(From Dr. Cain, 29 Sept 2000, by Brian Buschman)
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Virulence is the degree of pathogenesity of an organism. A high virulence is likely to take an organism.
Bacilus are rods
Coccus are spheres
Spirochete are spirals
Mycoplasm is a blob which has no cell wall.
Vibrio are curved rods.
Diphtheroid are clubs
1) Exposure to the etiologic agent. It may just be a change in the balance between the host and parasite when it comes to bacteria that are part of the normal flora.
2) Incubation is when the parasite survives the host defenses, settles in and multiplies.
3) The prodromal phase s when the host realizes that something is wrong.
4) The acute or chronic phase is the time when the infection is running it’s course.
5) The death phase is when the host overtakes the agent, kills it and has a increased immunity resulting from it.
Some bacteria are classified as gram positive because they stain blue due to their cell wall structure. They are surrounded by a lipid membrane which has a proteoglycan coat outside of it. Their peptidoglycan layer is thick and it has no endotoxins except for lysteria. There are six gram positive bugs in humans:
1) Streptococcus
2) Staphylococcus
3) Bacillus (makes endospores)
4) Clostridium (makes endospores)
5) Corynebacterium
6) Lysteria (has endotoxin)
Gram negative bacteria are tougher then the gram positives because they have two different cell membranes with the peptidoglycan layer between them. This area is called the periplasmic space. Unlike gram negative bugs they have porin channels and have LPS-A which is an endotoxin.
All bugs that are not gram positive are gram negative with two exceptions:
1) Mycobacterium are acid-fast little rods.
2) Mycoplasm which are neither because they have no cell wall.
Some organisms increase their virulence by secreting a capsule which they use to surround themselves. The capsule helps prevent their being eaten by microphages. Bacillus anthracis has a capsule of AAs but all others are sugars.
Only two types of bacteria have endospores, bacillus and clostridium (both are gram positive). Endospores are a way for bacillus and clostridium to lay dormant for years when there is a shortage of nutrients or the presence of harmful conditions. They can live through heat, cold, chemical exposure and drug treatment.
Some bacteria are able to hide inside WBCs by inactivating the fusion of lysosomes to phagosomes. The new host is unable to kill the antigen and protects the antigen from attack by antibodies and such.
Exotoxins are released from either gram positive or negative bacteria. They are proteins so they are heat liable. They may be neurotransmitters that act on the nervous system or enterotoxins for the GI. Enterotoxins block NaCl uptake or cause it’s release. This upset the osmotic balance and causes diarrhea. Enterotoxins come from either bacteria that live in the gut (infectious) or you can acquire enterotoxins by eating food that contains them if bacteria infected the food (food poisoning).
Pyrogenic exotoxins mess with cytokines to cause fever and rash. Tissue invasive toxins tunnel through tissues by messing up what the tissues do.
Endotoxins are “Lipid-A” on the outer membrane of gram-negative bugs but are a part of the peptidoglycan layer. It just projects to the outside. It is very toxic and is slowly released by shedding. If you treat the patient with antibiotics it will cause lysis and a rapid release of endotoxin. This may cause a patient’s condition to get worse before it gets better. Endotoxin is only seen in gram-negative bacteria and in the gram-positive bug lysteria.
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