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Medical Microbiology > Week 7 - Gram Negative Bacilli > Flashcards

Week 7 - Gram Negative Bacilli Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Enterobacteriaceae

A 
Most common GNB
Causes 50% of septicaemias, 60-70% GIT infections and 70% UTIs
Opportunistic pathogens
Many endogenous in gut and LUT
NF at large intestines
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2
Q

Enterobacteriaceae Characteristics

A 
Catalase Pos
Oxidase Neg 
Fermentative
Facultative anaerobes
Non-fastidious
Grey, moist, shiny colonies on BA
Slightly opaque centre than edge
Usually non-haemolytic
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3
Q

Enterobacteriaceae Overt Pathogens

A

Salmonella
Shigella
Yersinia
E.coli

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4
Q

Gram Negative Antigenic Properties

A 
Major antigens:
- H flagellar protein
- K capsular polysaccharide
- O somatic lipopolysaccharide (cell wall)
Other antigens
- F fimbrial (adherence)
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5
Q

What are the two non-motile Enterobacteriaceae?

A

Klebsiella

Shigella

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6
Q

Escherichia Species

A

Colonise GIT
Usually very biochemically active and motile
E.coli most common human bacterial pathogen

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7
Q

E.coli

A

Lactose fermenter - bright pink on MAC/ yellow on CLED
Motile
Indole Pos

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8
Q

Indole Production

A

Tests if an organism produces the enzyme tryptophanase

Tryptophanase breaks down amino acid tryptophan into indole

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9
Q

Diseases that E.coli causes

A 
Septicaemia
Wound infection
Peritonitis
UTI
Diarrhoael diseases
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10
Q

Indole Test Methods

A

Method 1
- bottle/tube and in API strips
- incubate inoculated peptone broth overnight
- add 5-10 drops of Kovacs reagent
- positive = pink ring on surface
Method 2
- few drops of Kovac’s reagent to piece of filter paper
- transfer a quantity onto filter paper
- positive = pink/red colour
Use BA as it has tryptophan unlike MAC or CLED

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11
Q

Klebsiella

A

NF in gut
Opportunistic invaders especially in moist conditions
Found in environment and plants
2 species
K.pneumoniae - causes pneumonia, septicaemia, UTI, nosocomial
K.oxytoca

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12
Q

Klebsiella Characteristics

A 
Lactose Fermenters - pale pink on MAC/pale yellow CLED
Non-motile
Capsulated - mucoid and sticky
K.oxytoca indole pos
K.pneumoniae indole neg
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13
Q

Enterobacter Characteristics

A

Lactose variable
Motile
Indole neg

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14
Q

Proteus, Providencia and Morganella Characteristics

A 
NF in GIT
UTI
Wound infections
Non lactose fermenters - blue on CLED/very pale pink on MAC
Phenylalanine deaminase/trytophan deaminase pos
Urea positive
Non-capsulated
Motile
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15
Q

How to prevent swarming of Proteus on MAC

A

Use a no salt or low salt formula

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16
Q

Zoonoses

A

Diseases of animals which may be transmitted to humans

17
Q

Diseases caused by Salmonella

A

Gastroenteritis
Enteric fever
Extra-intestinal infections
Carrier status

18
Q

Bacillary Dysentry

A 
Caused by Shigellae
Associated with humans only
Low infectious dose (10-100 organisms)
Invasion of wall of large intestine
Inflammatory response
Blood, mucous and pus
19
Q

Yersinia disease caused

A 
Yersinia enterocolitica main GIT pathogen of genus
Causes:
- Enterocolitis
- Fever
- Diarrhoea
20
Q

Pseudomonas

A

Soil, plants and water supplies
Opportunistic
- UTI
- Otitis externa

21
Q

Pseudomonas aeruginosa

A 
Non-fastidious
Obligate anaerobe
Motile
Oxidase pos
Oxidative
Flat, matt colonies
Shield shaped
22
Q

Haemophilus Characteristics

A

NF at URT
Small GNB or coccobacillus
Capnophilic
Fastidious
Grey/translucent, circular shiny colonies on CHOC
No growth on selective/differential media

23
Q

Neisseria gonorrhoeae

A

Strict human pathogen - not NF
Causes gonorrhoea
- pyogenic (pus producing) infection of urethra

24
Q

Neisseria meningitidis

A

NF of URT
Humans only reservoir
Spread by droplets
Causes meningococcal meningitis

25
Q

Meningococcal Meningitis

A

Inflammation of membranes surrounding brain and spinal cord
CNS damage
Rapid onset of fever, stiff neck, headache

26
Q

Moraxella catarrhalis

A

NF of URT
Most commonly associated with respiratory tract infections
- Otitis media
- Pneumonia

27
Q

Pseudomonas aeruginosa Distinctive Features

A

Produces pigment
- green pyocyanin
- yellow pyoverdin (fluoresces under UV light)
Metallic sheen when left on BA for 48 hours
Grape odour
Resistant to many antimicrobials and disinfectants

Medical Microbiology (7 decks)

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