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Y3 Medical Micro > L6 Gram negative bacteria > Flashcards

L6 Gram negative bacteria Flashcards

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USMLE® Step 1 flashcards
1
Q

what are the gram negative cocci

A

neisseria meningitidis
neisseria gonorrhoeae
moraxella catarrhalis

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2
Q

what is the gram negative cell wall

A 
outer membrane (LPS) contains adhesins
periplasmic space (thin PG)
cytoplasmic membrane
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3
Q

what is the shape of neisseria meningitidis and neisseria gonorrhoeae

A

diplococci

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4
Q

how do neisseria meningitidis and neisseria gonorrhoeae grow and what is the best plate they grow on

A

fastidious

grow well on chocolate agar at 37°C in 5% CO2

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5
Q

what are the neisseria meningitidis and neisseria gonorrhoeae colonies like

A

transparent
non-hemolytic
1-5mm diameter

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6
Q

are neisseria meningitidis and neisseria gonorrhoeae oxidase +/-

A

positive as have cytochrome

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7
Q

what do neisseria meningitidis and neisseria gonorrhoeae metabolise

A

both metabolise glucose
meningococcus also utilises maltose
form acid

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8
Q

what pathogen is neisseria meningitidis

A

obligate human pathogen

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9
Q

where does neisseria meningitidis infect

A

back of throat

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10
Q

how many of the population are asymptomatic to neisseria meningitidis and where do they carry

A

10%
nasopharyngeal carriage
cant infect the blood stream

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11
Q

how are neisseria meningitidis segregated

A

Meningococci are segregated into 12 serogroups – serogroups A, B, C, W and Y cause most infections

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12
Q

what vaccine is there available for neisseria meningitidis

A

ACWY

B

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13
Q

what does neisseria meningitidis cause

A 
bacterial meningitis in children and young adults 
septicaemia 
septic arthritis
endophthalmitis 
conjunctivitis
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14
Q

what are the effects of meningococcal meningitis

A

marked neck
stiffness
photophobia
arching back

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15
Q

how is meningococcal meningitis diagnosed

A

lumbar puncture = CSF fluid meant to be clear like water, but if have bacterial meningitis = cloudy caused by the WBC

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16
Q

what are the effects of meningococcal septicaemia

A

purpuric non-blanching rash

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17
Q

how is neisseria gonorrhoeae transmitted

A

common bacterial infection transmitted by sexual contact or perinatally

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18
Q

how are neisseria gonorrhoeae inoculated

A

dont tolerate drying - need to be inoculated onto appropriate media immediately

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19
Q

what are the samples for neisseria gonorrhoeae diagnosis

A

cervial, pharyngeal, rectal

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20
Q

what does neisseria gonorrhoeae cause

A

urethritis (men)
cervicitis (mainly women)
women are asymptomatic
in neonates - opthalmia neonatorum - eye infection

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21
Q

why do neisseria gonorrhoeae not tolerate drying

A

no capsule

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22
Q

what is the gram stain of urethral discharge like

A

many polymorphonuclear cells

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23
Q

what does disseminated GC cause

A

skin lesions

septic arthritis

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24
Q

what is indistinguishable between moraxella catarrhalis and the neisseria

A

gram stains

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25
Q

where does moraxella catarrhalis colonise

A

upper respiratory tract

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26
Q

how many people carry moraxella catarrhalis (harmless)

A

5% adults (harmless)

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27
Q

what does moraxella catarrhalis cause

A

otitis media
sinusitis
pneumonia in the elderly and in patients with other lung diseases

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28
Q

where is E. coli a commensal

A

flora in GI tract

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29
Q

what is the ‘respiration’ of E. coli

A

facultatively anaerobic

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30
Q

what are is the indole test for e. coli

A

positive (most strains)

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31
Q

what can e. coli ferment

A

lactose (most strains)

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32
Q

is e. coli motile

A

yes

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33
Q

what is e. coli similar genetically to

A

shigella

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34
Q

what infections does e. coli cause

A 
UTI 
neonatal adhesions
wound infection
intra-adbominal abscess
diarrhoea
haemolytic uraemic syndrome
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35
Q

what percentage of UTIs are caused by E. coli

A

70% as they have specific adhesion

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36
Q

what e. colis cause diarrhoea

A 
enteropathogenic (EPEC)
enteroaggregative (EAEC)
enterotoxigenic (ETEC)
enteroinvasive (EIEC)
verocytotoxin-producing (VTEC; eg O157)
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37
Q

what is the air required for camplyobacter

A

micro-aerophilic (lower oxygen)

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38
Q

what shape bacteria is campylobacter

A

spiral

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39
Q

what temp does campylobacter grow

A

42

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40
Q

what is the oxidase for camyplobacter

A

positive

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41
Q

what sample is used for campylobacter

A

stool

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42
Q

what is campylobacter caused by

A

food poisoning

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43
Q

when does campylobacter peak

A

summer

esp children/young adults

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44
Q

what does campylobacter look like on selective agar

A

water droplets

45
Q

what is the incubation period of campylobacter jejuni

A

3-4 days

sometimes 8-9

46
Q

which is the most common campylobacter

A

c. jejuni

47
Q

what are the symptoms of c. jejuni

A 
prodromal fever
headache
diarrhoea, (+/- blood)
vomiting 
abdominal pain
48
Q

c. jejuni treatments

A

erythromycin or ciprofloxacin if required

49
Q

how many pseudomonads species are there

A

> 200

50
Q

what environments are pseudomonads associated with

A

moist

51
Q

which pseudomonads is most associated with human disease

A

pseudomonads aeruginosa

52
Q

is pseudomonads sporing

A

no

53
Q

has pseudomonads got a capsule

A

no

54
Q

are pseudomonads motile

A

usually

55
Q

what is the ‘respiration’ for pseudomonads

A

strictly aerobic

56
Q

what do many pseudomonads strains make

A

pigments e.g. pyocyanin (green)

57
Q

what is pseudomonads metabolism

A

oxidative

58
Q

where does pseudomonads colonise

A

wounds
otits externa (ear infection)
maliganant otitis media (middle ear infection)
eyes

59
Q

what can pseudomonads infections cause

A

septicaemia in immunocompromised/ burn patients

pneumonia in cystic fibrosis patients

60
Q

what is seen on cystic fibrosis patients from pseudomonads infection

A

Lots of extra cellular polysaccharide production in CF patients

61
Q

what are examples of non-fermenting heterogeneous bacteria

A

acinetobacter
flavobacterium
alcaligenes

62
Q

what are non ferments like biochemically

A

biochemically inert

63
Q

what is the effect of antibiotics on non-fermenters

A

no effect - resistant

64
Q

what is the shape of vibrionaceae

A

short
comma shaped
bacilli

65
Q

are vibrionaceae motile

A

actively motile

66
Q

are vibrionaceae fermentative

A

yes

67
Q

are vibrionaceae oxidase +/-

A

positive

68
Q

are vibrionaceae halophilic

A

Halophilic (eg. V. vulnificus) or non-halophilic (eg. V. cholera)

69
Q

what plates can vibrionaceae be grown on

A

thiosulphate, citrate, bile-salt, sucrose (TCBS) agar

in alkaline peptone-water

70
Q

what enhances vibrionaceae growth

A

alkaline enviro

71
Q

growth of vibrionaceae on TCBS

A

ferments sucrose and makes yellow colonies

72
Q

what vibrionaceae cause epidemic cholera

A

v. cholerae O1 and O139

73
Q

how do you get infected with v. parahaemolyticus

A

food poisoning - shellfish

74
Q

what does v. vulnificus cause

A

fulminating septicaemia
cellulitis
acute diarrhoea

75
Q

what is important for cholera patients

A

replace the water lost

76
Q

what is the most common pathogen of haemophilus

A

h. influenzae

77
Q

what is the shape of haemophilus

A

pleomorphic (different lengths/shapes)

coccobacilli

78
Q

does haemophilus have a capsule

A

have capsular types a-f

but also non-capsulate strains are common

79
Q

what is the most important capsular type

A

b - polysacchairde polymer of ribosyl ribitol phosphate

80
Q

what agar does H. influenzae grow well on under what conditions

A

chocolate agar in CO2– requires haemin (X factor) and NADP (V fcactor)

81
Q

why is H. influenzae the most invasive

A

due to serotype b

82
Q

what does H. influenzae cause

A

major cause of severe sepsis in childhood

83
Q

is there a vaccine for H. influenzae

A

Hib vaccine

84
Q

can adults be infected with H. influenzae

A

occasional infections in adults with underlying disease

85
Q

examples of the invasive infections caused by H. influenzae

A 
meningitis
epiglottitis
bacteraemia
pneumonia
septic arthritis
cellulitis
86
Q

how is H. influenzae identified

A

grown on plate with XV factor, X factor onown and H. influenzae factor on own - only growth around the H. influenzae factor disk

87
Q

what is the habitat of legionellae

A

water

88
Q

what does legionellae cause

A

pneumonia

89
Q

what is the most important legionellae species

A

L. pneumophila serogroup 1 causes most infections

90
Q

how does legionellae infect

A

inhalation of aerosols from manmade water sources e.g. cooling towers

91
Q

how are legionellae detected

A

urine antigen detection often useful – capsule from organism excreted in urine = rapid test

92
Q

why cant legionellae be diagnosed via culturing and plating

A

Culture on Buffered charcoal yeast extract agar with alpha-ketoglutarate – grows slowly 5+ days needed

93
Q

why are legionellae still cultured even though takes too long to diagnose from plate

A

useful to detect where the source is from

94
Q

what does legionella look like on BCYE agar

A

ground glass colonies

95
Q

what are the gram-negative anaerobe species

A

Bacteroides / Prevotella / Fusobacterium spp.

96
Q

where are gram negative anaerobes a normal flora

A

GI tract

97
Q

how are gram negative anaerobes identified

A

colonial appearance
metronidazole sensitivity
biochemical reactions

98
Q

where is it best to isolate gram negative anaerobes from

A

pus or tissue specimens

NOT swab

99
Q

what do gram negative anaerobes cause

A 
intra-abdominal sepsis
abscesses 
wound infection
bacteraemia (rare)
aspiration pneumonia
Lemierre’s disease - rare
100
Q

what is the shape of Pasteurella multocida

A

pleomorphic bi-polar bacilli

101
Q

is Pasteurella multocida oxidase +/-

A

positive

102
Q

is Pasteurella multocida penicillin sensitive

A

yes unlinke other coliforms

103
Q

what agar cant Pasteurella multocida grow on

A

macconkey

104
Q

what does Pasteurella multocida cause

A

septicaemia and respiratory tract infection, often fatal

105
Q

what pathogen is Pasteurella multocida

A

animal

106
Q

can humans be infected by Pasteurella multocida

A

yes via animal bite

107
Q

what happens following Pasteurella multocida infected animal bite

A

cellulitis/local abscesses

occasionally septic arthritis or even meningitis

108
Q

what is the Moraxella catarrhalis like

A

intracellular
gram negative
diplococcus

Y3 Medical Micro (16 decks)

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