Pathogenic bacteria isolated from the respiratory or intestinal tracts of humans are
A capnophiles that prefer highly oxygenated growth conditions.
B strict aerobes that grow best in oxygen incubators.
C facultative anaerobes that require nitrogen for growth.
D capnophiles that grow best in carbon dioxide incubators.
The correct answer and explanation is :
The correct answer is D: capnophiles that grow best in carbon dioxide incubators.
Explanation:
Pathogenic bacteria that are commonly isolated from the respiratory or intestinal tracts of humans typically include species like Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis, and Escherichia coli. These bacteria are often classified as capnophiles, which are microorganisms that thrive in environments with elevated levels of carbon dioxide (CO₂).
Capnophilic Nature of Pathogenic Bacteria:
Capnophilic organisms require higher-than-atmospheric levels of CO₂ for optimal growth. In the human respiratory and intestinal tracts, the natural environment is enriched with CO₂, making it an ideal condition for these bacteria. For example, the human respiratory tract maintains a CO₂ concentration of about 5-6%, much higher than the 0.03% concentration in atmospheric air.
Many pathogenic bacteria, such as Neisseria and Haemophilus species, are often grown in laboratories in CO₂ incubators, which provide a controlled environment of approximately 5-10% CO₂. This helps replicate the natural environment of the human body, allowing for optimal growth and enabling the laboratory isolation of these bacteria for diagnosis and further study.
Why the Other Options Are Incorrect:
- A: Capnophiles that prefer highly oxygenated growth conditions: While capnophiles do require elevated CO₂ levels, they do not specifically require highly oxygenated conditions. Many pathogenic bacteria, especially in the intestines, may be anaerobic or facultative anaerobes, meaning they can survive in both oxygen-rich and oxygen-poor environments.
- B: Strict aerobes that grow best in oxygen incubators: Strict aerobes require oxygen to survive, but pathogenic bacteria from the respiratory and intestinal tracts are not typically strict aerobes. They can often tolerate or even require conditions with limited oxygen.
- C: Facultative anaerobes that require nitrogen for growth: Facultative anaerobes can grow in the presence or absence of oxygen, but they do not necessarily require nitrogen for growth. While nitrogen may be present in trace amounts in the atmosphere, it is not the defining factor for their growth in human body environments.
Thus, capnophilic bacteria in the human respiratory and intestinal tracts require high levels of CO₂ and grow best in environments where CO₂ concentrations are elevated.