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slides17 - Microbe-host interactions Ch 21 Science...

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Microbe-host interactions Nov 15, 2006 Ch. 21 Science 307:1915-20, 2005.
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Antimicrobial drug resistance Acquired ability to resist effects of a chemotherapeutic to which it is normally susceptible Common mechanisms 1. Lack structure drug targets 2. May be impermeable to drug 3. Organism may be able to modify drug to an inactive form 4. Organism may modify the target itself 5. Organism may develop a new pathway 6. Organism may be able to pump out the drug
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R factors Most drug resistant bacteria isolated from patients contain drug resistance genes on plasmids Many of these plasmids encode enzymes that inactivate drugs Multi-drug resistance plasmids predate medical use of antibiotics Widespread emergence of multi-drug resistance
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Resistance to all known drugs… 1950 Staphylococcus aureus 1960 Other gram-negative rods 1970 1980 1990 2000 2010 Shigella sp. Shigella dysenteriae Salmonella sp. Pseudomonas aeruginosa Neisseria gonorrhoeae Haemophilus influenzae Salmonella typhi Haemophilus ducreyi Streptococcus pneumoniae Enterococcus faecalis Acinetobacter sp. Mycobacterium tuberculosis Gram-negative Gram-positive Gram-positive/acid-fast • Methicillin- resistant Staphylococcus aureus (MRSA) • Vancomycin- resistant Enterococcus (VRE) Figure by MIT OCW.
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Healthcare-associated infections Healthcare-associated infections (HAIs) are infections that patients acquire during the course of receiving treatment for other conditions In hospitals alone, HAIs account for an estimated 2 million infections, 90,000 deaths, and $4.5 billion in excess health care costs annually http://www.cdc.gov/ncidod/dhqp/healthDis.html
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Changing patterns for HAIs • 1950s to 1960s gram positive bacteria were a major problem ( Streptococcus pyogenes and Staphylococcus aureus ) 1970s and 1980s gram negative bacteria became a major problem ( E. coli and Pseudomonas spp.) Currently, gram positive bacteria are again emerging as a major problem ( S. aureus and Enterococcus spp.)
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Methicillin-resistant Staphylococcus aureus N315 Image removed due to copyright restrictions. Hiramatsu et al. Trends Microbiol 9:486, 2001
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Terminology • Normal microbial “flora” or “microflora” – Better term is microbiota – Commensal (at the same table) • Pathogen – Infection versus disease • Virulence • Opportunistic pathogen
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Indigenous microbiota Microorganisms that inhabit body sites in which
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slides17 - Microbe-host interactions Ch 21 Science...

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