The variable drug resistance region of IncU R-plasmids may contain a heterogenic collection of drug resistance genes and transfer systems that can mediate recombination and VX-809 acquisition of additional resistance genes. In our study we used the 45 kb pRAS1 containing a class 1 integron, responsible for trimethoprim and sulfonamide resistance caused by dfr16 and sul1, respectively. In addition there is a Tn1721 transposon encoding tetracycline resistance by the Tet A determinant [14]. A highly conserved DNA backbone structure with a variable region encoding antibiotic resistance has been postulated for IncU group members

[14]. The IncU plasmid pFBAOT6 (84.749 bp) was sequenced [17] and found to be almost identical with the IncU backbone of another XL184 concentration plasmid RA3 (45.909 bp) [18]. Functional analysis of this broad-host-range IncU group of plasmids has demonstrated their self-transfer, replication and stable maintenance in alpha-, beta-, and gammaproteobacteria. The genetic functional transfer block of pRA3 consists of twenty-one different genes [18]. The mobility genes traD, virB11 and virD4 were selected from this functional block of the conjugative genetic system for analysis in this study. The expression of a wide number of genes responsible for innate immune responses towards microbes in the intestine of adult zebrafish has been evaluated [19–23]. A recent study

demonstrated the distribution of important innate antibacterial immunity mediators such as peptidoglycan recognition protein (pglyrp) and a factor that regulates neutrophilic see more cell densities and cytokines in the entire intestine of healthy zebrafish [24]. The bacterial pathogen recognition receptors (Toll-like receptors etc.) and signaling pathways activating the immune response (pro-inflammatory cytokines,

hepicidin and heptoglobin etc.) are similar to those in mammals [25]. The aim of this study was, therefore, to assess the expression Dichloromethane dehalogenase of transfer genes of pRAS1 caused by a pathogenic A. hydrophila in vivo in response to antibiotic treatments, while simultaneously monitoring selected inflammatory and innate immune system parameters. Methods Bacterial strains and growth conditions Aeromonas salmonicida 718 (NVI 2402/89) originally isolated from the head kidney of diseased Atlantic salmon in 1989, harboring a 25-MDa conjugative IncU plasmid, pRAS1, mediating resistance to oxytetracycline, trimethoprim and sulfadiazine was used as the donor strain. A. hydrophila strain (F315/10), originally isolated from a skin ulcer of freshwater reared salmon was used as the recipient strain, prior to zebrafish challenge. Both strains were cultured at 22°C on 5% cattle blood agar [blood agar base no 2, Difco] for 48 h (A. salmonicida) or 24 h (A. hydrophila). In vitro conjugation experiments Conjugal transfer experiments were performed as described by Schmidt et al. [26]. In brief, donor A. salmonicida 718 (carrying plasmid pRAS1) and recipient A.