from 2000 through 2005 , the french national reference centre for salmonella at the institut pasteur in paris reported 829 newport isolates among 69,759 salmonella clinical isolates . during this period and depending on the year
, serotype newport ranked between 6th and 10th in prevalence among human serotyped isolates . from 2000 through 2005 , the agence franaise de scurit sanitaire des aliments reported 2,160 newport isolates among 101,791 salmonella isolates collected from animals and food products .
antimicrobial drug susceptibility testing was performed on 585 human newport isolates and 342 nonhuman newport isolates by disk diffusion with 32 antimicrobial drugs ( additional information available from fxweill@pasteur.fr ) .
of 585 isolates tested , 46 ( 7.9% ) were resistant to third - generation cepalosporins .
the geographic origin of the isolates was mainly the paris metropolitan area and northern france ( appendix table ) .
resistant isolates during 2000 ( 15% ) and 2003 ( 17.5% caused by a small outbreak ) .
no third - generation cephalosporin resistance was detected in any of the nonhuman newport isolates tested . *
studied ; n , no . of isolates received at the french national reference centre for salmonella ( 1 per patient ) .
all but 1 of the newport isolates were resistant to cefoxitin ( appendix table ) .
these isolates showed 4 resistance phenotypes ; most ( 41 , 89.1% ) were resistant to streptomycin , sulfonamides , chloramphenicol , and tetracycline .
pcr and sequencing showed that the 45 isolates resistant to cefoxitin were positive for the blacmy-2 gene , and cefoxitin - susceptible isolates contained the extended - spectrum -lactamase gene blactx - m-1 .
mg / l to > 256 mg / l , and ceftazidime mics ranged from 64
three isolates with additional resistance to aminoglycosides contained a class 1 integron with the 1-kb gene cassette aada24 ( known to encode resistance to streptomycin and spectinomycin ) ( 11 ) .
the chloramphenicol / florfenicol resistance gene flor was detected in all but 1 cmy-2producing newport isolate .
clonal relatedness of newport isolates was assessed by multilocus sequence typing ( mlst ) and pulsenet standard method pulsed - field gel electrophoresis ( pfge ) ( figure 1 ) .
all 16 newport mdr - ampc isolates tested had a common sequence type ( st ) , st45 .
xbai - pfge identified 10 distinct profiles ( similarity 76.7% ) among all 45 newport mdr - ampc isolates .
single enzyme matches were found for 3 of the profiles ( 15 isolates ) in the us pulsenet national database ( www.cdc.gov/pulsenet ; appendix table ; figure 2 ) .
two pfge types ( new6 and new8 ) were divided into 24 subtypes because of additional band(s ) < 100 kb .
isolates from the 2003 outbreak showed 4 similar but distinct pfge profiles that differed by 12 bands , migrated between 60 and 100 kb , and were attributed to plasmid(s ) ( additional information available from fxweill@pasteur.fr ) .
if only cases with indistinguishable pfge profiles had been tested , potentially related cases would not have been linked to this outbreak .
therefore , during an outbreak investigation of newport mdr - ampc , analysis of plasmid content ( either by alkaline lysis or s1 nuclease , depending on size of additional bands ) might complete xbai - pfge profiles for isolates whose profiles differ by 1 or 2 additional bands of low molecular mass .
representative xbai pulsed - field gel electrophoresis ( pfge ) profiles of third - generation cephalosporin 
a dendrogram was generated with bionumerics software ( applied maths , sint - martens - latem , belgium ) . the pfge profile ( and if there were indistinguishable isolates in the pulsenet usa database [ www.cdc.gov/pulsenet ] , the corresponding centers for disease control and prevention pulsenet profile ) , the number of isolates , and the -lactamase genes are indicated .
representative psti restriction profiles ( a ) and blacmy-2 southern hybridization ( b ) of plasmids from escherichia coli dh10b transformants of cmy-2producing salmonella spp . clinical isolates .
lane 1 , dh10b/00 - 7490 ; lane 2 , dh10b/03 - 3349 ; lane 3 , dh10b/03 - 3367 ; lane 4 , dh10b/00 - 3525 ; lane 5 , dh10b/00 - 4165 ; lane 6 , dh10b/03 - 9969 ; lane 7 , dh10b/03 - 9243 ; lane 8 , dh10b/02 - 2049 .
the gel is focused on the resolution of high molecular mass bands ; smaller bands ( in particular , the 0.8-kb band ) are not well visualized .
alkaline lysis extraction showed that all but 1 of the newport mdr - ampc isolates harbored a plasmid > 125 kb that hybridized with a blacmy-2 probe ; the remaining isolate harbored a plasmid of 100 kb ( appendix table ) .
analysis with s1 nuclease showed that these plasmids were 100 kb370 kb . up to 3 additional plasmids ( 3.5 kb100 kb ) that did not have blacmy-2 were detected in most isolates ( appendix table ) .
cephalosporin resistance was transferred by electroporation of plasmid dna to eschericha coli dh10b for all 38 cmy-2positive isolates tested .
when present in the donor strain , resistance to sulfonamides , chloramphenicol , and tetracycline was also transferred .
restriction analysis of plasmids isolated from transformants showed 6 similar restriction profiles for newport isolates ( r1r6 ) ( figure 2 , appendix table ) .
newport plasmids r1r6 and agona plasmid r8 were shown by pcr to contain variant a / c2 replicons ( 13 ) , whereas typhimurium plasmid r7 contained the i1 replicon .
psti - digested plasmids analyzed by southern hybridization with a blacmy-2 probe ( figure 2 ) showed 4 hybridization profiles among newport isolates .
profiles h2 , h3 , and h4 differed from h1 by 1 additional band ( > 10 kb for h2 , 3.2 kb for h3 , and > 18 kb for h4 ) , which indicated that the blacmy-2 gene was partially or totally duplicated .
newport mdr - ampc isolates have been the source of sporadic cases and small outbreaks in humans in france during 20002005 .
all isolates had the same mlst type , st45 , and highly similar xbai - pfge profiles .
their plasmids carrying blacmy-2 were homogeneous ( same incompatibility group a / c2 , a main restriction type r1 , and a main hybridization type h1 ) .
these results support clonal expansion of 1 newport strain ( or a limited number of genetically related newport strains ) able to acquire and maintain a large inca / c2 mdr plasmid .
however , this strain was not found in french food animals or domestically produced food products ( additional information available from fxweill@pasteur.fr ) .
further investigation identified the source as a wholesaler who imported meat from belgium , the united kingdom , hungary , canada , brazil , argentina , uruguay , and australia ( 12 ) .
in contrast to europe , newport mdr - ampc has been frequently seen in the united states during the past decade .
furthermore , several characteristics were shared between us and french newport mdr - ampc isolates : st45 ( 15 ) , pfge profiles new5 , new6a , and new6b ( displayed by 15 isolates among the 45 studied ) , and blacmy-2 plasmid hybridization type h1 ( 14 ) .
we can reasonably hypothesize that during 20002005 some isolates likely entered france from north america through imported food .
alternatively , they could have come to france and north america from some other country .
 the multidrug - resistant ( mdr ) salmonella enterica serotype newport strain that produces cmy-2 -lactamase ( newport mdr - ampc ) was the source of sporadic cases and outbreaks in humans in france during 20002005 . because this strain was not detected in food animals , it was most likely introduced into france through imported food products . 