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Medicine Phase 2a > Microbiology Practicals > Flashcards

Microbiology Practicals Flashcards

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
Q

What HIV markers can be found in the blood

A

HIV Igs
HIV RNA
p24 antigen

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26
Q

How may a patient present with meningitis?

A

Headache
Fever
Photophobia
Neck stiffness

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27
Q

What Ix are required for suspected meningitis?

A

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

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28
Q

What antibody would you expect to find in an acute EBV infection?

A

IgM antibody

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29
Q

What antibody would you expect to find upon subsequent exposure to EBV or its reactivation?

A

IgG
VCA IgG
EBNA IgG

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30
Q

What are the uses of qPCR?

A

Quantitative PCR:
Look for the presence or absence of DNA/RNA
To quantify the level of virus in a tissue

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31
Q

What tests are performed to process a CSF sample?

A

Cell count and differential
Gram stain for organisms
qPCR for virus and bacterial pathogens
Protein and Glucose

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32
Q

What are the HIV markers tested for in the blood?

A

HIV Igs
HIV RNA
p24 antigen

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33
Q

What are the next steps if the HIV test yields:
+ lab ELISA
- Lab ELISA

A

+tve Lab ELISA:
Doctor explains +tve result to patient.
Needs a second confirmation blood sample

-tve Lab ELISA:
Confirmatory test with a different assay

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34
Q

What is the most common cause of meningitis in neonates?

A

Group B Strep - Strep Agalactiae

E.coli
Listeria

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35
Q

What is the most common cause of meningitis in infants?

A

S. pneumoniae
N. Meningitidis
H. influenza - now rare due to vaccine

36
Q

What is the most common cause of meningitis in adults?

A

S. pneumoniae
N meningitidis

37
Q

What is the most common cause of meningitis in the elderly?

A

S. pneumoniae
N. meningitidis
Listeria monocytogenes

38
Q

What is the most common cause of Encephalitis?

A

Viral - HSV-1
(accounts for 95% of cases)

39
Q

How are infections of the CNS diagnosed?

A

CSF analysis:
Cell count
Gram stain
Protein
Glucose
Culture on BA/Chocolate Agar and PCR

Nose/throat swab - Charcoal and Green viral swabs

40
Q

What are the results of CSF analysis for bacteria?
Cells
CSF appearance
Protein
Glucose

A

Cells: Neutrophilia
CSF appearance: Cloudy yellow
Protein: High
Glucose: Low (<50%)

41
Q

What are the results of CSF analysis for Viruses?
Cells
CSF appearance
Protein
Glucose

A

Cells: Lymphocytosis
CSF appearance: Clear
Protein: Normal - mildly elevated
Glucose; normal

42
Q

What are the results of CSF analysis for Fungi?
Cells
CSF appearance
Protein
Glucose

A

Cells: Lymphocytosis
CSF appearance: Yellow and fibrinous
Protein: High
Glucose: Low (<50%)

43
Q

What is the major risk factor of Meningococcal Septiciaemia?

A

Septic DIC

44
Q

How does Meningococcal septicaemia present?

A

Non-Blanching Purpuric Rash W/ Meningism signs

45
Q

What is the Treatment for meningococcal Septicaemia?

A

Immediate IM Benzylpenicillin

Then Transfer to Hospital

46
Q

What is the Treatment for Listeria suspected meningitis?

A

IV Amoxicillin

47
Q

What must be done after a diagnosis of Meningitis?

A

Inform PHE
Close Contact Tracing - Single dose Ciprofloxacin Prophylaxis

48
Q

What are the investigations and Mx for Encephalitis?

A

Typically Temporal Lobe affected on CT
CSF analysis (LP) and PCR to confirm HSV-1

Tx - IV Acyclovir

49
Q

What are the key samples to collect in Pneumonia, TB or COPD infection?

A

Bloods and Sputum

50
Q

What is the common bacteria involved in pneumonia?

A

S. pneumoniae - Causes Typical Pneumonia

Cultured on Blood Agar - Alpha Haemolytic and optochin Sensitive

51
Q

What is Typical Pneumonia?

A

Invades alveolar cavity and causes a productive rust coloured purulent sputum with a fever and headache

52
Q

What is the Treatment for Typical Pneumonia?

A

Amoxicillin - Covers most Strep and S. aureus sensitive strains

53
Q

What is the most common cause of Atypical Pneumonia?

A

Legionella pneumophilia - Suspected in Severe CAP and Recent Travel (spain)

54
Q

How are atypical pneumonias treated?

A

Macrolides - Erythromycin/clarithromycin

55
Q

What is the first line treatment for Legionella pneumonia?

A

1st Line - Clarithromycin

Inform PHE too

56
Q

What are some other causes of Atypical Pneumonia?

A

chlamydia psittaci
Mycoplasma Pneumonia
Chlamydia pneumonia
Coxiella

57
Q

What are the main bacteria involved in COPD exacerbations?

A

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
Q

How can TB be detected?

A

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
Q

What cause of pneumonia is common in HIV Px?

A

Pneumocystis Pneumonia caused by Pneumocystis Jirovecii

Shows cysts of Jirovecci Fungus

Tx with Co-Trimoxazole + Prednisolone if Type I Respiratory Failure present

60
Q

What Organisms often colonise the respiratory tract in bronchiectasis patients?

A

P. aeruginosa
Tx with Tazocin - Tazobactam + piperacillin

S. pneumonia
H. Influenza
Tx with Amoxicillin

61
Q

What is the common skin infection of the lower limb?

A

Cellulitis

DDx - DVT

62
Q

What are the cardinal Signs of Inflammation?

A

Calor
Dolor
Rubor
Tumor
Loss of function

63
Q

What is the pathogenesis of Cellulitis?

A

Breach in skin (Eczema, Athletes foot, Diabetic Foot)
Pathogen enters the soft tissues through the breach
Causes infection and inflammation

64
Q

What are the common Cellulitis organisms?

A

Group A Strep - S. pyogenes
S. aureus

65
Q

What is the Presentation of Impetigo?

A

Crusty lesions on chin and Cheek of a young person
(acute infection in children)

Which is itchy and grows as they Scratch it

66
Q

What is the Presentation of Impetigo?

A

Crusty lesions on chin and Cheek of a young person
(acute infection in children)

Which is itchy and grows as they scratchWhat

67
Q

What is the Presentation of Impetigo?

A

Crusty lesions on chin and Cheek of a young person
(acute infection in children)

Which is itchy and grows as they scratchWhat

68
Q

What swab is used to diagnose impetigo?

A

Black Charcoal Swab

69
Q

What is the treatment for Impetigo?

A

S. pyogenes - Benzylpenicillin
S. aureus - flucloxacillin
MRSA - Vancomycin or Teicoplanin

70
Q

What is the treatment for Cellulitis?

A

Give Empirical Abx until pathogen ID w/ culture then Review.

Empirical Abx: Flucloxacillin

71
Q

What are the 3 key features of taking a blood culture for Cellulitis?

A

Take good volumes of blood
Take from more than one site
Take on more than one occasion

72
Q

What are the features of a lower UTI?

A

LUTs:
Storage - FUNI
Voiding - SHITS

73
Q

What are the features of an upper UTI?

A

Pyelonephritis
Loin pain
Fever
Nausea and Vomiting

74
Q

What are the main UTI Organisms?

A

KEEPS
Klebsiella
E.coli (UPEC 80% of cases)
Enterobacter
Proteus Mirabilis
S. Saprophyticus /S. epidermidis

75
Q

What are the main causes of UTIs?

A

Obstruction
BPH
Renal Stones
Catheters
Sexual intercourse
Renal Tumours

76
Q

What is the first line investigation for a suspected UTI?

A

Urine Dipstick:
+ leukocytes
+ nitrites
+/- Protein

77
Q

What level of bacteria is significant for a UTI on Culture?

A

10^5

78
Q

What is the treatment for an uncomplicated UTI?

A

Nitrofurantoin (50mg 4x Daily) for 3 days

79
Q

What type of sample should urinalysis never be done on?

A

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
Q

What is the treatment for E. coli Pyelonephritis?

A

Co-amoxiclav for 7 days or Nitrofurantoin for 14 days

81
Q

Why should pregnant women have their urine screened?

A

Screen for Pre-Eclampsia
High BP and Proteinuria in pregnancy when otherwise well

82
Q

What is the most common cause of Infective Endocarditis?

A

S. aureus

83
Q

What is the treatment for Campylobacter infection?

A

Ciprofloxacin / Clarithromycin

84
Q

What is the treatment for C. difficile infection?

A

Stop C Abx
Vancomycin 125mg 4x Daily for 10 days

85
Q
A

Medicine Phase 2a (20 decks)

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