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Microbiology > M10- Gram negative bacteria 1 > Flashcards

M10- Gram negative bacteria 1 Flashcards

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Biology 101 flashcards
1
Q

what are the 4 main groups of gram -ve bacteria.

A
  • Cocci
  • Strict anaerobes
  • Facultative anaerobes
  • Curved rods
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2
Q

name aerobic and anaerobic cocci species.

A

• Aerobic :
- Neisseria
- Moraxella
• Anaerobic :Veillonella

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3
Q

Describe neisseria.

A

• Gram -ve facultative/aerobic
• Non-motile
• Cocci (beans), pairs, tetrads short chains & clusters
• Saccharolytic (generally)
• Pathogens
– Neisseria gonorrhoeae, & Neisseria meningitidis
– not considered to be normal oral flora

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4
Q

what oral neisseria are early tooth colonisers (not considered pathogenic)?

A

• Neisseria subflava
– the most commonly isolated
– mouth and dental plaque saccharolytic produces polysaccharide and a yellow green pigment
• Neisseria sicca
– mouth, similar to Neisseria subflava
– saccharolytic & poysaccharide producing
– no pigment produced

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5
Q

What type of aerobic gram -ve cocci allows nitrate to be used as terminal electron acceptor to allow growth anaerobically?

A

Neisseria

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6
Q

What type of aerobe gram -ve cocci has some strains which grow weakly under anaerobic conditions?

A

moraxella

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7
Q

Name a commensal of the mouth and upper respiratory tract?

A

moraxella catarrhalis

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8
Q

why is moraxella a significant pathogen?

A
  • Facultative intracellular life cycle that allows it to infect tonsillar B cells
  • meningitis, endocarditis, otitis media & maxillary sinusitis
  • since PCV vaccine increase in otitis media in children
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9
Q

what do most strains of moraxella produce?

A

β-lactamase

• Complicates antibiotic therapy

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10
Q

what bacteria does not ferment carbohydrates but uses lactic acid as an energy source?

A

veillonella (small gram negative anaerobic cocci)

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11
Q

How is veillonella parvula beneficial?

A

• Strict anaerobe
• Colonizes the oral cavity and intestines
– not particularly pathogenic,
– produces endotoxins & antigens which produce immune reactions
– rare cases of sepsis
• Catabolises lactic acid to weaker organic acids,
– raising pH

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12
Q

what do high numbers of veillonellae in dental plaque do?

A

raise plaque pH and REDUCE the cariogenicity of plaque

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13
Q

what does GNAB stand for?

A

gram negative anaerobic bacilli

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14
Q

Name 3 motile GNABs.

A
  • Selenomonas
  • Centipeda
  • Helicobacter
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15
Q

Name 3 non-motile GNABS.

A
  • Bacteriodes
  • Porphyromonas
  • Prevotella
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16
Q

what is the apperance of selenomonas?

A

Crescent (moon-shaped)

Gram -ve bacteria with many flagellae

17
Q

what is selenomonas associated with?

A

aggressive forms of periodontitis

18
Q

Describe features of centipede.

A

• flagellae arising from all round the cell.
• isolated from periodontitis sites & few
reports in healthy mouths
• importance unknown

19
Q

what is helicobacter pylori reported in?

A

dental plaque

20
Q

what is helicobacter pylori important in?

A

aetiology of gastritis, peptic ulcers & gastric cancers

21
Q

where are non-motile GNABs especially found?

A

gingival sulcus and periodontal pocket

22
Q

what roles do non-motile GNABS have?

A

oral, perioral & extra-oral infections

23
Q

what are bacteroides?

A

strictly anaerobic Gram -ve bacilli

24
Q

where is bacteroides fragilis found?

A

mouth and GI tract

25
Q

What are bactericides the main pathogen in?

A

– wounds, post-surgical infections, peritonitis, brain
abscesses etc.
– regarded as a member of the “normal” oral flora

26
Q

what is healthy gingival crevice mostly?

A

Gram postive cocci

27
Q

what are conditions below the gingival margins?

A
  • very different from the tooth surface
  • conditions more anaerobic
  • nutrients come from the gingival tissues rather than food and salvia
28
Q

Describe bacteria in the periodontal pocket.

A

1) plaque accumulates round neck of tooth causing gingivitis (can be reversed)- Streptococcus spp.
2) plaque grows down between tooth & gum to form pocket (difficult to reverse)
-Actinomyces spp.
3) pocket deepens, gingiva starts to recede,
bone begins to be lost (irreversible) -porphyromonas and prevotella intermedia

29
Q

what produces a dark pigment?

A

bacteriodes group

30
Q

why are porphyromonas a dark/purple -pigemneted GNAB?

A

– require external heme as iron source,

– Iron scavenging molecules on surface give dark appearance

31
Q

why is prophyromonas asaccharolytic?

A

– Obtain energy from environmental amino acids & peptides
– Produce proteases to access them
– Degrade serum albumin, Igs, haemoglobins, host tissue proteins

32
Q

why is P. gingivalis considered a periodontopathogen?

A

– frequent association with human periodontitis

– Demonstrated to cause periodontitis & bone destruction in experimental animals

33
Q

describe prevotella .

A
  • dark/purple pigmented & non
  • saccharolytic GNAB (doesn’t use carboydrates, breaks down sugars)
  • gingival sulcus & periodontal pocket
  • possible periodontopathogens
34
Q

Name the 2 prevotella species.

A

P. intermedia

P. dentalis

35
Q

what do P. intermedia numbers correlate with?

A

periodontitis severity

36
Q

what are the features of P.dentalis?

A

– Non-pigmented species (one of several)
– isolated from root canals and periodontal pocket
– no evidence that these bacteria produce any oral or other pathology

37
Q

when is the bacteria photosensitive?

A

iron free

38
Q

what is black pigmented bacteria treated with?

A 
blue light:
–  Excitation
–  energy transferred via porphyrin
–  produces reactive O2 species
–  destroy lipids, proteins, Nuclei Acids
39
Q

Summary of this lecture.

A

• Gram negative bacteria in mouth
– Diverse group with some key genera & species
• Important in plaque development – Neisseria early coloniser
– Veilionella degrades lactic acid
• Important in Periodontal disease – Poryphyromonas & Prevotella
– Selenomonas noxia
• Important in Perioral & extra oral diseases
– Moraxella source of β-lactamase
– Appear in community acquired pneumonia
– Oral isolates that cause other diseases, Bacteroides & Helicobacter

Microbiology (30 decks)

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