A Gram-positive bacterial strain is simultaneously treated with two different antimicrobials: Drug A, which targets a protein involved in cell wall synthesis, and Drug B, which targets ribosomes involved in translation. The bacteria continue to grow during the course of treatment, indicating resistance to both antimicrobials.

What are all the possible resistance mechanisms this bacterial strain could have?

A. Increased drug permeability
B. Altered drug target
C. Efflux pump overexpression
D. All of the above

A Gram-positive bacterial strain resistant to two antimicrobials could use the following mechanisms: altered drug targets, increased drug permeability, or overexpression of efflux pumps. Thus, the correct answer would be 'All of the above'.

Explanation:

The correct option is option B). The possible resistance mechanisms a Gram-positive bacterial strain could have when showing resistance to Drug A, targeting cell wall synthesis, and Drug B, targeting ribosomes, are:

Altered drug target: The bacteria may mutate the gene encoding for the drug's target protein, rendering the drug ineffective, such as alteration in penicillin-binding proteins for resistance to ß-lactams.
Increased drug permeability: Bacteria could alter membrane porins, reducing the uptake of antibiotics and preventing them from reaching effective concentrations inside the cell.
Efflux pump overexpression: The bacteria can utilize efflux pumps to actively transport antibiotics out of the cell, lowering drug concentrations to sub-therapeutic levels.

Considering these mechanisms, the most comprehensive answer to the question of what resistance mechanisms the bacterial strain could have would be D) All of the above.