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Antimicrobial susceptibility, integron carriage, genetic relationship and presence of some important virulence genes of the integron-carrier strains of Shigella sonnei (n5230) and Shigella flexneri (n522) isolated from stool samples of patients in Hungary between 1998 and 2008 were investigated. Sixty-seven per cent (168/252) of the strains were resistant to sulfamethoxazole/ trimethoprim (SxT) followed by streptomycin (S, 47 %), ampicillin (A, 32 %) and tetracycline (Tc, 28 %). Thirty-six per cent (90/252) exhibited multidrug resistance, mostly showing SSxTTc or ASSxTc, ASSxTTc resistance patterns. An S. sonnei strain of imported origin was resistant to cefotaxime and harboured a bla CTX-M-55 -type extended-spectrum b-lactamase gene. Altogether 33 % of the S. sonnei (n575) and 14 % of the S. flexneri (n53) strains had either class 1 or class 2 integrons or both. The variable regions encoded aadA1 or dfrA1-aadA1 genes for the class 1 and dfrA1-sat2-aadA1 or dfrA1-sat2 genes for the class 2 integrons. Pulsed-field gel electrophoresis analysis revealed that those strains that have different integron types represented different genetic clusters. The Shiga toxin (stx1) gene was identified in one S. sonnei strain and the cdtB gene was detected in an S. flexneri strain. The results reveal the high incidence of antibiotic resistance among Shigella isolates and the presence of the stx1 gene in S. sonnei and the cdtB gene in S. flexneri. The genetic diversity of Shigella spp. isolated recently in Hungary was also demonstrated.

The integron content of 52 DT104/U302 phage type strains and 53 non-DT104/U302 strains of Salmonella enterica serotype Typhimurium (S. Typhimurium) was studied in PCR experiments using a 5'-CS/3'-CS primer pair (Lévesque et al., 1995). Forty-three out of 44 streptomycin-and/or ampicillinresistant DT104 and related phage type strains were found to carry a 1 kb and/or 1.2 kb long integron. The other resistance markers did not affect the number and size of integrons; no integron-free multidrug-resistant (MDR) DT104 strains were found. The two large groups of DT104 strains (Felix-Callow's phage types 2 and 2c) proved to be identical in respect of integron patterns (IPs), supporting the views of those authors who consider DT104 a single clone. Strains of human and animal origin did not differ from each other in their IPs. Within the non-DT104 phage types, ampicillin-and/or streptomycin-resistant, integron-free MDR strains were also found. Based on amplicons varying between 290 and 3500 bp an IP system was suggested. The commonest amplicon sizes in non-DT104 strains were 1450 and 2050 bp. The IPs of DT104 strains and of non-DT104 strains containing an integron of 1 and 1.2 kb size were stable. In contrast, the IPs of other non-DT104 strains showed a varying degree of instability. Integron loss was frequently associated with spontaneous plasmid elimination and changes of R-type among the descendants of a given strain.Key words: Typhimurium, phage type, DT104, integron pattern, instability, PCR Since the early 1990s, the DT104 phage type of Salmonella enterica serotype Typhimurium (S. Typhimurium) has spread all over the world (Threlfall et al

By PCR using the ant(3")-Ia primer pair the aadA gene was detected in 34 streptomycin-and spectinomycin-resistant Salmonella enterica serotype Typhimurium strains. Out of them 12 belonged to DT104 and 22 to non-DT104 phage type. Using different primer combinations it was demonstrated that this gene was integron-associated in all cases: in the DT104 strains it was generally contained by a 1 kb integron while in the majority of the non-DT104 strains by a 2.05 kb (less often by a 1.9 or 1 kb) integron. In the case of integrons carrying multiple cassettes the cassette containing the aadA gene was located closer to the 3' end of the integron. The aadA genes of DT104 and non-DT104 strains were different: in the former group the aadA2 gene, while in the latter group (constituted by strains of five different phages types as well as unclassifiable and untypable strains) the aadA1 gene could be identified. The RH50/RH51 primer pair described by Collis and Hall (1992) proved to be suitable for rapid discrimination between the aadA1 and aadA2 genes on the basis that the RH51 primer bound exclusively to the aadA2 gene.Key words: Salmonella Typhimurium, streptomycin/spectinomycin resistance, aadA gene cassettes, sequencing Salmonella enterica serotype Typhimurium (S. Typhimurium) phage type DT104 has great epidemiological importance in Europe and in the United States (Threlfall et al., 1994;Low et al., 1997;Besser et al., 1997) and is usually characterised by the high prevalence of multidrug resistance to ampicillin (Amp), chloramphenicol (Chl), streptomycin (Sm), spectinomycin (Spc), sulphonamides (Su) and tetracycline (T) (Threlfall et al., 1996;Glynn et al., 1998;Ridley and Threlfall, 1998 Acta Veterinaria Hungarica 51, 2003 it had become the dominant phage type already by 1991 (Szmollény et al., 2000;Pászti et al., 2001). Within the DT104 phage type, only in Felix and Callow's (1951) phage type 2 group did the incidence of multiresistant strains substantially exceed the average level, while in the phage type 2c group it did not (Pászti et al., 2001).The aadA gene responsible for Sm/Spc resistance is the commonest integron-associated gene among isolates of Enterobacteriaceae in Europe (MartinezFreijo et al., 1999). Its variants constitute a gene family the two most important members of which are aadA1 sequenced by Hollingshead and Vapnek (1985), Fling et al. (1985) and Sundström et al. (1988), and aadA2 sequenced by Tait et al. (1985) and Bito and Susani (1994). Further variants (aadA3-A8, aadAsc) have been described from E. coli, Pseudomonas aeruginosa and Salmonella choleraesuis isolates (Leung et al., 1992;Naas et al., 1999;Adrian et al., 2000;Mazel et al., 2000;White et al., 2000;Peters et al., 2001). The integron nature of the aadA gene and the plasmid-and/or transposon-associated location of the integrons may have played a role in the excessive horizontal spread of aadA.In both of the above two groups of the DT104 strains analysed in this study, Sm/Spc resistance was closely associated with the presence of a 1 k...

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