Bacteria Types

Streptococcus mutans

- +ve cocci

- facultative anaerobe

- dental caries

- prod lactic acid from sugar metabolism, leading to enamel demineralisation

Streptococcus mitis

- +ve cocci (part of the viridans group of strep)

- can cause endocarditis

- prod biofilms & contributes to dental plaque formation

- alpha-hemolysis on blood agar (greenish discoloration)

- Optochin-resistant (differentiates from S. pneumoniae)

Streptococcus salivarius

- +ve cocci

- commensal in the mouth & URT

- contributes to early biofilm formation on teeth

- rarely pathogenic but can cause bacteremia in immunocompromised indv's

- facultative anaerobe; prod polysaccharides in sucrose-rich envs

Streptococcus pneumoniae

- +ve lancet-shaped cocci

- facultative anaerobe

- causes CAP; also ass w/ meningitis & otitis media

- virulence factors: polysaccharide capsule, pneumolysin

- alpha-hemolysis on blood agar (green discoloration)

- +ve bile solubility test

Streptococcus oralis

- +ve cocci

- associated w/ biofilm formation and mild infections.

- can contribute to endocarditis following dental procedures

- optochin-resistant, alpha-hemolytic on blood agar

Porphyromonas gingivalis

- -ve rod

- anaerobic

- periodontitis

- prod proteases (e.g., gingipains) that degrade host tissue

- black-pigmented colonies on blood agar (heme accumulation)

Prevotella intermedia

- -ve rod

- anaerobic

- found in perio pockets; associated w/ gingivitis & periodontitis.

- virulence incl proteolytic enzymes that degrade host tissues

- black-pigmented colonies on anaerobic blood agar

Lactobacillus spp.

- +ve rod

- facultative anaerobes

- found in OC & GIT; contributes to oral health

- rarely pathogenic but can cause bacteremia in immunocompromised pts

- prod lactic acid; catalase -ve

Mycobacterium tuberculosis

- +ve (acid-fast) bacilli

- aerobic

- causes chronic pneumonia; hallmark is granuloma formation in lungs.

- ZN stain

- grows on Lowenstein-Jensen agar (slow-growing)

Chlamydia pnemoniae

- -ve coccoid

- obligate intracellular pathogen

- causes atypical pneumonia, pharyngitis, & bronchitis

- associated w/ gradual onset and&prolonged cough.

- req cell culture for growth (unable to grow on standard media)

- detected using PCR or serology

Enterococcus faecalis

- +ve cocci

- facultative anaerobe

- causes root canal infections, UTI & endocarditis (secondary endodontic)

- known for high AB resistance (e.g., vancomycin-resistant enterococci, VRE).

- grows in 6.5% NaCl

- bile-esculin +ve (blackening of media)

Helicobacter pylori

- -ve spiral

- microaerophilic.

- causes peptic ulcers, gastritis, & gastric cancer

- virulence factors: urease, cytotoxins.

- urease test +ve (biopsy or breath test)

- grows on Skirrow agar

Treponema pallidum

- -ve spirochete

- causes syphilis, characterised by primary (chancre), secondary (rash), & tertiary (gummas) stages

- cannot be cultured in vitro.

- detected by DFM or serologic tests

Fusobacterium nucleatum

- -ve spindle

- anaerobe

- gingivitis, periodontitis, & dental abscesses

- forms biofilms & promotes coaggregation w/ other oral pathogens

- sensitive to kanamycin in culture

Bordatella pertussis

- -ve coccobacillus

- aerobic

- causes whooping cough

- virulence factors: pertussis toxin, tracheal cytotocin

- grows on Bordet-Gengou or Regan-Lowe agar

- PCR-based diag

Aggregatibacter actinomycetemcomitans

- -ve coccobacillus

- facultative anaerobe

- key pathogen in aggressive periodontitis

- prod leukotoxin & endotoxin.

- star-shaped colonies on agar

- catalase +ve

Tannerella forsythia

- -ve rod-shaped

- anaerobe, non-motile

- often found in conjunction w/ other pathogens in periodontitis.

- prod enzymes (e.g., sialidases) that degrade host tissues.

- identified through molecular methods (e.g., PCR)

Veillonella

- -ve cocci

- anaerobic

- associated w/ dental plaque & gingival health, as they metabolise lactate

- grows on anaerobic media

- does not ferment carbohydrates (uses lactate)

Actinomyces israelii

- +ve filaementous

- anaerobe

- causes actinomycosis, leading to lumpy jaw or chronic oral abscesses w/ S granules

- slow-growing colonies resembling "molar tooth" on agar

Haemophilus influenzae

- -ve coccobacillus

- facultative anaerobe

- causes CAP, esp in indv's w/ COPD or after viral infections.

Type b (Hib) strains cause more severe infections.

- req X (hemin) & V (NAD) factors for growth

- satellite phenomenon when grown near S. aureus

Staphylococcus aureus

- +ve cocci

- facultative anaerobe

- causes HAP & CAP; associated w/ necrotising pneumonia.

- catalase +ve, coagulase +ve

- beta-hemolysis on blood agar.

Mycoplasma pneumoniae

- -ve spindle pleomorphic

- lacks cw (not visible on Gram stain)

- causes "walking pneumonia," more common in younger pts, atypical pneumonia

- virulence factor: P1 adhesin.

- +ve cold agglutinin test

- req specialised media (e.g., Eaton's agar)

Legionella spp.

- -ve rod

- facultative intracellular

- causes Legionnaires’ disease (severe pneumonia) & Pontiac fever

- acquired via contaminated water systems (e.g., air conditioners)

- req buffered charcoal yeast extract (BCYE) agar

- +ve urinary antigen test for serogroup 1

Pseudomonas aeruginosa

- -ve rod

- aerobic, motile

- causes HAP, esp in immunocompromised or CF pts

- produces a characteristic green pigment (pyocyanin)

- oxidase +ve

- grows on MacConkey agar w/out lactose fermentation