Chapter 19: Gram-Positive Bacilli

Division of gram positive bacilli

• Based of presence or absence of endospores and acid-fastness

• Groups

  • Endospore formers

  • Non-endospore formers

  • Irregular shaped and staining properties

Endospore

• A dense survival unit that develops in a vegetative cell in response to nutrient deprivation

• Resistant to heat, drying, radiation, and chemicals, factor for survival, longevity, ecological niche, and pathogenicity of spore formers

Genus bacillus

• Gram positive, endospore forming, motile rods

• Aerobic and catalase positive

• Saprobic; Degrades complex macromolecules

• Primarily habitat is soil

• 2 species of medical importance

Genus clostridium

• Gram positive, spore forming, rods

• Anaerobic and catalase negative

• Synthesizes organic acids, alcohols, and exotoxins

• Causes wound infections, tissue infections, and food intoxications

Bacillus anthracis

• Large block shaped angular, nonmotile rods

• Central spores develop under all conditions except in the living body

• Cause of anthrax

Anthrax

• A zoonotic disease of herbovorous livestock

• Majority of cases are reported in livestock from africa, asia, and the middle east

• Treated with antibiotics along with raxibacumab to bind to toxins and prevent entry to the cell

• Vaccines available for high risk occupations and military personel

Virulence factors of B. anthracis

• Polypeptide capsule

• Exotoxins

  • Edema

  • Cell death

Types of anthrax

• Cutaneous

• Pulmonary

• Gastrointestinal

Cutaneous anthrax

• Spores enter through the skin

• Black sore = eschar

• Least dangerous; recovery is possible

Pulmonary anthrax

• Woolsorter’s disease

  • Inhalation of spores from animal products or soil

Gastrointestinal anthrax

• Ingested spores

• Rare but lethal

Bacillus cereus

• Common airborne and dust borne pathogen

• Usual methods of disinfection and antisepsis are ineffective

• Grows in food and spores survive cooking and reheating

• Cause of one type of food poisoning

B. cereus food poisoning

• Ingestion of toxin containing food causes nausea, vomiting, abdominal cramps, and diarrhea

• 24 hour duration

• No treatment

Clostridium perfringens

• Most frequent clostridia involved in soft tissue and wound infections

• Found in GI tract of multiple sclerosis patients

• Found in soil, human skin, intestine, and vagina

Predisposing factors of C. perfringens

• Surgical incisions

• Compound fractures

• Diabetic ulcers

• Septic abortions

• Puncture wounds

• Gunshot wounds

Virulence factors of C. perfringens

• Alphatoxin

  • Causes RBC rupture, edema, and tissue destruction

• Collagenase

• Dnase

  • Degrades DNA

Gas gangrene

• Infection caused by C. perfringens

• Two forms

  • Anaerobic cellulitis

  • True myonecrosis

Anaerobic cellulitis

• One form of gas gangrene

• The bacteria spreads within damage necrotic muscle tissue, producing toxins and gas, but the infection remains localized

Myonecrosis

• One form of gas gangrene

• More distructive and extensive

• Mimics some aspects of necrotizing fasciitis

• Spore germination, vegetative growth, and release of virulence factors

• Fermentation of muscle carbohydrates results in the formation of gas and further tissue destruction

Treatment and prevention of gangrene

• Immediate cleansing of dirty wounds, deep wounds, compound fractures, and infected incisions

• Debridement of diseased tissue

• Large doses or cephalosporin or penicillin

• Hyperbaric oxygen therapy

  • To prevent growth of anerobic bacteria

Clostridium tetani

• Common resident of cultivated soil and animal GI tracts

• Requires anaerobic environment for fegitative cells to grow and release toxins

Tetanus

• AKA lockjaw

• Neuromuscular disease causing early effects on the jaw muscle

• Spores enter the body through accidental puncture wounds, burns, the umbilicus, frostbite, and crushed body parts

Neonatal tetanus

Tetanus in neonates in developing countries

Tetanospasmin

• Neurotoxin released by C. tetani causes paralysis by binding to motor nerve endings

• blocking the release of neurotransmitter for muscular contraction inhibition

• Muscles contract uncontrollably

• Death is most often caused due to paralysis of the respiratory muscles

Treatment and prevention of tetanus

• Treatment is aimed at detering toxemia and infection

• Antitoxin therapy with human tetanus immune globulin (TIG) innactivates the circulating toxin but does not counteract the already bound toxin

• Vaccines available and booster needed every 10 years - Dtap

Clostridium difficile

• A normal resident of the intestine in low numbers

• Produces enterotoxins that damage intestines

C-diff infection (CDI)

• Clostridial disease caused by C. difficile

• Second most common intestinal disease after salmonellosis in industrialized countries

• Major cause of diarrhea in hospitals

Antibiotic associated colitis

• Treatment with broadspectrum antibiotics kill the other bacteria found in the intestines, allowing C. difficile to overgrow

• Irritation of the large intestine caused by infection

• If the colon becomes inflammed, membrane like patches form

Pseudomembranes

• Membrane like patches

• Found in antibiotic associated colitis

Treatment and prevention of c-diff

• Mild cases

  • Fluid and electrolye replacement

• Severe cases

  • Vancomycin

  • Metronidazole

  • Replacement cultures

Botulism

• Intoxication associated with inadequate food preservation

• Potent toxin, botulinum toxin is released and carried to neuromuscular junctions and blocks the release of acetylcholine, necessary for muscle contractions

• Doubled or blurred vision

• Difficulty swallowing

• Neuromuscular symptoms

Clostridium botulinum

• Spore forming anaerobe

• Commonly inhabits soil and water

• Spores are present on food when gathered and processed

Infant botulism

• Ingested spores that geminate and release toxin

• Immature neonatal intestine and resident microbiota allows the spores to germinate and produce neurotoxins

• Results in flaccid paralysis of the baby (floppy baby syndrome)

Wound botulism

• Spores enter a wound and cause food poisoning symptoms

Clostridium species involved in food poisoning

• Clostridium botulinum

• Clostridium perfringens

Clostridium botulinum (food poisoning)

Rare but severe intoxication usually from home canned food

Clostridial gastroenteritis

• Caused by C. perfringens

• Spores contaminate food that has not been cooked thoroughly

• Mild intestinal illness

• Second most common food poisoning world wide

Listeria monocytogenes

• Non-spore forming gram positive

• 1-4 flagella and lack capsules

• Are resistant to cold, heat, salt, pH extremes, and bile

• Crosses the placenta

Virulence of listeria monocytogenes

• Ability to replicate in the cytoplasm of cells after inducing phagocytosis

• Avoids humeral immune system

Listeriosis

• Caused by contamination of foods and grows during refrigeration

• Most associated with dairy products, poultry, and meat

• Pregnany women avoid certain foods

Corynebacterium diphtheriae

• Straight or curved rod that tapers at the ends with many pleomorphic variants

• Cells can be side by side in a palisades arrangement

Diphtheria

• Infection caused by C. diptheriae

• Is acquired via respiratory droplets from carriers/infected individuals

• Two stages of the disease

  • Local infection

  • Diptherotoxin production and toxemia

Pleomorphic

Cells having variations in size and shape

Palisades arrangement

• Arrangement of cells where cells look like picket fence

• Vertical and next to each other

Local infection by C. diphtheriae

• First stage of diphtheria

• Upper respiratroy tract inflammation; primary infection

  • Sore throat, nausea, vomiting, swollen lymph nodes

  • Pseudomembranes can cause asphyxiation

• Cutaneous diphtheria; secondary infection

Primary infection of diphtheria

Upper respiratory tract infection

Secondary infection of diphtheria

Cutaneous diphtheria

Diphtherotoxin production and toxemia

• Second stage of diphtheria

• Targets the heart and nerves

Propionibacterium acnes

• aerotolerant/anaerobic and nontoxigenic

• Morphology similar to corynebacterium

• Common resident of pilosebaceous glands of human skin

• Causes acne

Mycobacteria

• Acid-fast

• Gram positive, irregular

• Strict aerobes

• Produce catalase

• No capsules, flagella, or spores

• Grow slowly

Mycobacterium tuberculosis

• Bacteria that causes tuberculosis

• Produces no exotoxins or enzymes for infectiousness

Virulence factors of mycobacterium tuberculosis

• Complex waxes

• Cord factor

• Prevent destruction by lysosomes or macrophages

Tubercle

• hard , round nodule or growth

• In initial TB infection, are granulomas consisting of a central core containing bacilli surrounded by WBCs

Cord factor

• Lipid found in M. tuberculosis

• Protects the cell from destruction by lysosomes or macrophages by surrounding the cell

Caseous lesions

• Lesions formed due to the breakage of tubercles during primary TB

• Heal by calcification

Clinical tuberculosis types

• Primary TB

• Secondary TB

  • Reactivation or reinfection

• Disseminated TB

  • Extrapulmonary

Primary TB

• Infectious dose: 10 cells

• Bacterial cells are phagocytized by alveolar macrophages but do not die and instead multiply

• After 3-4 weeks, the immune system reacts by forming tubercles

• If the tubercles break, caseous lesions are left

Secondary TB

• Latent and recurrent

• If patient doesn't recover from primary TB, reactivation of bacilli occurs

• Tubercles expand and drain into the bronchioles and upper respiratory tract

• Symptoms are more severe

Symptoms of secondary TB

• Violent coughing

• Greenish or bloody sputum

• Fever

• Anorexia

• Weight loss

• Fatigue

• Untreated reactivated disease = 60% mortality rate

Disseminated TB

• Extrapulmonary

• During reactivated TB, bacilli disseminate to regional lymph nodes, kidneys, long bones, genital tract, brain, and meninges

• Grave

TB tests

• Tuberculin sensitivity

  • Mantoux test

• In vitro TB test

  • Quantiferon gold

• Chest X rays

• Acid fast staning

  • Sputum

• Cultural isolation

TB vaccine

Based on attenuated bacille Calmette-Guerin

TB antibiotics/drugs

• Isoniazid

• Rifampin

• Pyrazinamide

Mycobacterium leprae

• Strict parasite

• Slowest growing

• Multiplies within host cells in large groups = globi

• Causes leprosy

Leprosy

• Hansen’s disease

• Chronic disease that begins in the skin and mucous membranes and progresses into nerves

Forms of leprosy

• Tuberculoid

  • paucibacillary

• Lepromatous

  • Multibacillary

Tuberculoid (paucibacillary) leprosy

• Most superficial form

• Asymmetrical, shallow skin lesions containing very few bacili

• Causes dermal nerve damage

  • Local loss of pain reception

Lepromatous (multibacillary) leprosy

• Widespread dissemination of bacteria

• Deep nodular infection that causes sever disfigurment

• Many bacteria found in skin scrapings

• Causes sensory nerve damage

  • Predisposed patient to trauma and mutilation, blindness, or respiratory failure