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
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.
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
uptake of free "naked" DNA from solution
a bacterial virus (aka phage) that carries bacterial DNA into a new bacteria
movement of bacterial DNA within a cell
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)