Term
| What is the reason for streaking bacteria on a plate? |
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Definition
| It is similar to a serial dilution- you want to isolate individual colonies. |
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Term
| Why would you grow bacteria on a CNA plate? |
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Definition
The Colistin and Nalidixic acid inhibit growth of many Gram-negative bacteria, so it is used to select for gram-positives.
- Colistin is a Polymyxn antibiotic that is effective against most Gram-negative species, including Pseudomonas
- Nalidixic acid is a synthetic quinolone, which inhibits gram-negative bacteria as well
NaCl maintains osmotic balance
B vitamins for growth
Peptones for growth. |
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Term
| Why would you grow bacteria on a MacConkey agar plate? How does it work? |
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Definition
This plate selects for Gram-negative enterics, and can distinguish between lactose fermentors and non-lactose fermentors.
1) Lac+ bacteria such as E. coli, Enterobacter and Klebsiella will produce acid, which lowers the pH and results in the appearance of red/pink colonies
2) Lac- bacteria such as Salmonella, Proteus species, Pseudomonas aeruginosa and Shigella use peptone instead, increasing pH and growing clear.
3) The hydrophobic bile salts repel the hydrophilic O-antigens of gram-negative bacteria, protecting them from membrane breakdown and lysis. |
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Term
| Why grow bacteria on Chocolate agar? |
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Definition
| Nonselective media enriched with lysed RBCs which provide the nutrients necessary for the growth of fastidious organisms such an Haemophilus. |
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Term
| What do "alpha," "beta" and "gamma" mean in terms of RBC hemolysis activity by bacteria growing on a Blood agar plate? |
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Definition
Alpha= partial lysis/greenish pigment surround bacteria
Beta= Total hemolysis/good zone of clearing surrounding bacteria
Gamma= no hemolysis, but may observe growth. |
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Term
| How does one perform a gram stain? |
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Definition
Tells you cell wall type and morphology!
1) Fix organisms to slide with flame
1) Flood with Crystal Violet
2) Cross-link with mortem (iodine)
3) Decolarize with EtOH and then wash with tap water
4) Counter stain with Safranan for 30s
- Thick peptidoglycan walls that contain techoic acid in gram + species are unaffected by decolorization with alcohol, but single layer in gram - is drained of color |
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Term
| WHat is the Kirby-Bauer Method? |
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Definition
1) Paper discs containing different antibiotics are placed on agar plates that have been streaked with bacteria.
2) Measure "zone of inhibition" of each to determine susceptibilities (cant use for TB, because it is slow growing) |
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Term
| What do you learn from an Oxidase test? |
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Definition
-Tells you which organisms have cytochrome oxidase, and thus which organisms can use oxygen.
- In lab, Enterobacteria like Klebsiella are oxidase-, while Pseudomonas and Neisseria are oxidase + (dark purple/blue) |
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Term
| What do you learn from an indole test? |
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Definition
| Tests for organisms' abilities to metabolize tryptophan to indole. This is common in strains of E. coli |
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Term
| What does an API test tell you? |
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Definition
- Series of biochemical assays that is used to differentiate between Enteric Gram-negative rods.
- Recall, Enterobacteria are gram negative, facultative anaerobic rods and oxidase-negative. They are isolated from feces, urine, blood and CSF and can grow on MacConkey. They can be motile or non-motile |
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Term
| What is the differential diagnosis for typical versus atypical Pneumonia? |
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Definition
TYPICAL (with Sputum)
:
1) Streptococcus pneumoniae
2) Haemophilus influenzae
3) Staphylococcus aureus (especially post- influenza)
4) Enterobacteriaceae
ATYPICAL (w/o sputum)
1) Viral
2) Mycoplasma pneumoniae
3) Chlamydophila pneumoniae
4) Legionella pneumophila |
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Term
| Which standard antibiotics are provided for a pneumonia? |
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Definition
1) Macrolide (usually azithromycin)
2) Beta-lactam antibiotic (previously ceftriaxone was recommended, now it is ampicillin-sulbactam) |
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Term
| How do organisms cause pneumonia? |
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Definition
Microorganisms must first colonize the nasopharynx. This involves transmission by respiratory secretions and landing on the right surface.
Microaspirations during sleep normally provide route of entry into lower respiratory system. |
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Term
| How do pathogens associated with CA-pnuemo differ from those in HA-pneumo? |
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Definition
HA= Pseudomonas aeruginosa and Staphylococcus aureus.
CA= Klebsiella and others (easier to treat w/o risk factors and antibiotic resistance of HA) |
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Term
| Why might you use Dark-Field microscopy and how does it work? |
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Definition
Spirochetes- Treponema pallidum (Syphilis) and Rickettsia (RMSF)
1) Light source that comes in and is blocked by ANNULAR STOP (except light at edges), which gives the "darkness."
2) Scattered light light is refracted around organism (a shadow around them)
3) Light hits condenser lens and is magnified |
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Term
| How do Neisseria look on a gram stain? |
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Definition
| Gram-negative Dipplococci |
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Term
| Why would you use a Thayer Martin plate? |
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Definition
Selective media for Neisseria
1) Vancomycin (Gram +)
2) Colistin (gram – except Neisseria)
3) Nystatin (Fungals) |
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Term
| What serological tests are used to diagnose Syphillus? |
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Definition
Run EIA, RPR then EIA.
1) ELISA (indirect in Ag first)
2) Western Blot to confirm ELISA
3) Agglutination (RPR for Syphilis to detect Cardiolipin- nonspecific to detect cellular death). |
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Term
| How does an RPR test work and why would you run it? |
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Definition
Syphilis!
Carbon linked to Treponema antigen (look for distributed agglitination vs. restricted dot) |
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Term
| How does qPCR work in Chlamydia diagnosis? |
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Definition
target 18S ribosome and cryptic plasmid of Chlamydia
- Rapid and can determine viral load. |
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Term
| How can an Oxidase test help you distinguish between Neisseria and Chlamydia? |
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Definition
Neisseria is Oxidase-positive, since it is a facultatively intracellular
Chlamydia is an obgligate, intracellular pathogen that is Oxidase-negative |
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Term
| Why do you need Dark-Field Microscopy for Spirochetes? |
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Definition
| Can’t be gram-stained or cultured by ordinary media. |
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Term
| What major complications are associated with Chlamydia? |
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Definition
1) PID- "shuffle" and infertility
2) Perihepatitis (Fitzhugh-Curtis Syndrome)- ascites and peritoneal inflammation with no liver enzyme abnormalities
3) Conjunctivitis |
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Term
| Why can't you target Chlamydia with beta-lactam antibiotics? |
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Definition
| No peptidoglycan, so you cant target cross-linking! |
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Term
| What are 3 virulence factors associated with Neisseria gonnorhea? |
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Definition
1) Type IV pili are “grappling hooks” that pull 100,000X times their weight (twitching mobility). Genetic recombination prevents adaptive PMN access
2) Opa proteins bind immune cells to mitigate response, and help with adherence/invasion.
3) Porins- PorA and PorB that promote invasion
4) Iron aqcuisition |
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Term
| How do you treat Chlamydia and Neisseria? |
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Definition
| Azithromycin (Macrolide) or Doxicycline (tetracycline) |
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Term
| What clinical features are characteristic of Neisseria gonorrhea? |
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Definition
1) After attachment to an epithelial surface, followed by penetration between or through epithelial cells, there is a local inflammatory reaction that may or may not be accompanied by dissemination.
2) Local manifestations depending on site of inoculation: urethritis, pharyngitis, proctitis, conjunctivitis
3) Local extension: PID, perihepatitis (Fitz-Hugh-Curtis syndrome) Dissemination: cutaneous papular/pustular lesions, septic arthritis (especially monoarticular arthritis in sexually active patients) |
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Term
| How does blindness develop in Chlamydial infection? |
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Definition
Blindness develops from chronic conjunctivitis and scarring, ultimately involving the cornea.
Importantly, scarring of the eyelids leads to inversion of eyelashes that abrade, ulcerate, and scar the cornea. |
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Term
| What STI’s are reportable to the public health department? |
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Definition
1) Gonorrhea – N. gonorrheae
2) Syphilis- Treponema pallidum
3) Chancroid – Hemophilus ducryei
4) Chlamydia – Chlamydia trachomatis
5) Hepatitis B
6) HIV/AIDS |
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Term
| What test should you run if you expect TB? How can you confirm? |
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Definition
1) Acid-Fast stain for Mycobacteria
- Cell wall of mycobacteria is waxy and will take up dye but not de-colarize under acid wash.
WONT GIVE YOU SPECIES.
2) Traditional TB culture (4-6 weeks in special lab with >90% sensitivity and gold standard for specificity) followed by Niacin test to confirm.
3) Automated Liquid Culture- 9-10 days for + specimens and 16 days for - specimens and susceptibilities.
4) Direct PCR |
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Term
| Which organisms do not gram-stain well and why? |
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Definition
These Rascals May Microscopically Lack Color
1) Treponema pallidum (dark-field and IF)
2) Rickettsia (intracellular)
3) Mycobacteria (Lipid-content needs acid-fast)
4) Mycoplasma (No cell wall and high sterols)
5) Legionella pneumophila (intracellular- silver stain)
6) Chlamydia (Intracellular) |
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Term
| Which species can be stained by Giemsa? |
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Definition
1) Borrelia burdorfieri (lyme)
2) Plasmodium (malaria)
3) Trypanosomes (protoza for Chaga's and Meningo-encephalitis)
4) Chlamydia |
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Term
| Why might you use an india ink stain? |
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Definition
| To look for Cryptococcus neoformans yeast infections |
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Term
| When do you need a silver stain? |
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Definition
Fungi (Pneumocystic jirovici)
Listeria (can cause meningitis) |
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Term
| What special requirements are there for culturing H. influenzae? |
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Definition
| 1) Chocolate Agar (fastidious and needs V and X) |
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Term
| What special requirements are there for culturing N. gonorrhoeae? |
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Definition
| Thayer-Martin (VPN) media with Vancomycin (gram +), polymyxn (gram - except N. gonorrhea) and nystatin (fungal) |
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Term
| What special requirements are there for culturing C. diphtheriae? |
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Definition
| Tellurite plate with Loffler's media |
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Term
| What special requirements are there for culturing M. tuberculosis? |
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Definition
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Term
| What special requirements are there for culturing M. pnuemoniae? |
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Definition
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Term
| What special requirements are there for culturing Lactose-fermenting enterics such as E. coli? |
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Definition
| Pink colonies on MacConkey (also will grow black on EMB agar) |
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