Keywords: 1-8 Flashcards
1 PCR
Primer recognition of known viral or bacterial genetic sequences
1 Colonizers associated w/ disease states:
Viridans streptococci
HACEK
Fusobacterium spp.
Neisseria meningitidis
Candida albicans
Endocarditis
Endocarditis
Bacteremias
Meningitis
Thrush
1 Types of Cultures (3)
Qualitative: negative or positive
Semi-quantitative: negative, rare, light, moderate, or heavy growth
Quantitative: colony-forming units (CFU) per volume
1 Blood Culture Contamination
Blood should be collected from two different sites. Blood from each site is collected in 2 bottles; one to support aeroob growth and another to support anaeroob growth. Since the skin is covered by organisms, improperly collected blood cultures may be contaminated with bacteria such as coagulase negative staphylococci. Two samplings (2 sets of 2 bottles each) may differentiate between contamination and a true bacteremia. It is more useful to report the amount of positive sets than amount of positive bottles.
1 Detection of Antibodies (Serology)
Detection of antibodies (serology) against bacteria, fungi, viruses or parasites.
IgM production may not be apparent at the time of the patient presenting to
physicians; a “convalescent” sample (collected 10-14 days after presentation)
should be collected to detect late-occurring IgM and also changes in IgG titer.
1 Urine Collection Inflammation vs. Contamination
White blood cells –> inflammation
Epithelial cells –> contamination
> 100,000 bacteria/mL –> infection
Polymicrobial growth –> contamination
1 Respiratory Tract Secretion Contamination
Broncho-Alveolar Lavage (BAL) makes contamination less likely than a sputum culture
2 Virulence Factors
What the micro-organisms use to cause disease
Toxins: poisons made by micro-organisms that affect/infect the host
Adhesins: molecules that a pathogen uses to attach to host tissues or host cells
Capsules: molecules that help a micro-organism have anti-phagocytic properties
2 Virulence
The number of organisms it takes to start an infection
LD50: # of organisms you have to inoculate into an animal to kill 50% of the animals
ID50: # of organisms you have to inoculate into an animal to make 50% of the animals sick
ED50: # of organisms you have to inoculate into an animal to induce an effect (ex. fever) in 50% of the animals
2 Facultative vs. Obligate Intracellular Pathogens
Facultative: Can grow inside or outside host cells
Obligate: Have to have host cells or can’t replicate
3 Prokaryotes
No nucleus
Mainly bacteria
3 Bacteria:
Cells (y/n)
Nucleic Acid(s)
Ribosomes
Mitochondria (y/n)
Cell Wall Component
Motility
Binary Fission (y/n)
Yes
DNA & RNA
70S
No
Peptidoglycan (exceptions: Mycoplasma & Chlamydiae)
Some (cocci no, rods maybe, spirochetes yes)
Yes
3 Fungi:
Cells (y/n)
Nucleic Acid(s)
Ribosomes
Mitochondria (y/n)
Cell Wall Component
Motility
Binary Fission (y/n)
Yes
DNA & RNA
80S
Yes
Chitin
No
Yes
3 Parasites:
Cells (y/n)
Nucleic Acid(s)
Ribosomes
Mitochondria (y/n)
Cell Wall Component
Motility
Binary Fission (y/n)
Yes
DNA & RNA
80S
Yes
No
Usually
Yes
3 Peptidoglycan Crosslinking
Carried out by transpeptidases (aka penicillin binding proteins, PBPs)
Gram Stain Procedure
1) Stain (Crystal Violet)
- gram+ purple
- gram- purple
2) Mordant (Iodine)
- gram+ purple
- gram- purple
3) Decolorize (Alcohol)
- gram+ purple
- gram- clear
4) Counterstain (Safranin)
- gram+ purple
- gram- red
3 Lipoteichoic & Teichoic Acid
Structures/components unique to gram+ bacteria
Lipoteichoic: glycerol phosphate backbone (3C)
Teichoic: ribitol phosphate backbone (5C)
4 Nonclostridial Anaerobic Infections:
Key feature
Microbes
Bacteria involved
O2-requiring bacteria
Treatment
Virulence
Other characteristics
Abscess formation
Polymicrobic
Highly antibiotic-resistant bacteria (w/ intrinsic resistance or which carry resistance plasmids)
Can involve a mix of true anaerobes & facultative anaerobes (which consume O2, lowering local redox conditions)
Difficult b/c abscess has no blood supply for antibiotic delivery, so surgically drain abscesses & give multiple antibiotics
Low (takes many to start an infection) but fatal
Slow-growing, fastidious, produce fermentation gases
5 Minimum Inhibitory Concentration (MIC)
Lowest concentration of antibiotic that results in no visible growth (turbitity)
Minimum drug concentration it takes to inhibit replication of that organism
6 Bacterial Plasmid replication:
Plasmid Replicon
Copy #
Copmatible vs. Incompatible Plasmids
Plasmid replicon consists of:
- origin of replication (initiation site)
- rep gene (encodes initiator protein)
- copy control gene (controls replicaiton & copy #)
Copy #: # plasmids / chromosome
- Low copy #: large plasmids, conjugative
- High copy #: small plasmids, nonconjugative
Compatible plasmids: present in same host cell, maintained & replicated independently
Incompatible plasmids: unable to coexist in the same host cell
6 Origin of Antibiotic Resistance Genes
Many antibiotic producing bacteria such as Streptomyces are the source of the antibiotic resistance genes found in other organisms.
Many “housekeeping” genes may have evolved to encode proteins and enzymes involved in drug resistance.
There is a substantial pool of antibiotic resistance genes in nature and such genes can be transferred between different bacteria.
6 Integrons
Mobile DNA elements that carry antibiotic resistance genes into plasmids to confer new properties
Typically contain genes for resistance, toxins, etc.
Encode an integrase that integrates new DNA into current DNA/chromosme
6 Transposable Elements
Insertion sequences
Transposons
Structure
Replicative vs. Nonreplicative
Intermolecular vs. Intramolecular
Genet elements that can repeatedly insert at many different sites in a genome
Insertion sequences: small, carry genes for movement
Transposons: large, carry genes for movement & resistance, toxins, etc.
- tnpA (transposase)
- tnpR (repressor)
- Amp gene (bla) (beta-lactamase)
- Inverted repeats (repeated DNA sequences at ends of transposon)
Replicative: duplication of transposable element
Nonreplicative: simple insertion of transposon at target site
Intermolecular: within same genome
Intramolecular: b/n 2 genomes
7 Combination Therapy Uses (3)
Empiric therapy
- wide range of organisms suspected
- ex. bacterial meningitis
Synergy
- efficacy of combination exceeds sum of efficacy of each drug alone
- ex. ampicillin & gentamicin for enterococcal endocarditis
Prevent resistance
- ex. tuberculosis: RIPE (rifampin, isoniazid, pyrazinamide, thambutol)
- ex. HIV: 3 drugs needed for viral suppression
