Keywords: 1-8 Flashcards Preview

Micro Remediation > Keywords: 1-8 > Flashcards

Flashcards in Keywords: 1-8 Deck (26):
1

1 PCR

Primer recognition of known viral or bacterial genetic sequences

2

1 Colonizers associated w/ disease states:

Viridans streptococci

HACEK

Fusobacterium spp.

Neisseria meningitidis

Candida albicans

Endocarditis

Endocarditis

Bacteremias

Meningitis

Thrush

3

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

4

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.

5

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.

6

1 Urine Collection Inflammation vs. Contamination

White blood cells --> inflammation

Epithelial cells --> contamination

>100,000 bacteria/mL --> infection

Polymicrobial growth --> contamination

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1 Respiratory Tract Secretion Contamination

Broncho-Alveolar Lavage (BAL) makes contamination less likely than a sputum culture

8

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

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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

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2 Facultative vs. Obligate Intracellular Pathogens

Facultative: Can grow inside or outside host cells

Obligate: Have to have host cells or can’t replicate

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3 Prokaryotes

No nucleus

Mainly bacteria

12

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

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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

14

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

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3 Peptidoglycan Crosslinking

Carried out by transpeptidases (aka penicillin binding proteins, PBPs)

16

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

17

3 Lipoteichoic & Teichoic Acid

Structures/components unique to gram+ bacteria

Lipoteichoic: glycerol phosphate backbone (3C)

Teichoic: ribitol phosphate backbone (5C)

18

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

19

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

20

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

21

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.

22

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

23

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

24

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

25

7 PCN MICs for treating Streptococcus pneumoniae

PCN MIC ≤ 2: susceptible
- treat w/ IV PCN

PCN MIC = 4: intermediate
- treat w/ IV PCN or ceftriaxone
- higher doses of beta-lactams overcome PBP resistance

PCN MIC ≥ 8: resistant
- treat w/ vancomycin
- even high doses of beta-lactams can't overcome PBP resistance

PCN MIC breakpoints not applicable for meningitis due to blood brain barier
- PCN has lower achievable concs in CSF than in other compartments
- Susceptible: ≤ 0.06
- Resistant: ≥ 0.12

26

8 Where antibacterial resistance comes from (4)

1) Introduction of resistant strains from outside the community

2) Acquisition of antimicrobial resistance from another strain

3) Spontaneous mutation in the bacterial genome

4) Selection of resistant strains via antibiotic pressure