In vitro activity of gentamicin as an adjunct to penicillin against biofilm group B Streptococcus.

Ruppen, Corinne; Hemphill, Andrew; Sendi, Parham (2017). In vitro activity of gentamicin as an adjunct to penicillin against biofilm group B Streptococcus. Journal of antimicrobial chemotherapy, 72(2), pp. 444-447. Oxford University Press 10.1093/jac/dkw447

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Group B Streptococcus (GBS) increasingly causes invasive disease in non-pregnant adults, particularly in elderly persons and those with underlying diseases. Combination therapy with penicillin plus gentamicin has been suggested for periprosthetic joint infection. The postulated synergism of this combination is based on experiments with planktonic bacteria. We aimed to assess the efficacy of this combination against sessile bacteria.


Four different GBS strains were used. We compared results of MICs with those of minimal biofilm eradication concentrations (MBECs), applied chequerboard assays to the MBEC device and calculated the fractional inhibitory concentration index. Synergism was evaluated with time-kill assays against bacteria adherent to cement beads, using penicillin (0.048, 0.2 and 3 mg/L), gentamicin (4 and 12.5 mg/L) and a combination thereof. Results were evaluated via colony counting after sonication of beads and scanning electron microscopy.


MBEC/MIC ratios were 2000-4000 for penicillin and 1-4 for gentamicin. In chequerboard assays, synergism was observed in all four isolates. In time-kill assays, penicillin and 12.5 mg/L gentamicin showed synergism in two isolates. In the other two isolates 12.5 mg/L gentamicin alone was as efficient as the combination therapy.


These in vitro investigations show activity of 12.5 mg/L gentamicin, alone or as an adjunct to penicillin, against four strains of biofilm GBS. This concentration cannot be achieved in bone with systemic administration, but can be reached if administered locally. The combination of systemic penicillin plus local gentamicin indicates a potential application in orthopaedic-device-associated GBS infections. Studies with a larger number of strains are required to confirm our results.

Item Type:

Journal Article (Original Article)


05 Veterinary Medicine > Research Foci > Host-Pathogen Interaction
04 Faculty of Medicine > Department of Haematology, Oncology, Infectious Diseases, Laboratory Medicine and Hospital Pharmacy (DOLS) > Clinic of Infectiology
04 Faculty of Medicine > Service Sector > Institute for Infectious Diseases
05 Veterinary Medicine > Department of Infectious Diseases and Pathobiology (DIP) > Institute of Parasitology
05 Veterinary Medicine > Department of Infectious Diseases and Pathobiology (DIP)

UniBE Contributor:

Ruppen, Corinne; Hemphill, Andrew and Sendi, Parham


500 Science > 570 Life sciences; biology
600 Technology > 610 Medicine & health
600 Technology > 630 Agriculture




Oxford University Press




Annelies Luginbühl

Date Deposited:

08 Mar 2017 14:42

Last Modified:

01 Mar 2020 02:30

Publisher DOI:


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