Micro

Question 1

Gram Stain

Answer 1

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

Question 2

Peptidoglycan thickness

Answer 2

Gram positive - thick
Gram negative - thin

Question 3

Gram indeterminate bacteria

Answer 3

Mycobacterium

Question 4

Gram stain sample collection

Answer 4

sputum, blood, urine or any other specimen- in a sterile container sent to the lab

If collecting sample with a swab, separate swabs to avoid contamination

1 swab for gram stain
1 swab for culture and sensitivity

Question 5

Acid Fast Staining

Answer 5

Mycobacteria are resistant to acid decolorizing, so can’t identify with Gram staining

Used for quick identification when TB organism suspected

Generally need 3 consecutive days worth of samples. First morning sputum is the best.

Question 6

AFB Cultures

Answer 6

Mycobacteria is a slow growing organism requiring up to 6-8 weeks to confirm no growth

2 common organisms
Mycobacterium tuberculosis
Mycobacterium avium-intracellulare (MAC)

Question 7

QuantiFERON-TB Gold In-Tube (QFT-GIT)

Answer 7

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

does not differentiate between latent or active TB

does not react to a patient that received Bacille

Calmette-Guérin (BCG) vaccination
Mycobacterium bovis

Question 8

Sputum Sampling

Answer 8

Key is to get a deep sample with minimal contaminate

Good sample: high WBC, low epithelial cells

Normal flora: alpha-hemolytic strep, Neisseria species, diphtheroids, some Haemophilus species, pneumococcus

Pathogenic species: Strepococcus pneumonia, Mycobacterum tuberulosis, Klebsiella pneumoniae, H. influenzae, and many more

No spit!!!

Question 9

Culture and Sensitivity

Answer 9

routine cultures – C&S culture and sensitivity report

does not include acid-fast bacilli (mycobacterium)
does not include fungal (unless routine such as Candida species)

usually not include anaerobes (exception deep wound culture)

does not include less common pathogens requiring special media

Question 10

Antibiotic Sensitivity Results

Answer 10

Broken down into 3 types:

Sensitive
Intermediate
Resistant

Minimal Inhibitory Concentration (MIC)
Indicates the minimal amount of antibiotic needed to prevent growth

Rarely changes the dosage regimen, or choice of antibiotic

Question 11

Blood Cultures

Answer 11

Inoculating culture media with blood sample

Can identify 67% of pathogens within 24hrs; 90% within 72hrs

Pathogens generally enter blood via lymphatic system
Need to know which antibiotics have already been given!

Strange results often mean drawing another set to confirm
Staph epidermidis

Surveillance cultures are drawn to confirm clearing on infection

Question 12

Blood Culture Collection

Answer 12

Prep collection site with povidone-iodine wiping clockwise outward motion

Need to collect adequate amount, refer to culture vial
Two vials: 1 aerobic, 1 anaerobic

Need to collect from 2 sites when possible

Question 13

Urinalysis

Answer 13

Also known as “urine dipstick”

Can be done in the lab or in the office/hospital setting
Urine sample is collected from the patient

Question 14

Clean Catch

Answer 14

Clean-Catch=urethral area is cleaned with antiseptic wipe before urine is obtained in a sterile container

Inspect urine for color-yellow/straw colored=normal; dark yellow=dehydration; red=blood; brown=excess bilirubin or blood

Question 15

Urinalysis Inspection

Answer 15

Inspect for clarity- Clear=normal, Cloudy with
sediment= infection,

high protein content; Frothy= significant proteinuria

Odor-sweet=glucose in urine

Question 16

Urine Cluture

Answer 16

The external genitalia must be cleaned with an antiseptic wipe

Sample should be midstream
Best samples are first morning void

Catheterization can also be used for aseptic collection
Sometimes an initial dipstick is done first

Question 17

Urine Culture Results

Answer 17

Final results are given after 48hrs

More than 2 species normally indicates contamination. Get repeat sample.

Results also include the quantity of bacteria
<100,000 colonies/mL sometimes considered negative depending on clinical scenario

Medical diuresis can also effect results

Question 18

Throat Culture

Answer 18

Generally used to identify group A beta-hemolytic streptococci, also less often…

Neisseria meningitidis, C. diphtheria, B. pertussis, Staph aureus, H. influenzae, Candida species

Question 19

Gonorrhea and Chlamydial Testing

Answer 19

Standard for urogenital infections in men and women is a nucleic acid amplification (NAAT) urine testing

Oral and rectal testing needs to be performed with a swab culture

Cultures are still normally taken in cases of rape kits

Question 20

Wound Culture

Answer 20

Used to identify the pathogenic organism
Swab (more contaminates)

Curettage
Needle aspiration
Need separate samples for aerobic and anaerobic

Question 21

Suitable Anaerobic samples

Answer 21

blood
bile
bone marrow
cerebrospinal fluid

direct lung aspirate
tissue biopsy from a normally sterile site
fluid from a normally sterile site (like a joint)

dental abscess
abdominal or pelvic abscess
knife, gunshot, or surgical wound
severe burn

Question 22

Not suitable Anaerobic samples

Answer 22

coughed throat discharge (sputum)
rectal swab
nasal or throat swab

urethral swab
voided urine

Question 23

Types of Anaerobes

Answer 23

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

Question 24

Fungal Culture

Answer 24

Not routinely done

Fungemia generally only found in
immunocompromised

long term intravenous access
broad spectrum abx use
Topical fungal infection generally doesn’t require culture for treatment

Question 25

KOH Prep

Answer 25

Used for skin/nail scraping and vaginal swab for presence of fungus (dermatophytes or yeast) Tinea, Candida species Prep with potassium hydroxide (KOH)

Question 26

Vaginal Wet Mount (KOH)

Answer 26

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

Question 27

Vaginal Wet mount Interpretation

Answer 27

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

Question 28

Tzanck Smear

Answer 28

Used to find multinucleated giants 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

Question 29

Viral Culture

Answer 29

A swab of the infected area is placed with a culture of a cell type 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

Question 30

Viral Detection by Polymerase Chain Reaction (PCR)

Answer 30

Faster method of viral detection by rapid replication of viral genome

Question 31

Stool Culture

Answer 31

The GI tract is filled with organisms that are considered normal flora. Only looking for specific organisms Shigella, Salmonella, Campylobacter jejuni Make note of recent antibiotic therapy

Question 32

Clostridium Difficile Detection

Answer 32

Routine stool cultures are not used for detection of C.Diff 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

Question 33

C-Diff via PCR

Answer 33

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

Question 34

Stool Ova and Parasite

Answer 34

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

Question 35

CSF Analaysis

Answer 35

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 from LP. Lay flat 6 hours Get consent.

Question 36

Lumbar puncture adjoining test

Answer 36

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

Question 37

CSF Findings

Answer 37