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Medicine Phase 2a > Microbiology Practicals > Flashcards

Microbiology Practicals Flashcards

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1
Q

How is a gram stain prepared?

A

Come In And Stain:

Heat fix bacteria onto the slide
Crystal violet - primary stain
Iodine
Acetate/Alcohol - decolourise
Safranin - Counterstain

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2
Q

What colour do gram positive and gram negative bacteria stain?

A

Gram positive - Purple

Gram Negative - Pink

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3
Q

What is blood agar?

A

agar with horse/sheeps blood
used for growing lots of bacteria
least selective

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4
Q

What is chocolate agar?

A

heated to 80C for breakdown of haem & release of nutrients/factors that grow organisms w/ fastidious growth requirements [H.influenzae]

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5
Q

What is CLED?

A

differentiates between organisms in urine & allows classification of lactose fermenting (yellow) & non lactose fermenting (blue) gram-negative bacilli

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6
Q

What is MacConkey Agar?

A

grows gram negative bacilli (it has bile salts that inhibit the growth of gram positive). Has lactose & red dye

lactose fermenting = pink colonies
non lactose fermenting = white colonies

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7
Q

What is Gonococcus Agar?

A

Contains growth factors to promote the growth of Neisseria species as well as antibiotics & antifungal agents to inhibit the growth of other organisms.

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8
Q

What is Sabouraud’s Agar?

A

used to culture fungi. Has antibiotics to inhibit bacterial growth.

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9
Q

What is XLD Agar?

A

used to isolate Salmonella and Shigella [non lactose fermenting, gram negative]
Salmonella - Red with black centre (produces H2S)
Shigella - Red only

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10
Q

What colour will Staphylococcus aureus appear on blood agar and what colour would other staphylococcus species appear?

A

S.aureus - gold
S.other - white (S.epidermidis/ S.saprophyticus)

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11
Q

What are the sterile sites of the body?

A

Blood
CSF
pleural fluid
Peritoneum
Joints
Urinary Tracts
Lower Respiratory Tract

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12
Q

How can you tell the difference between various Gram Positive bacteria?

A

+tve Catalase Test = Staphylococcus:
(if positive then do Coagulase Test:)
+tve = S.aureus
-tve = S.epidermidis/S.saprophyticus

-tve Catalase Test = Streptococcus
(if negative then do Haemolysis on blood agar)

alpha haemolysis (partial/green) = requirement for Optochin Test
Optochin Sensitive = S.pneumoniae
Optochin Resistant = S. viridans group

Beta haemolysis (full) = requirement for Lancefield grouping via serology)
A = S.pyogenes
B = S.agalactiae
A,C, G = Tonsilitis, pharyngitis, skin infection
B = Neonatal sepsis + meningitis

Gamma Haeomolgysis (none) = Enterococcus

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13
Q

How can you tell the difference between various Gram Negative bacteria?

A

MacConkey Agar for lactose fermentation Test:
+tve lactose fermentation = E.coli/Klebsiella
-tve Lactose fermentation = Requirement to do Oxidase Test

Oxidase Test:
+tve Oxidase = Pseudomonas aeruginosa
-tve Oxidase = Requirement to do XLD test:

Colonies on XLD which are Red with black centers = Salmonella
Colonies on XLD which are Red only = Shigella

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14
Q

What are the 2 main approaches to diagnosing viral infection?

A

Electron Microscopy / PCR
Serology Testing - ELISA, IF, Complement Fixation Test.

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15
Q

What is an advantage and disadvantage to EM testing?

A

Very specific and sensitive but too expensive and too long

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16
Q

What is an advantage and disadvantage to PCR?

A

Very fast but high risk of false positives as it is very sensitive and so can easily be contaminated.

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17
Q

What is serology?

A

Detection of antibody responses in the serum - Especially IgG and IgM
IgM implies acute/new infection
IgG implies later infection

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18
Q

What virus causes shingles and how does it present?

A

Varicella Zoster Virus (VZV)

Red painful rash conferred to a single dermatome

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19
Q

What virus causes Glandular fever (infectious mononucleosis)?

A

Epstein Barr Virus (EBV)

Ix: FBC - Atypical lymphocytes
Serology for EBV Igs - ELISA Test

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20
Q

What is a differential Diagnosis to Glandular fever and how is this ruled out?

A

S.pyogenes throat infection - Both EBV and S.pyogenes present with purulent (pus) infection over the tonsils

Take black charcoal swab to rule out S.pyogenes

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21
Q

What other Sx can be caused by EBV?

A

Tonsilitis,
Cough
Fever
Splenomegaly

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22
Q

What is BALF?

A

Bronchoalveolar lavage fluid

Fluid collected from the lungs
Bronchi are washed and this fluid is sent for analysis using PCR

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23
Q

What condition can cytomegalovirus cause?

A

CMV colitis
Characteristic finding is OWL EYE INCLUSION BODIES

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24
Q

What is the treatment for CMV infection?

A

IV ganciclovir

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25
What HIV markers can be found in the blood
HIV Igs HIV RNA p24 antigen
26
How may a patient present with meningitis?
Headache Fever Photophobia Neck stiffness
27
What Ix are required for suspected meningitis?
Take CSF sample. CSF --> Increased WCC + protein Determine type of meningitis based on CSF glucose, CSF Protein, type of WCC and CSF appearance. If viral then use PCR to determine specific type
28
What antibody would you expect to find in an acute EBV infection?
IgM antibody
29
What antibody would you expect to find upon subsequent exposure to EBV or its reactivation?
IgG VCA IgG EBNA IgG
30
What are the uses of qPCR?
Quantitative PCR: Look for the presence or absence of DNA/RNA To quantify the level of virus in a tissue
31
What tests are performed to process a CSF sample?
Cell count and differential Gram stain for organisms qPCR for virus and bacterial pathogens Protein and Glucose
32
What are the HIV markers tested for in the blood?
HIV Igs HIV RNA p24 antigen
33
What are the next steps if the HIV test yields: + lab ELISA - Lab ELISA
+tve Lab ELISA: Doctor explains +tve result to patient. Needs a second confirmation blood sample -tve Lab ELISA: Confirmatory test with a different assay
34
What is the most common cause of meningitis in neonates?
Group B Strep - Strep Agalactiae E.coli Listeria
35
What is the most common cause of meningitis in infants?
S. pneumoniae N. Meningitidis H. influenza - now rare due to vaccine
36
What is the most common cause of meningitis in adults?
S. pneumoniae N meningitidis
37
What is the most common cause of meningitis in the elderly?
S. pneumoniae N. meningitidis Listeria monocytogenes
38
What is the most common cause of Encephalitis?
Viral - HSV-1 (accounts for 95% of cases)
39
How are infections of the CNS diagnosed?
CSF analysis: Cell count Gram stain Protein Glucose Culture on BA/Chocolate Agar and PCR Nose/throat swab - Charcoal and Green viral swabs
40
What are the results of CSF analysis for bacteria? Cells CSF appearance Protein Glucose
Cells: Neutrophilia CSF appearance: Cloudy yellow Protein: High Glucose: Low (<50%)
41
What are the results of CSF analysis for Viruses? Cells CSF appearance Protein Glucose
Cells: Lymphocytosis CSF appearance: Clear Protein: Normal - mildly elevated Glucose; normal
42
What are the results of CSF analysis for Fungi? Cells CSF appearance Protein Glucose
Cells: Lymphocytosis CSF appearance: Yellow and fibrinous Protein: High Glucose: Low (<50%)
43
What is the major risk factor of Meningococcal Septiciaemia?
Septic DIC
44
How does Meningococcal septicaemia present?
Non-Blanching Purpuric Rash W/ Meningism signs
45
What is the Treatment for meningococcal Septicaemia?
Immediate IM Benzylpenicillin Then Transfer to Hospital
46
What is the Treatment for Listeria suspected meningitis?
IV Amoxicillin
47
What must be done after a diagnosis of Meningitis?
Inform PHE Close Contact Tracing - Single dose Ciprofloxacin Prophylaxis
48
What are the investigations and Mx for Encephalitis?
Typically Temporal Lobe affected on CT CSF analysis (LP) and PCR to confirm HSV-1 Tx - IV Acyclovir
49
What are the key samples to collect in Pneumonia, TB or COPD infection?
Bloods and Sputum
50
What is the common bacteria involved in pneumonia?
S. pneumoniae - Causes Typical Pneumonia Cultured on Blood Agar - Alpha Haemolytic and optochin Sensitive
51
What is Typical Pneumonia?
Invades alveolar cavity and causes a productive rust coloured purulent sputum with a fever and headache
52
What is the Treatment for Typical Pneumonia?
Amoxicillin - Covers most Strep and S. aureus sensitive strains
53
What is the most common cause of Atypical Pneumonia?
Legionella pneumophilia - Suspected in Severe CAP and Recent Travel (spain)
54
How are atypical pneumonias treated?
Macrolides - Erythromycin/clarithromycin
55
What is the first line treatment for Legionella pneumonia?
1st Line - Clarithromycin Inform PHE too
56
What are some other causes of Atypical Pneumonia?
chlamydia psittaci Mycoplasma Pneumonia Chlamydia pneumonia Coxiella
57
What are the main bacteria involved in COPD exacerbations?
Haemophilus Influenzae (gram neg bacillus) Tx with Amoxicillin (if beta lactamase negative) or Co-amoxiclav (if Beta lactamase positive) S. pneumonia: Tx with Amoxicillin
58
How can TB be detected?
Stain: Ziehl Neelsen - AFB detected (not gram stain due to high mycolic acid content of TB prevents gram stain uptake) Auramine phenol fluorescence and Microscopy Solid TB Culture - Lowenstein Jensen Agar (TB Replicates every 15-20hrs so may take 6 weeks to grow NAAT/PCR - Much faster than solid culture Histologically - Granuloma w. Central Necrosis (caseating)
59
What cause of pneumonia is common in HIV Px?
Pneumocystis Pneumonia caused by Pneumocystis Jirovecii Shows cysts of Jirovecci Fungus Tx with Co-Trimoxazole + Prednisolone if Type I Respiratory Failure present
60
What Organisms often colonise the respiratory tract in bronchiectasis patients?
P. aeruginosa Tx with Tazocin - Tazobactam + piperacillin S. pneumonia H. Influenza Tx with Amoxicillin
61
What is the common skin infection of the lower limb?
Cellulitis DDx - DVT
62
What are the cardinal Signs of Inflammation?
Calor Dolor Rubor Tumor Loss of function
63
What is the pathogenesis of Cellulitis?
Breach in skin (Eczema, Athletes foot, Diabetic Foot) Pathogen enters the soft tissues through the breach Causes infection and inflammation
64
What are the common Cellulitis organisms?
Group A Strep - S. pyogenes S. aureus
65
What is the Presentation of Impetigo?
Crusty lesions on chin and Cheek of a young person (acute infection in children) Which is itchy and grows as they Scratch it
66
What is the Presentation of Impetigo?
Crusty lesions on chin and Cheek of a young person (acute infection in children) Which is itchy and grows as they scratchWhat
67
What is the Presentation of Impetigo?
Crusty lesions on chin and Cheek of a young person (acute infection in children) Which is itchy and grows as they scratchWhat
68
What swab is used to diagnose impetigo?
Black Charcoal Swab
69
What is the treatment for Impetigo?
S. pyogenes - Benzylpenicillin S. aureus - flucloxacillin MRSA - Vancomycin or Teicoplanin
70
What is the treatment for Cellulitis?
Give Empirical Abx until pathogen ID w/ culture then Review. Empirical Abx: Flucloxacillin
71
What are the 3 key features of taking a blood culture for Cellulitis?
Take good volumes of blood Take from more than one site Take on more than one occasion
72
What are the features of a lower UTI?
LUTs: Storage - FUNI Voiding - SHITS
73
What are the features of an upper UTI?
Pyelonephritis Loin pain Fever Nausea and Vomiting
74
What are the main UTI Organisms?
KEEPS Klebsiella E.coli (UPEC 80% of cases) Enterobacter Proteus Mirabilis S. Saprophyticus /S. epidermidis
75
What are the main causes of UTIs?
Obstruction BPH Renal Stones Catheters Sexual intercourse Renal Tumours
76
What is the first line investigation for a suspected UTI?
Urine Dipstick: + leukocytes + nitrites +/- Protein
77
What level of bacteria is significant for a UTI on Culture?
10^5
78
What is the treatment for an uncomplicated UTI?
Nitrofurantoin (50mg 4x Daily) for 3 days
79
What type of sample should urinalysis never be done on?
Catheterised sample urine: Bacteria is likely present regardless of infection or not compared to Mid-Stream which should be reliable as the urinary tract is normally sterile
80
What is the treatment for E. coli Pyelonephritis?
Co-amoxiclav for 7 days or Nitrofurantoin for 14 days
81
Why should pregnant women have their urine screened?
Screen for Pre-Eclampsia High BP and Proteinuria in pregnancy when otherwise well
82
What is the most common cause of Infective Endocarditis?
S. aureus
83
What is the treatment for Campylobacter infection?
Ciprofloxacin / Clarithromycin
84
What is the treatment for C. difficile infection?
Stop C Abx Vancomycin 125mg 4x Daily for 10 days
85

Medicine Phase 2a (20 decks)

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