Pathology - Gram Negative Bacteria Flashcards
Gram Negative Bacteria
Bacteria containing an OM and IM containing a pg cell wall within a periplasm, highly resistance to bacteria.
What are the two groups of GNB in regards to ICU patients?
Enterobacteriacea and Nonfermenting
Enterobacteriaceae
A group of GNB, facultative anaerobic Bacilli typically inhabiting mammallian gut.
Nonfermenting gram negative bacilli
Aerobic, non-spore forming bacilli that can degrade carbohydrates in ways other than through fermentation.
Bacterial fermentation
Anaerobic catabolic reactions producing ATP by substrate-level phosphorylation.
What are the three layers that can exist exterior to the OM in GNB?
Capsule and S-layers.
Capsule
A gel like- polysachharide rich layer exterior to the outer membrane.
What is the first line of defense for bacteria?
The capsule.
What is the structure of the Capsule in Gram POSITIVE Bacteria?
A viscous layer of carbs covalently bound to the cell wall.
How do CPS achieve virulence?
Masking the more conserved, immunogenic components of bacteria.
What are some characterisitcs of the PS?
Diverse structures with HMW and are water saturated.
What does the plateua of CPS do?
Creates a water saturated layer that blocks infection, limits dessication and thrwarts phagocytosis by phagogcytes by restricting antigen access.
What are the three LPS regions?
Lipid A, Oligosaccharide and the O Antigen
Structure of Lipid A
A diphosphorylated N-Acetylglucosamine disaccharide with acyl chains extending from them.
What is the structure of the Core Oligosaccharide?
Has an inner core bound to Lipid A and an outer core linked to a terminal heptose of the inner core.
What is the structure of the O Antigen?
A repetitive glycan chain varying in composition and lenght, masked from the envrionment.
What bacteria can have Exopolysaccharides?
Both GPB and GNB
ExoPolysaccharides
An ECM macromolecule excreted as a tightly bound capsule or loosely attached slime layer.
What is the function of exopolysaccharides?
Determinants of biofilm formation
S-Layers
A layer Potentially protecting the cell from phagocytosis, harmful enzymes and other aggressions.
What are the different mechanisms of antibiotic resistance?
Efflux pumps
Alteration of drug binding sites
Membrane permeability alteration
Degradative enzymes
Inactivation of drugs through inhbiition
Whats the most immunogenic constituetn of GNB?
OM LPS
What does TLR4-LPS binding result in?
Chemokine/Cytokine exppression and release.
How many GNB bacteria are Enterobacteriaceae
About 80%
What are characterisitcs of Enterobacteriaea?
Limited Mobility, Bacilli structure, Facultatative Anaerobes, Cytochrome Oxidase Negative and can reduce nitrate to nitrie.
Cytochrome oxidsase Negative
Bacteria lacking cytochrome c oxidase of the OP
How can Enterobacteria resist antibiotics?
Diffusion of plasmids by conjugation.
Conjugation
The union of unicellular organisms with exchange of genetic material
Carbapenemases
B lactamases with very versatile hydrolytic capabilities
What is the function of carbapenemases?
They can hydrolyse penicillin.
What are characteristics of Non-fermenting bacteria?
Aerbobic, Non sporulated and incapable of sugar fermentation.
Multiresistance Gram Negative Bacteria
A type of GNB with resistance to multiple antibiotics.
When did carbapenemases emerge?
About 20 years ago.
