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Clinical Microbiology- Test 1
Terms in this set (136)
List the systematic approach for selection of antimicrobials
Confirm the presence of infection
Identify the pathogen
Select empiric therapy considering every infected site
Monitor therapeutic response
T or F- Infected body materials must be sampled if possible or practical
What are cultures we can obtain
Describe the microbiology lab workflow
1. Collect a sample
2. In minutes to hours you will have the microscopy (gram stain) results.
3. You can then plate the bacteria on a media
4. 24-48 hours later you will identify the organism
5. 24 hours after you identify it you can find the antibiotic sensitivity of the organism
**** after you collect the sample you can start empiric therapy.
Total time to organism identification and susceptibility = ______
What are standards of care of specimen management?
- Specimens of poor quality must be rejected
- "Background noise" must be avoided when possible
- Tissues, aspirates, and fluids are specimens of choice
- Specimen should be collected prior to administration of antibiotics
- Specimens must be labeled accurately and completely
What is background noise?
For instance you need a sputum culture but you notice there are epithelial cells in it- this tells you that the culture contains cells and bacteria from your mouth. * You want just a culture from your lungs
What are characteristics of gram positive bacteria cell wall
Thick peptidoglycan layer
One inner membrane
What are the characteristics of gram negative bacteria cell wall
Thin peptidoglycan layer
Two membranes- outer and inner
What is the gram stain used for?
Two separate the organisms into two groups: gram negative and gram positive
Gram ____ organisms absorb the crystal violet and hold onto it which is why they have a blue purple color
Gram ______ cannot absorb the crystal violet due to their thin peptidoglycan layer inside the outer membrane, therefore the crystal violet is washed off by the alcohol and the cells are able to absorb the safranin and appear red/ pink
List the steps that occur in gram staining
1. Fixation on the slide
2. Crystal violet is applied.
3. Treatment with iodine
5. counter stain with safranin
Morphology of gram positive bacteria?
Morphology of gram - bacteria
After you do the gram stain what is your next step
Plate your cultures on media (agar)
Media are used to do what?
Used to grow bacterial colonies
What is blood agar?
Non selective medium
Supports growth of a wide range of organisms
Gram positive are divided into _____ and _____
Gram positive cocci are divided into ____ and _____
Name the gram positive clusters
Name the gram positive chains/ pairs
Gram positive rods are divided into _____ and ______
non spore producing
Gram positive rods that are spore producing ____
Gram positive rods that are not spore producing
So we do a gram stain and we have a gram positive bacteria, how do we determine if it's in clusters (staph) or in chains/ pairs (strep)?
Do the catalase test
What is the catalase test?
All staphylococcus have catalase and strep do not. You mix catalase with the bacteria on the agar. If it bubbles up you have a positive test (this means it is staph). If it does not bubble up (strep).
After doing the catalase test we have now determined that we have staph. What are the two major categories of pathogenic staphylococcus?
Coagulase- negative staphylococcus
Coag negative staph includes ______ and ______
Of the pathogenic staph species only ________ is coagulase positive
How do you determine if the staph is coag positive or negative?
You take an organism and mix it with a reagent. If it bubbles up like in the second circle it's a positive coagulase test. Therefore we would know that it's staphylococcus aureus.
T or F- staph aureus causes a wide range of infections
Name the coagulase- negative staph
Staph ______ is mainly associated with infections involving foreign objects
epidermidis (when a patients has a catheter, heart valve, prosthetic joint, etc). This bacteria can latch onto hardware and cause infections
Staph ______ is a common cause of community acquired urinary tract infections
Gram stain of staph:
Gram positive clusters
Staph catalase test _____
Coagulase ____ for staph aureus
Coagulase ___ for staph epidimidis
What are the two ways we classify strep?
Name the lancefield antigens
*** she said only need to know A,B,D
Name the hemolytic ability classification
What is alpha hemolytic
What is beta hemolysis
Total hemolysis- eats through the blood agar
What is gamma hemolysis
No hemolysis at all
Although there are more than 30 species of strep, only ______ are significant human pathogens
Name the alpha hemolytic strep
Name the beta hemolytic strep
Strep pyogenes (group A)
Strep agalactiae (group B)
Name the gamma hemolytic strep
Strep bovis (Group D)
Group A strep
Group B strep
Group D strep
What is viridans group strep associated with?
Huge group of species
Colonizes GI tract
Dental infections, endocarditis, abscesses
What is strep bovis associated with?
Colonizes GI tract
Association with malignancy
What is strep pneumonia associated with
What is strep progenies associated with?
Toxic shock syndrome
What is strep agalactiae associated with
Colonizes female genital tract
Neonatal meningitis, pneumonia, sepsis
Enterococcus is a resident of ______
normal bowel flora
Enterococcus causes what things?
urinary tract infections, biliary tract infections, bacteremia, intra-abdominal infections, wound infections, endocarditis
***common cause of infection in hospitalized and immunocompromised patients
What are the two main pathogenic species of enterococcus
Gram stain enterococcus _____
Catalase ____ for enterococcus
Hemolysis and lance field group for strep pyogenes
Hemolysis and lance field group for strep agalactiae
Group B- beta hemolysis
Hemolysis and lance field group for strep pneumoniae
Hemolysis and lance field group for strep bovis
D- gamma hemolysis
Hemolysis and lance field group for viridans group strep
Hemolysis and lance field group for enterococcus
Gram negative rods are divided into _____ and _____
Enterobacteriaceae is divided into _____ and ____
lactose fermenters and non lactose fermenters
Name the lactose fermenters
Name the non lactose fermeneters
Name the other- non lactose fermenters that are not enterobacteriaceae
Name the gram negative diplococci
Name the gram negative coccobacilli
What culture media is used to determine the difference between gram negative lactose fermenters vs non lactose fermenters
How can you tell if it's a gram - lactose fermenter vs. non lactose fermenter
lactose fermenters will utilize the lactose in the media and cause the pH to change, you will see hot pink colonies. Non lactose fermenters cannot use lactose therefore you will only see white colonies on the agar
Why don't we have growth of gram positive bacteria on the macConkey agar?
The agar contains bile salts and crystal violet dye to inhibit the growth of gram-positive organisms
What are enterobacteriaceae?
Enteric gram negative rods
Lactose fermenters vs. non lactose fermenters
Enterobacteriacae are a major cause of ____
community and hospital acquired infections
Name the community acquired enterobacteriaceae infections
Name the hospital acquired enterobacteriaceae infections
E. coli, Proteus, Klebsiella, Enterobacter, Serratia, Citrobacter, Providencia, Morganella
If you are trying to determine an organism, you know it's a gram negative organism and it's not an enterobacteriacea. You also know it's a non lactose fermenter. What is your next step
Oxidase positive test- You take oxygen and mix it with the organism. Only pseudomonas uses oxygen for energy, therefore if it's pseudomonas it will be positive and a purple color. Negative oxidase tests won't have a color.
Pseudomonas causes what?
Causes pneumonia, urinary tract infections, wound infections, bacteremia
Risk factors for pseudomonas?
IV drug abusers
Acinetobacter causes what?
Causes pneumonia, bacteremia, wound infections
Is acinetobacter usually community or hospital acquired?
Mainly hospital acquired (you see this a lot at Grady)
Stenotrophomonas maltophilia causes ____
Important nosocomial pathogen capable of causing respiratory, bloodstream, and urinary infections
With _____ treatment is complicated due to an array of resistance mechanisms
List agents you can use for pseudomonas
Piperacillin/ Tazobactam, Ticarcillin/ Clavulanate
Meropenem, Imipenem, Doripenem
Gentamicin, Tobramycin, Amikacin
What is chocolate agar and what is it used for?
- Non-selective, enriched growth medium
- Variant of the blood agar plate containing red blood cells that have been lysed
- Used for growing fastidious organisms- Haemophilus influenza and Neisseria meningitidis
What is haemophilus influenza
Gram negative coccobaccilis
What is Neisseria meningitidis
Gram negativ diplococci
What are the two species of Neisseria that case disease in humans?
Neisseria meningitidis causes _____
meningitis and sepsis
Neisseria gonorrhoeae causes ______
What are high risk groups for neisseria meningitidis
Infants age 6 months- 2 years
military in close quarters
_____ = blood loving
How is haemophilus influenza transmitted?
via respiratory route
Haemophilus influenzae causes ____
Pneumonia, sinusitis, otitis media, meningitis
Anaerobic bacteria can be divided into _____ and _____ morphology
The anaerobic cocci are _______
The anaerobic bacilli are ______
Gram positive or gram negative
Name the gram positive anaerobic bacteria
Name the gram positive bacilli
Name the gram negative bacilli
____ are unable to grow in the presence of physiologic concentrations of oxygen
anaerobic bacteria usually inhabit _______
the human oral cavity, GI tract, and female genital tract
When does infection of anaerobic bacteria occur?
Infections occur following disruption of mucosal surfaces
Which agents are used empirically to cover anaerobes?
Beta-lactam/beta-lactamase inhibitor combinations
2nd generation cephalosporins
Which bacteria are unable to be gram stained?
Name the atypical bacteria
Chlamydia, mycoplasma, legionella
Why are atypical bacteria unable to be gram stained?
Lack a peptidoglycan layer to take up a Gram stain adequately
Name the mycobacteria
M. tuberculosis, Mycobacterium avium complex
Why won't mycobacteria gram stain?
High concentrations of lipids in their cell walls does not allow Gram stain
______ are slow growing organisms that can cause chronic disease
Why should susceptibility testing be done?
1. Important to confirm susceptibility to chosen empiric antimicrobial agent or to detect resistance in bacterial isolates
2. Susceptibility testing is important with species that may possess acquired resistance mechanisms
List the quantitative susceptibility testing methods
Broth dilution tests
Automated instrument systems
List the qualitative susceptibility test
What is the broth dilution test?
Prepares 2-fold dilutions of antibiotics in a liquid growth medium. Once the medium is colorless this is what gives us the MIC
Advantage to the broth dilution test?
Generation of quantitative result [MIC]
Disadvantage to broth dilution test
Tedious, labor intensive
What is the E test?
Thin, plastic, test strips that are impregnated with a dried antibiotic concentration gradient. You can find a zone of inhibition, where it crosses is the MIC
What are advantages to the E test
Flexible - can test drugs of the labs choosing
Correlates well with MICs generated by broth dilution
What are disadvantages to the E test
Can be expensive if testing multiple drugs
What is disk diffusion?
- Bacteria applied to Meuller-Hinton agar plate
- Antibiotic disks are placed on the agar surface
- Zones of growth inhibition around each disk are measured to determine susceptibility
*** does not give you a concentration value. The zone of inhibition is measured by diameter and equates to different MIC's. The bigger the zone of inhibition the more likely that bacteria is susceptible
What are advantages to the disk diffusion test
What are disadvantages to the disk diffusion test
Lack of automation of the test
What are advantages to automated instrument systems
- Standardize reading of end points
- Produce susceptibility in shorter time than manual readings
What are disadvantages to the automated instrument system
Limited by antimicrobials available on panels
Name the organism: Gram-positive cocci, Catalase positive, coagulase positive, Causes wide array of infections
Name the organism: Gram-negative organism, Not a member of Enterobacteriaceae, Lactose non-fermenter, oxidase positive
Name that organism: Gram-positive organism
Beta hemolytic, Associated with infections in neonates
Group B- strep agalactia
Name the organism: Gram-negative organisms, Members of Enterobacteriacae, Lactose fermenters
Name the organism: Gram-negative diplococci, Some strains cause meningitis, Some strains cause gonorrhea
Name the organism: Gram-positive organism
Catalase positive, coagulase negative, Associated with infections involving foreign objects
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