14 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 14 The Firmicutes and Actinobacteria The gram-positive Bacteria fall into two major

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PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 14 The Firmicutes and Actinobacteria
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http://www.mbio.ncsu.edu/MB451 ( Actinobacteria ) ( Firmicutes ) The gram-positive Bacteria fall into two major phylogenetic subdivisions Gram-positive bacteria have no outer membrane and are bound only by the cytoplasmic membrane and a thick cell wall containing many layers of peptidoglycan (although some lack a cell wall). There are two distinct phylogenetic groups which were originally named based on their genomic G+C content. They are common in soil and sediment environments, where they are generally the predominant bacteria, and there are a number of clinically-relevant human pathogens in this group.
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Staphylococci are facultative aerobes that are common commensals and parasites of humans and animals • In humans, two major species are recognized. Staphylococcus epidermidis is a non-pigmented, non-pathogenic organisms usually found on the skin or mucous membranes. S. aureus (left) is a yellow pigmented species that is most commonly associated with pathological conditions including boils, pimples, pneumonia, osteomyelitis, meningitis, and arthritis. • Tolerate reduced water potential and can be easily isolated in selective media containing 7.5% salt. • Catalase positive phenotype allows differentiation from Streptococcus . • Ability to form acid under aerobic and anaerobic conditions distinguishes it from Micrococcus , which is an obligate aerobe.
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Methicillin-resistant Staphylococcus aureus (MRSA) • Each year, nearly 2 million patients in the United States develop a nosocomial infection. • 10% of these infections are caused by S. aureus and they are difficult to treat because the vast majority are multi-drug resistant. • Methicillin is one of the newest penicillin derivatives and resistance to this drug has more than doubled over the last decade. • Since the first reported episode of MRSA infection in the US in 1968, the proportion of S. aureus isolates resistant to methicillin causing infections in hospitalized patients has risen significantly from 2% in 1974 to about 40% 1997. • Over the past 20 years, infections with MRSA have been limited primarily to patients in hospitals or long-term care facilities. However, recent reports of "community-acquired" MRSA infections raise concern. picasaweb.google.com/FitzA6/FA6/photo#5059932489530991634 MRSA infection http://www.cdc.gov/ncidod/aip/research/mrsa.html
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MRSA protect themselves from β lactam antibiotics by producing an alternative target that is resistant to inhibition by the antibiotic The transpeptidation reaction in peptidoglycan synthesis is catalyzed by an enzyme (a penicillin- binding protein; PBP) that is no longer catalytically active when bound by β lactam antibiotics. In the absence of new wall synthesis, the activity of autolysins (lysozyme-like enzymes
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This note was uploaded on 08/04/2009 for the course BIOL 4125 taught by Professor Christner during the Spring '08 term at LSU.

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14 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 14 The Firmicutes and Actinobacteria The gram-positive Bacteria fall into two major

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