M10- Gram negative bacteria 1

Question 1

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

Answer 1

• Cocci
• Strict anaerobes
• Facultative anaerobes
• Curved rods

Question 2

name aerobic and anaerobic cocci species.

Answer 2

• Aerobic :
- Neisseria
- Moraxella
• Anaerobic :Veillonella

Question 3

Describe neisseria.

Answer 3

• 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

Question 4

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

Answer 4

• 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

Question 5

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

Answer 5

Neisseria

Question 6

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

Answer 6

moraxella

Question 7

Name a commensal of the mouth and upper respiratory tract?

Answer 7

moraxella catarrhalis

Question 8

why is moraxella a significant pathogen?

Answer 8

• 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

Question 9

what do most strains of moraxella produce?

Answer 9

β-lactamase

• Complicates antibiotic therapy

Question 10

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

Answer 10

veillonella (small gram negative anaerobic cocci)

Question 11

How is veillonella parvula beneficial?

Answer 11

• 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

Question 12

what do high numbers of veillonellae in dental plaque do?

Answer 12

raise plaque pH and REDUCE the cariogenicity of plaque

Question 13

what does GNAB stand for?

Answer 13

gram negative anaerobic bacilli

Question 14

Name 3 motile GNABs.

Answer 14

• Selenomonas
• Centipeda
• Helicobacter

Question 15

Name 3 non-motile GNABS.

Answer 15

• Bacteriodes
• Porphyromonas
• Prevotella

Question 16

what is the apperance of selenomonas?

Answer 16

Crescent (moon-shaped)

Gram -ve bacteria with many flagellae

Question 17

what is selenomonas associated with?

Answer 17

aggressive forms of periodontitis

Question 18

Describe features of centipede.

Answer 18

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

Question 19

what is helicobacter pylori reported in?

Answer 19

dental plaque

Question 20

what is helicobacter pylori important in?

Answer 20

aetiology of gastritis, peptic ulcers & gastric cancers

Question 21

where are non-motile GNABs especially found?

Answer 21

gingival sulcus and periodontal pocket

Question 22

what roles do non-motile GNABS have?

Answer 22

oral, perioral & extra-oral infections

Question 23

what are bacteroides?

Answer 23

strictly anaerobic Gram -ve bacilli

Question 24

where is bacteroides fragilis found?

Answer 24

mouth and GI tract

Question 25

What are bactericides the main pathogen in?

Answer 25

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

Question 26

what is healthy gingival crevice mostly?

Answer 26

Gram postive cocci

Question 27

what are conditions below the gingival margins?

Answer 27

- very different from the tooth surface - conditions more anaerobic - nutrients come from the gingival tissues rather than food and salvia

Question 28

Describe bacteria in the periodontal pocket.

Answer 28

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

Question 29

what produces a dark pigment?

Answer 29

bacteriodes group

Question 30

why are porphyromonas a dark/purple -pigemneted GNAB?

Answer 30

– require external heme as iron source, | – Iron scavenging molecules on surface give dark appearance

Question 31

why is prophyromonas asaccharolytic?

Answer 31

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

Question 32

why is P. gingivalis considered a periodontopathogen?

Answer 32

– frequent association with human periodontitis | – Demonstrated to cause periodontitis & bone destruction in experimental animals

Question 33

describe prevotella .

Answer 33

* dark/purple pigmented & non * saccharolytic GNAB (doesn't use carboydrates, breaks down sugars) * gingival sulcus & periodontal pocket * possible periodontopathogens

Question 34

Name the 2 prevotella species.

Answer 34

P. intermedia | P. dentalis

Question 35

what do P. intermedia numbers correlate with?

Answer 35

periodontitis severity

Question 36

what are the features of P.dentalis?

Answer 36

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

Question 37

when is the bacteria photosensitive?

Answer 37

iron free

Question 38

what is black pigmented bacteria treated with?

Answer 38

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

Question 39

Summary of this lecture.

Answer 39

• 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