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Phase 2a Sheffield Medicine > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is a gram stain?

A
  • A type of stain which differentiates gram positive and gram negative bacteria.
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2
Q

What colour will gram positive bacteria go on a gram stain?

A
  • Purple (retain crystal violet)
  • Mainly cocci
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3
Q

What colour will gram negative bacteria go on a gram stain?

A
  • Pink (fuchsin or safranin)
  • Mainly bacilli
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4
Q

What is ‘Come In And Stain’?

A
  • Crystal Violet
  • Iodine
  • Acetate / Alcohol
  • Safarin counterstain
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5
Q

What are some exceptions to the rule that most cocci are gram positive?

A
  • N. meningitidis and N. gonorrhoea are both gram negative (diplo-)cocci
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6
Q

What are some exceptions to the rule that most bacilli are gram negative?

A
  • C. diff and Listeria are both gram positive bacilli
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7
Q

What is blood agar?

A
  • Either horse or sheep’s blood
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8
Q

What is chocolate agar?

A
  • Blood agar + steroids, which has been cooked at 80 degrees for 5 minutes.
  • Useful for more fastidious organisms such as H. influenzae
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9
Q

What is CLED agar?

A
  • Cysteine Lactose Electrolyte Deficient agar
  • Mainly for urinary bacteria analysis
  • Can differentiate lactose fermenting positive bacteria.
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10
Q

What is MacConkey agar?

A
  • Contains natural red dye and lactose
  • Differentiates lactose fermenting gram negative bacilli.
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11
Q

How would you differentiate E. coli, Shigella and Salmonella using agar?

A
  • Either CLED agar or MacConkey agar.
  • CLED agar. E. coli goes yellow. Salmonella and Shigella goes blue
  • MacConkey agar. E. coli goes Pink. Salmonella and Shigella goes yellow/colourless.
  • Lactose fermenting and non-lactose fermenting respectively
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12
Q

What is Gonococcus agar?

A
  • Used to grow Neisseria cultures
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13
Q

What is XLD agar?

A
  • Used to differentiate Salmonella and Shigella.
  • Salmonella appears red with black centres
  • Shigella appears red only
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14
Q

What is Sabourard agar?

A
  • A fungal culture.
  • e.g. Candida albicans or aspergillus
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15
Q

What is Löwenstein–Jensen medium?

A
  • A medium used for the culture of mycobacterium
  • e.g. Tuberculosis
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16
Q

How would you differentiate S. aureus from other staph bacteria and why is it important?

A
  • S. aureus is much more virulent as it has Coagulase and DNAase
  • Two ways:
    1. Coagulase test. S. aureus will coagulate rabbit plasma, other staph will not.
    2. Culture on blood agar. S. aureus colonies are gold (aureus = gold), other staph will be colourless.
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17
Q

What are the sterile sites within the body and what are the infections with each associates site?

A
  • Blood - Sepsis -> Septicaemia -> Septic shock
  • CSF - Meningitis
  • Pleural fluid - pericarditis, pleural effusion
  • Peritoneum - SBP
  • Joints - septic arthritis
  • Urinary tract - UTI
  • Lower respiratory tract - TB and pneumonia
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18
Q

What are the two ways that viral infection can be detected?

A
  • Viral detection - electron microscopy or PCR
  • Serology testing - ELISA, immunofluorescence, complement fixation test
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19
Q

What are the problems with electron microscopy?

A
  • It takes too long
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20
Q

What are the advantages and disadvantages of PCR?

A
  • It is very fast and very sensitive
  • It has a risk of a false positive and you need to suspect a specific virus beforehand
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21
Q

What are the disadvantages of using serology testing for viruses?

A
  • You are looking for the Igs vs the actual virus
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22
Q

What does VZV cause?

A
  • Shingles - A red painful rash confined to a single dermatome
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23
Q

What HIV markers should you test for?

A
  • HIV IgG
  • HIV RNA
  • p24 antigen
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24
Q

What pathogens are likely to cause meningitis in neonates (< 3 months)?

A
  • Group B beta haemolytic streptococcus
  • E. coli
  • Listeria
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25
Q

What pathogens are likely to cause meningitis in infants (3 months - 6 years)?

A
  • S. pneumonia
  • N. meningitidis
  • H. influenza (now rare due to vaccine)
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26
Q

What pathogens are likely to cause meningitis in adults (6-60 years)?

A
  • S. pneumonia
  • N. meningitidis
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27
Q

What pathogens are likely to cause meningitis in elderly (60+ years)?

A
  • S. pneumonia
  • N. meningitidis
  • Listeria
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28
Q

What is the most common cause of meningitis?

A
  • Enteroviruses (coxsackie, echovirus)
  • HSV-2
  • CMV
  • HIV
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29
Q

What would you expect to see in the CSF for: appearance, protein content, WCC and glucose levels for a bacterial meningitis?

A
  • Appearance - Yellow
  • Protein - increased
  • WCC - neutrophilia
  • Glucose - <50% serum (decreased)
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30
Q

What would you expect to see in the CSF for: appearance, protein content, WCC and glucose levels for a viral meningitis?

A
  • Appearance - Clear
  • Protein - increased
  • WCC - Lymphocytosis
  • Glucose - >60% serum (the same)
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31
Q

What would you expect to see in the CSF for: appearance, protein content, WCC and glucose levels for a TB or fungal meningitis?

A
  • Appearance - Yellow, Fibrinous
  • Protein - increased
  • WCC - Lymphocytosis
  • Glucose - <50% serum (decreased)
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32
Q

What type of bacteria is N. meningitidis?

A
  • A gram negative diplococcus.
  • Causes a blanching purulent rash
33
Q

What would the diagnoses be if there is a purulent rash and meningism? what is the treatment?

A
  • Gonococcal meningitis
  • DO NOT NEED CSF SAMPLE
  • IV Ceftriaxone or IV Cefotaxamine and IV dexamethasone
34
Q

What is the prophylactic treatment for meningitis symptoms within the community?

A
  • IM Benzylpenicillin
  • Send them to hospital for admission
35
Q

What would be the antibiotics for Listeria induced meningitis?

A
  • IV amoxicillin
36
Q

What are the close contact rules for meningitis?

A
  • Notify Public Health England Immediately
  • Close contacts should be given single dose ciprofloxacin prophylaxis
37
Q

What is the treatment for encephalitis caused by HSV-1?

A
  • IV acyclovir
38
Q

What would the appropriate treatment be for pneumonia caused by s. pneumoniae?

A
  • Amoxicillin
39
Q

What would the appropriate treatment be for pneumonia caused by legionella pneumonia?

A
  • Clarithromycin
  • Can also use: Erythromycin
40
Q

Is Legionella a notifiable disease?

A
  • Yes. Public Health England must be notified
41
Q

What would the treatment be H. influenzae in COPD?

A
  • A gram negative bacillus
  • B lactamase +ive (resistant) - Co-amoxiclav
  • B lactamase -ive (non resistant) - Amoxicillin
42
Q

What would the treatment be S. pneumoniae in COPD?

A
  • Amoxicillin
43
Q

What is a Ziehl-Neelsen stain?

A
  • An acid fast stain used for mycobacterium
44
Q

Why can’t mycobacterium use gram staining?

A
  • They have mycolic acid in their cell wall which means very waxy and it will not take up the stains.
45
Q

What is the problems with culturing TB? what are the alternatives?

A
  • It grows very slowly, 15-20 hours doubling time, therefore may take up to 6 months.
  • MGIT (Mycobacteria growth indicator tube) or PCR can be used
46
Q

What is meant by an AIDS defining illness?

A
  • A CD4+ count of less than 200
47
Q

What is the treatment for pneumocystis pneumonia?

A
  • Cysts of p. Jirovecci fungi
  • Co-trimoxazole
  • and prednisolone if type 1 respiratory failure
48
Q

What do 1/3 cases of bronchiectasis have a history of?

A
  • TB
  • Whooping cough
  • Measles
  • CF
49
Q

What organisms are implicated in bronchiectasis?

A
  • Pseudomonas aeruginosa (an oxidase negative, gram negative bacillus)
  • S. pneumoniae
  • H. influenzae
  • NOTE. CF organisms are the same
50
Q

What is the treatment for bronchiectasis?

A
  • S. pneumoniae and H. influenzae -> Amoxicillin
  • Pseudomonas aeruginosa -> Piperacillin/Tazobactam
51
Q

What are the side effects of vancomycin and gentamicin?

A
  • Nephrotoxicity
52
Q

What are the side effects of gentamicin?

A
  • Nephrotoxicity
  • Ototoxicity
53
Q

What are the UTI organisms?

A

K: Klebsiella spp.
E: Enterococcus faecalis / Enterobacter cloacae - 80%
E: Escherichia coli
P: Pseudomonas aeruginosa / Proteus mirabilis
S: Staphylococcus saprophyticus / Serratia marcescens

54
Q

What is the management for uncomplicated UTI?

A
  • Trimethoprim 200mg twice daily for 3 days (contraindicated in pregnancy: tetragenic)
  • Nitrofurantoin 50mg four times daily for 3 days if pregnant
55
Q

What is the treatment for pyelonephritis?

A
  • Co-amoxiclav for 7 days
  • OR Cefalexin and Trimethoprim for 14 days
56
Q

What is the main cause of infective endocarditis?

A
  • S. aureus
57
Q

What is the main salmonella serotype which causes diarrhoea?

A
  • Salmonella enteritidis
58
Q

What are the main salmonella serotypes which cause thyphoid fever?

A
  • S. typhi
  • S. paratyphi
59
Q

What is the treatment for thpoid fever?

A
  • Fluoroquinolones (ciprofloxacin)
  • 4th generation cephalosporins (ceflatrixone)
  • Azithromycin
60
Q

What are the viral causes of diarrhoea and gastroenteritis?

A
  • Adults -> Norovirus
  • Children -> Rotavirus
61
Q

What are the differences between gram positive and gram negative bacteria?

A
  • Gram positive - contain a single thick peptidoglycan cell wall and secrete exotoxins with a specific action.
  • Gram negative - contain two thinner cell walls made from peptidoglycan and secrete endotoxins (LPS) which have a non-specific action.
62
Q

What are the differences between gram positive and gram negative bacteria?

A
  • Gram positive - contain a single thick peptidoglycan cell wall and secrete exotoxins with a specific action.
  • Gram negative - contain two thinner cell walls made from peptidoglycan and secrete endotoxins (LPS) which have a non-specific action.
63
Q

What antibiotics affect the cell wall?

A
  • B lactams.
  • penicillin’s and cephalosporins
  • Good coverage against gram positive bacteria - strep and staph
64
Q

When would vancomycin be used?

A
  • To treat MRSA or patients with a penicillin allergy
65
Q

What antibiotics affect the folate pathway?

A
  • Trimethoprim and Nitrofurantoin
  • Cotrimoxazole for PCP
  • They inhibit dihydrofolate reductase and stop mTHF -> THF
66
Q

What are DNA gyrase antibiotics?

A
  • Fluoroquinolones (e.g. Cirpfloxan)
  • They are very good against gram negative bacteria
67
Q

What are RNA polymerase antibiotics?

A
  • Rifampicin which is used in TB.
68
Q

What is the treatment for TB and what are the complications of each?

A

RIPES
- R - Rifampicin - Orange urine, hepatotoxicity
- I - Isoniazid - Peripheral neuropathy, neurotoxicity, hepatoxicity
- P - Pyrazinamide - hyperuricemia, arthralgia, hepatotoxicity
- E - Ethambutol - Optic neuritis
- S - Streptomycin - Peripheral neuropathy, neurotoxicity, hepatotoxicity

69
Q

What are the antibiotics that effect protein synthesis?

A
  • Macrolides (Clarithromycin, Erythromycin, Azithromycin)
  • Aminoglycosides (Gentamicin)
  • Tetracyclines (Doxycycline)
70
Q

What is intrinsic antibiotic resistance?

A
  • Natural ability to be resistant to a bacteria.
71
Q

What is extrinsic antibiotic resistance?

A
  • Spontaneous mutations
  • OR horizontal gene transfer
72
Q

What are the three types of horizontal gene transfer for bacteria?

A
  • Conjugation - bacterial sex pilus transfers plasmid DNA
  • Transformation - uptakes DNA plasmid from the environment
  • Transduction - bacteriophage mediates DNA exchange between bacteria
73
Q

What are the three types of protozoa?

A
  • Amoeboids
  • Sporozoa
  • Flagellates
74
Q

Give an example of an Amoeboid and the disease it causes?

A
  • Entamoeba histolytica
  • Causes parasitic diarrhoea
75
Q

Give an example of a Sporozoa and the disease it causes?

A
  • Plasmodium genus which causes malaria
  • Toxoplasma gondii which causes encephalitis (rarely)
76
Q

Give an example of a Flagellate and the disease it causes?

A
  • Giardia lamblia which causes severe gastroenteritis
  • Trichomonas vaginalis causes vaginal infection
77
Q

Name the treatment of fungal infection?

A
  • Azole antifungal
  • Amphotericin B antifungal
78
Q

What fungus causes athletes foot?

A
  • Tinea Pedis (foot ringworm)
79
Q

What are the three helminths/worms and what is an example of each?

A
  • Nematode - Roundworm
  • Trematodes - Flatworm
  • Cestode - Tapeworm

Phase 2a Sheffield Medicine (10 decks)

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