The most frequently identified macrolide resistance
mechanisms are methylation of the target site associated
with the ermB gene or efflux encoded by the mef genes.
These two mechanisms have been identified worldwide,
where testing has been performed. However, distribution
of these genes has been suggested to be continent
dependent. Macrolide resistance in the USA and Canada
is predominantly mediated by the mef genes and so has
the M phenotype. While in Europe, macrolide resistance
is mostly associated with the presence of the ermB gene
and the MLSB phenotype. Recently, the resistance pro-
file of Europe has begun to change as resistance data has
been collected from countries other than those with a
high level of macrolide resistance. The most recent
publications currently indicate that within Europe resistance
to macrolides due to the mef gene is increasing,
whereas resistance due to the ermB gene is remaining
static. This is happening both in countries with high
macrolide resistance, such as Italy [29] and low macrolide
resistance such as Finland [30]. The efflux phenotype is
the predominant macrolide resistance mechanism in the
UK, Sweden, Finland, Germany, Switzerland and Austria
[31,32]. Are these isolates or their genes spreading to the
rest of Europe? The total European picture is unclear but
there are trends emerging that the mef gene mediated
resistance is beginning to take over the ermB-based
resistance. If this is the case then we need to know
how this is happening and why. This is of most impor