For respiratory specimens such as sputum or BAL, which combination of media and conditions is appropriate?

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Multiple Choice

For respiratory specimens such as sputum or BAL, which combination of media and conditions is appropriate?

Starting with the idea that respiratory specimens contain a mix of organisms with different growth needs, the lab uses a set of media and atmospheres to maximize recovery: blood agar in a CO2 environment, chocolate agar in CO2, and MacConkey agar in ambient air. Blood agar in CO2 helps capnophilic organisms like Streptococcus pneumoniae grow well and be detected promptly; a 24-hour incubation often suffices for colony appearance and preliminary identification. Chocolate agar in CO2 is used for fastidious organisms such as Haemophilus influenzae and some Neisseria species. These bacteria require the additional growth factors present in chocolate agar, and incubating for up to 48 hours allows slower growers to form visible colonies. MacConkey agar in ambient air targets Gram-negative bacteria, including Moraxella and various enteric pathogens that can appear in respiratory samples. A 24-hour incubation is typically enough to observe colonies and differentiate lactose fermenters. Putting this together for a respiratory specimen yields the best overall recovery when you plate on blood agar in CO2 for about 24 hours, chocolate agar in CO2 for about 48 hours, and MacConkey agar in ambient air for about 24 hours. This combination covers the common pathogens encountered in sputum or BAL and respects their distinct growth requirements.

Starting with the idea that respiratory specimens contain a mix of organisms with different growth needs, the lab uses a set of media and atmospheres to maximize recovery: blood agar in a CO2 environment, chocolate agar in CO2, and MacConkey agar in ambient air.

Blood agar in CO2 helps capnophilic organisms like Streptococcus pneumoniae grow well and be detected promptly; a 24-hour incubation often suffices for colony appearance and preliminary identification.

Chocolate agar in CO2 is used for fastidious organisms such as Haemophilus influenzae and some Neisseria species. These bacteria require the additional growth factors present in chocolate agar, and incubating for up to 48 hours allows slower growers to form visible colonies.

MacConkey agar in ambient air targets Gram-negative bacteria, including Moraxella and various enteric pathogens that can appear in respiratory samples. A 24-hour incubation is typically enough to observe colonies and differentiate lactose fermenters.

Putting this together for a respiratory specimen yields the best overall recovery when you plate on blood agar in CO2 for about 24 hours, chocolate agar in CO2 for about 48 hours, and MacConkey agar in ambient air for about 24 hours. This combination covers the common pathogens encountered in sputum or BAL and respects their distinct growth requirements.

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