Which bacteria are capable of surviving in anoxic (oxygen-free) conditions?

Correct Answer: A

Rationale: The correct answer is A: Obligate anaerobes. These bacteria can only survive in the absence of oxygen as they lack the enzymes needed for aerobic respiration. They typically use fermentation or anaerobic respiration for energy production. Incorrect choices: B: Facultative anaerobes can switch between aerobic and anaerobic metabolism based on oxygen availability. C: Obligate aerobes require oxygen for survival and cannot survive in anoxic conditions. D: Microaerophiles require low levels of oxygen for growth and are not capable of surviving in completely anoxic conditions.

Correct Answer: C

Rationale: The correct answer is C: cell wall composition. Gram staining differentiates bacteria based on the structure of their cell walls. It classifies bacteria into Gram-positive (thick peptidoglycan layer) and Gram-negative (thin peptidoglycan layer). This differentiation is crucial for identifying bacterial species and guiding treatment choices. Size and shape (choice A) are not specific to Gram staining. Presence of flagella (choice B) is related to bacterial motility, not Gram staining. Genetic material (choice D) is not directly assessed by Gram staining. Overall, the unique composition of the cell wall is the key factor in distinguishing bacteria through Gram staining.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Blue-green pigment + fruity odor are characteristic of Pseudomonas aeruginosa. 2. P. aeruginosa is a Gram-negative bacterium commonly associated with wound infections. 3. P. aeruginosa is known for its ability to produce pyocyanin (blue-green pigment) and a sweet, fruity odor. 4. Other choices like E. coli, K. pneumoniae, and P. mirabilis do not typically produce blue-green pigment or fruity odor. 5. Therefore, based on the characteristics observed, the likely causative agent is Pseudomonas aeruginosa. Summary of other choices: - Escherichia coli: Does not produce blue-green pigment or fruity odor. - Klebsiella pneumoniae: Does not typically produce blue-green pigment or fruity odor. - Proteus mirabilis: Does not produce blue-green pigment or fruity odor.

Correct Answer: B

Rationale: Answer B, Infectious mononucleosis, is not caused by enteroviruses. Infectious mononucleosis is primarily caused by the Epstein-Barr virus, a member of the herpesvirus family, not by enteroviruses. Enteroviruses are known to cause diseases such as myocarditis, herpangina, and Boston exanthema. Therefore, B is the correct answer. Myocarditis, herpangina, and Boston exanthema can all be caused by enteroviruses, making choices A, C, and D incorrect, respectively.

Correct Answer: B

Rationale: The correct answer is B: parasitism. In parasitism, one organism (parasite) benefits at the expense of the other organism (host). The parasite derives nutrients or resources from the host, causing harm or even death in some cases. This relationship is characterized by asymmetry, where one organism benefits while the other is negatively impacted. Commensalism (A) is a relationship where one organism benefits while the other is unaffected. Synergism (C) is a mutually beneficial relationship where both organisms benefit. Antagonism (D) is a relationship where both organisms are harmed or inhibited.

Correct Answer: A

Rationale: Rationale for correct answer (A: Escherichia coli): 1. Endo agar selects for Gram-negative bacteria. 2. Red colonies on Endo agar indicate lactose fermentation, characteristic of E. coli. 3. E. coli is a common cause of pneumonia, especially in immunocompromised patients. Summary of why other choices are incorrect: - B: Klebsiella pneumoniae: Typically forms mucoid colonies on agar. - C: Pseudomonas aeruginosa: Produces characteristic greenish-blue colonies on agar. - D: Proteus mirabilis: Does not typically ferment lactose, so would not produce red colonies on Endo agar.

Correct Answer: B

Rationale: The correct answer is B because live vaccines can potentially revert to a virulent form, although this is extremely rare. This is due to the live attenuated virus in the vaccine potentially mutating back to a more dangerous form. Live vaccines are designed to be weakened but there is a small risk of reversion. Therefore, statement B is not correct. A: This statement is correct as immunocompromised individuals may have adverse reactions to live vaccines due to their weakened immune system. C: This statement is correct as microbes with many serotypes can make it challenging to develop a vaccine that covers all variations. D: This statement is correct as side effects to vaccination, although usually mild and temporary, can occur in some individuals.

Correct Answer: D

Rationale: The correct answer is D: Proteus vulgaris. This is because Proteus species are non-lactose-fermenting, Gram-negative rods that produce gas in nutrient broth. They are known to cause severe abdominal pain due to their ability to invade the intestinal mucosa. A: Salmonella enterica is a lactose-fermenting organism and typically does not produce gas in nutrient broth. B: Shigella dysenteriae is a lactose-negative organism but does not produce gas in nutrient broth. C: Escherichia coli is a lactose-fermenting organism and does not typically produce gas in nutrient broth. In summary, the presence of non-lactose-fermenting, gas-producing Gram-negative rods points towards Proteus vulgaris as the most likely causative agent of the severe abdominal pain.

Correct Answer: A

Rationale: The correct answer is A: Sabouraud's peptone agar. This agar is specifically designed for the isolation of yeast and molds due to its low pH and high sugar content, creating an environment conducive for their growth. Yeast-like fungi thrive in this selective medium, while inhibiting the growth of bacteria and other contaminants. Summary: - Sabouraud's peptone agar is ideal for cultivating yeast-like fungi. - Endo agar is used for isolation of gram-negative bacteria, not fungi. - Milk-salt agar is used for lactobacilli and streptococci, not fungi. - Meat infusion agar is a general-purpose medium for cultivation of a wide range of microorganisms, not specifically for yeast-like fungi.