Microbio

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Bacteria that don't stain well with gram stain
- Acid fast bacteria (i.e. mycobacteria)--waxy coat of murein and lipids prevent gram staining
- Mycoplasmas (i.e. pneumoniae never have a cell wall
- L-forms--wall-less. Bacteria that have lost their cell walls but can re-grow them under right conditions
- spirochetes (syphilis). stained by fluorescene or silver staining
Plasmids
- small extrachromosomal autonomously replicating pieces of DNA that carry genes NOT essential for a cell's survival.
- They carry genes for antibiotic resistance and genes for enterotoxins and exotoxins
- Purpose: make up an extra pool of gene alleles, enlarging the effective gene pool of the population
- F plasmids (fertiility) has set of genes that makes conjugation possible. F+ contains these genes. Those that lack these genes are F-
Four ways bacteria can inter-transfer DNA. This allows means for the dissemination (spread) of antibiotic resistance genes.
- Conjugation
- Transformation
- Transduction
- Transposition
Conjugation
- direct cell to cell transfer
- main way antibiotic resistance is transferred
- Needs F+ and F-
- works in gram -ve bacteria
- gram +ve have adhesins that cause aggregation
Transformation
- uptake of free "naked" DNA from solution
- Avery/McCleod experiment
Transduction

a bacterial virus (aka phage) that carries bacterial DNA into a new bacteria
Transposition
- movement of bacterial DNA within a cell
- TN=transposable element
- Involves the movement of sequences throughout the genome with no requirement for sequence homology. The simplest of these elements are insertion sequences, which contain a transposase gene flanked by inverted repeats.
Methicillin Resistant Staph aureus = MRSA
- Community acquired MRSA is from the incorporation of a mobile genetic element called Staphylococcal cassette chromosome mec (SCCmec. mec stands for methicilin resistance gene)
- SCCmec is a transposable element that inserts in a site-specific location in the S. aureus genome. mecA gene produces penicillin binding proteins that bind to beta-lactam antibiotics at much lower efficiency that the intrinsic set of PBPs in S. aureus thus penicillin doesn't prevent cell wall synthesis.
- Larger cassettes encode multiple antibiotic resistance genes as well as other virulence factors
- There are different strains of MRSA differentiated by which SCmec cassette they harbor and which other virulence genes they possess. These different strains are categorized by MLST (multilocus sequence typing)

Author

scherzetude

235041

Card Set

Microbio

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microbio

Updated

2013-09-16T00:46:47Z

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