Evolution of erythromycin resistance in Streptococcus pneumoniae in Italy.
OBJECTIVE
To evaluate erythromycin resistance in recent invasive isolates of Streptococcus pneumoniae in Italy, to study the phenotypic and genotypic characteristics of the isolates, and to compare data with those obtained in a previous survey.


METHODS
Invasive pneumococcal isolates were obtained from 56 laboratories throughout the country, in 2001-2003. Isolates were serotyped and antimicrobial susceptibilities determined by Sensititre panels and Etest. A new PCR was performed to detect erythromycin resistance genes. Typing methods for selected erythromycin-resistant isolates included PFGE and multilocus sequence typing (MLST).


RESULTS
One hundred and fifty-five isolates out of 444 (34.9%) were resistant to erythromycin: 95 isolates (21.4%) carried erm(B), 56 (12.6%) carried mef(A) and three carried both genes. One isolate, carrying neither erm(B) nor mef(A), showed a point mutation in domain V of the 23S rRNA genes. The mef(A)-positive isolates carried subtype mef(A) (47 isolates), subtype mef(E) (nine isolates), and both subtype mef(E) and erm(B) (three isolates). All subtype mef(A) strains, except two, belonged to serotype 14, appeared to be clonally related by PFGE and related to the England14-9 clone by MLST. The two isolates belonging to other serotypes showed different genetic backgrounds.


CONCLUSIONS
Erythromycin resistance in S. pneumoniae has increased in the last few years in Italy. erm(B) is still the predominant resistance determinant; however, the increase in erythromycin resistance (34.9% versus 28.8% of the previous years) is mainly due to an increase in the proportion of isolates carrying the efflux pump mef(A), whereas the proportion of isolates carrying erm(B) has not changed.
Monaco
Monica
M
Department of Infectious, Parasitic and Immunomediated Diseases, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy.
Camilli
Romina
R
D'Ambrosio
Fabio
F
Del Grosso
Maria
M
Pantosti
Annalisa
A
D024881:Drug Resistance, Bacterial / Q000187:drug effects / Q000235:genetics*; D004917:Erythromycin / Q000494:pharmacology* / Q000627:therapeutic use; D019143:Evolution, Molecular; D006801:Humans; D007558:Italy / Q000453:epidemiology; D011008:Pneumococcal Infections / Q000188:drug therapy / Q000235:genetics; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification
D004917:Erythromycin