Which of the following listed microorganisms is strictly anaerobic? _______________?
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Answer: B. Bacteroides
Explanation
Bacteroides species are Gram-negative bacilli that completely lack the enzymes needed to process oxygen. They cannot utilize molecular oxygen for cellular respiration and are killed by exposure to oxygen. Therefore, Bacteroides species are classified strictly as anaerobic microorganisms in clinical microbiology. Strict anaerobes require oxygen-free environments to survive, grow, and replicate successfully. Bacteroides represent a major component of the normal human intestinal microbiota residing in the colon. Enzymes like superoxide dismutase and catalase are typically absent or deficient in strict anaerobic bacteria.
Intra-abdominal abscesses frequently involve Bacteroides species mixed with facultative enteric bacteria. Specimens suspected of containing anaerobic bacteria must be processed using specialized anaerobic jars or chambers. Empiric antibiotic therapy for abdominal sepsis must include coverage against anaerobic Gram-negative bacilli. Option A represents Escherichia coli, a facultative anaerobe capable of growing with or without oxygen. Option C represents Pseudomonas, an obligate aerobe that requires oxygen for its respiratory metabolism. Option D represents Klebsiella, a facultative anaerobic bacterium belonging to the Enterobacteriaceae family.
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