ID = MacConkey agar 
red colonies (red bile salts + lactose)
coliforms break down lactose (gut environment anaerobic)
oxidase negative

Answer 8

mainly e.coli

clinical sites:
UTI
perforation injuries post surgery
ventilator associated pneumonia

sources:
urine (UTI) = uropathogenic e.coli
gut = enteropathogenic e.coli
blood = community acquire septicaemia 
CSF = meningitis associated e.coli

Question 9

pseudomonas aerugonisa

oxidase positive
non lactose fermenting
catalase positive
pigment = fluoresce under UV blue/green

Answer 9

aerobic and can break down oxygen

associated with:
respiratory tract infections
GI infections

clinical relations:
catheter related
ventilator (cystic fibrosis)
neutropenic sepsis
air borne

Question 10

gram negative: cocci

chocolate agar
oxidase positive

Answer 10

neisseria meningitis (diplococcus)

subsides in the nasal pharynx and can progress to meningitis and meningococcal septicaemia

bacteria sticks to endothelial in capillaries causes vasculature to block

skin rash = purpura

Question 11

types of bacterial meningitis

Answer 11

nisseria meningitis = 55%
s pneumoniae = 25%
haemophilus influenza B = 20%

Question 12

gram positive: cocci catalase positive

S. Aureus
coagulase positive i.e. breaks down fibrinogen to fibrin

S. epidermidis
coagulase negative

Answer 12

staphylococcus aureus:

grows in nasal pharyngeal tract and is normally commensal

infections causes:
abscess
osteomyelitis
septicaemia

staphylococcus epidermidis:
grows on skin and commensal

Question 13

gram positive: cocci catalase negative

blood agar
alpha/S. pneumoniae cannot break down RBCs

beta/S. pyogenes can break down RBCs

Answer 13

streptococci:
S. pyogenes
S. pneumoniae

S. pyogenes:
breaks down RBCs and beta haemolysis

associated with pharyngitis, impetigo, necrotising fasciitis, puerpural sepsis, post infective infections such as rheumatic fever and glomerulonephritis

S. pneumoniae:
resident in upper respiratory tract but sneaks down into lungs

produces hydrogen peroxide

Question 14

gram positive rods: clostridia

anaerobes
when spore can resist high temp
switch between rod and spore

Answer 14

clostridium types:
C. botulinum
C. difficile

Question 15

gram positive: non gram staining

ziehl neelsen stains red
acid fast bacilli

Answer 15

mycobacteria

types: tuberculosis complex
M. Tuberculosis
M. bovis
M. africans

types: non tuberculosis
M. leprae

Question 16

M. tuberculosis infection

test: sputum test and ziehl neelsen stains red
lowenstein jensen medium 
catalase +
oxidase -
slow growth 

chest X - Ray = Gohn’s complex (fibrosis)

CT scan = contrast fluorodeoxyglucose (FDG)

Answer 16

complex cell wall, lipid synthesis 10% of genome function

survive phagocytosis and initiate infective cycle inside the phagocytes. They then enter lymph and are undetected. Inside the macrophages they cause caseous necrosis and change the macrophage into epithelial like cell. Immune system forms complex of immune cells around it = granuloma

neutrophil infiltrate is replace by T cells and macrophages

Question 17

M. tuberculosis immunological detection

Answer 17

1. Mantoux test PPD (purified protein derivative):
   if exposed to TB very large induration/swelling > 10mm

erythema is not measured

does not differentiate between other mycobacterium i.e. not specific for TB

does not work in children

2. interferon gamma release assay (IGRA)
   Quantiferon TB gold

distinguishes TB from other mycobacterium

synthetic TB peptides are used to stimulate blood cells and if there is a T cell interferon response then this suggests there is an infection

does not distinguish between latent and active TB

Question 18

TB + infliximab

Answer 18

monoclonal antibody to TNF alpha

it can promote latent TB to active TB by reducing granuloma formation and promoting dissemination