we screened 31,615 s. enterica serovar enteritidis isolates that had been collected from clinical specimens during 20052010 and deposited in the culture collection of the health protection agency salmonella reference unit . a total of 14 serovar enteritidis isolates showing this resistance phenotype were detected and subsequently examined for the presence of integron - located dfra7 . of the 14 isolates , 11 were positive and their plasmid content was analyzed by s1 pulsed - field gel electrophoresis ( pfge ) ( 2 ) and by the kado and liu methods ( 7 ) ; we used serovar enteritidis strains nrl - salm - pt4 and cnm4839/03 as controls for psev and puo - sevr1carrying isolates , respectively . the 11 isolates harbored 1 plasmid of variable size ( 6095 kb ) ; among these , 9 isolates hybridized with dfra7-specific and spvc - specific probes ( with plasmids of 8595 kb ) ( figure ) . these 9 isolates contained a vr - hybrid plasmid similar to puo - sevr1 and were selected for further analyses ( table 1 , table 2 ) . the remaining 2 isolates carried the normal psev plasmid ( 60 kb ) , in which spvc hybridized ; dfra7 was chromosomally located . genomic macrorestriction of salmonella 
 enterica serovar enteritidis isolates : pulsed - field gel electrophoresis profiles for xbai ( left panel ) and s1 ( right panel ) . lane m , xbai - digested dna of s. enterica serovar braenderup h9812 , used as size standard ; lane 1 , nrl - salm - pt4 ; lane 2 , cnm4839/03 ; lane 3 , h051860415 ; lane 4 , h070360201 ; lane 5 , h070420137 ; lane 6 , h073180204 ; lane 7 , h091340084 ; lane 8 , h091800482 ; lane 9 , h095100307 ; lane 10 , h100240198 ; lane 11 , h101700366 . the strain nrl - salm - pt4 was used as control for the most commonly found xbai - profile in s. enterica serovar enteritidis . * all isolates contained a virulence - resistance hybrid plasmid similar to puo - sevr1 . recovered from the same patient . * psev , serovar - specific v plasmid of s.enterica serovar enteritidis ; mlva , multilocus variable number tandem repeat analysis ; mlst , multilocus sequence typing ; vr , virulence - resistance ; pt , phage type ; na , no amplification from this locus ; amp , ampicillin ; chl , chloramphenicol ; str streptomycin ; sul , sulfonamides ; tet , tetracycline ; tmp , trimethoprim ; st , sequence type ; nd , not done . size of the variable region amplified with the 5cs and 3cs primers ( 2 ) . two new primer pairs were devised for detection of srga : srgab - fw1/rv1 ( 5-cgccttccgtgtatgtcc / gcgagtcactcaccgacag-3 ) and srgab - fw2/rv2 ( 5-gttgcacaggagtgggagtc / gtccgggttccatgtcag-3 ) . the forward primers anneal at different positions within srga ; the reverse primers anneal at different positions within srgb . in the 9 isolates carrying vr - hybrid plasmids , the r - type acssuttm was encoded by the r - genes blatem-1 , 
 cata2 , stra - strb , sul1 , sul2 , tet(a ) , and dfra7 , which were located on the puo - sevr1like plasmids as determined by southern blot hybridization . by pcr amplification , using previously described primers and conditions ( 5,8 ) ( table 2 ) , and by southern blot hybridization ( 5 ) , we tested for the presence of incfii and incfib replicons , parab ( partition ) , spvrabcd , rck ( resistance to complement killing ) , mig-5 ( macrophage - induced gene ) , pefabcdi ( pef fimbriae operon ) , and srga ( sdia - regulated gene ; next to orf7 ) , all carried by psev . the 9 plasmids were positive for the 2 replicons and for all genes screened except pefc and pefd ( absent in h070360201 and h070420137 ) , pefi - orf7 ( absent in all ) , and srga ( either absent [ h051860415 , h073180204 , and h091800482 ] or truncated [ in the remaining isolates ] ) ( table 2 ) . isolate subtyping was conducted by phage typing , multilocus variable number tandem repeat analysis ( mlva ) , multilocus sequence typing ( mlst ) , and xbai - pfge ( 9,10 ) ( http://mlst.ucc.ie/mlst/dbs/senterica ; www.pulsenetinternational.org ) . the 9 s. enterica serovar enteritidis isolates belong to phage type ( pt ) 42 , in contrast with cnm4839/03 , which belongs to pt14b ( table 2 ) . we identified 4 mlva profiles , which were all single - locus variants of the highly variable locus sentr5 , indicating that the isolates are closely related ( table 2 ) . the isolate from spain and 3 of the 9 isolates from the united kingdom , selected as representative of each mlva profile , were also analyzed by mlst ( table 2 ) . cnm4839/03 and h091340084 were assigned to sequence type ( st ) 11 , the most commonly found st in serovar enteritidis ( http://mlst.ucc.ie/mlst/ ) . the remaining 2 isolates could be ascribed to st1479 , the first examples of this single - locus variant of st11 in the mlst database ( table 2 ) . according to xbai - pfge , the control strain nrl - salm - pt4 showed a clearly distinct profile in comparison with cnm4839/03 and the 9 isolates containing puo - sevr1like plasmids , which generated 6 closely related patterns ( figure ) . most isolates differed by 1 band of variable size ( 8595 kb ) , which corresponded to the xbai - linearized vr - hybrid plasmids . as an exception , isolate h070420137 showed additional differences in chromosomal bands of 150 and 300 kb . because isolates h070420137 and h070360201 came from the same patient ( table 1 ) and shared the same v and r genotypes and other typing markers , 1 isolate could have evolved from the other ; however , co - infection of the patient with 2 closely related strains can not be ruled out . in addition , considering the typing results of h095100307 , h100240198 , and h101700366 , the identical size of their plasmids , and the fact that they were isolated from the same patient ( table 1 ) , these 3 isolates can be considered the same strain . all except 2 of the uk isolates carrying puo - sevr1like plasmids were recovered from the blood of patients who had recently returned from an african country or who had an african name ( table 1 ) . supporting the possible african origin , similar xbai - pfge profiles and mdr phenotypes ( ampicillin , trimethoprim , sulfonamides , and tetracycline ) have been identified in clinical s. enterica serovar enteritidis isolates involved in outbreaks and community infections in different african countries . these isolates caused bacteremia , meningitis , diarrhea ( 1113 ) , and high case - fatality rates ; they affected mainly children , whereas most clinical isolates analyzed in our study were obtained from adults with bacteremia ( table 1 ) . the detection of the 700-bp / dfra7 integron in s. enterica serovar enteritidis isolates from africa ( 14 ) also supports an african origin of the mdr serovar enteritidis isolates harboring puo - sevr1like plasmids . of note , resistance derivatives of pslt , the v - plasmid specific to s. typhimurium , have been found in the epidemic st313 clone of this serovar , which has been considered a major cause of invasive disease in sub - saharan africa ( 15 ) . closely related mdr s. enterica serovar enteritidis isolates carrying puo - sevr1like plasmids were recovered in the united kingdom . most were isolated from the blood of patients linked to africa , and they showed common features with serovar enteritidis isolates involved in outbreaks on that continent . the possibility that this potentially invasive clone of s. enterica serovar enteritidis can be spread through human travel , together with the detection of vr - plasmids in the serovar most frequently associated with human infections , is of public health concern and requires surveillance .
in developing countries , salmonella enterica serovar enteritidis causes substantial illness and death , and drug resistance is increasing . isolates from the united kingdom containing virulence - resistance plasmids were characterized . 
 they mainly caused invasive infections in adults linked to africa . 
 the common features in isolates from these continents indicate the role of human travel in their spread .