When bacteria like Streptococcus (a type of bacteria that causes pneumonia and meningitis) are frequently exposed to antibiotics, the bacteria can become resistant to the drugs. MAC preventive therapy uses antibiotics, but this can make it difficult to treat other infections caused by bacteria that have become resistant in HIV-infected persons. If MAC preventive therapy is delayed, Streptococcus in the body may be less likely to develop resistance. Therefore, if the patient does get a Streptococcus infection, it will be easier to treat because it is not resistant to the antibiotics.