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33 Cards in this Set

  • Front
  • Back
When is the gram stain helpful in non-sterile body sites
When pathogens can be distinguished from non-pathogens by microscopic appearance (Clostridium tetani, Bacillus sp., Neisseria gonorrhoeae)
What are the uses of the Gram stain in sterile body sites
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)
What is a nutritive medium
Contains basic nutrients for growth of non-fastidious bacteria
Tryptic soy digest agar (TSA)
What is an enriched medium
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
What is a selective medium
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
What is a differential medium
Contains substrates and often pH indicators such that bacteria with different biochemical properties can be distinguished
MacConkey agar
In which areas of the body is a gram stain not useful
Respiratory tract (pharyngitis); Urinary tract; Gastrointestinal tract; Systemic infections, bacteremia (blood)
In which areas of the body is a gram stain useful
Lower respiratory infectious; Genital tract; Skin and wound infections; Deep tissue; Central nervous system
A throat swab is not adequate for what bacteria that may cause Pharyngitis
Bordetella pertussis. A nasopharyngeal swab should be taken and plated at the bedside (Bordet-Gengou or Regan-Lowe agar)
With pharyngitis, a throat swab should be taken to screen for what
Group A, beta hemolytic streptococci (Strep pyogenes)
When checking pharyngitis, the lab must be alerted if you want them to look for what disease
In lower respiratory infections, a predominance of epithelial cells vs. sputum indicates what
Epithelial cells indicates saliva. Sputum should contain predominantly inflammatory cells (PMNs)
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)
What are the normal flora of the respiratory tract
Staphylococcus species
Alpha hemolytic streptococci (several species)
Beta hemolytic streptococci other than group A
Neisseria species
Haemophilus parainfluenzae
Corynebacterium species
Numerous oral anaerobic bacteria
Although urine is typically sterile, collection invariably introduces contamination. What is the exeption
Suprapubic aspiration
What are the general rules for collecting a sample from the urinary tract
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
What is the normal flora found in urine
Skin flora, vaginal and rectal contaminants
How do you isolate Neisseria gonorrheae
Collect exudates with swab and plate directly onto Thayer Martin agar at bedside. Be sure to consider Chlamydia
Genital lesions are not likely to be bacterial and are generally not cultured. What is the exception
Haemophilus ducreyi, very fastidious, must be plated at bedside
What is the normal flora of the male urethra
Skin flora (Staphylococci, streptococci, corynebacteria)
What are the normal flora of the female genital tract
Lactobacillus species
Alpha hemolytic streptococci
Various gram negatives including glucose non-fermenters, some yeast, and large numbers of anaerobes
What are the normal flora of the gastrointestinal tract
Huge numbers of enteric facultative gram negative rods
Alpha hemolytic streptococci
Huge numbers of anaerobic bacilli and cocci
How is a sample obtained from the gastrointestinal tract
Submit a fresh fecal sample or rectal swab in transport medium
How is a sample taken for skin and wound infections
Swab within the lesion, avoid surrounding skin, submit in transport medium (collect an additional swab for smear)
What is the normal flora of the skin
Staphylococcus species
Corynebacterium species
Proprionobacterium species
Transient surface contaminants such as Gram negative bacilli
How is a sample obtained from Deep tissue and sterile body fluids (synovial, pleural, etc.)
Aspirate fluid with a syringe; send plugged syringe to the lab or aspirate into vial of pre-reduced transport medium
How is a sample taken from the Central nervous system
Thoroughly decontaminate skin; Submit last tube collected to microbio; Gram stain result is very important for early diagnosis
How is a sample collected for systemic infections and bacteremia
Decon the skin carefully with iodine; Collect three times over 24 hours; Culture in 1:10 dilution in broth, anaerobically and aerobically
What are some special circumstances that require further comm with the lab
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
What are some examples of agents that are so fragile or fastidious that they will not survive transport
Neisseria gonorrheae
Haemophilus ducreyi
Bordetella pertussis
What are some examples of agents that are slow growing or have specific culture requirements
Legionella pneumophila
Leptospira species
Bartonella species
What are two examples of agents that cannot be grown on culture medium
Chlamydia species
Treponema pallidum (syphilis)
What are some examples of highly pathogenic bacteria that most clinical laboratories are not equipped to safely culture
Bacillis anthracis
Brucella species
Francisella tularensis