kjlm The Korean Journal of Laboratory Medicine Korean J Lab Med 2383-5702 2383-5710 The Korean Society for Laboratory Medicine 10.3343/kjlm.2007.27.4.292 kjlm-27-292 Original Article In Vitro Activity of Arbekacin Against Clinical Isolates of Staphylococcus species and Gram-negative Bacilli LeeJonghanM.D. 1 2 KimChang KiM.D. 1 2 RohKyoung HoM.D. 3 LeeHyukminM.D. 4 YumJong HwaM.D. 2 YongDongeunM.D. 1 2 LeeKyungwonM.D. 1 2 ChongYunsopM.D. 1 2 Department of Laboratory Medicine, Yonsei University College of Medicine, Seoul, Korea Research Institute of Bacterial Resistance, Yonsei University College of Medicine, Seoul, Korea Department of Laboratory Medicine, Korea University College of Medicine, Seoul, Korea Department of Laboratory Medicine, Kwandong University College of Medicine, Goyang, Korea 022007 10022007 27 4 292 297 12052007 13062007 13062007 Copyright © 2007 The Korean Society for Laboratory Medicine 2007 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Background

Methicillin-resistant Staphylococcus aureus (MRSA) and some gram-negative bacilli are very prevalent nosocomial pathogens, commonly causing mixed infections, and are often resistant to multiple drugs. Arbekacin is an aminoglycoside used for the treatment of MRSA infections, but is also active against some gram-negative bacilli. The aim of this study was to determine in vitro activity of arbekacin against recent clinical isolates of staphylococci and gram-negative bacilli.

 Materials and Methods

The strains were isolated from clinical specimens of patients at Severance Hospital in 2003. Antimicrobial susceptibility was tested by the Clinical and Laboratory Standards Institute agar dilution method. The following arbekacin breakpoints were used: susceptible, ≤4 μg/mL; and resistant, ≥16 μg/mL.

 Results

All isolates of staphylococci tested were inhibited by ≤4 μg/mL of arbekacin, regardless of their methicillin susceptibility. The MIC90s of arbekacin, 1–4 μg/mL, were 8->32-fold and >32–128-fold lower than those of amikacin and gentamicin, respectively. The resistance rates of MRSA, methicillin-susceptible S. aureus, methicillin-resistant coagulase-negative staphylococci (CNS) and methicillin-susceptible CNS were 0% to arbekacin, 0–54% to amikacin, and 24–79% to gentamicin. The MIC90s of arbekacin for Escherichia coli and Citrobacter freundii, 1 μg/mL and 16 μg/mL, were 2–4-fold and 8–16-fold lower than those of amikacin and gentamicin, respectively. However, The MIC90s of arbekacin for other species of gram-negative bacilli, 64->128 μg/mL, were similar to those of other aminoglycosides.

 Conclusions

Arbekacin may be a useful alternative to glycopeptides for the treatment of monomicrobial methicillin-resistant staphylococcal infections, as well as mixed infections with gram-negative bacilli, as most isolates of E. coli, C. freundii and some other gram-negative bacilli were also susceptible to arbekacin.

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Activities of antimicrobial agents against Staphylococcus species

Organism (N tested) Antimicrobial agent* MIC (μg/mL)
 Susceptibility (%)
Range 50% 90% S I R
Methicillin-resistant Oxacillin 32->128 >128 >128 0 −† 100
S. aureus Vancomycin 0.5–2 1 1 100 0 0
(52) Amikacin 4->128 64 >128 39 8 54
  Gentamicin 0.25->128 64 >128 21 0 79
  Arbekacin 0.5–4 1 4 100 0 0
Methicillin-susceptible Oxacillin 0.06–1 0.5 0.5 100 − 0
S. aureus Vancomycin 0.5–1 0.5 1 100 0 0
(33) Amikacin 0.5–32 2 8 97 3 0
  Gentamicin 0.06->128 0.5 128 73 3 24
  Arbekacin 0.06–2 0.5 1 100 0 0
Methicillin-resistant CNS Oxacillin 0.5->128 4 64 0 − 100
(26) Vancomycin 0.25–2 1 2 100 0 0
  Amikacin 0.12–64 2 32 81 12 8
  Gentamicin 0.06–128 16 64 27 15 58
  Arbekacin 0.06–2 0.25 1 100 0 0
Methicillin-susceptible CNS Oxacillin 0.06–0.25 0.12 0.25 100 − 0
(29) Vancomycin 0.5–2 1 2 100 0 0
  Amikacin 0.5–16 1 8 100 0 0
  Gentamicin 0.06–128 0.12 128 69 7 24
  Arbekacin 0.06–2 0.12 1 100 0 0

Arbekacin breakpoint was applied as susceptible, ≤4 μg/mL; intermediate, 8 μg/mL; resistant, ≥16 μg/mL.

Not applicable. Abbreviations: MIC, Minimum inhibitory concentration; CNS, coagulase-negative staphylococci.

Activities of antimicrobial agents against gram-negative bacilli

Organism (N tested) Antimicrobial agent* MIC (μg/mL)
 Susceptibility (%)
Range 50% 90% S I R
E. coli Cefotaxime ≤0.03–128 0.06 0.25 93 0 7
(30) Gentamicin ≤0.12–64 0.5 16 87 0 13
  Amikacin 0.5–32 2 4 97 3 0
  Arbekacin 0.25–16 1 1 93 0 7
  Ciprofloxacin ≤0.03–64 ≤0.03 32 73 0 27
K. pneumoniae Cefotaxime ≤0.03->128 0.5 128 57 27 17
(30) Gentamicin 0.5->128 1 >128 63 0 37
  Amikacin 1->128 4 >128 53 13 33
  Arbekacin 0.5->128 2 >128 50 3 47
  Ciprofloxacin ≤0.03–128 0.06 32 53 0 47
C. freundii Cefotaxime ≤0.03->128 0.25 64 73 0 27
(15) Gentamicin 0.5->128 1 128 80 7 13
  Amikacin 1->128 2 32 87 7 7
  Arbekacin 0.5->128 1 16 80 0 20
  Ciprofloxacin ≤0.03–8 0.12 4 80 7 13
E. cloacae Cefotaxime ≤0.03->128 0.25 128 60 7 33
(15) Gentamicin 0.25->128 0.5 >128 67 0 33
  Amikacin 1->128 2 >128 80 7 13
  Arbekacin 0.5->128 1 >128 67 7 27
  Ciprofloxacin ≤0.03–4 0.5 4 73 0 27
S. marcescens Cefotaxime 0.12->128 0.5 >128 57 0 43
(14) Gentamicin 0.5->128 1 >128 64 0 36
  Amikacin 2->128 4 >128 64 0 36
  Arbekacin 1->128 4 >128 57 0 43
  Ciprofloxacin 0.06–32 0.12 32 64 7 29
A. baumannii Cefotaxime 4->128 16 >128 40 20 40
(15) Gentamicin 0.5->128 2 >128 60 0 40
  Amikacin 0.5->128 8 >128 73 7 20
  Arbekacin 0.5->128 1 >128 60 13 27
  Ciprofloxacin 0.06->128 0.25 128 53 7 40
P. aeruginosa Cefotaxime 8->128 32 >128 3 62 35
(29) Gentamicin 0.5->128 2 >128 59 3 38
  Amikacin 1->128 8 >128 72 14 14
  Arbekacin 0.5–64 2 64 59 10 31
  Ciprofloxacin 0.06->128 0.25 32 69 0 31

Arbekacin breakpoint was applied as susceptible, ≤4 μg/mL; intermediate, 8 μg/mL; resistant, ≥16 μg/mL.

Abbreviation: MIC, Minimum inhibitory concentration.