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33 Cards in this Set
- Front
- Back
When is the gram stain helpful in non-sterile body sites
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When pathogens can be distinguished from non-pathogens by microscopic appearance (Clostridium tetani, Bacillus sp., Neisseria gonorrhoeae)
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What are the uses of the Gram stain in sterile body sites
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Fluids, cerebrospinal fluid, synovial fluid, amniotic fluid: Very helpful fast indication of infectious agent
Blood: not helpful, even in sepsis Urine: Numbers visible corresponds to number indicative of significant infections (10^5 CFU per ml) |
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What is a nutritive medium
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Contains basic nutrients for growth of non-fastidious bacteria
Tryptic soy digest agar (TSA) |
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What is an enriched medium
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Supplemented with nutrients for bacteria that are fastidious and require pre-synthesized nutrients such as hemin, iron, or serum
5% sheep blood agar; chocolate agar |
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What is a selective medium
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Contains growth inhibitors that repress growth of certain classes of organisms and promote the growth of desired species
Staph 110 agar (elevated NaCl); MacConkey agar |
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What is a differential medium
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Contains substrates and often pH indicators such that bacteria with different biochemical properties can be distinguished
MacConkey agar |
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In which areas of the body is a gram stain not useful
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Respiratory tract (pharyngitis); Urinary tract; Gastrointestinal tract; Systemic infections, bacteremia (blood)
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In which areas of the body is a gram stain useful
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Lower respiratory infectious; Genital tract; Skin and wound infections; Deep tissue; Central nervous system
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A throat swab is not adequate for what bacteria that may cause Pharyngitis
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Bordetella pertussis. A nasopharyngeal swab should be taken and plated at the bedside (Bordet-Gengou or Regan-Lowe agar)
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With pharyngitis, a throat swab should be taken to screen for what
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Group A, beta hemolytic streptococci (Strep pyogenes)
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When checking pharyngitis, the lab must be alerted if you want them to look for what disease
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Diphtheria
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In lower respiratory infections, a predominance of epithelial cells vs. sputum indicates what
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Epithelial cells indicates saliva. Sputum should contain predominantly inflammatory cells (PMNs)
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In lower respiratory infections, routine bacterial culture is not adequate for what three microorganisms?
What cultures are? |
Mycobacterium tuberculosis (acid fast culture, molecular probes)
Mycoplasma pneumoniae (diagnosed serologically-elevated IgM or cold agglutinin) Chlamydia pneumoniae (diagnosed serologically) |
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What are the normal flora of the respiratory tract
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Staphylococcus species
Alpha hemolytic streptococci (several species) Beta hemolytic streptococci other than group A Neisseria species Haemophilus parainfluenzae Corynebacterium species Numerous oral anaerobic bacteria |
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Although urine is typically sterile, collection invariably introduces contamination. What is the exeption
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Suprapubic aspiration
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What are the general rules for collecting a sample from the urinary tract
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Perineal cleansing followed by collection of mid-stream urine to reduce contamination
Do not take urine from the collection bag of a catheterized patient Refrigerate the sample or deliver to the lab immediately. 100,000 CFU/ml is significant |
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What is the normal flora found in urine
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Skin flora, vaginal and rectal contaminants
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How do you isolate Neisseria gonorrheae
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Collect exudates with swab and plate directly onto Thayer Martin agar at bedside. Be sure to consider Chlamydia
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Genital lesions are not likely to be bacterial and are generally not cultured. What is the exception
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Haemophilus ducreyi, very fastidious, must be plated at bedside
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What is the normal flora of the male urethra
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Skin flora (Staphylococci, streptococci, corynebacteria)
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What are the normal flora of the female genital tract
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Lactobacillus species
Alpha hemolytic streptococci Various gram negatives including glucose non-fermenters, some yeast, and large numbers of anaerobes |
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What are the normal flora of the gastrointestinal tract
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Huge numbers of enteric facultative gram negative rods
Alpha hemolytic streptococci Enterococci Yeasts Huge numbers of anaerobic bacilli and cocci |
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How is a sample obtained from the gastrointestinal tract
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Submit a fresh fecal sample or rectal swab in transport medium
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How is a sample taken for skin and wound infections
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Swab within the lesion, avoid surrounding skin, submit in transport medium (collect an additional swab for smear)
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What is the normal flora of the skin
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Staphylococcus species
Streptococci Corynebacterium species Proprionobacterium species Transient surface contaminants such as Gram negative bacilli |
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How is a sample obtained from Deep tissue and sterile body fluids (synovial, pleural, etc.)
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Aspirate fluid with a syringe; send plugged syringe to the lab or aspirate into vial of pre-reduced transport medium
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How is a sample taken from the Central nervous system
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Thoroughly decontaminate skin; Submit last tube collected to microbio; Gram stain result is very important for early diagnosis
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How is a sample collected for systemic infections and bacteremia
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Decon the skin carefully with iodine; Collect three times over 24 hours; Culture in 1:10 dilution in broth, anaerobically and aerobically
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What are some special circumstances that require further comm with the lab
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The agent is so fragile or fastidious that it will not survive transport
The agent is slow-growing or has specific culture requirements The agent cannot be grown on culture medium The agent is not generally found in the area The agent is highly pathogenic |
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What are some examples of agents that are so fragile or fastidious that they will not survive transport
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Neisseria gonorrheae
Haemophilus ducreyi Bordetella pertussis |
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What are some examples of agents that are slow growing or have specific culture requirements
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Legionella pneumophila
Leptospira species Bartonella species |
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What are two examples of agents that cannot be grown on culture medium
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Chlamydia species
Treponema pallidum (syphilis) |
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What are some examples of highly pathogenic bacteria that most clinical laboratories are not equipped to safely culture
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Bacillis anthracis
Brucella species Francisella tularensis |