Aerobic

• Aerobic Gram-Positive Bacilli


  • Non-Spore-Forming, Nonbranching Catalase-Positive Bacilli
  • Non-Spore-Forming, Nonbranching Catalase-Negative Bacilli
  • Non-Spore-Forming, Branching Aerobic Actinomycetes
  • Spore-Forming, Nonbranching Catalase-Positive Bacilli

  
• Non-Spore-Forming, Nonbranching Catalase-Positive Bacilli

  • Corynebacterium
  • Rothia
  • Undesignated CDC Coryneform Groups
  • Listeria monocytogenes
• Corynebacterium


  • Normal biota on skin and mucous membranes
  • Cell walls contain meso-diaminopimelic acid (m-DAP) and mycolic acids
  • Catalase-positive
  • Nonmotile
  • Nonlipophilic species

  
• Corynebacterium


  Slightly curved, gram-positive rods with unparallel sides and slightly wider ends ("club shape" or coryneform)

  
• Disease caused by C. diphtheriae is referred to as diphtheria
• Other Corynebacterium species that produce disease in humans

  • C. bovis
  • C. ulcerans
  • C. xerosis
  • C. jeikeium
  • C. pseudodiphtheriticum
  • C. pseudotuberculosis
• Corynebacterium diphtheriae


  • Diphtheria toxin is the major virulence factor
  • Produced by strains infected with a lysogenic phage carrying the tox gene
  • Potent and lethal
  • Blocks protein synthesis
  • Nontoxic until exposed to trypsin
  • Fragment A: cytotoxicity
  • Fragment B: mediates entry of fragments
• Two forms of Corynebacterium diphtheriae disease

  • Respiratory Diphtheria
  • Cutaneous Diphtheria
• Respiratory Diphtheria


  • Spread by droplet or hand-to-mouth contact
  • Most common site: tonsil or pharynx
  • Cell necrosis + exudate = tough gray to white pseudomembrane
  • Potential for suffocation
  • Can produce systemic effects
• Cutaneous Diphtheria


  • Consists of nonhealing ulcers with a dirty gray membrane
  • Treatment: Anti-toxin
  • Drug of choice: Penicillin or erythromycin
• Corynebacterium diphtheriae microscopy


  • Highly pleomorphic gram-positive bacillus that appears in palisades or as individual cells lying at sharp angles to another in V and L formations
  • Club-shaped swellings and beaded forms are common
  • Metachromatic areas: Babѐs-Ernst granules (accumulation of polymerized polyphosphates)

  
• Corynebacterium diphtheriae culture characteristics

  • Facultative anaerobe
  • Requires eight essential amino acids
  • Better growth is observed on a medium containing blood or serum such as Loeffler serum or Pai agars
  • On SBA, organisms may have a very small zone of β-hemolysis

  
• Cystine-tellurite blood agar (CTBA)

  • Modification of Tinsdale medium
  • Contains sheep RBCs, bovine serum, cystine, and potassium tellurite
  • Both selective and differential
  • Potassium tellurite inhibits non-coryneform bacteria
  • Corynebacteria form black or brownish colonies
  • A brown halo surrounding the colony, due to cystinase activity, is a differentiating feature
• Corynebacterium diphtheriae identification


  • Catalase positive
  • Nonmotile
  • CTBA medium
  • Urease (-)

  
• Elek test


  • In vitro diphtheria toxin detection procedure
  • Immunodiffusion test
• Corynebacterium jeikeium


  • Most common cause of diphtheroid prosthetic valve endocarditis in adults
  • Lipophilic
  • Strict aerobe
  • Non-hemolytic
  • Urease positive
  • Reduces nitrate
  • Drug of choice: Vancomycin
• Corynebacterium pseudodiphtheriticum


  • Nasopharynx normal flora
  • Respiratory tract infections in immunocompromised individuals
  • Does not show pleomorphic morphology
• Corynebacterium pseudotuberculosis


  • Veterinary pathogen
  • Human infections associated with contact with sheep
  • Causes granulomatous lymphadenitis
  • Produces dermonecrotic toxin
  • Brown halo on CTBA
  • On SBA, forms small yellowish-white colonies
• Corynebacterium striatum


  • Nonlipophilic and pleomorphic
  • Produces small, shiny, convex colonies
  • Resistant to penicillins
• Corynebacterium ulcerans


  • Veterinary pathogen
  • Mastitis in cattle
  • Contact with animals or ingestion of unpasteurized dairy products
  • Isolated from skin ulcers and exudative pharyngitis
  • Brown halo on CTBA
• Corynebacterium urealyticum


  • One of the most frequently isolated
  • Urinary pathogen
  • Urine isolates with pinpoint, nonhemolytic, white colonies that have characteristic diphtheroid morphology
  • Lipophilic
  • Strict aerobe
  • Rapidly urease positive
  • Drug of choice: Vancomycin
• Corynebacterium xerosis


  • Grows well on SBA and forms dry, pigmented (yellow to tan) colonies
• Rothia


  • Normal human oropharyngeal microbiota
  • Rothia dentocariosa: Found in saliva and supragingival plaque, resembles coryneform bacteria (short gram + bacilli) but also those of facultative actinomycetes (branching filaments), Nitrate +, Nonmotile, Esculin hydrolysis +, Urease negative
• Listeria monocytogenes


  • Important human pathogen
  • L. ivanovii - animal pathogen
  • Recovered from animal products such as raw milk, cheese, poultry, processed meats
  • Also isolated from crustaceans, flies, and ticks
  • Causes serious infection of neonates, pregnant women, elderly, and immunocompromised hosts
• Listeria monocytogenes virulence factors

  • Hemolysin (listeriolysin O)
  • Catalase
  • Superoxide dismutase
  • Phospholipase C
  • Surface protein (p60)
• Listeria monocytogenes disease in

  • Pregnant women
  • Newborns
  • Immunosuppressed host
• Listeria monocytogenes disease in pregnant women

  • Most commonly seen during third trimester
  • Responsible for spontaneous abortion and stillborn neonates
• Listeria monocytogenes disease in newborns

  • Early-onset: Results from intrauterine infection, Sepsis
  • Late-onset: Days to weeks after birth, Meningitis
• Listeria monocytogenes disease in immunosuppressed host

  • Most common manifestations are CNS infection and endocarditis
  • Infection of healthy individuals may occur through the intestinal tract when eating contaminated food
  • Preferred drug: Ampicillin
• Listeria monocytogenes microscopy


  • Gram-positive coccobacillus
  • Arranged singly, in short chains, or in palisades
• Listeria monocytogenes culture characteristics

  • Grows well on SBA and chocolate agar
  • Prefers slightly increased CO2 tension
  • Colonies are small, round, smooth, and translucent
  • Surrounded by a narrow zone of β-hemolysis
  • Resembles S. agalactiae
  • Optimal growth temp: 30°-35°C
  • Growth occurs over a wide range (0.5° to 45°C)
  • Cold enrichment technique (4°C)
• Listeria monocytogenes identification


  • Catalase (+)
  • Motile at room temp.
  • Wet mount preparation: Tumbling (end-over-end motility)
  • Motility medium: Characteristic "umbrella" pattern at room temp.
  • Hippurate hydrolysis (+)
  • Bile esculin hydrolysis (+)
  • CAMP (+), more pronounced when Rhodococcus equi is used, "Block" type hemolysis
• Non-Spore-Forming, Nonbranching Catalase-Negative Bacilli

  • Erysipelothrix rhusiopathiae
  • Arcanobacterium
  • Gardnerella vaginalis
• Erysipelothrix rhusiopathiae


  • Gram-positive
  • Catalase negative
  • Non-spore-forming
  • Pleomorphic
  • Has the tendency to form long filaments
  • Human cases result from occupational exposure (handling fish and animal products)
  • Route of infection: Cuts or scratches on the skin
  • Resistant to salting, pickling, and smoking
• Three types of Erysipelothrix rhusiopathiae disease in humans

  • Erysipeloid (localized skin disease)
  • Septicemia (often associated with endocarditis)
  • Generalized, diffuse cutaneous infection
• Erysipeloid


  • Most common infection
  • Resembles streptococcal erysipelas
  • Lesions are seen on the hands and fingers
  • Painful and swollen
  • Characteristic lesion: Sharply defined, slightly elevated, purplish-red zone

  
• Erysipelothrix rhusiopathiae microscopy


  • Thin, rod-shaped, gram-positive organism that may form long filaments
  • Arranged singly, in short chains, or in a V shape
  • Decolorizes easily (gram-variable)
• Erysipelothrix rhusiopathiae culture characteristics

  • Specimens: Tissue biopsy or aspirates from skin lesions
  • Inoculate to a nutrient broth with 1% glucose and incubate in 5% CO2 at 35°C
  • SBA: Colonies are nonhemolytic and pinpoint
  • After 48 hours incubation, two distinct colony types are seen: smaller, smooth form and larger, rough colonies
  • α-hemolytic after few days of growth
• Erysipelothrix rhusiopathiae identification


  • Catalase-negative
  • Nonmotile
  • Pleomorphic
  • Aerobic or facultatively anaerobic
  • H2S (+)
  • Urease (-), VP (-), Esculin hydrolysis (-)
  • Growth in gelatin stab: "Test tube brush-like" pattern at 22°C
• Arcanobacterium


  • Three medically important species: A. haemolyticum, A. pyogenes, A. bernardiae
  • All three are catalase negative