Micro Flashcards
Gram Stain
Useful initial test to determine presence of Gram positive or Gram negative bacteria
Peptidoglycan thickness
Gram positive - thick
Gram negative - thin
Gram indeterminate bacteria
Mycobacterium
Gram stain sample collection
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
Acid Fast Staining
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.
AFB Cultures
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)
QuantiFERON-TB Gold In-Tube (QFT-GIT)
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
Sputum Sampling
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!!!
Culture and Sensitivity
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
Antibiotic Sensitivity Results
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
Blood Cultures
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
Blood Culture Collection
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
Urinalysis
Also known as “urine dipstick”
Can be done in the lab or in the office/hospital setting
Urine sample is collected from the patient
Clean Catch
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
Urinalysis Inspection
Inspect for clarity- Clear=normal, Cloudy with
sediment= infection,
high protein content; Frothy= significant proteinuria
Odor-sweet=glucose in urine
Urine Cluture
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
Urine Culture Results
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
Throat Culture
Generally used to identify group A beta-hemolytic streptococci, also less often…
Neisseria meningitidis, C. diphtheria, B. pertussis, Staph aureus, H. influenzae, Candida species
Gonorrhea and Chlamydial Testing
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
Wound Culture
Used to identify the pathogenic organism
Swab (more contaminates)
Curettage
Needle aspiration
Need separate samples for aerobic and anaerobic
Suitable Anaerobic samples
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
Not suitable Anaerobic samples
coughed throat discharge (sputum)
rectal swab
nasal or throat swab
urethral swab
voided urine
Types of Anaerobes
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
Fungal Culture
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
KOH Prep
Used for skin/nail scraping and vaginal swab for presence of fungus (dermatophytes or yeast)
Tinea, Candida species
Prep with potassium hydroxide (KOH)
Vaginal Wet Mount (KOH)
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
Vaginal Wet mount Interpretation
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
Tzanck Smear
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
Viral Culture
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
Viral Detection by Polymerase Chain Reaction (PCR)
Faster method of viral detection by rapid replication of viral genome
Stool Culture
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
Clostridium Difficile Detection
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
C-Diff via PCR
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
Stool Ova and Parasite
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
CSF Analaysis
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.
Lumbar puncture adjoining test
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
CSF Findings
