Meticillin-resistance spread by horizontal gene transfer

Meticillin-resistant Staphylococcus aureus (MRSA) bacteria owe their resistance to a penicillin-binding protein with low affinity for antibiotics, encoded by the mecA gene. In a research letter in May 26 Lancet, Camiel Wielders and colleagues from University Hospital Utrecht, The Netherlands, provide evidence that a new MRSA genotype can emerge in vivo by transfer of the meticillin-resistance gene from one staphylococcal species to another.

Wielders et al isolated a successive pair of mecA- and mecA+ S. aureus strains from a baby whose initial meticillin-susceptible infection had been treated with β-lactam antibiotics, and who then subsequently developed a MRSA infection. Although the two S. aureus genotypes were almost indistinguishable the mecA DNA from the MRSA sample was identical to that in a S. epidermidis strain isolated from the same baby (Lancet 2001, 357:1674-1675).

Because this mecA+ genotype was isolated from an infant younger than...