Gram (+) Rods

• Corynebacteria:

  • Small, slender, pleomorphic rods that stain unevenly
  • Non-motile
  • Unencapsulated
  • Do not form spores
• Corynebacterium diphtheriae Epidemiology:

  • Found in the throat and nasopharynx of carriers and in patients with diphtheria
  • Local infection, usually of the throat, spread by respiratory droplets
• Corynebacterium diphtheriae Pathogenesis:

  • Caused by a single exotoxin inhibiting eukaryotic protein synthesis
  • Toxin composed of two fragments, A and B
  • Toxin is a heat-labile polypeptide
• Corynebacterium diphtheriae Clinical Significance:

  • Upper Respiratory Tract Infection (URTI) symptoms
  • Cardiac conduction defects, myocarditis, neuritis of cranial nerves
  • Cutaneous diphtheria symptoms
• Corynebacterium diphtheriae Immunity:

  • Vaccine (formalin treated toxin)
  • DTaP @ infancy with 10-yr interval booster doses
• Corynebacterium diphtheriae Treatment:

  • Single dose of horse serum antitoxin
  • Erythromycin or Penicillin to prevent further toxin production
• Bacillus anthracis:

  • Form endospores
  • Strict aerobes or aerotolerant anaerobes
  • Most found in soil & water
• Bacillus anthracis Epidemiology:

  • Enzootic disease transmitted to humans by contact with infected animal products or contaminated dust
  • Spores may remain viable for many years
  • Potential bioterrorism agent
• Bacillus anthracis Pathogenesis:

  • Unique capsule comprised of poly-D-glutamic acid
  • 2 plasmid-coded exotoxins: edema toxin and lethal toxin
  • Edema factor causes severe edema, Lethal factor causes tissue necrosis
• Bacillus anthracis Clinical Significance:

  • Cutaneous anthrax symptoms and treatment
  • Pulmonary anthrax symptoms and treatment
• Bacillus anthracis Prevention:

  • Vaccine for high-risk workers
  • Post-exposure prophylaxis with Ciprofloxacin or Doxycycline
• Listeria monocytogenes:

  • Slender, short rods
  • Do not form spores
  • Catalase (+)
• Listeria monocytogenes Epidemiology:

  • Infections are usually foodborne
  • Most common in pregnant women, fetuses, newborns, and immunocompromised individuals
• Listeria monocytogenes Pathogenesis:

  • Organism attaches to and enters mammalian cells
  • Escapes phagocytic vacuole by listeriolysin O toxin
• Listeria monocytogenes Clinical Significance:

  • Listeriosis symptoms
  • Treatment with Ampicillin or Trimethoprim/Sulfamethoxazole
• Propionibacterium acnes:

  • Anaerobic or microaerophilic rods
  • Common inhabitants of normal skin
  • Causes acne
• Lactobacillus:

  • Part of the commensal flora of human mucous membranes
  • Produce lactic acid during fermentation
  • Acid production may play a role in dental caries
• Corynebacterium diphtheria

  Clinical significance type A

  URTI (upper respiratory tract infection) - thick, grayish, adherent exudate (pseudomembrane) - cell debris and inflammatory products in the throat - coats throat and may extend into nasal passages or respiratory tract, where exudate sometimes obstructs leading to suffocation - cardiac conduction defects & myocarditis leading to congestive heart failure - neuritis of cranial nerves & paralysis of palate or eye
• Corynebacterium diphtheria

  Clinical significance

  B. Cutaneous diphtheria - puncture wound or cut in the skin can result in introduction into the subcutaneous tissue - chronic, non-healing ulcer with a gray membrane
• Bacillus anthracis causes anthrax, a rare disease in the US
• From 1984 to 1997, only 3 cases of cutaneous anthrax were reported
• In 2001, 20 new cases of anthrax occurred, with 10 being cutaneous and 10 being inhalation cases
• Anthrax powder was sent through the mail
• Epidemiology of Bacillus anthracis:

  • Enzootic disease of worldwide occurrence
  • Domestic herbivores (sheep, goats, and horses) transmit the disease to humans through contact with infected animal products or contaminated dust
  • Disease is initiated by the subcutaneous inoculation of spores through incidental skin abrasions
  • Inhalation of spore-laden dust can cause a pulmonary form of anthrax
  • Spores can remain viable for many years in contaminated pastures, bones, wool, hair, hides, and other animal materials
  • Highly resistant to physical and chemical agents
• • Potential bioterrorism agent due to ease of growth in large quantities, resistance to destruction, and ability to be formulated into an aerosol for wide dissemination
• Unique capsule comprised of poly-D-glutamic acid and is antiphagocytic
• 2 plasmid-coded exotoxins: edema toxin and lethal toxin
• Both exotoxins are AB type toxins with Activity and Binding domains
• Binding subunit: protective antigen mediates cell entry of both toxins
• Activity subunits:

  • Edema factor causes severe edema
  • Lethal factor is responsible for tissue necrosis
• Lethal factor + protective antigen = lethal toxin
• Cutaneous anthrax:

  • 95% of human cases
  • Upon introduction of organisms or spores that germinate, a papule develops into a painless, black, severely swollen “malignant pustule,” which eventually crusts over
  • Organisms may invade regional lymph nodes and then the general circulation, leading to fatal septicemia
  • Treatment: Ciprofloxacin, Rifampicin, Clindamycin
• Pulmonary anthrax (woolsorter’s disease):

  • Caused by inhalation of spores
  • Progressive hemorrhagic lymphadenitis & hemorrhagic mediastinitis
  • Mortality rate of 100% if left untreated
  • Treatment: Ciprofloxacin, Rifampicin, Vancomycin
  • Vaccine recommended for workers in high-risk occupations
  • Post-exposure prophylaxis with Ciprofloxacin or Doxycycline
• Bacillus cereus - Uncommonly, other species of bacillus are implicated in opportunistic lesions, particularly following trauma or the placement of artificial devices and catheters - Causes food poisoning by means of enterotoxins with either emetic or diarrheal effects.
• Listeria characteristics:

  • Slender, short, with peritrichous flagella
  • Do not form spores
  • Sometimes occur as diplobacilli or in short chains, and may be seen within the cytoplasm of host cells in tissue samples
  • Catalase positive
  • Tumbling motility by light microscopy in liquid medium at 25°C
  • Non-motile at 37°C
  • Distinguished from Streptococcus (catalase negative) or Corynebacterium (non-motile) species
• Listeria monocytogenes epidemiology:

  • Only species that infects humans, while Listeria species are widespread among animals in nature
  • Infections may occur as sporadic cases or in small epidemics, usually food-borne (processed dairy products like ice cream and cheese, ground meats)
  • Most common in pregnant women, fetuses, newborns, and immunocompromised individuals (older adults and those receiving steroids)
• Listeria monocytogenes pathogenesis:

  • Organism attaches to and enters a variety of mammalian cells by normal phagocytosis
  • Once internalized, it escapes from the phagocytic vacuole by elaborating a membrane-damaging toxin called listeriolysin O
• Listeria monocytogenes

  Clinical significance: Listeriosis - Septicemia - Meningitis Treatment: - Ampicillin - Trimethoprim/Sulfamethoxazole - Prevention through proper food preparation and handling, as well as removal of contaminated products from the food supply
• Propionibacterium acnes - Anaerobic or microaerophilic rods of diphtheroid-like morphology - Common inhabitants of normal skin, and, in rare instances, have been reported as causes of endocarditis and infections of plastic implants - Acne
• Lactobacillus - Part of the commensal flora of human mucous membranes - Produce large quantities of lactic acid during fermentation and have been thought to assist in maintaining the acid pH of normal mucous epithelia - Acid production by oral lactobacilli may play a role in the progression of dental caries, especially in dentine