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Microorganisms + Disease > Gram negative bacterial pathogens L3 > Flashcards

Gram negative bacterial pathogens L3 Flashcards

1
Q

what are the three layers of gram negative cell wall

A

outer membrane
periplasmic space
cytoplasmic membrane

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2
Q

what colour are gram positive strains in dye

A

blue

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3
Q

what colour are gram negative strains in dye

A

pink/red

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4
Q

what shape is Neisseria meningitidis and Neisseria gonorrhoeae

A

Gram-negative diplococci

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5
Q

what does Neisseria meningitidis and Neisseria gonorrhoeae

require for growth

A

Fastidious – grow well on supplemented chocolate agar at 37°C in 5% CO2 in air

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6
Q

what are Neisseria meningitidis and Neisseria gonorrhoeae

colonies like

A

Colonies transparent, non-haemolytic, 1-5 mm in diameter

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7
Q

what oxidase is Neisseria meningitidis and Neisseria gonorrhoeae

A

oxidase positive

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8
Q

what does Neisseria meningitidis and Neisseria gonorrhoeae

do to glucose

A

Metabolize glucose (meningococcus also utilises maltose) to acid

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9
Q

what is Neisseria meningitidis

A

Obligate human pathogen

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10
Q

where is Neisseria meningitidis found

A

Asymptomatic nasopharyngeal carriage in c. 10% population

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11
Q

when does Neisseria meningitidis cause disease

A

bacterium enters the bloodstream and crosses the blood/brain barrier

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12
Q

how are meningococci segregated

A

13 serogroups – serogroups A, B, C, W135 and Y cause most infections

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13
Q

what causes bacterial meningitis in children & young adults – may cause epidemics

A

Neisseria meningitidis

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14
Q

what does Neisseria meningitidis cause

A

sepsis, septic arthritis, endophthalmitis, conjunctivitis etc.

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15
Q

what vaccines are available for Neisseria meningitidis

A

C and B

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16
Q

what are symptoms of Meningococcal meningitis

A

marked neck
stiffness
photophobia
purpuric non-blanching rash

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17
Q

what is CSF

A

Cerebrospinal fluid

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18
Q

what is gonorrhoea and an example of a bacteria that causes it

A

Gonorrhoea is a common bacterial infection transmitted by sexual contact or perinatally
Neisseria gonorrhoeae

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19
Q

what are gonococci like

A

do not tolerate drying, hence samples should be inoculated onto appropriate media immediately

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20
Q

what does Neisseria gonorrhoeae cause

A

acute urethritis in men and cervicitis (predominantly) in women
in neonates – causes eye infection (ophthalmia neonatorum)

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21
Q

what is Gram-stain of urethral discharge

made of

A

Numerous polymorphonuclear cells

Intra-cellular gram-negative diplococci

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22
Q

what can Ophthalmia neonatorum

cause

A

Purulent ocular discharge

May cause blindness if untreated

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23
Q

what is Moraxella catarrhalis

A

Gram-negative diplococcus indistinguishable from Neisseria by Gram staining

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24
Q

where does Moraxella catarrhalis colonise

A

Colonises upper respiratory tract in c. 5% of adults

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25
Q

what does Moraxella catarrhalis cause

A

Otitis media, Sinusitis, pneumonia in the elderly and in patients with Chronic Obstructive Pulmonary Disease (COPD)

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26
Q

what are examples of Enterobacteriaceae

A 
Escherichia
 Klebsiella
 Proteus / Morganella
 Salmonella
 Serratia
 Shigella
 Yersinia
27
Q

what is an increasing problem with Enterobacteriaceae

A

antibiotic resistance is an increasing problem in these organisms
many produce enzymes that degrade commonly used antibiotics
enzymes are called Extended Spectrum Beta lactamases – ESBLs)

28
Q

what is Escherichia coli and where does it colonise

A

Commensal flora in human and other animals GI tract where they do not normally cause any problems
survive in soil and water

29
Q

what is Escherichia coli like

A

Facultatively anaerobic
Bacilli
Motile

30
Q

what does Escherichia coli do to lactose

A

Most strains ferment lactose and are indole positive

31
Q

what can Escherichia coli cause

A

UTI
Neonatal meningitis
Wound infection Intra-abdominal abscess
Sepsis – bacteria enter the bloodstream

32
Q

how does a UTI form due to Escherichia coli

A

persons own gut flora due to contamination of the urethra - ascends to the bladder and may reach the kidneys in some cases

33
Q

what does Escherichia coli cause

A

Some strains of E.coli cause diarrhoea

34
Q

how does Escherichia coli lead to disease

A

Disease follows ingestion of contaminated/uncooked food or contact with faeces - sources of contamination : animals or environmental contamination

35
Q

how are Escherichia coli grouped

A

Based on biochemical/serological properties and the types of pathogenic mechanism used, strains are placed into different groups

36
Q

what bacteria causes the commonest food poisoning

A

Campylobacter

then salmonella

37
Q

what is Campylobacter associated with

A

Most cases sporadic, associated with poultry and raw milk
Contamination of chicken – where they naturally live
When slaughter they get contaminated with the faecal material

38
Q

what is Campylobacter like

A

Spiral bacterium, micro-aerophilic, grows at 42°C

39
Q

oxidase test on Campylobacter

A

oxidase positive

40
Q

what does Campylobacter jejuni cause

A

Prodromal fever (fever before they see any symptoms), headache
Diarrhoea
vomiting
Abdominal pain
Rare systemic infections – fever & positive blood cultures

41
Q

why can there be blood in diarrhoea if infected with Campylobacter jejuni

A

move from the gut and get into the blood – due to the damage of the mucus lining

42
Q

what is Helicobacter pylori like

A

Pleomorphic rod – microaerophilic (doesn’t like too much oxygen)
many spiral shaped

43
Q

what does Helicobacter pylori cause

A

infection in the stomach (gastric acid in stomach usually kills everything, but this organism has evolved to survive) and duodenum
Powerful urease enzyme, colonise gastric mucosa

44
Q

what does Helicobacter pylori need for growth

A

Selective media for culture from tissue biopsies

45
Q

what is the most common bacteria to cause infection

A

Helicobacter pylori

46
Q

what can be used for diagnosis from biopsies

A

helicobacter pylori produces a powerful urease enzyme allowing colonisation of the gastric mucosa – used in diagnosis from biopsies

47
Q

what is the effect of Helicobacter pylori

making urease

A

Urease breaks down urea produces ammonia, it neutralizes gastric acid around organism

48
Q

what are Pseudomonads and non-fermenters associated with

A

Associated with moist environments

P. aeruginosa most associated with human disease

49
Q

what are Pseudomonads and non-fermenters like

A 
Non-sporing
Non-capsulate (no capsule)
Usually motile
Strictly aerobic (under most conditions will only grow when there is oxygen around)
Thin GNB (gram negative bacillus)
50
Q

what do many strains ofPseudomonads and non-fermenters produce

A

produce pigments (thought to be part of virulence mechanism) e.g. pyocyanin

51
Q

what is the Pseudomonads and non-fermenters metabolism

A

Oxidative metabolism (compared to the Enterobacteriaceae-fermentative)

52
Q

where does Pseudomonas aeruginosa commonly colonise

A

colonises wounds

53
Q

what can Pseudomonas aeruginosa cause

A

outer (otitis externa) and inner (malignant otitis) ear infections
eye infections
sepsis

54
Q

what can Pseudomonas aeruginosa cause in cystic fibrosis patients

A

pneumonia

55
Q

what are non-fermenters

A

Heterogeneous group including Acinetobacter it is biochemically inert and resistant to many antibiotics

56
Q

what are vibrionaceae like

A

Short, comma-shaped bacilli
Actively motile
Fermentative

57
Q

what oxidase are Vibrionaceae

A

oxidase positive

58
Q

what is halophilic and and example

A

Halophilic live in salt water (eg. V. vulnificus)

59
Q

what is non halophilic and an example

A

non-halophilic live in non salt water (eg. V. cholera)

60
Q

how does Vibrionaceae cause infection

A

occurs through ingestion of contaminated food or water

61
Q

what agar is Vibrionaceae grown on

A

thiosulphate, citrate, bile-salt, sucrose (TCBS) agar or in alkaline peptone-water

62
Q

what does Vibrionaceae cholerae need for growth and what does it produce

A

grown on TCBS – ferments sucrose and produces yellow colonies

63
Q

what is Vibrionaceae cholerae like

A

has a flagellum so is motile

Gram-negative bacilli

Microorganisms + Disease (16 decks)

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