Abstract: 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.