Diagnostic Micro Flashcards
Gram stains are important because
It gives the relative abundance - double checks that everything grew
Diagnostic Microbiology is focused on the study of what?
Bacterial pathogens
What is purulence?
Pus
How are gram stains used as a diagnostic tool from a primary sample?
Confirm physician suspicion of etiology of infection
Aid in correct antibiotic selection
Screen adequacy of specimen
Identify cellular components & debris of inflammation
Presumptive diagnosis
What are some examples of primary cultures?
Smears from swabs
Smears from thick liquids
Smears from thick mucoid material
Smears from thin fluids
What is the cytospin used for?
Thin fluids with low cellularity
What does the cytospin do?
Maximize cell recovery from a liquid & deposit the sediment on a slide
How do you make a smear from a plate?
Emulsify material in a drop of water on a slide
What does PMN stand for?
Poly morphonuclear leukocytes
What is an example of contaminatin of a sample?
Epithelial cells
What is quality control?
When known positive & negatives are stained
Direct gram stain from primary sample better match what grows on the plates - internal control
Is there a larger peptidoglycan layer in gram-positive or gram-negative bacteria?
Gram-positive
Do endotoxins stain gram positive or negative?
Gram-negative
The peptidoglycan layer consists of what two alternating peptides?
NAG & NAM
The NAG & NAM chains are cross-linked to form a thick network of what?
Peptide bridge connected to the tetra-peptides on the NAM
What are two special acids that are part of gram-positive cell walls?
Teichoic acid & lipo-techoic acid
Are gram-negative cell walls thick or thin?
Thin
What type lipid is an endotoxin?
Lipid A
What is endotoxin responsible for?
Producing fever & shock in patients infected with gram-negative bacteria
What is the outer membrane of gram-negative bacteria a barrier to?
Hydrophobic compounds
What does the outer membrane do?
It is a sieve
Allows water soluble molecules to enter through porins
What are porins & what do they do?
Protein lined channels
Provides attachment sites that enhance attachment to host cells
What gets released and becomes endotoxins?
Lipopolysaccharides
What is chromosomal DNA?
One circular supercoiled ds DNA
What are plasmid (extrachromosomal) DNA?
Non-essential circular supercoiled DNA fragments - low or high copy
Copied to daughter cells & spread by conjugation
What are three mobile genetic elements present in bacterial DNA?
Insertion sequences
Transposons
Cassettes
What are insertion sequences?
Short DNA that code for transposase
They may jump into a gene & activate or inactivate it
What are transposons?
Longer pieces of DNA that are mobile & have more genes
An example is antibiotic resistance
What are cassettes?
More sophisticated DNA inserts with multiple genes & regulatory elements
How big is a bacterial chromosome?
2.8 Mb
What is he size of a plasmid?
˜5 Kb
What is the size of an insertion sequence?
1000 bp
What is the size of an SCC cassette in MRSA?
20.9 to 66.0 kb
What are three types of genome change?
Antibiotic resistance
Mutations
Genetic recombination
How does the genome change to spread antibiotic resistance?
Acquisition of plasmids & other forms of mobile genetic elements that spread the antibiotic resistance
What are the types of mutations that causes genome change?
Point - one base
Frameshift - disrupts amino acid sequence
Deletions
Insertions from mobile elements
Where is the genome change caused by genetic mutation?
Between 2 DNA molecules
What are the three mechanisms of gene transfer?
Transformation
Transduction
Conjugation
What is transformation?
Uptake & incorporation of naked DNA from the environment
Cells must be competent to take it up
What is transduction?
Transfer of genes by bacteriophage
Genes are incorporated into genome - lysogengy
What is conjugation?
DNA from a donor strain integrates into the genome
Which mechanism admires the naked form?
Transformation
Which mechanism has conjugal visits?
Conjugated
Which mechanism duct tapes viruses into the bacteria?
Transduction
What does eukaryote mean?
True nucleus
What is the structure of chromosomes in eukaryotic cells?
Linear complexed with histones & proteins
What are present in extrachromosomal DNA?
Mitochondria & chloroplasts
Eukaryotic have what components that are not present in prokaryotic cells?
Membrane bound organelles
Endoplasmic reticulum
