Download Gram Positive Bacilli

Gram-positive Bacilli
Ken B, Waites, M.D. F(AAM)
Professor of Pathology
Director of Clinical Microbiology
Objectives
• To review and discuss:
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microbiological characteristics
epidemiology
virulence factors
associated diseases
laboratory detection
of clinically important gram-positive bacilli.
Organism groups to be discussed include:
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Bacillus
Listeria
Erysipelothrix
Corynebacterium
Rhodococcus
Nocardia
Tropheryma
Bacillus
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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
• Thick walled structures formed by vegetative cells
• Resistant to radiation, chemicals, heat,
desiccation (dipicolinic acid)
• Steam autoclaving necessary for destruction
Bacillus: Clinical Significance
• Common environmental commensals
• Occasional opportunistic pathogens &
culture contaminants
• B. cereus group
• B. anthracis
• Others
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
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Rare in US due to control in animals
Enzootic in middle east
Transmitted by contact with animal products
eschar
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
Gram stain with spores
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-1beta, kills infected cells
Anthrax Vaccine
• Made from avirulent,
nonencapsulated B. anthracis strain
• Requires series of injections and
annual boosters
• Used in military
Listeria monocytogenes
•Gram-positive
bacilli/coccobacilli
•Catalase-positive
•Motile
•Esculin positive
• hemolytic
•Multiplies at 4 o C
Umbrella
motility
• 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
• Organism adapted to grow at low
temperatures
• Multiplies in cytoplasm of macrophages
and epithelial cells
• Listeriolysin O (hemolysin)
• Asymptomatic carriage reservoir
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
• Gram-positive, catalase-positive rods
• Occur in soil and decaying vegetation
+ mycolic acid
Mycobacterium
Corynebacterium
- mycolic acid
Nocardia
Streptomyces
Rhodococcus
Tropheryma
Others
Corynebacterium
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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)
• 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
• 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
• Epidemiology
– Ubiquitous in environment
• Inhalation
• Cutameous inoculation
• Pathogenesis
Filamentous gram-positive bacilli
– Cord factor – prevents
phagolysosome fusion &
intracellular killing in
phagocytes
– Catalase
– Superoxide dismutase
Partial Acidfast Smear
Nocardia Diseases
• Opportunist (HIV, Malignancy)
– Pneumonia
– Lung Abscess
– Brain Abscess/Meningitis
– Cellulitis/ulceration
– Mycetoma
Suppurative granulomas
Fibrosis
Necrosis
Sinus tracts
Nocardia
6 year-old boy with HIV with 2-month-history of fever & cough.
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
• 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
• 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