M10- Gram negative bacteria 1 Flashcards
what are the 4 main groups of gram -ve bacteria.
- Cocci
- Strict anaerobes
- Facultative anaerobes
- Curved rods
name aerobic and anaerobic cocci species.
• Aerobic :
- Neisseria
- Moraxella
• Anaerobic :Veillonella
Describe neisseria.
• 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
what oral neisseria are early tooth colonisers (not considered pathogenic)?
• 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
What type of aerobic gram -ve cocci allows nitrate to be used as terminal electron acceptor to allow growth anaerobically?
Neisseria
What type of aerobe gram -ve cocci has some strains which grow weakly under anaerobic conditions?
moraxella
Name a commensal of the mouth and upper respiratory tract?
moraxella catarrhalis
why is moraxella a significant pathogen?
- 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
what do most strains of moraxella produce?
β-lactamase
• Complicates antibiotic therapy
what bacteria does not ferment carbohydrates but uses lactic acid as an energy source?
veillonella (small gram negative anaerobic cocci)
How is veillonella parvula beneficial?
• 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
what do high numbers of veillonellae in dental plaque do?
raise plaque pH and REDUCE the cariogenicity of plaque
what does GNAB stand for?
gram negative anaerobic bacilli
Name 3 motile GNABs.
- Selenomonas
- Centipeda
- Helicobacter
Name 3 non-motile GNABS.
- Bacteriodes
- Porphyromonas
- Prevotella
what is the apperance of selenomonas?
Crescent (moon-shaped)
Gram -ve bacteria with many flagellae
what is selenomonas associated with?
aggressive forms of periodontitis
Describe features of centipede.
• flagellae arising from all round the cell.
• isolated from periodontitis sites & few
reports in healthy mouths
• importance unknown
what is helicobacter pylori reported in?
dental plaque
what is helicobacter pylori important in?
aetiology of gastritis, peptic ulcers & gastric cancers
where are non-motile GNABs especially found?
gingival sulcus and periodontal pocket
what roles do non-motile GNABS have?
oral, perioral & extra-oral infections
what are bacteroides?
strictly anaerobic Gram -ve bacilli
where is bacteroides fragilis found?
mouth and GI tract
What are bactericides the main pathogen in?
– wounds, post-surgical infections, peritonitis, brain
abscesses etc.
– regarded as a member of the “normal” oral flora
what is healthy gingival crevice mostly?
Gram postive cocci
what are conditions below the gingival margins?
- very different from the tooth surface
- conditions more anaerobic
- nutrients come from the gingival tissues rather than food and salvia
Describe bacteria in the periodontal pocket.
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
what produces a dark pigment?
bacteriodes group
why are porphyromonas a dark/purple -pigemneted GNAB?
– require external heme as iron source,
– Iron scavenging molecules on surface give dark appearance
why is prophyromonas asaccharolytic?
– Obtain energy from environmental amino acids & peptides
– Produce proteases to access them
– Degrade serum albumin, Igs, haemoglobins, host tissue proteins
why is P. gingivalis considered a periodontopathogen?
– frequent association with human periodontitis
– Demonstrated to cause periodontitis & bone destruction in experimental animals
describe prevotella .
- dark/purple pigmented & non
- saccharolytic GNAB (doesn’t use carboydrates, breaks down sugars)
- gingival sulcus & periodontal pocket
- possible periodontopathogens
Name the 2 prevotella species.
P. intermedia
P. dentalis
what do P. intermedia numbers correlate with?
periodontitis severity
what are the features of P.dentalis?
– Non-pigmented species (one of several)
– isolated from root canals and periodontal pocket
– no evidence that these bacteria produce any oral or other pathology
when is the bacteria photosensitive?
iron free
what is black pigmented bacteria treated with?
blue light: – Excitation – energy transferred via porphyrin – produces reactive O2 species – destroy lipids, proteins, Nuclei Acids
Summary of this lecture.
• 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
