Gram Negative Organisms: Neisseria Species

Gram-Negative Organisms

Diplococci

Neisseria species

• Aerobic, Gram-negative, nonmotile, kidney bean-shaped diplococci
• Oxidase test positive
• Oxidize carbohydrates
• Culture: Thayer-Martin/Modified Thayer-Martin on Mueller-Hinton Agar with 5% chocolate sheep blood
• Antibiotics: Colistin (inhibits growth of other Gram-negative bacteria except Neisseria), Vancomycin (inhibits Gram-positive), and Nystatin (inhibits yeast)

Neisseria gonorrhea

• Small, mucoid, oxidase-positive colonies
• Ferments glucose only
• Culture Appearance: "Opaque Colonies" (specimen from symptomatic male), "Transparent Colonies" (specimen from asymptomatic male)
• Habitat: human genital tract
• Transmission: sexual contact or during passage through birth canal
• Specimens: urethra, cervix, rectum, conjunctiva, throat, synovial fluid
• Gram stain: many diplococci within PMNS (presumptive diagnosis)
• Gold standard test: Nucleic Acid Amplification Tests (NAATs)

Spectrum of Disease

• Gonococcal urethritis: urethritis and epididymitis in men
• Ophthalmia neonatorum: purulent conjunctivitis in newborns
• Cervical gonorrhea: can progress to pelvic inflammatory disease

Neisseria meningitidis

• Encapsulated with large polysaccharide capsule
• Ferments glucose and maltose
• Oxidase-positive colonies on chocolate agar
• Habitat: URT
• Transmission: via respiratory droplets
• High carriage rate in close quarters (dormitories, camps, travel)

Spectrum of Disease

• Meningitis: most common cause among 2-18 years old
• Meningococcemia: meningococci disseminates into the bloodstream, multiorgan disease, consumptive coagulopathy, petechial or purpuric rash (purpura fulminans)
• Waterhouse-Friderichsen Syndrome: most severe form of meningococcemia, high fever, shock, widespread purpura, disseminated intravascular coagulation, thrombocytopenia, adrenal insufficiency

Coccobacilli

Haemophilus influenzae

• Found in the upper respiratory tract
• Non-motile, small Gram-negative (coccobacillary) rods
• Fastidious organism
• Flat, grayish, translucent colonies on chocolate agar
• Satellite phenomenon around S. aureus colonies
• Hemolysis by S. aureus liberates factor V needed by H. influenzae
• Positive quellung test

Quellung Test

• A biochemical reaction in which antibodies bind to a bacterial capsule, allowing species with a positive Quellung reaction to be visualized under a microscope.

Diagnosis

• Requires factor X (hemin) and V (NAD) for growth
• X -- hemin
• V - NAD (can be replaced by nicotinamide adenine dinucleotide)
• Grown on IsoVitaleX-enriched chocolate agar
• Satellite phenomenon: grows around colonies of Staphylococci

Spectrum of Disease

• Sinusitis, otitis media, pneumonia
• Meningitis
• Epiglottitis
• COPD exacerbations

Haemophilus ducreyi

• Small Gram-negative rods in strands
• Requires X factor but not V factor
• Causes chancroid

Bordetella pertussis

• Minute, Gram-negative coccobacilli resembling H. influenza
• Bordet-Gengou agar or Regan-Lowe charcoal medium
• Habitat: URT
• Transmission: via respiratory droplets
• Spectrum of Disease: pertussis (hacking coughs accompanied by production of copious amounts of mucus, that end with an inspiratory "whoop")

Bacilli

Pseudomonas aeruginosa

• Obligate aerobe
• Oxidase-positive, non-lactose-fermenter
• Culture: grown on Cetrimide agar
• Greenish, metallic colonies on blood agar
• Produces pyocyanin, pyoverdin
• Sweet grape-like odor
• Habitat: environmental water sources (e.g., humidifiers)
• Inhabits skin, URT, and colon of people
• Transmission: via water aerosoles, aspiration, fecal contamination
• Spectrum of Disease:
  • Skin and Soft Tissue Infections: burn wound infections, hot tub folliculitis, green nail syndrome
  • Ear Infections: otitis externa, swimmer's ear, chronic suppurative otitis media
  • Pneumonia: ventilator-acquired pneumonia, high-risk CAP in immunocompromised
  • Urinary Tract Infection: one of the most common causes of nosocomial UTIs

Salmonella spp.

• Facultative anaerobes
• Non-lactose-fermenting
• Produces H2S
• Motile
• Widal test detects antibodies in patient's serum
• Cultured in XLD medium
• Habitat: human colon (S. typhi), enteric tract of humans and animals (S. enteritidis)
• Transmission: via fecal-oral route
• Spectrum of Disease:
  • Enterocolitis: nausea and vomiting, then progresses to abdominal pain and non-bloody diarrhea
  • Typhoid fever

Shigella spp.

• Slender, non-motile Gram-negative rods
• Facultative anaerobes
• Oxidase-negative
• Non-lactose-fermenter
• H2S non-producer
• Culture medium: XLD
• Convex, circular, transparent colonies with intact edges
• Spectrum of Disease: enterocolitis

Proteus Mirabilis

• Facultative anaerobic gram-negative rods
• Non-lactose-fermenting
• Urease-positive
• Swarming motility
• Wave-like pattern extending from the point of inoculation
• Spectrum of Disease: complicated UTI, UTI associated with nephrolithiasis

Escherichia coli

• Facultative gram-negative rods
• Lactose-fermenting colonies on EMB or MacConkey agar
• Green metallic sheen on EMB agar
• Habitat: human colon
• Colonizes vagina and urethra
• Transmission: ascending infection in UTI, during birth in neonatal meningitis, fecal-oral route in diarrhea
• Spectrum of Disease:
  • UTI: most common cause
  • Intestinal infection: 4 strains (ETEC, EPEC, EHEC, EIEC)
  • Neonatal meningitis: 2nd most common cause
  • Hemolytic Uremic Syndrome: triad of hemolytic anemia, thrombocytopenia, and uremia
  • Pyogenic liver abscess

Klebsiella pneumoniae

• Urease positive
• Facultative, non-motile, gram-negative rods with large polysaccharide capsule
• Habitat: URT and GIT
• Transmission: aspiration/inhalation or ascending spread of fecal
• Spectrum of Disease:
  • Lobar Pneumonia
  • UTI

Campylobacter jejuni

• Comma- or S-shaped
• Microaerophilic
• Positive oxidase and catalase tests
• Grows well at 42°C on Skirrow agar
• Habitat: human and animal feces (cattle, chickens, and dogs)
• Transmission: via fecal-oral route
• Spectrum of Disease: one of the most common causes of bacterial gastroenteritis, watery, foul-smelling diarrhea followed by bloody stools accompanied by fever and severe abdominal pain
• Disease association: Guillain-Barré syndrome, reactive arthritis (Reiter syndrome)

Vibrio cholerae

• Comma-shaped gram-negative rods
• Motile
• Shooting star motility
• Oxidase-positive
• Ferments sucrose and mannose but not arabinose
• Spectrum of Disease: cholera, one of the most common causes of bacterial gastroenteritis