Corynebacterium striatum is an opportunistic pathogen, often multidrug-resistant, which has been associated with serious
infections in humans.
Aminoglycosides are second-line or complementary
antibiotics used for the treatment of
Corynebacterium infections. We investigated the susceptibility to six
aminoglycosides and the molecular mechanisms involved in
aminoglycoside resistance in a collection of 64 Corynebacterium striatum isolated in our laboratory during the period 2005-2009. Antimicrobial susceptibility was determined using E-test. The mechanisms of
aminoglycoside resistance were investigated by PCR and sequencing. The 64 C. striatum were assessed for the possibility of clonal spreading by Pulsed-field Gel Electrophoresis (PFGE).
Netilmicin and
amikacin were active against the 64 C. striatum isolates (MICs90 = 0.38 and 0.5 mg/L, respectively). Twenty-seven of the 64 C. striatum strains showed a MIC90 for
kanamycin > 256 mg/L, and 26 out the 27 were positive for the aph(3')-Ic gene. Thirty-six out of our 64 C. striatum were
streptomycin resistant, and 23 out of the 36 carried both the
aph(3")-Ib and
aph(6)-Id genes. The gene aac(3)-XI encoding a new
aminoglycoside 3-N acetyl
transferase from C. striatum was present in 44 out of the 64 isolates, all of them showing MICs of
gentamicin and
tobramycin > 1 mg/L. CS4933, a C. striatum showing very low susceptibility to
kanamycin and
streptomycin, contains an
aminoglycoside resistance region that includes the aph(3')-Ic gene, and the tandem of genes
aph(3")-Ib and
aph(6)-Id. Forty-six major PFGE types were identified among the 64 C. striatum isolates, indicating that they were mainly not clonal. Our results showed that the 64 clinical C. striatum were highly resistant to
aminoglycosides and mostly unrelated.