Microbiology Flashcards
Gram Stain is used for
Useful initial test to determine presence of Gram positive or Gram negative bacteria, arrangement, shape
Positive Gram stain shows
Thick peptidoglycan outer cell layer
Negative Gram stain shows
Thin peptidoglycan outer layer
Acid fast stain is used for
Mycobacterium, cannot identify with Gram stain.. resistant to acid decolorizing
When collecting sample swabs you need
1 swab for gram stain
1 swab for culture and sensitivity
Mycobacterium using acid-fast staining represents
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*
How long does mycobacteria take to grow in AFB cultures?
slow growing… takes up to 6-8 weeks to confirm.
- Mycobacterium TB
- Mycobacterium Avium intracellulare (MAC).. immunocompromised
QuantiFERON-TB Gold in Tube (QFT-GIT) measures what?
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?
What is the key to sputum sampling?
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!!!
Culture and sensitivity are routine reports
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
What is the sensitivity results broken down into?
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
In blood cultures, what can you identify?
67% of pathogens within 24 hrs
90% within 72 hrs
- pathogens generally enter blood via lymphatic system
- detecting which antibiotics have already been given!
What is the prep collection site for blood culture collection?
with povidone- iodine wiping clockwise outward motion*
2 vials : 1 aerobic/1 anaerobic
- Need to collect from 2 sites if possible
When you have strange results in blood cultures what do you do?
Drawing another set to confirm. Surveillance cultures are drawn to confirm clearing on infection.
- Ex: Staph Epidermidis is a very bad infection of skin*
Steps to taking proper urine cultures is
- Clean external genitalia with antiseptic wipe
- Catch Midstream sample
Morning Void the best
Catheterization can also be used for aseptic collection.
- sometimes initial dipstick is done first*
How long does it take for urine culture results to come back?
48 Hours
More than 2 species indicates what on urine culture results?
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
Generally throat cultures in peds and outpatient world is used to identify
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**
Gonorrhea and Chlamydial standard testing is doing
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
In wound cultures
you identify pathogenic organisms -Swab (more contaminates) - Curettage... chip bone - aspiration Need separate samples for aerobic and anaerobic*
It is very hard to get anaerobic samples so you can only get it with
Blood, Bile, Bone marrow, CSF, Direct lung aspirate, tissue biopsy, Fluid, dental abscess, abdominal/pelvic abscess, knife, gunshot, surgical wound, severe burn
What are some examples where anaerobic pathogens are impossible to detect?
Coughed up sputum, rectal swab, nasal/throat swab, urethral swab, voided urine
What are the 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
Since fungal cultures are 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
- TPN high risk fungal infections
