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
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)