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Introduction Gentamycin belongs to aminoglycosides' class of antibiotics. It displays environment-dependent bacteriocidal activity and rapid and inoculum-independent action. Aminoglycoside accumulation leads to the phenomenon referred to as the post-antibiotic effect (PAE). Broad antimicrobial spectrum of aminoglycosides includes Gram(-) rods (besides Haemophilus), Gram(+) cocci (Staphylococcus); Mycobacterium tuberculosis and other species including intracellular pathogenic bacteria such as Yersinia pestis and Brucella abortus. Aminoglycosides display weak activity against S. pyogenes, S. pneumoniae and anaerobic species. Aminoglycosides are ineffective against Enterococcus when used as a single drug, however they may be used when antibiotics destroying bacterial cell wall are applied concurrently; with exception of HLAR mechanism-possessing strains. Above-mentioned aminoglycoside features are of beneficial impact in term of treatment of severe nosocomial infections caused by Gram(+) and Gram(-) bacteria and also for empiric therapy together with beta-lactams, glycopeptides, quinolones, metronidazole and rifampicin. However, in the recent years increase of bacterial resistance against aminoglycosides is observed. According to ECDC (Antimicrobial resistance surveillance in Europe 2013), relatively low percentage of resistant strains is observed for E. coli and Pseudomonas aeruginosa (10-24%), while analogical value for Klebsiella pneumoniae and Acinetobacter baumanii reaches 50-60%. There are three distinct resistance mechanisms to aminoglicosides: in enzymatic mechanism amine and hydroxylic groups are modified by acetylotransferases, posphotransferases and nucleotidylic transferases; the other mechanism works through receptor alterations (changes of 30S ribosomal subunit, such as methylation performed by plasmid-encoded methylases) and, last but not least, by the transport mechanisms (impermeability of cell wall for drug or active efflux). It seems likely that the last two of above- -mentioned mechanisms might be at least partially overcame by local use of high antibiotic concentration. The local use of antibiotics is presently less frequently applied than previously, however it is acceptable to locally use registered, gentamycin- -containing products, such as collagen sponge that releases high concentration of this antibiotic. Aim Compare using in vitro methods, resistance and sensitivity of bone and wound pathogens against gentamycin released locally from collagen sponge and to establish experimental setting imitating in vivo conditions. To obtain these goals we used hydroxyapatite (HA) discs with preformed biofilm on it and we cultured it in rich medium. Additionally we tried to evaluate if resistance of planktonic cells could be overcame by application of high gentamycin concentration. Material and methods The MIC of gentamycin for clinical Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella pneumoniae planktonic and biofilmic forms was evaluated using microdilution method, E-test method and quantitative techniques using HA discs and polystyrene surface. As the gentamycin carrier, Garamycin® sponge (130 mg of gentamycin/200 mg of gentamycin sulphate - 1,3 mg/cm2 + collagen carrier (EUSA Pharma)). The 1 cm² sponge fragments containing 1300 μg/ml gentamycin concentration were applied. The HA discs of 9.6 mm diameter were performed by Wroclaw Technical University "Bad-Mat" laboratory from hydroxyapatite powder MT3300 (LOW-WET, Tomita Pharmaceutical Co.). The quality of product was confirmed by confocal microscopy and micro-CT tomography. Results and Conclusions Planktonic, gentamycin-sensitive strains (MIC>2 μg/ml) when transformed into biofilm displayed resistance profile (MIC=64-1024 μg/ml) that was overcame only by application of local, high drug concentration - as it happens when Garamycin® sponge is applied. All investigated strains, although they were in highly resistant biofilmic form were completely eradicated as compared to control samples that were not gentamycin- treated. The clinical trials indicate that local concentration of gentamycin remains high >1300 μg/ml up to 48 hours after implantation. Moreover, planktonic strains that displayed elevated MIC (4-96 times higher above sensitivity baseline) and were gentamycin-resistant were also eradicated by gentamycin released from sponge. Also gentamycin-resistant KPC K. pneumoniae strains (KPC+; MIC=3, 4, 12 μg/ml) were eradicated. Contrary, K. pneumoniae NDM-1+ strains (MIC=256) were not eradicated. Efficient effect was observed also for resistant strains of Pseudomonas aeruginosa of MIC=96-128. These strains that displayed high resistance pattern (MIC<256 μg/ml for planktonic forms and MIC<2000 μg/ml for biofilmic forms), were not eradicated. The stress should be put on the fact that gentamycin-containing sponge in orthopedics, surgery and cardiac surgery is a somewhat exceptional because presently local application of antibiotics is being withdrawn. However, garamycin sponge seems to be feasible for eradication of bacteria from infected bones and wounds - if these bacteria display sensitivity or low profile of resistance (dependence of efficacy to MIC value needs further experiments) and if a sponge is applied according to manufacturer's guidelines. [ABSTRACT FROM AUTHOR]