SLIDE 1:

Isolation & Characterization of Antimicrobial-Resistant Salmonella from Retail Meats

Jianhong Meng, DVM, Phd
Department of Nutrition and Food Science
College of Agriculture and Natural Resources
University of Maryland

SLIDE 2:

Retail Meats

Antimicrobial Resistance Profiles among Salmonella Isolates

Integron & Resistance Gene Transfer

SLIDE 3:

Campylobacter, Salmonella, and E. coli in Retail Meats

• Two trials
  • Trial I: Summer 1998
  • Trial II: July 1999 - July 2000
• Objectives:
  • 1. Prevalence in retail meats
  • 2. Antimicrobial resistance of the meat isolates

SLIDE 4:

Sampling Plan (trial I)June to September 1998

• 3 retail stores selected
• Ground meatschicken, turkey, beef and pork
• 3 samples for each meat obtained every Monday

SLIDE 5:

Sampling Plan (trial II)July 1999 to July 2000

• Identify stores of 4 supermarket chains
  • 97 stores identified
• Create store database
  • assign ID to each store
• Randomly select 5 stores using SAS before sampling
  • 4 stores sampled every other Monday;
  • the 5th store as a backup

SLIDE 6:

Sampling Plan (trial II)July 1999 to July 2000

• 8 samples per store
  • Chicken carcass -- 2
  • Turkey breast (frozen) -- 2
  • Beef steak -- 2
  • Pork chop -- 2
• 32 samples collected from 4 stores for each visit

SLIDE 7:

Map of D.C. Metro Area (Maryland Side)

Map

SLIDE 8:

No. of Sampling Visit/Store

SLIDE 8:

Retail Meat Surveys

SLIDE 10:

Salmonella in Retail Meats

SLIDE 11:

Salmonella Serotypes from Ground Meats

SLIDE 12:

Phagetype of S. Typhiumurium

SLIDE 13

An Image

SLIDE 14:

Resistance of Salmonella from Trial I

An Image

SLIDE 15:

Resistance of Salmonella from Trial II

An Image

SLIDE 16:

Multi-Resistance among Salmonella Serotypes

SLIDE 17:

Resistance Profiles of S. Agona and S. Typhimurium

• S. Agona (5 isolates)
  • Amp-Amo-Cef-Cet-Cep-Str-Sul-Tet-Tri
• S. Typhimurium:
  • 1 Typhimurium: SuTTri
  • 1 DT104b: ACSSuT
  • 4 DT104: ACSSuT
  • 2 DT208 (different PFGE patterns):
• Amp-Amo-Cef-Cet-Cep-Cml-Ffc-Gen-Kan-Str-Sul-Tet

SLIDE 18:

Dissemination and Diversity of Antimicrobial Resistance

• Plasmids
• Transposons
• Integrons

SLIDE 19:

Transfer of Antibiotic Resistance

• Plasmids
  • R factors
  • Possess multiple resistance genes
  • Conjugal (mediate their own transfer)

SLIDE 20:

Transfer of Antibiotic Resistance

• Integrons
  • Mobile DNA elements
  • Possess single or groups of resistance genes
    • ß-lactamases
    • aminoglycoside modifying enzymes
    • sulfa/trimethoprim
    • chloramphenicol
  • Plasmid and/or chromosome
  • 4 classes recognized

SLIDE 21:

Structure of Class 1 Integron

An Image

SLIDE 22:

Class I Integron and bla(CMY) in Salmonella

SLIDE 23:

Conjugation

• Donor strain
  • S. Typhimurium DT208 (StrR)
• Recipient strain
  • E. coli O157:H7 JM263 (NalR)
• Selective markers
  • Streptomycin (125 µg/ml)
  • Nalidixic acid (100 µg/ml)

SLIDE 24:

Transformation by Electroporation

• Plasmids (ca. 40-45 kb)
  • isolated from S. Typhimurium DT208 (StrR)
• Bacterial host strain
  • E. coli JM109
• Selective marker
  • Streptomycin (125 µg/ml)

SLIDE 25:

Results of Conjugation & Transformation

SLIDE 26:

Summary

• Prevalence of Salmonella in retail meats was low (2.5%) except ground meats (21%)
• Most Salmonella developed resistance to multiple antimicrobials (66% resistant to ?3)
• Resistance genes readily transferred between species through conjugation and transformation

SLIDE 27:

Acknowledgement

• David White
• Shaohua Zhao
• David Wagner
• Robert Walker
• Patrick McDermott
• Robert Sudler
• Lucy Zhao
• Beilei Ge
• Juan De Villena
• Sheng Chen
• Emily Yeh
• David Ingram