Bacteria Lectures Flashcards
phase variation
Control of transcription by DNA rearrangement
eg: reversible switching in the synthesis of two alternative flagellar antigens alternation between several antigenic forms of pili expressed on the cell
transposon
discrete segment of DNA which is capable of moving itself (or a copy of itself) from one chromosomal location to a new location within the cell
may transpose and become stabley and permanently integrated into the bacterial chromosome.
Insertion Sequences
(IS elements) are transposons that simply
encode transposase. Play a role in genome evolution by inactivating genes into which they transpose, or turning on expression of adjacent genes.
Complex transposons
carry additional genes such as those encoding
antibiotic resistance, toxins, adhesins and other virulence factors.
F plasmid
prototype self-transmissible plasmid
Autonomous replication of the plasmid DNA
ii. Synthesis of sex pili (F pili) which are essential for mediating pair formation between donor and recipient cells
iii. Conjugative transfer of F DNA to recipient (F-) cells
iv. Ability to integrate into the bacterial chromosome
Conjugative transposons
mobile elements which mediate conjugation
between pairs of cells, in which the transferred DNA is the conjugative transposon itself
Lipopolysaccharides (LPS) of gram negative bacteria
LPS is an example of a pathogen-associated molecular pattern (PAMP) that is recognized by the innate immune system and elicits host responses by a pathway
Toxins that stimulate cytokine production
superantigens are the most potent known T cell activators. They act by binding both to major histocompatibility (MHC) class II molecules on antigen-presenting cells and to specific Vβ chains on T cells at a site that is different from the antigen-binding site, and they activate much larger numbers of T cells than any specific antigen does. Superantigens stimulate excessive production of cytokines (including interleukin-2, interferon gamma, and others), thereby causing pathologic effects.
Shiga toxins of Shigella dysenteriae and E. coli, and the plant toxin ricin
inhibit protein synthesis
inactivating the ribosomes
Diphtheria toxin and Pseudomonas aeruginosa exotoxin A
inhibit protein synthesis
inactivate elongation factor 2 (EF-2)
Toxins that modify intracellular signaling pathways.
Pertussis toxin
Heat-labile enterotoxins of Vibrio cholerae and Escherichia
Anthrax
coli
Toxins that inhibit release of neurotransmitters
Botulinum toxin
Tetanus toxin
Toxins with intracellular targets must cross the plasma membrane before they can exert their toxic effects.
They typically use normal membrane constituents as receptors.
usually enter target cells by endocytosis
β-lactam resistance
β-lactam antibiotics act by irreversibly binding to and inactivating the transpeptidase reaction of penicillin-binding proteins, thereby inhibiting peptide cross-linking and peptidoglycan synthesis
β-lactamases are enzymes that inactivate β-lactam antibiotics by splitting the amide bond of the β-lactam ring, and thereby protect the activity of penicillin binding proteins.
ESBLs (extended spectrum beta-lactamases): can even attack up to 3rd gen cephalosporins
ampC-encoded β-lactamase
Enterobacter, Pseudomonas,
not inhibited by betalactamase inhibitors
The mutational events that lead to permanent high-level expression of ampC can occur during therapy!
