Streptococci spp Flashcards
Gram Positive Cocci
Staph
Strep
GPC chains + clusters
Strep
Strep culture conditions
Aerobic 37C CO2 Blood Agar
Strep Pneumonia Optochin Susceptibility Test procedure
- Divide BA plate into 3 sections.
- Prepare suspension in reduced volume of sterile water.
- Lawn one half of the agar with suspension of test organism
- Lawn other half with Pos control (S.Pneumonia) + Neg control (S. Viridans).
- Place optochin disk in centre of each inoculum.
- Incubate BA plate overnight at 37C.
Positive = zone of inhibition >5mm = S.pneumoniae
Negative = no inhibition = Strep. viridans.
Streptococcus pneumonia infections
Non-invasive
1. Acute bacterial pneumonia = LRT (older, can spread to BS - sepsis)
2. Otitis Media
Invasive
3. BSI - Sepsis
4. Meningitis
Strep specimens
Sputum, pleural/lung fluid, pus, aspirates.
CSF, blood taken straight for molecular detection.
Strep pneumonia colonies types
Alpha haemolysis
Draughtsman colonies (flat w/ depressed centre)
Mucoid colonies
Strep pneumonia Basic Characterisation
Gram positive diplococci (lancet-shaped) - chains + clusters
Catalase negative !!
Oxidase negative
KOh negative
Presumptive a-haem Strep tests
- Optochin susceptibility test
= S. Pneumonia is susceptible = clear zone
Strep pneumonia- what to do if clinically significant
- AST
- Penicillin , Erythromycin, Cefotaxime
Strep pneumonia additional confirmatory tests
- Vitek/ MALDI TOF identification
- MALDI not very good at distinguishing a-haem strep! - CSF sent to IMSRL - Temple Street perform real time PCR on capsule to serogroup.
Strep Viridans spp (2) + infection
Strep oralis/mitis -> Streptococcal Endocarditis - infection of inner most layers of the heart.
Strep mutans -> biofilm in mouth/teeth - plaque formation + tooth decay.
S. viridans basic characteristics
Gram positive cocci in chains
Catalase negative
Oxidase negative
Facultative anaerobe.
Fastidious
Beta haemolytic strep colonies
Beta haemolysis
Pinpoint colonies
Colourless.
Presumptive B-haemolytic Strep tests
- Lancefield Grouping
- Bacitracin Susceptibility Testing
- MacConkey Agar
Strep. Lancefield grouping test procedure
Use Oxoid Streptococcal Grouping kit
Controls = Pos. S.pyogenes, Neg. Enterococcus.
1. Dispense 0.4ml extraction enzyme into labelled test tube + add 2-5 test colonies.
2. Incubate for 10 mins at 37C in water bath.
3. After 5 mins incubation remove tube and shake vigourly for 2-3seconds, continue incubation.
4. Remove and allow to cool to room temp.
Agglutination test:
1. Bring latex reagents to room temp by warming in hands + mix by shaking.
2. Dispense 1 drop of each latex reagent (A,B,C, D, F, G) in the circular rings on card.
3. Using pipette add 1 drop of extract to each of the 6 rings.
4. Mix using separate stick for each ring.
5. Gently rock card - agglutination should occur within 30s.
Group A = Strep pyogenes
Group B = Strep agalactiae
Group D = Enterococcus
BH Strep Bacitractin susceptibility test procedure
Used for Group A (S.pyogenes) identification
1. Divide blood agar into 3
2. Prepare suspension using reduced water volume.
3. Lawn one half with test organism + other half with controls (pos= S.pyogenes, neg= enterococcus). Leave margins.
4, Place bacitracin disk in centre of each inoculum.
5. Incubate BA plate overnight 37C.
Pos = zone of inhibition >5mm = S. pyogenes (group A).
BH Strep MacConkey Agar Test procedure
Lancefield groups A, C, G will NOT grow on media containing bile.
Group D grows on media with bile.
1. Split agar into 3.
2. Light zig-zag inoculum of test organism + PC (Enterococcus) + NC (S.pyogenes) on MacConkey agar.
3. Incubate plates at 37C overnight.
Positive = Group D (enterococcus) will grow - magenta colonies.
Strep pyogenes infection
Non-invasive skin infection
1. Pharyngitis (URT)
2. Scarlet fever
3. Skin infections - impetigo, cellulitis, erysipelsia
Invasive skin infection
4. Necrotising Fascitis
Toxin mediated
5. TSS
2. Scarlet fever
Non-suppurative sequelae (1-5wks post infection)
6. Rheumatic fever
7. Glomerulus Nephritis
Presumptive non-haem Enterococci tests
- Lancefield grouping
- MacConkey agar
- Bile Aesculin test
Non-haem strep Bile Aesculin test procedure
Identify Group D Strep
1. Split agar into 3
2. Spot inoculate test organism onto plate as 10mm circle
3. Inoculate PC (Enterococcus) + NC (S.pyogenes) onto other half.
4. Incubate plate at 45C overnight + record blacking of medium.
Growth + black = enterococcus
Beta haem Strep treatment
Penicillin
Clarithromycin (allergy)
Necrotizing fascitis = surgery + clindamycin
Enterococci infections
Normal commensal of GI tract
Most infections are endogenous
Often HAI
1. UTI
2. Intra abdominal abscess
3. Endocarditis
4. BSI
