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Correct Answer: most aerobic blood collection bottles contain 25% – 35% co2.
when discussing the culturing of blood specimens, particularly the statement that "most aerobic blood collection bottles contain 25% – 35% co2," it is important to clarify why this is incorrect. in microbiology, the environment in which specimens are cultured can significantly affect the growth and detection of microorganisms. aerobic blood culture bottles are designed to promote the growth of organisms that require oxygen for their metabolism.
typically, aerobic blood collection bottles do not contain high concentrations of co2 because these organisms thrive in an atmosphere that closely resembles atmospheric air, which contains approximately 0.04% co2. however, to better support the growth of certain aerobic bacteria, these bottles are often supplemented with a small percentage of co2, generally around 5% to 10%. this is much lower than the 25% to 35% co2 content mentioned in the incorrect statement.
the purpose of adding this amount of co2 (5% - 10%) is to mimic the physiological conditions some bacteria might encounter in the human body, particularly in areas such as the respiratory tract where co2 levels are slightly elevated compared to atmospheric levels. this concentration is enough to enhance the growth of capnophilic bacteria, which require increased levels of carbon dioxide, but it is not so high as to create an environment more suited to anaerobic or microaerophilic organisms.
in contrast, anaerobic bottles, designed for the culture of organisms that grow in environments devoid of oxygen, do not require co2 for aerobic respiration and thus typically do not have enhanced co2 levels. these bottles are created to maintain an oxygen-free environment to support the growth of anaerobes.
therefore, the statement "most aerobic blood collection bottles contain 25% – 35% co2" is incorrect as it misrepresents the environmental conditions conducive to the growth of most aerobic microorganisms. the correct co2 concentration for aerobic blood culture bottles is typically within the range of 5% to 10%, which supports the growth of a broad range of aerobic bacteria without skewing conditions towards those favorable for anaerobic bacteria.
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