(From Micro, 8 Oct 2000, by Brian Buschman)
Return to Semester Three Goodies
Return to The Unofficial Ross Page
Bacillus is one of he two gram-positive spore forming rods. The other is clostridium. The difference between the two is that bacillus is aerophobic while clostridium is aerophilic. Both work by releasing various exotoxins.
Anthrax is a nasty and fast acting without penicillin treatment. Anthracis is the only bacteria with a protein capsule. This blocks phagocytosis. Anthrax is usually acquired from spores found in animal products from countries that have anthrax like drums from Haiti.
There are three forms of anthrax:
1) Cutaneous anthrax involves local tissue necrosis with a PAINLESS lesion. It will proliferate without antibiotic treatment.
2) Respiratory anthrax is from inhalation of the spores and causes fever, cough, respiratory distress, pulmonary edema and death.
3) GI anthrax is from meat and causes necrotic legions in the GI, vomiting, bloody diarrhea and abdominal pain.
Anthrax has three exotoxins:
1) Edema factor (EF) is an extracellular form of adenylate cyclase which causes all sorts of problems when taken up.
2) Protective antigen (PA) is a mediator that helps EF to be taken up into the cells.
3) Lethal factor (LF) causes pulmonary edema in lab rats.
To better ID the anthrax you look to see if it is non-hemolytic and non-motile.
B. cereus is a non-encapsulated, motile and resistant to penicillin. It grows in food and auses food poisoning in only 4 hours being the quickest to do it. Because it is spore forming the spores can live through the cooking process.
It makes two toxins, the first being heat liable causing food poisoning in 12-24 hours. It also has a heat-stable toxin that causes food poisoning with nausea without diarrhea.
Antibiotics don’t help because the toxins are already in the system. It just has to run it’s course.
Remember that clostridium are anaerobic, spore forming, gram-negative rods.
C. botulinum causes botulism by releasing a neurotoxin that blocks ACh receptors. In adults the neurotoxin is gained by eating canned goods. It causes paraplasis and ventilator support is needed till it wears off. It can be helped some by an antitoxin that binds neurotoxin that is not already bound to a receptor.
In infants it’s much better because it gets them from infected honey. It grows in their guts and causes some production of the neurotoxin. The doses are so much less then that of the adult form so they the babies will be OK without treatment. You just have to let it run it’s course.
In C. tetani infections there is a neuron called tetanospasmin that causes tetani in muscles causing lockjaw, risus sardonicus and respiratory failure. It happens because tetanospasmin causes inhibition of GABA and Gly interneurons.
Tetanus is treated by:
1) Administration of neutralizing toxin with human tetanus Ig.
2) Give them a tetanus booster shot.
3) Clean the wound to remove remaining organisms.
4) Treat with penicillin to help kill remaining organisms.
5) Provide life support until the toxin clears out.
In tetanus you se spasticity while in botulinum you see flaccidity.
C. perfringens is an anaerobic bacteria that if it gets into damaged tissues will grow (in the anoxic environment) and cause necrosis and gas gangrene.
1) Cellulitis is from wound infection where it gets into local tissues. It spreads on the fascia layers.
2) Clostridial myonecrosis is when it invades muscles.
It can also cause food poisoning.
In broad spectrum antibiotics the gut is wiped clean and C. difficule can get in the colon and release two exotoxins:
1) Toxin A causes diarrhea.
2) Toxin B is cytotoxic.
You see cramping, diarrhea and fever (cytotoxic). They also develop a white pseudomembrane in the colon visible on colonoscopy. You can test for C. difficile toxin in a stool sample.
Tx is with oral vancomycin or metronidazol. The metro and the van go straight down the GI without being absorbed so they can work on flora in the colon.
Return to Semester Three Goodies
Return to The Unofficial Ross Page