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Lab Med > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Gram Stain is used for

A

Useful initial test to determine presence of Gram positive or Gram negative bacteria, arrangement, shape

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2
Q

Positive Gram stain shows

A

Thick peptidoglycan outer cell layer

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3
Q

Negative Gram stain shows

A

Thin peptidoglycan outer layer

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4
Q

Acid fast stain is used for

A

Mycobacterium, cannot identify with Gram stain.. resistant to acid decolorizing

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5
Q

When collecting sample swabs you need

A

1 swab for gram stain

1 swab for culture and sensitivity

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6
Q

Mycobacterium using acid-fast staining represents

A

Quick identification when TB organism is suspected

- need to wait 3 consecutive days worth of samples while being in an airborne room… First morning sputum is the best*

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7
Q

How long does mycobacteria take to grow in AFB cultures?

A

slow growing… takes up to 6-8 weeks to confirm.

  • Mycobacterium TB
  • Mycobacterium Avium intracellulare (MAC).. immunocompromised
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8
Q

QuantiFERON-TB Gold in Tube (QFT-GIT) measures what?

A

Interferon gamma released by T cells in response to the presence of mycobacteria TB presence

  • not helpful for people with history of TB
  • doesn’t differentiate between latent or active TB or react to a pt with Bacille Calmette- Guerin (BCG) vaccination
  • Mycobacterium bovis?
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9
Q

What is the key to sputum sampling?

A

TO get DEEP sample with minimal contaminate.
Good sample- High WBC, low epithelial cells
Normal flora- alpha hemolytic strep, Neisseria species diphtheriods, some Haemophilus species, pneumococcus
PATHOGENIC SPECIES: Streptococcus pneumoniae, Mycobacterium tuberculosis, Klebsiella pneumoniae, H. influenzae, and many more
No spit!!!

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10
Q

Culture and sensitivity are routine reports

A

That doesn’t include acid-fast bacilli (mycobacterium)!

  • Not include fungal.. unless routine for Candida species
  • Not anaerobes (except wound culture)
  • not include less common pathogens requiring specific media
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11
Q

What is the sensitivity results broken down into?

A

Sensitive, Intermediate, Resistant
- MIC.. minimal inhibitory concentration is indication of the minimal amount of antibiotic needed to prevent growth… rarely changes dosage regime or choice of antibiotic so its rarely used*** usually SET already

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12
Q

In blood cultures, what can you identify?

A

67% of pathogens within 24 hrs
90% within 72 hrs
- pathogens generally enter blood via lymphatic system
- detecting which antibiotics have already been given!

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13
Q

What is the prep collection site for blood culture collection?

A

with povidone- iodine wiping clockwise outward motion*
2 vials : 1 aerobic/1 anaerobic
- Need to collect from 2 sites if possible

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14
Q

When you have strange results in blood cultures what do you do?

A

Drawing another set to confirm. Surveillance cultures are drawn to confirm clearing on infection.
- Ex: Staph Epidermidis is a very bad infection of skin*

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15
Q

Steps to taking proper urine cultures is

A
  1. Clean external genitalia with antiseptic wipe
  2. Catch Midstream sample
    Morning Void the best
    Catheterization can also be used for aseptic collection.
    - sometimes initial dipstick is done first*
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16
Q

How long does it take for urine culture results to come back?

A

48 Hours

17
Q

More than 2 species indicates what on urine culture results?

A

contamination. … get repeat sample
- Quantity of bacteria is also shown where <100,000 is considered negative depending on scenario. Should generally be >100,000 colonies
- Keep in mind Medical Diuresis

18
Q

Generally throat cultures in peds and outpatient world is used to identify

A

Group A beta- hemolytic streptococci less often… Neisseria meningitidis, C. diphtheria, B. pertussis, Staph aureus, H. influenzae, Candida species

  • AVOID TONGUE/CHEEKS
  • Viral cultures use diff swab and media… herpes**
19
Q

Gonorrhea and Chlamydial standard testing is doing

A

A urine test checking for genetic nucleic acid amplification (NAAT)

  • Oral/Rectal testing needs to be performed with swab culture
  • cultures normally taken in cases of rape kits
20
Q

In wound cultures

A 
you identify pathogenic organisms
-Swab (more contaminates)
- Curettage... chip bone
- aspiration
Need separate samples for aerobic and anaerobic*
21
Q

It is very hard to get anaerobic samples so you can only get it with

A

Blood, Bile, Bone marrow, CSF, Direct lung aspirate, tissue biopsy, Fluid, dental abscess, abdominal/pelvic abscess, knife, gunshot, surgical wound, severe burn

22
Q

What are some examples where anaerobic pathogens are impossible to detect?

A

Coughed up sputum, rectal swab, nasal/throat swab, urethral swab, voided urine

23
Q

What are the types of anaerobes?

A

Obligate: harmed by the presence of oxygen

Aerotolerant: cannot use oxygen for growth, but tolerate its presence

Facultative: which can grow without oxygen but use oxygen if it is present

24
Q

Since fungal cultures are not routinely done…

A

Fungemia generally only found in

  • immunocompromised
  • long term intravenous access
  • broad spectrum abx use
  • Topical fungal infection generally doesn’t require culture for treatment
  • TPN high risk fungal infections
25
Q

KOH prep is used for

A

Used for skin/nail scraping and vaginal swab for presence of fungus (dermatophytes or yeast)

  • Tinea, Candida species
  • prep with potassium hydroxide and throw under microscope
26
Q

Vaginal Wet mount (KOH) is used to diagnose

A

Also used to diagnose bacterial vaginosis and trichomoniasis

Same procedure as KOH prep, different finding

Not done during menstruation, or within 24 hours of sex or vaginal irrigation

27
Q

Interpreting Vaginal Wet Mount

A

Vaginal candidiasis: hyphae and buds

BV: >20% are clue cells
Thin, milky, fishy odor discharge
pH >4.5

Trichomoniasis: yellow-green, foamy, foul smelling
Mobile trichomonads visible

28
Q

Tzanck Smear is used to identify

A

Used to find multinucleated giant cells
Herpes simplex, Herpes zoster/Varicella, Pemphigus, Cytomegalovirus
-Similar to KOH but fixated with methanol and stained with Giemsa, methylene blue or Wright’s stain

29
Q

In Viral Cultures

A

A swab of the infected area is placed with a cell type (LIQUID MEDIA)that the virus can infect
- Detection of antigens produced by infected cells indicates a positive test
Viruses that can be identified
adenovirus, cytomegalovirus, enteroviruses, herpes simplex virus, influenza virus, parainfluenza virus, rhinovirus, respiratory syncytial virus, varicella zoster virus, measles and mumps

30
Q

What is a faster method of viral detection by rapid replication of the viral genome?

A

Viral Detection by Polymerase Chain Reaction (PCR)

31
Q

Since we don’t really do Stool cultures because we base it on history of pt

A

You would only do this for specific organisms you think are there like Shigella, Salmonella, Campylobacter Jejuni. GI tract filled with normal flora.
- note any recent antibiotic therapy

32
Q

Clostridium Difficile Detection (C Diff) shows

A

C.Diff specific cultures can be used but are slow to produce results

Toxin A and B ELISA

True negative require 3 samples from separate days
- no stool cultures for C diff

33
Q

Clostridium by PCR

A 
Probably the most common
More sensitive than ELISA testing
Specific for Toxin B gene
Cannot distinguish between active and inactive disease
Sample MUST be liquid
No need to repeat testing
34
Q

Stool Ova and Parasites

A

Round worms, hook worms, tape worms, amoebas, giardia
Need to avoid mineral oil (enemas), bismuth (pepto), antidiarrheals, barium, antibiotics for 7 – 10 days prior to samples
3 samples from 3 consecutive days

35
Q

What test for pinworms?

A

Scotch tape test

36
Q

CSF Analysis

A

Purpose
Measure CSF pressure
Aid diagnosis of bacterial or viral meningitis, subarachnoid hemorrhage, tumors, and brain abscess
Aid diagnosis of neurosyphilis
Prepare patient that it takes at least 15 minutes
Sometimes followed by headache
Get consent

37
Q

Always obtain a head CT prior to an LP to rule out a mass occupying lesion
Concern for brain herniation when removing fluid below the brain****

A

For lumbar puncture!

Lab Med (4 decks)

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