Three familial cases of drug-resistant Mycoplasma pneumoniae infection

Mycoplasma pneumoniae infection is believed to result from defective host immune response rather than from direct cell injury by the organism itself. In this context, emergence of drug-resistant M. pneumoniae may provide us with special opportunities to study the pathogenesis from a clinical point of view. In this report, three patients with intrafamilial M. pneumoniae infection are presented. M. pneumoniae was isolated with a Hayflick pleuropneumonia-like organism diphasic medium. Minimal inhibitory concentrations of antibiotics were determined by a broth microdilution method. Polymerase chain reaction and restriction fragment length polymorphism analysis were done to determine point mutation in domain V of the 23S rRNA gene. As a result, all three strains from the three intrafamilial cases had the same drug-resistant point mutation, specifically A-to-G transition at position 2063. However, their clinical courses were quite different; a 6-year-old girl suffered severe pneumonia, a 5-year-old girl had mild pneumonia, and a 3-year-old boy had only a fever of 1-day duration without pneumonia. Conclusions: Our clinical and laboratory observations strongly support the idea that the host immune maturity, rather than a virulence factor of the organism, is a major determinant factor of disease severity of M. pneumoniae infection and that drug resistance does not necessarily lead to a serious clinical outcome.