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2A content- Sameera > 4A. MICROBIOLOGY PRACTICALS > Flashcards

4A. MICROBIOLOGY PRACTICALS Flashcards

1
Q

4 steps of gram stain test

A

add crystal violet stain
add iodine to bind
decolonise with ethanol
counterstain with safranin

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2
Q

why can’t mycobacterium be stained by gram stain

A

they have waxy cell walls that do not retain stain

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3
Q

two results of gram stain test and explain why

A

pink= gram negative bacteria- thinner peptidoglycan layer so crystal violet is not retained when washed with ethanol
Purple= gram Positive bacteria-thicker peptidoglycan layer= retention

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4
Q

what is the first test for gram negative bacteria?

A

macconkey lactose test

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5
Q

What does Macconkey agar include (3)

A

salts, lactose and a pH indicator

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6
Q

results of macconkey test

A

pink= lactose fermenting
colourless= non-lactose fermenting

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7
Q

how does the macconkey test work

A

if bacteria ferments lactose it will produce lactic acid= pH colour change

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8
Q

results of macconkeys test

A

pink= lactose fermenting
colourleSS= non-lactose fermenting

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9
Q

bacteria examples for lactose fermenting (2)

A

E.Coli and Klebsiella pneuonomiae

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10
Q

bacteria examples for non-lactose fermenting (4)

A

eg shigella, salmonella, proteus, pseudomonas

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11
Q

how can shigella and salmonella be differentiated and what is a positive result for each

A

XLD test
red colonies only= shigella
red colonies with black centres= salmonella

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12
Q

what are the 3 agars that can be used for lactose fermenting testing

A

uses MacConkey, CLED or XLD agar

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13
Q

what type of bacteria is the oxidase test for

A

gram negative non-lactose fermenting bacteria

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14
Q

what substance does the oxidase test test for

A

detects presence of cytochrome oxidase in bacteria

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15
Q

what does a + and - oxidase test result say about the bacteria

A

positive results mean a bacteria is aerobic
negative results mean a bacteria can be aerobic or anaerobic= colliform

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16
Q

postive result for oxidase test

A

positive test= disk turns blue

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17
Q

example of 4 bacteria that test + in oxidase test

A

V. cholerae, campylobacter, helicobacter, Pseudomonas aeruginsa

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18
Q

what is serotyping, what type of bacteria is this for and how can this identify bacteria

A

identifying cell surface antigens of gram negative bacteria
identifiable species due to distinct pathogenic genome

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19
Q

what are 4 modern methods of clinical bacterial identification

A

API strip
RNA gene sequencing
mass spectrometry
serotyping

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20
Q

what is the first and second test for gram + bacteria (and what do they differentiate between)

A
  1. catalase test- staph and strep
    2a. coagulase test to differentiate between staph
    2b. haemolysis test to differentiate between strep
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21
Q

what type of bacteria does the coagulase test test

A

differentiates types of staphylococcus

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22
Q

what enzyme does the coagulase test test for and what is the function of this enzyme then explain how the test works

A

test for coagulase- an enzyme that causes fibrin clotting
adds plasma containing fibrinogen which is converted to fibrin for clotting if coagulase enzyme is present

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23
Q

what is the + and - result of coagulase test and 1 example of bacteria each

A

positive test= clumps formed eg S. aureus
negative test= no clumps formed eg all other staphylococcus eg S.epidermis

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24
Q

what is lancefield grouping test? on what group of bacteria is this used? what is a + test?

A

further test for beta haemolytic bacteria by detecting surface antigens
clumping to show antigen-antibody complexes are formed

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25
Q

name bacteria that are lancefield group A, B, D and G positive

A

A= S.pyogenes
B= S.agalactiae
D= S.bovis
G= S.dysgalactia

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26
Q

What do the surface antigens on bacteria group A, B, C, D and G mean the infection is

A

Group A, C, G= tonsilitis and skin infection
Group B= neonatal sepsis and meningitis
Group D= UTIs

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27
Q

what bacteria does haemolysis differentiate between and what is it done on

A

types of stretococci, blood agar

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28
Q

alpha haemolysis colour, how much lysis and example

A

partial lysis, green colour eg S. pneumoniae

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29
Q

beta haemolysis colour, how much lysis and 2 examples

A

complete lysis, colourless eg S, progenies and S. agalactiae

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30
Q

gamme haemolysis colour, how much lysis and example

A

no lysis eg S. bovis, no colour change

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31
Q

what are the follow up identification tests for haemolytic bacteria (2)

A

alpha- optochin test
beta- lancefield grouping test

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32
Q

what does the optochin test differentiate between

A

differentiates between alpha haemolytic streptococcus

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33
Q

how is the optochin test donw

A

optochin soaked disc placed in agar of bacteria

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34
Q

two results of optochin test and an example for each

A

resistance= bacteria grows around it eg S. viridans
non-resistance= bacteria doesn’t grow around it eg S. pneumonaeie

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35
Q

what does the optochin test differentiate between

A

differentiates between alpha haemolytic streptococcus

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36
Q

what is the most common cause of community acquired pneumonia

A

Streptococcus pneumoniae

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37
Q

what are the most common cause of healthcare acquired pneumonia (3)

A

Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae

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38
Q

what are the 2 methods of diagnosing viral infections and what do each of them detect

A

viral detection- presence of virus in body
serology- presence of immunoglobulins against virus

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39
Q

two methods of viral detection and mention adv/disadv

A

electron microscopy- too expensive and long
PCR- cheap, quick, sensitive, can detect several viruses, but risk of false negatives

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40
Q

give 3 examples of serology test

A

ELISA
immunofluoroscence
complement fixation test

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41
Q

what are the two diagnotic swabs and what is their purpose

A

green viral swab
charcoal swab for bacteria
allows for suitable transport and storage of the pathogen in a favorable environmetn

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42
Q

what is infective endocarditis

A

infection of the endocardium of the heart

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43
Q

what are the two complications of infective endocarditis and what can both of these lead to

A

embolism
aortic regurgitation murmur
heart failure

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44
Q

what is the main cause of infective endocarditis and what are some other causes (2)

A

bacteria that enters the blood and travels to the heart
fungal and viral infections

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45
Q

what are the most common bacteria to cause infective endocarditis and how do they enter the blood (3)

A

staph epidermis via contaminated Hickman lines
coliforms from UTI/
staph aureus from skin/ pneumonia

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46
Q

what are the three risk factors of infective endocarditis

A

immunosuppression
history of rheumatic fever
lines eg cathetors, Hickman

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47
Q

what are the general symptoms of infective endocarditis (3)

A

fever, sweats, weight loss

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48
Q

what are the cardiac symptoms of infective endocarditis (3)

A

murmur, breathlessness, chest pain

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49
Q

what are the pathagnomonic signs of infective endocarditis (4)

A

Roth’s spots, Janesway lesions, Osler’s nodes, Splinter haemorrhages

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50
Q

what are the two main investigations for suspected infective endocarditis

A

blood cultures and echocardiogram

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51
Q

how to do blood cultures for infective endocarditis

A

3 samples from different sites over 24 hours and before antibiotics

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52
Q

what two main things can diagnose infective endocarditis

A

positive blood culture with a microorganisms that typically causes infective endocarditis
new valvular regurgitation

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53
Q

what is the typical treatment for infective endocarditis

A

antibiotics

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54
Q

what are examples of broad spectrum antibiotics

A

ceftriaxone, penicillins and vancomycin

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55
Q

give an example of a narrow spectrum antibiotic

A

gentamicin

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56
Q

what is Roth’s spots

A

retinal haemorrhages

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57
Q

what are Janesway lesions and what are they caused by

A

non-painful lesions on palms and soles
caused by septic micro emboli from valve

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58
Q

what are Osler’s nodes and what is caused by

A

painful lesions on tips of fingers or toes cause by localised immune response

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59
Q

what are splinter haemorrhages and what is it caused by

A

thin red line of blood under nails, running in the direction of nail growth
caused by haemorrhages from small capillaries under the nails

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60
Q

what agar is used to culture stool samples

A

macconkey

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61
Q

what is dysentery and a common cause

A

bloody diarrhoea
shigella

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62
Q

what two drugs can be first line for C diff infections

A

oral metronidazole/ oral vancomycin

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63
Q

what drugs is given for severe diarrhoea

A

oral vancomycin

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64
Q

what drugs is effective against anaerobes

A

metronidazole

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65
Q

what do worm infections not usually have

A

diarrhoea like symptoms

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66
Q

how is the salmonella species further classified

A

Kauffman white scheme

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67
Q

what does API stand for and what is it

A

Analytical profile index. Bacterial cultures r placed in individual tubes with biochemical tests and seen if there r positive or negative reactions (tests their metabolic and enzymatic properties)

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68
Q

what causes the black appearance on XLD and for which bacteria

A

hydrogen sulphide
salmonella

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69
Q

how r campylobacter bacterium cultured and what does it stand for

A

CCDA plates
charcoal cefazolin sodium deoxycholate agar

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70
Q

what is immunoflurescence

A

staining with fluorescent antibodies

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71
Q

why can bacteria and viruses not be detected with stool microscopy

A

bacteria- requires culture for isolation
viruses- to small to see with light microscopy

72
Q

what is the treatment for many viral infections

A

supportive treatment

73
Q

under what condition do norovirus infections require isolation of the patient

A

if they show signs of norovirus gastroenteritis

74
Q

what r risk factors for C diff infection (5)

A

nursing home
hospital
recent antibiotics
PPI use
elderly

75
Q

what is fecal microbiotica transplant used for

A

for patients with recurrent C diff infections

76
Q

what needs to happen to a patient suspected of a c diff infection and when does this need to happen until

A

isolation until 48 hours free of diarrhoea

77
Q

what antibiotics should be started for a suspected appendicitis whilst awaiting results from the labs (2)

A

Cefuroxime & Metronidazole

78
Q

what does cefuroxime act against (1)

A

coliforms

79
Q

what type of bacteria is flucloxacillin active against

A

gram + bacteria

80
Q

why is a Mz disc used on blood agar plates and what is Mz

A

metronidazole
if the bacteria is not resistant= confirms presence of anaerobic bacteria

81
Q

what is prescribed for upper GI infections

A

co-amoxiclav

82
Q

how can viral gastroenteritis be diagnosed

A

PCR

83
Q

what r the 5 causes of diarrhoea in enteric (GI) infections

A

bacteria, viral, protozoa, food poisoning, antibiotic associated

84
Q

what type of E coli can cause diarrhoea

A

escherichia e coli

85
Q

what is a red weeping lesion that crusts on face of young children, what does it start off as and what is causing it?

A

impetigo
an itchy growing spot
bacterial cause

86
Q

what bacteria have gold colonies on a CBA plate

A

S aureus

87
Q

what is the 1st line antibiotic treatment for S aureus and what is the alternative for penicillin allergies

A

flucloxacillin
clarithromycin

88
Q

what antibiotic is given for MRSA and is this okay for penicillin allergies

A

vancomycin
yes

89
Q

what is cellulitis and symptoms 3

A

bacterial skin infection
redness, swelling and pain

90
Q

what is the cause of cellulitis 2 and how do they cause infection

A

staph/ strep bacteria that were commensals but caused infection by going through a break in the skin

91
Q

what test involves suspending colonies in water and mixing them with antibody coated latex beads

A

lancefield

92
Q

first line for treating S pyogenes and alternative for penicillin allergy

A

penecillin
clarithromycin

93
Q

if a cannula is infected, what r the 3 microbiological samples that should be sent to the lab

A

cannula tup, blood cultures, black charcoal swab of skin at site

94
Q

what does MRSA stand for

A

methicillin (meaning penicillin) resistant staphylococcus aureus

95
Q

alternative to vancomycin for MRSA treatment

A

teicoplanin

96
Q

what r the follow up investigations that need to be done with S aureus bacteria infections 3

A
  1. take blood cultures daily until negative
  2. echocardiogram to rule out infective endocarditis
  3. if back pain/ spinal tenderness than MRI of spine needed to look for osteomyelitis
97
Q

one contraindication of vancomycin and why, can this still be given?

A

acute kidney failure
nephrotoxic
yes to patients with kidney issues but requires closer monitoring to ensure blood vancomycin levels r stable

98
Q

what is the 1st line to treat UTI (2) and why might one be chosen over the other

A

nitrofurantoin or trimethoprime
nitro chosen as it can be taken during most of the pregnancy and there r fewer resistant bacteria to this compared to trimethoprim

99
Q

what does yellow and blue/ green on a CLED plate mean

A

yellow= lactose fermenting
blue= non lactose fermenting

100
Q

why r blood cultures done for cellulitis 1

A

to see if sepsis has occurred

101
Q

what does mixed growth of multiple bacteria on a plate mean and is this diagnostic

A

suggests contamination of sample
no

102
Q

what is microscopy not performed on urine inside a catheter bag 2

A

bacteria can grow in bag but this may not necessarily be from the patient and a catheter will produce a urethral mucosal inflammatory response producing leukocytes

103
Q

why is urine collected from asymptomatic pregnant women 2 and how is this screeened for in women 1

A

common to have asymptomatic bacteria in pregnant women which can cause infection and pylonephritis
mid stream urine samples

104
Q

what is meningitis and what layers are typically affected

A

inflammation of meninges (typically) pia and arachnoid mater

105
Q

what is the triad of symptoms of patients with meningism what r the general symptoms 3

A

triad: neck stiffnes, photophobua, severe headache
general symptoms: fever, malaise, rash

106
Q

what is the rash characteristic in meningococcal meningitis

A

non blanching pruritic rash

107
Q

what is the main cause of meningitis and give 2 examples

A

viruses eg enteroviruses and herpesviruses

108
Q

what is usually the bacterial cause of meningitis 3 and who does this typically affect 3

A

strep. pneumonia and neisseria meningitidis and listeria monocytogenes in neonates/ elderly/ immunocompromised

109
Q

what is encephalitis

A

inflammation of cerebral cortex

110
Q

what r the 3 symptoms of encephalitis

A

fatigue, fever, reduced consciousness

111
Q

what is the main cause of encephalitis

A

viruses- same an meningitis

112
Q

what is meningo-encephalitis

A

combination of encephalitis and meningitis

113
Q

how is a CSF sample obtained and what is its usual appearance and when r results received

A

CSF sample obtained via lumbar punture- usually gin clear and pressure of <15cm of H20, results within a few hours

114
Q

what further tests should be done for meningo-encephalitis and for what types of pathogens

(2->2, 2-> 1)

A

do blood cultures/ PCR for strep. pneumonia and neisseria meningitidis

do stool and nose/ throat swab PCR for enteroviruses

115
Q

what antibiotics be prescribed for bacteria 2 causing meningitis and 2 reasons why they r preferred over penecillins

A

IV cefotaxime/ ceftriaxone
good CNS penetration and broad spectrum activity against all common gram + and - bacteria

116
Q

how can WCC % help determine the type of pathogen in a CSF sample

A

in CNS lumbar puncture, a WCC of mostly neutrophils indicates bacterial infection and lymphocyte= a viral infection

117
Q

What bacteria grows on chocolate agar not on blood agar, why and what is its appearance on chocolate agar 1 1 2

A

H influenzae (Hib)
fastidious
small white colonies

118
Q

what two things should be given immediately if there is a bacteria causing meningitis and why

A

ntibiotics should be started along with IV dexamethosome (reduces the risk of long term neurological complications)

119
Q

how do recently born babies get group B causing meningitis

A

from mothers genital tract

120
Q

what is a appearance of listeria monocytogenes and what test is this on

A

small semi transparent colonies
alpha haemolytic blood agar

121
Q

what antibiotic therapy should be commenced for immunocompromised and two things about the way it is given

A

high dose and frequency IV amoxicillin

122
Q

what is another meningitis causing bacteria that has poor growth on blood agar and better growth on chocoalte and what is significant about this bacteria 2 what is prophylaxis for this

A

neisseria meningitidis

PHE notifiable disease and close contacts offered antibiotic prophylaxis with a single dose of oral ciprofloxaci

123
Q

when is there no need for lumbar puncture and how is diagnosis done for meningitis instead 2

A

no need for lumbar puncture if characteristic rash and presentation raises strong clinical suspicious of meningitis- diagnosis done instead by peripheral blood culture/ PCR

124
Q

what does a high lymphocyte count in WCC in lumbar puncture suggest

A

viral meningitis/ encephalitis

125
Q

when should IV acyclovir be given as a treatment for meningitis

A

for viral unknown cause yet (no results from lab yet) or herpes simplex

126
Q

what are the characteristic physical signs of pneumonia 3

A

fever
pleural effusion (stony dullness)
consolidation (bronchial breathing and dullness to percussion)

127
Q

what are the signs of pneumonia on an x ray 3

A

consolidation
parenchymal shadowing
with or without cavities or pleural effusion

128
Q

what are the 2 most common causes of community acquired pneumonia

A

streptococcus pneumoniae
Haemophilus influenza

129
Q

what two pathogens that cause community acquired pneumonia cannot be identified through gram culture or stain and what is their treatment 2

A

mycoplasma pneumoniae
chlamydia pneumoniae
macrolide or fluroquinolones

130
Q

what samples are key to collect for respiratory infections 4

A

blood cultures
sputum
urine
serum

131
Q

explain how to test S. pneumoniae 1 and all of its results 3

A

culture on blood agar:
gram + cocci
optochin sensitive
alpha haemolysis

132
Q

treatment for pneumonia

A

amoxicillin

133
Q

presentation for typical pneumonia 3, what does it invade

A
  1. productive rust coloured sputum
  2. fever
  3. headaches
    invades alveolar cavity
134
Q

presentation for atypical pneumonia 2, what does it invade

A
  1. dry cough
  2. little fever and headache
    invades alveolar interstitum
135
Q

what causes typical pneumonia 1

A

S. pneumoniae

136
Q

what causes atypical pneumoniae 4

A

-> legionella pneumophila
-> chlamydia pneumoniae
-> mycoplasma pneumoniae
-> Coxiella burnetii

137
Q

treatment of atypical pneumoniae 1, 3

A

macrolides eg clarythromycin, doxycycline, ciprofloxacin

138
Q

when should legionelle pneumophila be suspected 2, its treatment 1 and what has to be done when it is diagnosed 1

A

suspect in severe community acquired pneumonia and travel history eg spain
1st line: clarythromycin
notifiable to PHE

139
Q

1st line antibiotic treatment for mild, moderate and severe CAP (community acquired pneumonia). What is the alternative for penicillin allergies

A

mild- amoxicillin
mod- amoxicillin
severe- clarithromycin/ co-amoxiclav
alternative= clarithromycin

140
Q

when should a chest x ray be ordered when CAP is presented

A

within 4 hours

141
Q

what test can classify pneumonia severity

A

CURB 65

142
Q

what is s pneumoniae from CAP called when it goes beyond the respiratory tract

A

invasive pneumococcal disease

143
Q

what container is the urine and the serum collected in for CAP tests

A

urine- universal container
serum= yellow top vacutainer tube

144
Q

why does H influenza respiratory infections have significant complications

A

leads to disease if immune defences are compromised eg chronic airway disease like COPD

145
Q

what does H influenza need to grow and what is its presentation on blood agar

A

factors X and V on agar
grows in region around paper disc with factors X and V and nowhere else

146
Q

what is the 1st and 2nd line treatment for COPD/ bhronchitis exacerbations and why for each

A

1st- doxycycline (less resistance to this compared to penecillins/ macrolides)
2nd- co-amoxiclav (2nd because it is broader so it promotes resistance)

147
Q

alternative stain for mycobacterium (not Z-N stain) and what is the advantage of this stain

A

auramine phenol fluorescent stain
faster and more sensitive detection under microscope

148
Q

what is the culture medium for the auramine phenol fluorescent stain and why is this used instead of normal culture medium

A

Lowenstein Jensen slope
contains growth factors that promote faster mycobacterial growth

149
Q

what is a rapid culture technique for mycobacteria 1 and what is it 3

A

mycobacteria growth indicator tube
liquid broth with growth factors and fluorescent indicator

150
Q

what is an better alternative to sputum microscopy and how does it work

A

GeneXpert
detects DNA sequences specific to Mycobacterium Tuberculosis

151
Q

what are the 6 methods of detecting TB

A
  1. ziehl nelson stain
    2 auramine phenol fluorescence microscopy
  2. lowenstein jensen culture
  3. mycobacteria growth indicator tube
  4. GeneXpert PCR
  5. histology: granulomas with central caseous necrosis
152
Q

what is pneumocytisis pneumonia and what type of people does it affect

A

fungal infection caused by P. jirovecci
immunocompromised

153
Q

what two species cause TB

A

Mycobacterium tuberculosis and Mycobacterium bovis.

154
Q

describe the difference between primary and secondary tuberculosis and compare symptoms for both

A

primary= organisms inhaled into the lungs and local granuloma formation occurs, mild symptoms
secondary= dormant organisms reactivate due to reduction in the host’s immune system, severe symptoms: fever, weight loss, haemoptysis

155
Q

what two test are done to get sputum in a patient that is not spontaneously producing sputum and what is an additional advantage

A
  1. Induced sputum
  2. Broncho-alveolar lavage
    greater sensitivity than sputum
156
Q

define COPD

A

production of sputum on most days over at least three months for more than
two years

157
Q

what can cause COPD 2

A

smoking
previous infections

158
Q

physical presentation of a COPD exacerbation 3

A

increased GREEN sputum production, cough and shortness of breath

159
Q

what are the 2 main bacteria involved in acute exacerbations of COPD and which is most common and treatment for each

A
  1. H influenzae MC
  2. S. pneumoniae
    treatment= amoxicillin unless beta lactamase resistant (H influenza is sometimes), then co-amoxiclav
160
Q

what virus can cause COPD 2

A

influenza, seasonal coronovirus

161
Q

how is sputum cultured for COPD diagnosis 2

A

chocolate agar incubated aerobically, 37oC.
blood agar incubated anaerobically, 37oC

162
Q

what is the designated microbiology test for atypical pathogens

A

sputum

163
Q

how is a P. jiroveci infection diagnosed and why

A

by PCR from induced sputum or Broncho-alveolar lavage
cant be cultured in vitro

164
Q

treatment for pneumocytitis pneumonia 2

A

co-trimoxazole and prednisolone if there is respiratory failure/ oxygen before 8kPa

165
Q

what is a good test to collect lower respiratory tract organisms if there aren’t enough in the upper respiratory tract 1

A

induced sputum

166
Q

what is bronchiectasis and what is the cause

A

permanent damage to airways
causes unknown

167
Q

associations of bronchiectasis 4

A

1/3 of cases have history of severe pneumonia, TB, whooping cough, cystic fibrosis

168
Q

what colour is mucus in bronchiectasis and how can this change

A

yellow sputum
changes to green if bacterial exacerbation

169
Q

treatment for bronchiectasis and alternative and what is this for 2

A

1st line: amoxicillin
p. auruguosa give pipercillin-tazabactam

170
Q

what 3 bacteria cause bronchiectasis and cystic fibrosis

A

p aruguosa
s pneumoniae
h influenzae

171
Q

what class of drug is piperacillin-tazobactam

A

antipseudomonal beta lactam

172
Q

what two things does sabouraud agar contain and give one example of what it grows

A

peptones and dextrose
candida albicans

173
Q

what pathogen commonly contaminates RESPIRATORY samples ONLY and therefore is unlikely to be the infectious pathogen

A

candida albicans

174
Q

how is bronchiectasis and cystic fibrosis diagnosed

A

sputum culture

175
Q

what can cystic fibrosis lead to

A

bronchiectasis

176
Q

what does candida albicans cause in immunocompromised

A

thrush

2A content- Sameera (21 decks)

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