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A2. This is a very interesting question. In antimicrobial research, the ability of an antibiotic to produce a three-log kill (decrease the bacterial load by three logs) is an important characteristic. In theory, if an antibiotic is able to produce a threelog kill, the host’s immune system can usually kill the remaining bacterial population. However, with an immunocompromised host, such as an HIV patient, little to no immune function exists to fight infection. Furthermore, it is believed that the remaining bacterial population (after a three-log kill) is less susceptible to the antimicrobial (assuming a fairly normal distribution of MICs among the population). Therefore, in theory, an immunocompromised host would be more likely to develop a resistant infection because their immune system is unable to “take over,” and the less susceptible population is allowed to grow. This idea supports the common practice of discontinuing prophylaxis for opportunistic infections in HIV patients once their CD4 count is above a certain level.