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TITLE:  Characterization of antimicrobial-resistant Salmonella isolated from imported foods
 
AUTHORS:  Zhao S;McDermott PF;Friedman S;Qaiyumi S;Abbott J;Kiessling C;Ayers S;Singh R;Hubert S;Sofos J;White DG;
 
YEAR:  2006
 
JOURNAL ABBREV:  J Food Prot
 
MONTH:  Mar
 
TYPE:  JOUR
 
REFMAN INDEX:  211
 
JOURNAL FULL:  Journal of food protection
 
VOLUME:  69
 
ISSUE:  3
 
START PAGE:  500
 
END PAGE:  507
 
KEYWORDS:  Ampicillin;analysis;Anti-Bacterial Agents;Chloramphenicol;classification;Colony Count,Microbial;Consumer Product Safety;Dna;DNA Gyrase;drug effects;Drug Resistance,Bacterial;Drug Resistance,Multiple,Bacterial;Electrophoresis,Gel,Pulsed-Field;Food;Food Contamination;Food Microbiology;genetics;Integrons;isolation & purification;Kanamycin;Maryland;methods;Microbial Sensitivity Tests;microbiology;Mutation;Nalidixic Acid;pharmacology;Phylogeny;Point Mutation;Polymerase Chain Reaction;Research;Salmonella;Serotyping;Streptomycin;Sulfamethoxazole;Tetracycline;United States;veterinary;Veterinary Medicine;
 
ABSTRACT:  Two-hundred eight Salmonella isolates recovered from over 5,000 imported foods entering the United States in 2001 were tested for antimicrobial susceptibilities and further characterized for quinolone resistance mechanisms, integron carriage, and genetic relatedness. Salmonella Weltevreden (20%), Salmonella Newport (6%), Salmonella Lexington (5%), and Salmonella Thompson (4%) were the four most common serotypes recovered. Twenty-three (11%) isolates were resistant to at least one antimicrobial, and seven (3.4%) to three or more antimicrobials. Resistance was most often observed to tetracycline (9%), followed by sulfamethoxazole (5%), streptomycin (4%), nalidixic acid (3%), and trimethoprim/sulfamethoxazole (2%). One Salmonella Schwarzengrund isolate recovered from squid imported from Taiwan exhibited resistance to eight antimicrobials, including ampicillin, chloramphenicol, gentamicin, kanamycin, nalidixic acid, sulfamethoxazole, tetracycline, and trimethoprim/sulfamethoxazole. Six isolates (Salmonella Bareilly, Salmonella Derby, Salmonella Ohio and three Salmonella Schwarzengrund) contained class 1 integrons, which carried several resistance genes including dhfrI/dhfrXII, aadA, pse-1, and sat1, conferring resistance to trimethoprim/sulfamethoxazole, streptomycin, ampicillin, and streptothricin, respectively. Five of six nalidixic acid-resistant isolates possessed DNA point mutations at either Ser83 or Asp87 in DNA gyrase. One ciprofloxacin-resistant isolate possessed double mutations in DNA gyrase at positions Ser83 and Asp87 as well as a single mutation at Ser80 in parC. The top three serotypes identified, Salmonella Weltevreden (n = 41), Salmonella Newport (n = 13), and Salmonella Lexington (n = 11), were further characterized for genetic relatedness by pulsed-field gel electrophoresis. Fifty-five distinct pulsed-field gel electrophoresis patterns were observed among the 65 isolates, indicating extensive genetic diversity among these Salmonella serotypes contaminating imported foods
 
AFFILIATIONS:  Division of Animal and Food Microbiology, Office of Research, Center for Veterinary Medicine, U.S. Food and Drug Administration, 8401 Muirkirk Road, Laurel, Maryland 20708, USA
 
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