bacterial disease testing Flashcards
What can alter bacterial testing results?
improper technique, transport, transient bacteremia, abx
What are the general culture interpretation guidelines?
infection considered if >10^5. Organisms found
< 10^1 usually contaminant. Pure isolate more likely causative agent than mixed flora. organism isolated known to cause disease at this site
What is the normal flora found on the skin?
Staph epidermidis, *S. aureus, Micrococcus, few gram neg bacilli moist skin, Corynebacterium, Propionibacterium acnes
What are pathogenic organisms found on the skin?
Streptococcus pyogenes. Pseudomonas. Proteus
What are pathogenic organisms found in the mouth?
Strep pneumoniae, Strep pyogenes, Neisseria meningitidis, Haemophilus influenza, Neisseria gonorrheae
What are pathogens found in the oropharynx?
Mycoplasma, Bordatella pertussis, Staph aureus,
Pseudomonas
What is the normal flora of the conjunctiva?
Cornyebacterium, Neisseria, Moraxellae, Staph and Strep, Haemophilus and Parainfluenza
What are pathogenic organisms found in the conjunctiva?
Pneumococcus, Pseudomonas, Strep
What are pathogenic organisms of the GI tract?
Clostridium difficile, Salmonella, toxic strains E. coli, Helicobacter pylori
What are pathogenic organisms of the urethra?
Chlamydia, Gonorrhea, Syphilis
What are pathogenic organisms of the vagina?
Candida, trichomonas
Describe the proper handling of a specimen?
Obtain specimen before antibiotics. aseptic technique. Minimize contamination by skin and mucous membranes. Collect an adequate volume and send tissue or fluid rather then a swab when possible. Label appropriately.Fill out requisition slips completely
How should specimens be transported?
Notify the lab if special tests are requested for unusual pathogens. Specimens should be in sterile leak proof containers in sealed plastic bags, and should arrive within 1-2 hours of collection…if delay is unavoidable most specimens (except blood, CSF, joint fluid and cervical secretions for gonorrhea) should be refrigerated
How long does it take to get cultures back?
Blood cultures: 48-96 hours. Most routine cultures (urine, throat, sputum) 24-48 hrs. Anaerobes: 48-72 hours
Describe how to obtain a wound culture
Round up some pus on an applicator. Culture of specimens from the skin edge is less accurate than the suppurative material
How should you culture an abscess/boil/furuncle?
Incised fluid or material swabbed with culture swab. Important to get pus/exudate from deep in the wound to avoid surface contamination
How should you culture conjunctiva?
Gently swab to collect drainage. Place in appropriate container and send to lab at 25 C
How should you culture a throat?
Inform lab if trying to identify N. gonorrheae (requires special medium—Thayer-Martin agar). Swab posterior pharynx and tonsils. Avoid touching any other part of the mouth. Send to the lab at 25 C
When is a sputum culture not necessary?
most outpatient community acquired pneumonias. Management of bronchitis. management of acute exacerbations of COPD
How do you obtain a sputum collection?
Obtain prior to antibiotic treatment. Have the patient rinse their mouth prior to expectoration. No food 1-2 hours prior to expectoration. Inoculation of the culture media immediately after the specimen if obtained
What is different about atypical pneumonias sputum cultures?
with mycoplasma and legionella the sputum will have abundant PMNs, and few or no organism will be seen on gram stain
What are indications for a blood culture?
mainly be considered in patients with temp >101 suspected of having endocarditis or other systemic pathogens, inpatients with pneumonia prior to starting abx.
How should you obtain a blood culture?
Two specimens obtained from two separate sites 15 minutes apart (Total 30-40 ml blood). Clean site w/ETOH than with Betadine. Wipe bottle tops with alcohol. Go to lab immediately. Do not draw blood cultures through central lines or IV’s.
How should you obtain a urine sample?
Midstream clean catch urine by patient: Need at least 1 ml. Transport at 4 C. Indwelling catheter: Disinfect port w/ alcohol and remove 5-10 ml of urine w/ needle and syringe—transfer to sterile container; 4 C. Suprapubic aspirate: at least 1 ml, at 4 C. ALWAYS Send as UA and urine C & S
What are indicators of possible pyuria?
Leukocyte esterase-If positive on dipstick likely indicates pyuria. Nitrite- Indicates the presence of enerobacteriaceae. If negative but + symptoms of UTI still want urine culture
Describe the microscopic analysis of urine?
Evaluation of urine sediment from a spun sample
Presence of squamous epithelial cells = contamination from genital region
Normals- RBC/WBC: 0-5 HPF, Bacteria: absent, Casts: 0-4, hyaline LPF, Crystals
What are indications for a lumbar puncture?
suspected subarachnoid hemorrhage, isolating organism causing meningitis or brain abscess
How should you collect CSF from a lumbar puncture?
collect 1-5ml of CSF. Transport at 25 degrees C. Gram stain and Bacterial culture. 4 tubes:
(1) Cell count, (2) gram stain and culture, (3) glucose & protein, (4) cell count to compare to tube 1
Describe purposes of thoracentesis and what it can be used to test?
Therapeutic-relieves dyspnea. Diagnostic-Test the fluid for TB, fungus, CEA level (tumor marker), cytology, culture, gram stain, pH
In general how do you obtain peritoneal, pericardial, pleural, or synovial body fluids?
Aspirate using sterile technique into sterile syringe.
Remove needle and cap syringe to send to lab. Minimum of 1-10cc at 4 degrees C
When should you swab genital tract in women?
the cervix for gonorrhea, chlamydia as well as other organisms in suspected PID. Swabs of the urethra or urine testing for chlamydia
What are instructions for a vaginal/cervical culture?
No douching or tub bathing for 24 hrs prior to collection
When would you use a wet mount?
Helpful in evaluating vaginitis: Saline wet mount of vaginal discharge can show epithelial cells covered with bacteria suggestive of bacterial vaginosis, Trichomonas. Can reveal multiple PMN’s. KOH (potassium hydroxide) wet mount can reveal candida organisms
How would you evaluate the urethra of men?
Special smaller swabs for urethral sampling for gonorrhea and chlamydia. Urine samples for GC and chlamydia for nucleic acid amplification. Nucleic acid amplification more sensitive then culture
Describe an urethral culture?
Usually on men. Rapid enzyme test available. Thayer martin/new York media. Anaerobic transport
What are indications for a stool culture?
for those with prolonged diarrhea who haven’t been on antibiotics or hospitalized: >2 grams; 4 C. Test of choice for those who develop diarrhea on antibiotics or in hospital > 3 days: need > 5 ml; 4 degrees C
What are you checking for with stool cultures?
ova & parasites. Usually look for Staph.,Salmonella, shigella, c.difficile.
