week 1- microbiology Flashcards
• What are the types of morphologies of microorganisms?
o Coccus - round (cocci = plural); Streps, staphs, Neisseria
o Diplococcus - cocci in pairs (diplococci = plural), Strep. pneumoniae
o Bacillus or rods - parallel sides (bacilli = plural) ; E. coli
o Spirochetes - curved or spiral organisms ; Treponema pallidum
• What is the gram stain used for?
o Screens for presence of bacteria
o Provides good info on what abx to use: most bacteria are either G(+) or G(-)
o (+): stain purple, ex: Strep, staph
o (-): stain pink or red; ex: E. coli, Neisseria
• What is the procedure for analyzing human samples for bacteria w microscope?
o 1) Apply d/c to glass slide and air dry
o 2) Fix with methyl alcohol
o 3) Report bacteria according to morphology& staining reaction
o 4) Note presence/absence of WBCs
• How does the gram stain work? Procedure?
o Gram (+) have this peptidoglycan wall outside of membrane, retains crystal violet o Gram (-) have thin peptidoglycan layer, w outside LPS layer; crystal violet gets decolorized, and stain pink with counterstain o Fixation → crystal violet → iodine tx → decolorization →counter stain (safranin)
• What are the types of media for bacteria culture?
o Liquid – diffuse growth
o Solid – discrete colonies- can isolate one strain
• What is bacteria culture used for?
o Detect STI
o Dx blood, GI, UTI, URI/LRI
o Dx active TB
o Eval & tx infx of wounds & soft tissues
o Determine abx sensitivities: place disc w abx on agar, assess for zone of inhibition
• How are culture specimens collected?
o Get before initiation of any antimicrobial tx
o Explain procedure completely to pt
o Follow universal precautions
o Collect according to lab’s requirements
o Label completely: pt name, date & time of collection, source/site of specimen
• What parts of the urinary tract are sterile?
o Sterile above urethra
o Urine normally sterile
o Must pass thru contaminated regions during specimen collection (noninvasive)
o Quantitative methods discriminate contamination and colonization from infx
o Urine collected via invasive methods (suprapubic aspiration) should be sterile
o Distal portion of urethra colonized
o Many organisms are same as found in genital tract
o Some transient colonizers are potential pathogens
• What are the resident flora of the urinary tract?
o Same as Genital tract flora- mixture of: o Lactobacillus o Alpha-hemolytic Streptococcus sp. o Diptheroids o Gardnerella vaginalis o Yeast
• How is a urine culture obtained?
o Obtain “clean catch midstream” sample to avoid contamination from skin & genital tract
o Transfer urine to tube with preservative (48 hrs) to prevent multiplication of bacteria after sample collection (or refrigerate, 24 hrs)
o Lab will process specimen & report “colony count” of isolated organisms:
o 50 colonies, would report as “50,000 bacteria per ml of urine.”
o E. coli is mc bacteria responsible for UTIs
• What are the mc pathogens of the UT?
o Community acquired: E. coli mc; Klebsiella sp and other Enterobacteriaceae; Staphylococcus saprophyticus
o Hospital acquired: E. coli, Klebsiella, other Enterobacteriaceae; Pseudomonas aeruginosa
o Enterococci and Staphylococci
• What is a throat culture for?
o To determine pharyngitis etio: bacterial, gonococcal, viral, candida
o Perform if “sore throat,” fever of unknown cause, chronic carriers of recurrent infections
• How is a throat culture collected?
o Pt tilt head back & open mouth. Depress tongue with wooden blade
o Swab
o 1. Both tonsillar faucies (between palatal glossal arch & palatal pharyngeal arch)
o 2. Posterior pharynx.
o 3. Any areas of inflammation, exudates, or ulcers
o 4. Avoid touching any other part of mouth or tongue
• What are common agar plates used in throat culture?
o Routine culture involves blood agar plate to identify mc bacterial pathogen: Group A -hemolytic Strep(pyogenes)
o Candida albicans mb isolated on blood agar, esp in immune suppressed pt
o Chocolate Agar Plate (named for color): Media required to grow: N. gonorrhoeae, N. meningitides, H. influenzae
• How is a Rapid Strep test done?
o Head back, open mouth, depress tongue w wood blade
o Swab both tonsillar faucies, posterior pharynx & any areas of inflam, exudates, or ulcers
o Avoid touching any other part of mouth or tongue
o Place swab in test kit, add reagent to extract cell wall Ag
o (+) = pink line dt reaction of extracted Ag w Ab in filter paper
• What are other special considerations for throat culture?
o If suspect diphtheria, must notify lab to use special media of tellurite agar.
o Bordetella pertussis, whooping cough: swab nasopharyngeal, inoculate charcoal plate, place in transport media, & send to State lab
o Modern detection is DNA PCR, from swab of back of nose. Result can be obtained in 24-48 hrs
• What is the optimal timing for dx testing for pertussis?
o Culture: 0-2 wks after cough onset
o PCR: 0-4 wks
o Serology: 2-12 wks
• How are viral respiratory cultures obtained?
o Collect sample from site of infx
o Compare nasal & nasopharyngeal swabs, and nasopharyngeal wash specimens w expanded gold standard in Quidel QuickVue influenza test
o Nasopharyng swab has highest sens and spec
• When and how do you do a lower respiratory culture (sputum)?
o If suspect Lung CA or TB; abn CXR, productive cough & negative bronchoscopy; Bronchoscopy & lung bx used more often now.
o First morning sample is best; Instruct patient to elicit sputum via deep cough (first rinse mouth and 3 respirations)
o Expectorate in sterile container: thick mucus, without saliva
o Refrigerate sample: NO preservative
o Interfering Factors: Failure to adequately rinse mouth prior to sample; Saliva submitted instead of sputum
• How does a lab process a sputum culture? Clinical significance?
o inoculate sputum onto supportive media to grow
o If pathogens recovered, perform abx sensitivity testing (extra charge).
o Malignancies of trachea, bronchus, lung
o Benign cellular changes dt infx vs exposures
o Potential bacterial pathogens: Staph aureus, Strep pneumonia, Haemophilus influenza, Klebsiella pneumoniae, etc.
• What are the mc labs for TB?
o 1. Acid fast (bacilli) smear → AFB
o 2. Cultivation of the organism→ Culture
o 3. Organism Speciation→ DNA probe, rRNA amplification
o most useful body fluid for analysis is sputum:
o Identification of M. tuberculosis in any body fluid or tissue is diagnostic of active TB since active growth always produces dz
• When is acid fast stain or sputum culture indicated?
o Persistent productive cough >3 wks o Anorexia o Unexplained weight loss o Night sweats & Fever o Hemoptysis o Chest pain o Fatigue o High risk pts: immunocompromised, alcoholic, recent exposure to TB
• What is the acid fast stain for TB?
o “acid-fast” procedure drives stain into lipid rich cell wall (CW is gram stain resistant)
o Collect 3 AM sputums, > 5 ml, consecutive days
o tested w/in 24 hrs
o More rapid but less sensitive than Culture
o Detects 10,000 - 100,000 organisms/mL
o (+)= red tubercle bacilli
o A NEG smear does NOT rule out dz (mb light infxn)
o Positive AFB smears may indicate TB, but does not confirm TB dx, as some AFB’s are NOT M. tuberculosis.
o Monitor tx, should be NEG after 2 months antimicrobial tx.
• How is organism speciation done for TB?
o PCR DNA probe: Takes 36-48 hrs, on sputum culture sample
o MTD (direct) Test [Gen-Probe] (FDA approved 1995): Takes 5-6 hours
o Uses rRNA: Amplification techniques with enzymes, one billion fold replication, and chemiluminescent labels; Sens 95.5%, Spec 100%
• What is the TB culture?
o Remains gold standard for confirming TB dx
o Culture all specimens, even if smear or NAA negative
o Results in 4–14 d when liquid medium systems used
o Culture monthly until conversion, i.e., 2 consecutive (-) cultures
o Colonies: whitish mounds, bubbly
• When is a blood culture done? Catheter culture?
o If suspect Systemic bacterial infx (usu have fever & chills)
o If suspect septicemia, do when patient manifests chills → correlates with “showers” of bacteria in bloodstream
o Catheter Culture: Specimens drawn through IV catheter for catheter sepsis only
• What are the terms for systemic infections?
o Sepsis: SIRS response triggered by infx
o Septicemia: sepsis originating from infx in bloodstream
o Systemic Inflammatory Response Syndrome – systemic immune response, w 2+ criteria: T > 100.4 ˚F or < 96.8 ˚F; HR > 90 bpm; RR > 20; Extreme high/low WBCs
• What are sources of blood infxs?
o Complex wounds (open fractures) o Dirty wounds (debris) o Burns o Puncture wounds o Impaled Objects o Crush Injuries
