Fastidious Gram (-) Rods

Gardnerella vaginalis, Bordetella pertussis, Haemophilus influenzae, Legionella pneumophila, Mycoplasma and Ureaplasma, Spirillaceae, Actinobacillus, Eikenella, Capnocytophaga, Cardiobacterium

• Mouth flora

• Pathogenic in immunocompromised hosts; causes:

  • Peridontal and jaw abscesses

  • Bacterial vaginosis

  • Bacteremia

• Grow slowly and require 5-10% CO₂; NO growth on MAC

Fastidious Gram Neg Rods

• Bacterial vaginosis

• “Clue cells” - high number of squamous epithelial cells colonized with gram variable rods

• 10% KOH added to discharge causes “fishy” odor

• Tiny colonies at 48 hrs on BAP and chocolate

• Catalase and oxidase negative; hippurate and starch positive

Gardnerella vaginosis

• Gram negative coccobacilli; causes “whooping cough”

• Require special media

  • Classic = Bordet-Gengou (potato infusion with glycerol and 20% SRB’s) and penicillin

  • Regan and Lowe (oxoid charcoal agar, 10% horse blood, cephalexin); longer shelf life

  • Old method for collection - cough plate; better to collect NP swab and plate directly; fluorescent antibody technique more rapid

• Colony

  • Incubate 72-96 hrs, 35^oC

  • Pinpoint, “mercury droplet” colonies

Bordetella pertussis

• Small, non-motile gram negative rod

• Requires growth factors

  • X factor = hemin

  • V factor = NAD

  • Both factors fond in blood, but need heat to break down red cells and release factors, so chocolate used

Haemophilus influenzae

Infections of Haemophilus influenzae

• Meningitis -

  • 2-4 years

  • Preceded by nasopharyngeal colonization and bacteremia

• Epiglottis

  • Ages up to 2 years; do NOT collect throat culture (blood culture best)

  • May require intubation

• Pneumonia <5 years, >60 years

• Conjuctivitis (“pink eye”)

  • Very contagious

• Chancroid

  • Painful genital ulcers or soft chancres

  • Gram stain of drainage shows tiny gram negative coccobacilli with a “school of fish” arrangement

• Growth only on chocolate, not BAP (unless mixed with S. aureus)

• Use X and V discs on Mueller-Hinton agar to detect growth requirements

• Susceptibility zone interpretations from conventional K - B zones

• Perform beta lactamase to determine sensitivity to ampicillin; cefuroxime, ceftriaxone, cefotaxime

Characteristics of H. infleunzae

• Legionnaires’ disease - severe pneumonia; Pontiac fever = milder form

• 75% illness due to this organism’s subgroups 1 and 6

• Sources - Potable water, faulty air conditioner vents, lakes and ponds

Legionella pneumophila

How to identify Legionella pneumophila?

• Specimen - sputum, bronchial washing, pleural fluid, lung aspirate or biopsy

• Growth on BYCE (buffered charcoal yeast extract) with or without antibiotics but not on chocolate or blood

• Direct exam - Giemsa and Gram stain with basic fushsin counter stain

• Smallest free-living microorganisms (125-250nm)

• Lack cell wall (bound by single triple layered membrane)

• Does not stain with Gram’s stain; can use Dienes stain

• Center of colony grows into special media (contains sterols) giving appearance of inverted “fried egg”

Mycoplasma and Ureaplasma

• Primary atypical pneumonia or “walking” pneumonia

• Causes positive cold agglutinin titer (>1:32); false positive RPR

• Treat with erythromycin or tetracycline

M. pneumoniae

• Non-gonococal, non-chlamydial urethritis, especially in males

• Produces urease

• Treat with tetracycline or spectinomycin

Ureaplasma urealyticum

• May colonize GU tract; post partum fever

• Tetracycline; resistant to erythromycin (all other organism are sensitive)

M. hominis

Rigid, helically curved rods with one of more turns; corkscrew motility by polar flagella; gram negative

Spirillaceae

• “Rat bite” fever

• Visualize by darkfield or stain with Giemsa

• 2-3 spirals and bipolar polytrichous tufts of flagella

• No growth on artificial media

Spirillum minor

“Clue” cells; 10% KOH added to discharge = “Fishy” odor

Gardnerella vaginalis

Bordet-Gengou media; NP Swab and plate directly

Bordetella pertussis

Require X and V factor

Haemophilus

No growth routine media

Legionella pneumophilia

Dienes stain NOT Gram stain

Mycoplasma/Ureaplasma