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To determine the antibiotic resistance pattern and resistance plasmids, we studied 23 antibioticresistant clinical isolates of Enterococcus spp. which caused infection in Bayındır-Ankara Hospital, Turkey. Biochemical and physiological identification tests were applied by the Vitek system and compared with the results of protein profiles by SDS-PAGE. From 23 isolates, 20 were identified as E. faecalis, 2 as E. faecium and 1 as E. gallinarum. Twenty four antibiotics belong to 10 different groups were used in susceptibility tests. Multiple antibiotic resistance was determined in 10 of 23 Enterococcus spp. Overall resistance to the used antibiotics was 47.3% and low level resistance was 16.6%. Among the isolates tested, 8.7% demonstrated high level gentamicin resistance, 17.4% demonstrated high level streptomycin resistance, and 43.5% demonstrated penicillin resistance. High level vancomycin resistant Enterococcus spp. rate was 34.8%, and 60.9% exhibited low level resistance to vancomycin and teicoplanin. They contain plasmids which varied in numbers between 1 and 11 and the plasmid sizes ranged from 2.08 to 56.15 kb. In curing experiments with acriflavine, two different plasmids were shown in different molecular sizes of 33.49 and 13.6 kb while the first determined glycopeptide and penicillin resistance, the second one determined either glycopeptide or penicillin resistance in two different E. faecalis strains. On the other hand, a 22.58 kb plasmid, determining kanamycin resistance, was detected in an E. faecium strain. After the curing experiments, an elimination of 37.17 and 44.47 kDa protein bands was shown in E. faecium EFA1 and E. faecalis EFA13 in SDS-PAGE, respectively. This survey indicates the increase of antibiotic-resistant enterococci, especially to vancomycin in our hospital isolates.

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e14610 Background: Suicide gene therapy is one of the promising treatment modalities in cancer treatment. Combination of an immunotherapy modality with suicide gene therapy would increase the tumor eradciating efficacy of either treatment strategy used alone. Methods: In the current study, we constructed adenoviral vectors carying ytosine deaminase (CD), granulocyte macrophage-colony stimulating factor (GM-CSF) vectors. We tested the in vitro efficacy of the vectors in both human and mouse tumor cell lines and in a syngeneic mouse model of colon cancer with tumor explants of CRL 2638 cells. Results: Our results show that the vectors carrying CD/GM-CSF transcription units are effective in terms of killing of tumor cells when 5-FC added. Addition of GM-CSF transgene induced a significant amount of GM-CSF secretion (250 pg/ml/105 cells) of infected cells. In the syngeneic colon cancer model, addition of GM-CSF significantly increased tumor-specific cellular immune response when compared to suicide gene therapy alone. (p<0.01). Likewise, GM-CSF addition caused a 8 times reduction in the ratio of Tregs infiltrating the tumor nodules (p<0.001). Accordingly, GM-CSF decreased the tumor growth by 2 times an d increased the median survival time by 50% (p<0.01). Conclusions: These impressive results of in-vitro cytotoxicity and encouraging results of in-vivo testing of the our newly constructed GM-CSF carrying vector suggest a potential for the use of the vector for the treament of established tumors by inducing tumor specific immune response. No significant financial relationships to disclose.

Background: Combination of cytotoxic treatments with immunotherapeutic agents seem more efficacious than using either strategy alone. Oncolytic viral vectors carrying immunostimulatory genes like GM-CSF have emerged as treatment options in various tumors. Previously, we have shown that combination of suicide gene therapy either with GM-CSF or vector-induced dendritic cells has significant anti-tumor efficacy. In the current study, we aimed to combine the cytotoxic effect of the suicide gene cytosine deaminase and the immunostimulatory effect of granulocyte macrophage colony stimulating factor in a single vector construct. Methods: We have constructed a bicistronic adenoviral vector carrying cytosine deaminase (CD) and granulocyte macrophage-colony stimulating factor (GM-CSF) genes combined with an IRES element and driven by CMV promoter (Ad-CMV-CDiresGMCSF). We tested the in vitro efficacy of the vector in various tumor cell lines and in a mouse model of colon cancer. Results: Our bicistronic vector Ad-CMV-CDiresGMCSF showed significant in-vitro cytotoxic effects on tumor cell lines similar to the vector carrying CD gene alone when 5-FC added. Likewise, the GM-CSF producing efficacy of the bicistronic vector was comparable to the vector carrying GM-CSF gene alone. In the syngeneic colon cancer model, the bicistronic vector carrying CD and GM-CSF genes yielded significant tumor shrinkage and overall survival when compared to the control suicide vector carrying CD gene alone. Accordingly, anti-tumor immune response parameters including CTL assay and immune cell infiltration of tumor tissue were significantly improved in the Ad-CMV-CDiresGMCSF vector treated group (p&lt;0.01). Conclusions: The Ad-CMV-CDiresGMCSF vector construct suggests a potential for the treatment of established tumors by inducing significant tumor killing and tumor-specific immune response. Citation Format: Hakan Akbulut, Arzu Coleri, Gunce Sahin, Yucheng Tang, Albert Deisseroth, Fikri Icli. A bicistronic adenoviral vector carrying cytosine deaminase and GM-CSF genes significantly improves antitumor immunity and overall survival in colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5911.