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Phase 2a > Microbiology > Flashcards

Microbiology Flashcards

1
Q

why is chocolate agar useful

A

easier to grow organism not easily grown

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2
Q

why is MacConkey agar useful

A

contains bile salts = inhibit gram positive growth

stains lactose = lactose fermenters pink, nonlactose fermenters white

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3
Q

why is CLED agar useful

A

differentiate microorganisms in urine

classify lacotse/nonlactose fermenters in gram negative bacilli

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4
Q

why is gonoccocus agar useful

A

promote growth of neisseria gonorrhoea and other neisserias

contains antibiotics/antifungals to inhibit growth of other organisms

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5
Q

why is XLD agar useful

A 
very selective
isolates salmonella
red at pH 7.4
shigella/salmonella = red
other gut bacteria = yellow
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6
Q

why is sabouraud agar useful

A

grows funghi inhibits bacteria

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7
Q

what is a pathogen

A

organism capable of causing disease

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8
Q

what is a commensal

A

organism which colonises the host but normally causes no disease

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9
Q

what is an opportunistic pathogen

A

microbe that only causes disease if host defence are compromised

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10
Q

what is pathogenicity/virulence

A

degree to which a given organism is pathogenic/damage causing
virulence factor = product or strategy which contributes to virulence

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11
Q

what is an asymptomatic carriage

A

when a pathogen is carried harmlessly at a tissue site where it causes no disease

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12
Q

what is a gram stain

A

method to determine bacteria type between gram positive and gram negative

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13
Q

what is a capsule

A

peptigoglycan layer that surrounds some bacteria = allows it to hide from immune system and is antiphagocytic

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14
Q

what are funghi

A

eurokaryotic cells with chitinous cell walls

heterotrophic and generate spores

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15
Q

name 3 common fungal infection

A

nappy rash
vulvovaginal candidiasis
athletes foot

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16
Q

what are the 3 common life threatening fungal infections

A

candida line infections
intra-abdominal infections
fungal asthma

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17
Q

infectivity definition

A

ability to become established in the host (adherence and immune defence)

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18
Q

invasiveness definition

A

ability to penetrate mucosal surfaces to reach sterile sites

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19
Q

what is chronic carrier state

A

steady state between virus replication in host cells and virus death through host responses

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20
Q

what is an endotoxin

A

component of outer membrane of bacterium from gram negative bacteria ONLY = LPS based

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21
Q

what is an exotoxin

A

secreted proteins of gram negative and gram positive bacteria which causes harm to the host = protein based

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22
Q

how does bacteria directly cause harm

A

destroy phagocytes/cells

endo/exooxins

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23
Q

how does bacteria indirectly cause harm

A

inflammation
immune pathology
diorrhoea

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24
Q

name a gram positive coagulase positive bacteria

A

staphylococcus aureus

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25
Q

name a gram positive catalase positive coagulase negative bacteria

A

staphylococcus epidermidis

staphylococcus saproplyticus

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26
Q

what is the difference between staphylococcus and streptococcus

A 
staphylococcus = catalase positive
streptococcus = catalase negative
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27
Q

describe alpha haemolytic streptococcus

A

greening on agar

viridans group strep

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28
Q

how to determine if bacteria is strep pneumoniae

A

optochonin test

if sensitive to optochonin disc = positive

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29
Q

describe beta haemolytic streptococcus

A

clearing on agar

different groups A,B,C, G

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30
Q

what is lancefield grouping

A

bacteria have carb cell surface antigens e.g. A, B etc
antiserum for each group added to a suspension of bacteria
agglutination = recognition

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31
Q

give examples of each group of streptococcus

A 
A = tonsilitis
B = sepsis, meningitis
C = UTI
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32
Q

what are the features of enterobacter

A

rods with flagella

facultatively anaerobic

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33
Q

what does the outer layer of gram negative bacteria contain

A

lipid A = toxic
core antigens
somatic antigens

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34
Q

name 5 important enterobacter

A 
escherichia coli
shigella
salmonella
proteus mirabilis
klebsiella pneumoniae
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35
Q

how do allylamines work

A

= fungicidal
inhibit biosynthesis pathway of ergosterol metabolism = affect membrane = kills fungus
high first pass metabolism

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36
Q

how do azoles work

A

= fungistatic
inhibit ergosterol synthesis
used for more invasive fungus
high doses = hepatitis

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37
Q

how do polyenes work

A

= fungicidal
affect activity of membrane bound proteins = disrupt insertion of molecules into membrane
cause nephrotoxicity

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38
Q

what are the 4 main features of antifungals

A
  1. poor bioavailability
  2. poor penetration to difficult areas
  3. have few drug interactions
  4. limited drug toxicity
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39
Q

name 2 gram negative bacillus that ferments lactose

A

E.coli

klebsiella

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40
Q

name 2 gram negative bacillus that does not ferment lactose

A

Shigella

salmonella

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41
Q

what are the sterile sites in the body

A 
blood
CSF
lower respiratory tract
pleural fluid
peritoneal cavity
joints
urinary tract
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42
Q

which sites would you be able to culture normal flora

A 
mouth
skin
vagina
urethra
large intestine
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43
Q

the HIV envelope contains

A

RNA
capsid
reverse transcriptase

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44
Q

describe antimicrobial resistance in MRSA

A

s.aureus is resistant to vancomycin

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45
Q

what are the clinical signs of sepsis

A 
temp = above 38.3 or below 36
heart rate above 90
WBC above 12
hypoxia
low BP
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46
Q

definition of antibiotic

A

molecule that binds to bacteria target site and affects reactions critical to bacterial survival

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47
Q

what are beta lactams and how do they work

A

penicillins, cephalosporins, carbapenems

bind to peptidoglycan PBP on gram positive bacteria = inhibit cell wall synthesis = bactericidal

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48
Q

how does metronizadole and rifampicin work on bacteria

A

interfere with nucleic acid synthesis and function

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49
Q

how do flouroquinolones work on bacteria

A

inhibit DNA gyrase

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50
Q

how do sulphonamides and trimethoprim work on bacteria

A

inhibit folate synthesis and carbon metabolism

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51
Q

how do macrolides and tetracyclines work

A

inhibit 30S ribosome = inhibit protein metabolism

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52
Q

what does is mean if an antibiotic is bacteriostatic

A

inhibits bacterial growth by inhibiting protein synth, DNA replication + metabolism = reduce endotoxin production
= will eventually kill 90%
minimum inhibitory concentration required MIC

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53
Q

what does bactericidal mean

A

inhibit cell wall synthesis = kills bacteria = good for hard to treat infections
minimum bactericidal conc required MBC

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54
Q

what should the ratio of MIC to MBC be

A

MIC:MBC > 4

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55
Q

why is the concentration of antibiotic important

A

drug must occupy adequate number of binding sites

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56
Q

why is the time of action of an antibiotic important?

A

drug must stay at binding site for long enough time to interfere with bacteria

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57
Q

what is conc dependent killing

A

depends on height of conc above MIC = aminoglycosides have high conc dependent killing

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58
Q

what is time dependent killing

A

depends on time that conc stays above MIC = beta lactams, macrolides have high time dependent killing

59
Q

what are cephalosporins used for

A

= beta lactams
used in penicillin allergies
resistant bugs
hard to reach places e.g. meningitis

60
Q

what antibiotics are used for gram positive bacteria

A

beta lactams

61
Q

what is vancomycin used for

A

gram positive bacteria
MRSA
penicillin allergy

62
Q

what are macrolides used for

A

e.g. clarithromycin, erythromycin
gram +ve bacteria
atypical pneumonias

63
Q

what are lincosamides used for

A

e.g. clindamycin
gram +ve
anaerobic cellulitis

64
Q

what are tetracyclines used for

A

e.g. doxycycline
cellulitis
chest infection
penicillin allergy

65
Q

what is ciprofloxacin used for

A

gram -ve specific
UTI
gallbladder/abdominal infections

66
Q

what is trimethoprim used for

A

gram -ve UTI

67
Q

what is nitrofurantoin used for

A

gram -ve UTI

68
Q

what is the significance of beta lactamases

A

= enzymes produced by bacteria that provide resistance to beta lactam antibiotics

69
Q

what are beta lactamase inhibitors

A

class of medicine that block the activity of beta lactamases = prevent degradation of beta lactams

70
Q

what antibiotics are protected against beta lactamases

A

co-amoxiclav
cephalexin
cefuroxime

71
Q

where can nematodes be found in the body

A

= roundworms
intestinal
under skin
tissue

72
Q

where can trematodes be found in the body

A

= flatworms
intestinal
blood
liver

73
Q

what is the pre-patent period (PPP)

A

interval between infection and presence of eggs in stool

74
Q

what is the largest and most common worm

A

ascaris lumbricoides

75
Q

what are the symptoms of loaffler’s syndrome

A 
= larvae in lungs
cough
wheeze
fever
eosinophilia
positive chest XR
76
Q

what conditions can E.coli be responsible for

A 
wound infections
UTI
gastroenteritis
traveller's diarrhoea
bactereamia
77
Q

describe entero-toxigenic ecoli ETEC

A

virulence factors = toxin and pili/fimbriae

act in small intestine = watery diarrhoea in tourists

78
Q

describe entero-pathogenic ecoli EPEC

A

virulence factor = pedestal formation (lumps on epithelium)

acts in small intestine = watery diarrhoea less than 1 year

79
Q

describe entero-haemorrhagic ecoli EHEC

A

virulence factor = pedestal formation and shiga like toxin

acts in large intestine = bloody diarrhoea and HUS = food borne

80
Q

describe entero-invasive ecoli EIEC

A

virulence factors = invasins leading to inflammation/ulceration
acts in large intestine = bloody diarrhoea/dysentry (in children)

81
Q

describe entero-aggregative ecoli EAEC

A

virulence factors = pili and cytotoxin = shorter villi + mucus production
acts in large intestine = chronic diarrhoea in children

82
Q

describe uro-pathogenic ecoli UPEC

A

virulence factors = haemolysin = inflammation

acts in urinary tract = UTI in women

83
Q

describe the pathogenicity of entero-toxigenic ecoli

A
  1. toxins cause G protein modification = locking in ON state

2. increased cAMP production = loss of Cl and H2O§

84
Q

describe the pathogenicity of pedestal formation and which forms of ecoli does this occur with

A
  1. pathogen adheres to microvilli with pathogenic pilli
  2. T3SS acts like syringe = disrupts tight junctions and ion activity (diarrhoea)
  3. microvilli reform into pedestal holding pathogen
    = in entero-pathogenic and entero-haemorrhagic
85
Q

which bacteria are obligate intracellular

A

rickettsia
chlamydia
coxellia

86
Q

which bacteria have no cell wall

A

mycoplasma pneumoniae

87
Q

which bacteria has filament growth

A

actinomyces
nocardia
streptomyces

88
Q

which bacteria are spirochaetes

A

leptospira
treponema
borrelia

89
Q

describe the growth cycle of chlamydia

A 
elementary bodies
= infectious stage
enters cell
inhibits phagosome function
become reticulate bodies
reticulate bodies
= not infectious stage 
intracellular replication
convert back to EB 
cell lysis and EB release
90
Q

name the 3 most important types of chlamydia

A 
C.trachomatis = most common STD, conjunctivitis
C.pneumoniae = atypical CAP pathogen
C.psittaci = severe pneumonia
91
Q

name 6 typical bacteria that commonly cause CAP

A 
strep. pneumoniae
hameophilus influenzae
staph. aureus
group A strep
moraxella catarrhalis
aerobic gram negative bacteria e/g/ klebsiella/e.coli
92
Q

name 3 atypical bacteria that commonly cause CAP

A

legionella
mycoplasma pneumoniae
chlamydia pneumoniae

93
Q

name 4 viruses that commonly cause CAP

A

influenza A and B
parainfluenza virus
rhinovirus
adenovirus

94
Q

describe a spirochete bacterium

A

has endoflagellum between outer membrane and peptodoglycan = allows corkscrew movement

95
Q

describe borrelia burgdorferi

A

= lyme disease
tick-borne
cause rash/flu-like symptoms
spreads through extracellular matrix to bloodstream and other organs

96
Q

descrive leptospira interrogans

A

spread from animal urine to human through mucous membrane

cause flu-like symptoms - Weil’s disease in severe cases

97
Q

describe treponema pallidum

A

= syphilis
primary stage = localised infection v. infectious
secondary stage = systemic infection lymph nodes, skin, joints, vessels
tertiary stage = granuloma in soft tissue = cardio/neurosyphilis
treat with flucloxacillin

98
Q

name 3 important mycobacteria

A

M. tuberculosis = TB
M. leprae = leorosy
M. avium complex (MAC) = infection in AIDS and chronic lung disease

99
Q

what are the 4 types of protozoa and give an example for each

A 
flagellates - trypanosoma (sleeping sickness), 
trichromonas vaginalis (STI), GIARDIA LAMBLIA

sporozoans - plasmodium, toxoplasma gondii (toxoplasmosis)

amoebae - entamoeba histolytica (amoebic dysentery)

ciliates - balatidium coli (colonic ulceration)

100
Q

what is significant to remember about trichomonas vaginalis

A

dont confuse it with chlamydia

101
Q

name the 4 disease causing plasmodium

A

p. falciparum
p. ovale
p. vivax
p. malariae

102
Q

what is the vector for malaria

A

female anopheles mosquito around stagnant water = 3-4 week infected lifecycle

103
Q

what is the hypnozoite stage in the malaria life cycle

A

after schizonts rupture in hepatocyte releasing merozoites into the bloodstream = p.ovale and p.vivax can lie dormant in the liver and reactivate

104
Q

what are most protozoa treated with

A

metronizadole

105
Q

what is giardia lamblia

A

parasitic microorganism that infects the small intestine
causes giardiasis = diarrhoea/bloating/cramps
foecal oral spread
travel associated
stool microscopy diagnosis
metronizadole treatment

106
Q

describe the process of a gram stain

A
  1. fixation
  2. crystal violet
  3. iodine
  4. decolorisation using ethanol
  5. application of safranin as counter stain
  6. gram positive bacteria not decolourised by ethanol = purple
    gram negative is decolourised so retain pink of safranin counterstain
107
Q

describe zeihl-neelson staining for mycobacteria

A
  1. cells stained using carbol fuchsin = red
  2. washing with acid alcohol = removes carbol fuschin from background cells = mycobacterium remain red because it is acid-fast (holds fast to the dye)
  3. slide stained with methylene blue
  4. mycobacterium stained purple = identified
    need 10,000 acid fast bacilli per ml
108
Q

name 3 methods of culturing mycobacteria

A
  1. soft culture
  2. liquid culture
  3. nucleic acid detection
109
Q

what are cytopathic effects

A

viruses have to be grown in cells so cannot be cultured

CPE = effects observed when viruses are cultured inside living cells

110
Q

what is serology

A

study/detection of antibodies in serum
mainly IgM/IgG
IgM appears within a week of infection and remains in blood up to 12 weeks
IgG appears later but remains within blood for years for immunity

111
Q

what swabs are used for bacterial and viral infection

A 
green = viral
black/charcoal = bacterial
112
Q

how do mycobacteria cause disease in the body

A
  1. mycobacteria engulfed by macrophage = phagolysosome = APC
  2. CD4 T cells recognise APC = interferons and interleukins stimulate macrophage activity
    granuloma formation
113
Q

describe granuloma formation as part of mycobacterial disease

A
  1. highly stimulated macrophages = become epithelioid cells = fuse to become Langhans giant cells = fibroblasts laid down around granuloma
  2. central tissue necrosis = caseating necrosis = cavity in tissues e.g. in the lungs in TB
114
Q

describe the immunology of tuberculoid leprosy

A

Th1 response (IFN+TNF) = tissue hypersensitivity and granulomas = tissue damage

115
Q

describe the immunology of lepromatous leprosy

A

Th2 response (IL 4,5,10) = lesions full of bacilli and NO granuloma = skin lesions

116
Q

what 4 drugs are used to treat TB

A 
RIPE
rifampicin
isoniazid
pyrazinamide
ethambutol
117
Q

name 3 viruses that cause direct host cell destruction

A

hip!
HIV
influenza
polio

118
Q

name 2 viruses that cause modification of host cell function/structure

A

HIV

rotavirus

119
Q

name 3 viruses that cause an over-reactive host response

A

Hep B
Hep C
HIV

120
Q

name a virus that causes cell proliferation and immortalisation

A

HPV

121
Q

describe 3 ways viruses evade host cell defence

A

persistence (measles)
variability (flu)
host defence modulation (all viruses)

122
Q

describe a rotavirus infection

A
  1. acid resistant rotavirus invades jejunal epithelial cells = cause villi and microvilli to atrophy
  2. reduced SA and enzyme conc = no sugar absorption = hyperosmosis = diarrhoea
123
Q

describe a Hepatitis B infection

A
  1. HBV infection causes antibody and cytotoxic T lymphocyte response = hepatocyte destruction = liver damage
  2. steady state reached between hepatocyte destruction and viral replication = no spread
124
Q

describe cervical carcinoma development

A
  1. HPV infects superbasal layer of genital tract = replicates as mucosal cells move up
  2. HPV and host cell genome integration = p53 suppression = carcinogenesis
125
Q

what is wuncheria bancroftii

A

human parasitic worm = filariworm

causes lymphatic filariasis = lymphoedema

126
Q

what disease do schistosome flatworms cause

A

schistosomiasis which can cause bladder cancer

127
Q

what disease is associated with the hookworm

A

iron deficient anaemia

128
Q

describe the humoural response to viruses

A

IgA and IgM block viral binding and aid agglutination

complement and GB antibody = opsonisation and cell lysis

129
Q

describe the cell mediated response to viruses

A

interferon prevents infection of non-infected cells

cytotoxic T lymphocytes directly kill infected cells and activate antibody dependent cell destruction

130
Q

which viruses virulence factors include direct cell cytotoxicity

A 
flu = respiratory epithelium
shingles = skin cells
HIV = T cells
131
Q

which viruses show antigenic variation

A

rhinovirus
influenza
HIV

132
Q

which viruses cause immune suppression

A

MMR
EBV
HIV
CMV

133
Q

name 3 ways protozoa evade host defence

A

surface antigen variability
intracellular phase
shed outer coat

134
Q

describe a delayed type hypersensitivity reaction (type 4) for example in TB

A
  1. intracellular infection (TB) = Tdth cells stimulated = influx of inflammatory cells
  2. second contact = Tcth secretes IFN TNF IL = macrophage recruitment
  3. prolongued DTH = granuloma formation = lytic enzymes cause tissue damage
135
Q

name 3 ways bacteria can resist phagocytosis

A

polysaccharide capsule
M protein
phagolysosome escape

136
Q

what is an API strip

A

card with self contained series of biochemical reaction tubes which identify bacteria based on metabolic and enzymatic properties

137
Q

what is B.fragilis

A

anareobic gram negative bacteria lives naturally in the colon
is usually commensal but can cause infection after surgery/trauma or if displaced into bloodstream

138
Q

what is a Mz disc

A

contains metronidazole

confirms presence of anaerobic bacteria if prevents bacteria growth

139
Q

what number of bacteria cultured indicate significant bacteriuria

A

10^5 bacteria/ml

140
Q

what number of bacteria cultured suggests doubtful significance of bacteriuria

A

between 10^4-10^5 bacteria/ml

141
Q

(simply) how does HIV cause immune dysfunction

A
  1. CD4 cell death =
    - direct cytotoxicity
    - impaired homeostasis
    - premature apoptosis
    - reduce T cell production
  2. CD8 CTL increased activation but decreased cytotoxic function
  3. B cells increased activation but antibodies non specific
  4. decreased function of
    - natural killer cells
    - macrophages
    - neutrophils
142
Q

describe the progression of an HIV infection

A
  1. acute primary infection = low then high CD4 count
  2. asymptomatic phase = progressive loss of CD4
  3. early symptomatic phase = manifestation of clinical features
    (roughly 5-10 years later)
  4. AIDS = CD4 < 200
143
Q

what are the HIV infection markers

A

CD4 count

HIV viral load = RNA concentration

144
Q

how is malaria treated

A 
non p.falciparum:
chloroquine
primaquine to prevent relapse
p.falciparum:
complicated = quinine + IV artesunate
non-complicated = oral quinine + riamet

Phase 2a (15 decks)

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