19.1Medically Important Gram-Positive Bacilli

Chapter Outline

19.1Medically Important Gram-Positive Bacilli

A. Twelve or so genera

B. Differentiated by

1. Endospore formation

2. Acid-fastness

3. Cell morphology

19.2Gram-Positive Spore-Forming Bacilli

A. General Characteristics of the Genus Bacillus-aerobic, spore-forming rods

1. Bacillus anthracis

a. Cutaneous anthrax

b. Pulmonary anthrax

c. Gastrointestinal anthrax

d. Treatment and prevention

i. Biothrax- vaccine

ii. Antibacterial therapy: penicillin, tetracycline, or ciprofloxacin

2. Bacillus cereus

B. The Genus Clostridium

1. Anaerobic, exotoxins that are tissue specific

2. Clostridium perfringens

a. Gas gangrene/Myonecrosis

b. Pathology

c. Treatment and prevention of gangrene

i. Debridement

ii. Penicillin or cefoxitin

iii. Hyperbaric oxygen therapy

3. Clostridium difficile-Associated Disease (CDAD)

a. Antibiotic-associated (pseudomembranous) colitis

4. Clostridium tetani tetanus or lockjaw

a. Tetanospasmin toxin- spastic paralysis

b. Treatment

i. Human tetanus immunoglobulin (TIG)

ii. Penicillin or tetracycline

iii. Muscle relaxants

c. Prevention

i. DTaP vaccine

5. Clostridium botulinum- food poisoning

a.Pathogenesis

i. Botulin toxin-flaccid paralysis

b. Infant and wound botulism

c. Treatment and prevention of botulism

i. Trivalent horse antitoxins

ii. Proper food handling and preparation

19.3Gram-Positive Regular Non-Spore-Forming Bacilli

A. Listeria monocytogenes

1. Epidemiology-contaminated meat and dairy products

2. Pathology of listeriosis

3. Diagnosis and control of listeriosis

B. Erysipelothrix rhusiopathiae-

1. Epidemiology- zoonotic pathogen-swine

2. Pathogenesis

3. Treatment and control

19.4Gram-Positive Irregular Non-Spore-Forming Bacilli

A. Corynebacterium diphtheriae

1. Epidemiology of diphtheria

2. Pathology of diphtheria

a. Local infection-pseudomembrane

b. Toxin production- diphtherotoxin

i. Target organs- heart and nerves

3. Diagnostic methods for Corynebacterium

a. Alkaline methylene blue stain

b. Elek Test

4. Treatment and prevention of diphtheria

a. Diphtheria antitoxin

b. DTaP Vaccine

B. The Genus Propionibacterium

1. Propionibacterium acnes- aerotolerant or anaerobic and nontoxigenic

19.5Mycobacteria: Acid-Fast Bacilli

A. Mycobacterium tuberculosis- acid fast, large amount of mycolic acid and wax in cell wall, strict aerobes

1. Epidemiology and transmission of tuberculosis

2. Pathology

a. Initial infection and primary tuberculosis

i. Tubercle formation

b. Latent and recurrent/reactivated tuberculosis

i. Months or years later

ii. More severe symptoms

iii. Extrapulmonary tuberculosis-spreads to other tissues/organs

3. Clinical methods of detecting tuberculosis

a. Mantoux Test-inject PPD and wait for 48-72 hours and size of induration

b. Roentgenography ( Chest X-rays)-

i. Suggestive

ii Can correct false positives by Mantoux

iii. Used for comparative studies between older infections and newly activated disease

c. Acid-fast staining or fluorescent staining

d. Laboratory cultivation- slow and laborious

e. Genetic testing( PCR) for rapid identification to initialize treatment

4. Management and prevention of tuberculosis

a. Antimicrobial combination therapy for 6-24 months

b. Early stage treatment, high-risk groups

c. Resistant strains exist world-wide

d. Vaccine (BCG)-only those who may be exposed to carriers

B. Mycobacterium leprae-slowest growing of all Mycobacterium species

1. Epidemiology and transmission of leprosy

2. The course of infection and disease

a. Tuberculoid leprosy

b. Lepromatous leprosy

3. Diagnosing leprosy

a. Symptoms and signs ( characteristics of lesions)

b. Patient history

c. Feather test

d. Acid fast bacilli in lesions

4. Treatment and prevention of leprosy

a. Antimicrobial drugs- in early stages of disease

b. Treatment of contacts

c. Isolation of patients

C. Infections by Nontuberculous Mycobacteria (NTM)

1. Disseminated mycobacterial infections in AIDS

2. Nontuberculous lung disease

3. Miscellaneous Mycobacterial infections

19.6Actinomycetes: Filamentous Bacilli

A. Actinomycosis

1. Actinomyces israelii-oral cavity and intestinal infections

B. Nocardiosis

1. Nocardia brasiliensis- pulmonary disease that progresses to cutaneous nodules