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Gram-positive Bacilli. Ken B, Waites, M.D. F(AAM) Professor of Pathology Director of Clinical Microbiology. Objectives. To review and discuss: microbiological characteristics epidemiology virulence factors associated diseases laboratory detection

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gram positive bacilli

Gram-positive Bacilli

Ken B, Waites, M.D. F(AAM)

Professor of Pathology

Director of Clinical Microbiology

objectives
Objectives
  • To review and discuss:
      • microbiological characteristics
      • epidemiology
      • virulence factors
      • associated diseases
      • laboratory detection

of clinically important gram-positive bacilli.

Organism groups to be discussed include:

    • Bacillus
    • Listeria
    • Erysipelothrix
    • Corynebacterium
    • Rhodococcus
    • Nocardia
    • Tropheryma
bacillus
Bacillus
  • Ubiquitous in soil worldwide
  • Endospore-forming
  • Aerobic/facultative anaerobic
  • Gram-positive bacilli
  • Can be gram-variable
  • Often  hemolytic & motile
    • (except B. anthracis)
  • Usually catalase positive

B. cereus - Gray, spreading

-hemolytic colonies

on SBA

bacillus endospores
Bacillus Endospores
  • Thick walled structures formed by vegetativecells
  • Resistant to radiation, chemicals, heat, desiccation  (dipicolinic acid)
  • Steam autoclaving necessary for destruction
bacillus clinical significance
Bacillus: Clinical Significance
  • Common environmental commensals
  • Occasional opportunistic pathogens & culture contaminants
  • B. cereus group
  • B. anthracis
  • Others
bacillus cereus group
Bacillus cereus Group
  • Gastroenteritis
    • Heat-stable enterotoxin (emetic form)
    • Heat-labile enterotoxin (diarrheal form)
      • Similar to V. cholera – stimulates cAMP watery diarrhea
      • Contaminated rice, meat, vegetables
  • Other Clinical conditions
    • Ocular infections after trauma
      • Necrotic toxin, hemolysin, phospholipase C
    • IV-catheter-related sepsis, endocarditis, meningitis
      • Immunocompromised persons and drug abusers
b anthracis anthrax
B. anthracis: Anthrax
  • Rare in US due to control in animals
  • Enzootic in middle east
  • Transmitted by contact with animal products
  • Spores remain infectious for years
  • Usually cutaneous inoculation - slow healing ulcer, bacilli spread to lymphatics and bloodstream
    • 20% mortality if untreated
    • Respiratory anthrax is usually fatal even if treated
    • GI anthrax also occurs in some Asian countries
  • Excellent biological warfare agent

eschar

Gram stain with spores

anthrax pathogenesis
Anthrax Pathogenesis
  • Poly-D-glutamic acid (protein) capsule – antiphagocytic
  • 3 component exotoxin
    • Protective antigen (PA) - binds to cells, forms channel that permits EF and LF to enter
    • Edema factor (EF) – adenyl cyclase causes fluid to accumulate at the site of infection and inhibit immune function
    • Lethal factor (LF)
    • disrupts cell's functions, stimulates TNF-alpha and IL-1-beta, kills infected cells
anthrax vaccine
Anthrax Vaccine
  • Made from avirulent, nonencapsulated B. anthracis strain
  • Requires series of injections and annual boosters
  • Used in military
listeria monocytogenes
Listeria monocytogenes
  • Gram-positive bacilli/coccobacilli
  • Catalase-positive
  • Motile
  • Esculin positive
  •  hemolytic
  • Multiplies at 4 o C

Umbrella motility

slide11
Habitat & Sources of Infection
    • Intestines of mammals, birds
    • Cheese, other dairy products
    • Vegetables
    • Undercooked meat
  • Epidemiology & Disease
    • Asymptomatic carriage
    • Meningitis/sepsis in immunocompromised host
    • Foodborne illness
    • Neonatal infections (transplacental)
listeria pathogenesis
Listeria: Pathogenesis
  • Organism adapted to grow at low temperatures
  • Multiplies in cytoplasm of macrophages and epithelial cells
  • Listeriolysin O (hemolysin)
  • Asymptomatic carriage reservoir
erisipelothrix rhusopathiae
Erisipelothrix rhusopathiae
  • Gram-positive bacillus
  • Common in animals
  • Transmitted to humans by skin wound
  • Occupational hazard in butchers, farmers, veterinarians
  • Self-limited skin lesions with erythema & eruption
  • May spread to bloodstream
aerobic actinomycetes
Aerobic Actinomycetes
  • Gram-positive, catalase-positive rods
  • Occur in soil and decaying vegetation

+ mycolic acid

- mycolic acid

Nocardia

Streptomyces

Rhodococcus

Tropheryma

Others

Mycobacterium

Corynebacterium

corynebacterium
Corynebacterium
  • Gram-positive, curved pleomorphic rods
  • “Chinese Letters”
  • Aerobic/facultatively anaerobic
  • Grow readily on Sheep blood agar
  • Catalase & oxidase positive
  • Usually non-motile
  • Commensals on skin
  • Some species pathogenic
diphtheria c diphtheriae
Diphtheria (C. diphtheriae)
  • Spreads by droplet
  • Phospholipase D increases vascular permeability & promotes spread
  • Phage-coded exotoxin (A&B subunits) acts on respiratory mucous membranes interfering with protein synthesis by inactivating EF-2
  • Pseudomembrane of fibrin, bacteria, epithelial & phagocytic cells impairs breathing
  • Toxin spreads to heart, CNS, & adrenals
  • Selective media (cysteine-tellurite)
  • Identify in Public Health Labs
  • Protect by toxoid vaccination - DaPT
  • < 5 cases/yr in US
other pathogenic corynebacteria
Other Pathogenic Corynebacteria
  • C. jeikeium (JK)
    • Opportunistic bloodstream infections in bone marrow transplant recipients
    • Multiple antibiotic resistance - except vancomycin and tetracycline
    • Commonly carried on skin of hospitalized persons
  • C. urealyticum
    • Occasional cause of UTI & stones (splits urea)
nocardia
Nocardia
  • Epidemiology
    • Ubiquitous in environment
      • Inhalation
      • Cutameous inoculation
  • Pathogenesis
    • Cord factor – prevents phagolysosome fusion & intracellular killing in phagocytes
    • Catalase
    • Superoxide dismutase

Filamentous gram-positive bacilli

Partial Acidfast Smear

nocardia diseases
Nocardia Diseases
  • Opportunist (HIV, Malignancy)
    • Pneumonia
    • Lung Abscess
    • Brain Abscess/Meningitis
    • Cellulitis/ulceration
    • Mycetoma

Suppurative granulomas

Fibrosis

Necrosis

Sinus tracts

nocardia1
Nocardia

6 year-old boy with HIV with 2-month-history of fever & cough.

nocardia lab diagnosis
Nocardia Lab Diagnosis
  • Stained smears
  • Culture - slow growth ~ 7 days in 5% CO2
  • Several species associated with human disease
  • Identify by PCR

Nocardia colonies

Middlebook 7H11 agar

Aerial hyphae

rhodococcus equi
Rhodococcus equi
  • Gram-positive weakly acidfast bacilli that sometimes revert to coccoid forms
  • Common in animals & environment
  • Opportunistic lung infections in AIDS & transplant patients
  • Facultative intracellular pathogen that survives in macrophages, leading to granuloma & abscess

Slow-growing, mucoid salmon-colored colonies of R. equi on chocolate agar

tropheryma whippeli
Tropheryma whippeli
  • Actinomycete etiologic agent of Whipple’s Disease – a malabsorptioin syndrome affecting the small bowel
  • Organism cannot be cultured except in tissue culture
  • Diagnose by histopathology & PCR