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Unformatted text preview: Microbiology 6-13-05 Second Half of Lecture Host-Parasite Interactions – interaction between the patient (host) and the organism (parasite) Key Definitions – Dynamic Balance – We want to think of these things as dynamic balance – an ever changing balance between the patient and the organism. Even though we always seem to think that a certain organism is always a pathogen and another organism is never a pathogen – this is not a proper way to think about things. An organism with a relatively low weapon system – no virulence factors can cause disease in a relatively unprotected patient – and someone who is very healthy may be exposed to the plague and be extremely healthy. It is not an “always” thing – that an organism always causes disease, nor is it a “never” thing. It depends on the patient. So, in general, we have different statuses of patients. Infection Types : Community – In a community acquired setting we have a wide variety of people with different immune systems. In general, in a community, most people are well protected with their immune systems. Obviously “healthier” people tend to get this kind of infection, and in general – less antimicrobial resistance. Nosocomial (hospital) – In a hospital setting, however, the opposite is true. Most people are in a somewhat compromised manner. For example – a patient is getting an IV put in their arm. That bypasses the skin which is a defense system. Also a catheter that is in someone for weeks is an opening that can get infected. On the other hand, we could have an AIDS patient or a leukemia patient whose defense systems are really low. So, we have this dynamic balance. We DO NOT want to every say ALWAYS or NEVER in terms of whether an organism can cause a problem or not. Nosocomial means to acquire the agent in a health care facility – this does NOT mean that you became ill in the hospital. You ACQUIRE it in the hospital. There are many patients that come down with or die from a Nosocomial infection. It depends on their immune system status also as to how severe the infection may be. The organisms that usually cause Nosocomial infections are those that usually have multiple antibiotic resistance because we select for the antimicrobial resistance (around the hospital). They are hard to treat; they occur in patients who are somewhat compromised (immune system is not very good potentially), and the organism has multiple antibiotic resistance. They are very hard to treat. Case Study A man who acquired TB in 1957 (but is surrounded by a granuloma – so it is inactive) suddenly has a reactivation of the TB. He has had TB since 1957 so is that organism going to be easier or harder to treat than someone who has just acquired TB last week. It is going to be easier to treat....
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- Spring '08