EUCAST Expert Rules in Antimicrobial Susceptibility Testing - eibne.gr

Table 11. Interpretive rules for macrolides, lincosamides and streptogramins
Rule
no.
Organisms Agents tested Agents affected Rule
11.1 All Erythromycin Azithromycin,
clarithromycin,
roxithromycin
11.2 Staphylococcus
spp.
Erythromycin,
clindamycin
IF susceptible, intermediate or
resistant to erythromycin, THEN
report the same category of
susceptibility for azithromycin,
clarithromycin, roxithromycin .
Exceptions, scientific basis and
comments
Erythromycin is the class representative
for 14- and 15-membered ring
macrolides. Resistance to erythromycin is
generally due to the production of a
ribosomal methylase encoded by erm
genes conferring the macrolidelincosamide-streptogramin
B (MLSB)
phenotype or by production of an efflux
pump. In both cases, there is crossresistance
between erythromycin and the
other 14- and 15-membered ring
macrolides.
Clindamycin IF resistant to erythromycin but Staphylococci resistant to macrolides but
susceptible to clindamycin, THEN susceptible to clindamycin produce Erm
test for inducible MLSB resistance. IF ribosomal methylases conferring the
negative, THEN report susceptible to inducible MLSB phenotype or express
clindamycin. IF positive, THEN efflux pumps. In case of inducible MLSB report as resistant to clindamycin or resistance, constitutively resistant
report as susceptible with a warning mutants can be selected by clindamycin.
that clinical failure during treatment In the case of resistance by efflux, the
with clindamycin may occur by risk for selection of mutants resistant to
selection of constitutively resistant clindamycin is not greater than that for
mutants and the use of clindamycin erythromycin susceptible isolates. Both
is probably best avoided in severe clinical failures and successes with
infections.
clindamycin have been reported for
Evidence
grade
C [59]
References
B [59,60]