Gram-Positive Bacilli of Medical Importance

Chapter 19

Spore-formers, non-spore-formers, acid fast

Gram-positive spore-forming bacilli, motile;

Spore - survival structure - resists heat, drying, radiation, chemicals


A. Aerobes:

Bacillus - Aerobic, catalase +, degrades complex macromolecules - exoenzymes - antibiotics

Endospore - widespread dispersal - dust, water, plants, animals fur


1. Bacillus anthracis - BIG - 3-5x1-1.2 microns, central spores

Polypeptide capsule, Exotoxins necrosis and swelling

Easily grows, sporulates in soil - grazing animals

Common in cattle - vaccines, destroy herds -

US cases - fur trimmed souveniers Bioterrorism



Cutaneous Anthrax - Lesion lump (papule) -black, enlarging, eschar

Pulmonary Anthrax (woolsorter's disease)

lungs - germinates exotoxins - septicemia -

death in a few hours - capillary clots, shock

Gastrointestinal Anthrax - rare - contaminated meat

Treatment: penicillin, tetracycline - toxemia not affected by treatment

Prevention: vaccines of live attenuated spores and toxoid for livestock

Humans - purified toxoid (at risk humans) (vets, now military)

Contaminated animals disinfected, carcasses burned, not buried.

Fur, hides, etc gas sterilized


2. Bacillus cereus - food, rice, potatoes, meat

cook, reheat, Enterotoxins: N/V/D abdominal cramps -

usually self-limiting in about 24 hours


B. Anaerobes

Clostridium, terminal, swollen spore; catalase - ,

Ubiquitous, not communicable

enter skin, wounds or foods - exotoxins,


1. Clostridium perfringens -Gas gangrene -

anaerobic cellulitis - localized toxin and gas

myonecrosis - progressive, toxins diffuse to healthy tissue

Surgical, compound fractures, sores, septic abortions,

Puncture, gunshot wounds, crushing injuries with dirt

Not very invasive, need dead tissue, anaerobic conditions

Exotoxin - alpha toxin = Lecithinase,

rupture RBCs, swelling, tissue destruction

Collagenase, hyalurminidase, DNase

Ferments carbohydrates in muscle producing gas

Treatment: debridment of damaged, infected tissues

Cephalosporin (cefoxitin) or penicillin

Hyperbaric oxygen


2. Clostrium difficile - Antibiotic-associated colitis -

normal flora - after ampicillin, clindamycin, cephalosporins,

Diarrhea, cramps, fever, WBC's elevated, inflammation,

cecal perforation fatal

pseudomembrane -epithelium sloughs off fibrin attached.

Treatment: Stop antibiotics, electrolytes

Oral vancomycin until intestinal flora restored (yoghurt)

Spores in stools, prevent spread to others


3. Clostrium tetani Tetanus /lockjaw

Spores - wounds, burns, umbilical stumps, surgical procedures

Exotoxins - tetanospasmin - neurotoxin - local nerves - spinal neurons

block release of neurotransmitter of "inappropriate contraction"

Jaw muscles - first affected, then back, arms, legs, death due to respiratory collapse

Treatment:Antitoxin (HTIg) inactivates toxin


4. Clostridium botulinum - rare, serious - intoxication -

Spores found in soil, water, intestinal tract of animals

Poorly preserved foods, low acid - vegetables, meat, fish, dairy.

No effect on taste or smell - small intestine, blood, lymphatics

Affect neuromuscular junction of muscles,

block release of acetylcholine (signal for contraction)

12-72 hours - constipation, double vision, dizziness,

difficulty swallowing, respiratory complications

*Infant Botulism -2wks - 6 mo, spores ingested - honey implicated

poor sucking reflex, limp-baby

*Wound botulism - flaccid paralysis (IVDU)

Treatment: ID foods;antitoxin, penicillin

Prevention: improve home-canning, boil for 10 min


II. Gram Positive Regular Non-Spore-forming Rods

Lactobacillus, Listeria, Erysipelothrix, Kurthia, Caryophanon, Bronchothrix, Renibacterium


1. Listeria monocytogenes - ubiquitous, motile, short to long filaments in palisades, beta-hemolytic, resists cold, heat, salt, pH extremes and bile.

Contaminated dairy, poultry, meat, especially raw milk cheeses -

grows during aging process

Adults: mild, fever, sore throat, diarrhea

Transmitted to fetus/ neonate

Intrauterine - premature abortion, neoates -meningitis

Treatment: penicillin, ampicillin, erythormycin

Prevention: cook foods, pasteurize dairy products


2. Erysipelothrix rhusiopathiae

Animals and environment (tonsils of pigs- swine erysipelas ),

water, sewage

Handlers, slaughterhouse workers, butchers, vets

Lesion: swollen, dark red, burning itching, Endocarditis, septicemia

Treatment: pencillin or erythomycin Vaccine for pigs.

III. Gram-positive Irregular Non-spore-forming Rods

Pleomorphic, stain unevenly, catalase +, mycolic acids, peptidoglycan


1. Corynebacterium diphtheriae -

Respiratory tract infection , cutaneous form

Successful vaccine, healthy carriers, affects susceptible 1-10 year olds

Aerosole transmission, fomites, milk

local infection - tonsils,pharynx, larynx, trachea

toxin production - diffusion - toxemia - diphtherotoxin

two polypeptide fragments - B fragment heart and nervous cells

A blocks protein synthesis

local inflammatory response, low-grade fever, sore throat, nausea, vomiting enlarged lymph nodes, severe swelling in neck

pseudomembrane - greenish-gray solidified fibrous exudate cells, fluid

stuck on - pull off- bleeding

Toxemia - heart = inflamed ; nerves/cranium - weakness and paralysis

Treatment: diphtheria antitoxin (horses) Pencillin, erythromycin

Prevented: vaccine DPT


2. Proprionibacterium -

Aerotolerant anaerobe, no toxins

Proprionibacterium acnes - oil glands - acne vulgaris


III. Mycobacterium Acid-Fast

Mucolic acids in layers - waxy coat - resists drying, chemicals, acids,

Long slender straight or curved, filamentous or branching, granules,

no spores, aerobic


1. Mycobacterium tuberculosis

prevalent to 50 years ago - antibiotic therapy

Predisposing conditions: poverty, inadequate nutrition, unsanitary living conditions, debilitation of immune system, lung damage, genetics.

No toxins or enzymes, waxes prevent destruction even when phagocytised

Infants infected, dormant, reactivated in 20's

15 mil in US 1/3 of world carry TB

ONLY 5% of those infected may manifest the disease

Primary TB - tiniest aerosols, inhaled into alveoli, ~10 cells

phaocytized by macrophages, multiply intracellularly, mild fever

3-4 weeks - cell mediated response - monocytes migrate - tubercules

Tubercle = TB, macrophages, fibroblasts/lymphocytes/neutrophils

Necrosis of tubercle = calcification

Tuberculin reaction

Secondary TB - tubercules expand, drain into broncioles

- coughing, greenish or bloody sputum, fever, anorexia, weight loss, extreme fatigue, night sweats, chest pain wasting of body = consumption

*Extrapulmonary - lymph nodes, kidneys, long bones, genital tract, brain, meninges

Detection: 1 tuberculin test 2. X ray 3. ID acid-fast

Tuberculin testing: purified protein, cell-mediated hypersensitivity

Treatment: sufficient to kill bacillus 6-24 months

Two drugs - Isoniazide, rifampin, ethambutol, streptomycin, pyrazinamide, thioactazone, para-aminosalicylic acid

Prevention: vaccine BCG (bacille Calmet-Guerin strain of M.bovis)

- 20-80% protective for several years


2. Mycobacterium leprae - Hansen's bacillus- Leprosy

Strict parasite (armadillo), slow grower

chronic progressive disease of skin and nerves - severe disfigurement

Not readily communicated - no even sure of transmission

Asia, Africa, Central and South American and Pacific Islands, Siberia, Korea, China, Hawaii, Texas, California, Louisiana (2-3K in US)

T cell response factor determines progressiveness

Tuberculoid - shallow skin lesions

Leproid - nose, eyes, eyebrows, chin, testes - thickening -lepromas

Treatment: dapsone

Rifampin and dapsone for tuberculoid

Rifampin, dapsone and clofazimine (2-10 years)