Comparison of Salmonella enterica serovar Heidelberg susceptibility testing results.
OBJECTIVE
Disk diffusion and broth dilution assays are conventionally used for antimicrobial susceptibility testing (AST) of bacteria. The goal of this study was to determine the correlation of results from different AST methods for the Salmonella enterica serovar Heidelberg.


METHODS
S. enterica serovar Heidelberg (n=105) strains were tested using 4 different AST methods: agar disk diffusion, broth microdilution using Sensititre with the NARMS (CMV1AGNF) panel, manual broth microdilution and Vitek with GNS-207 cards.


METHODS
AST was performed using standardized methods and Clinical and Laboratory Standards Institute recommended quality control organisms. Eight drugs were common to all testing methods including amikacin, amoxicillin/clavulanic acid, ampicillin, chloramphenicol, ciprofloxacin, gentamicin, tetracycline and trimethoprim/sulfamethoxazole.


RESULTS
No resistance to amikacin and ciprofloxacin was detected. Overall, the agreement of the AST results among all four methods for the drugs tested was: amikacin (100%), amoxicillin/clavulanic acid (96.1%), ampicillin (97.1%), chloramphenicol (96.2%), ciprofloxacin (100%), gentamicin (80.0%), tetracycline (80.0%) and trimethoprim/sulfamethoxazole (94.3%). There was 97.1%, 95.5% and 98.0% overall agreement between the reference diffusion method and the manual broth microdilution, Sensititre microdilution and Vitek methods, respectively.


CONCLUSIONS
The study indicated that AST methods correlated with one another when testing S. enterica serovar Heidelberg isolates, with a few exceptions. In general, discrepancies among the methods were due to isolates being interpreted as intermediately susceptible or due to an increased number of resistances detected with Sensititre and a lower number with Vitek.
Nayak
Rajesh
R
National Center for Toxicological Research, United States Food and Drug Administration, Jefferson, Arkansas, USA.
Call
Veronica
V
Kaldhone
Pravin
P
Tyler
Cynthia
C
Anderson
Gwendolyn
G
Phillips
Sarah
S
Kerdahi
Khalil
K
Foley
Steven L
SL
D000583:Amikacin / Q000494:pharmacology; D019980:Amoxicillin-Potassium Clavulanate Combination / Q000494:pharmacology; D000667:Ampicillin / Q000494:pharmacology; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002701:Chloramphenicol / Q000494:pharmacology; D002939:Ciprofloxacin / Q000494:pharmacology; D015169:Colony Count, Microbial / Q000379:methods* / Q000592:standards; D004338:Drug Combinations; D004352:Drug Resistance, Microbial; D005839:Gentamicins / Q000494:pharmacology; D007201:Indicator Dilution Techniques / Q000592:standards; D008826:Microbial Sensitivity Tests / Q000379:methods* / Q000592:standards; D011200:Poultry; D011786:Quality Control; D019779:Salmonella enterica / Q000145:classification / Q000187:drug effects / Q000302:isolation & purification*; D013419:Sulfamethizole / Q000494:pharmacology; D013752:Tetracycline / Q000494:pharmacology; D014295:Trimethoprim / Q000494:pharmacology; D000096926:Benzenesulfonamides
D000583:Amikacin; D019980:Amoxicillin-Potassium Clavulanate Combination; D000667:Ampicillin; D000900:Anti-Bacterial Agents; D002701:Chloramphenicol; D002939:Ciprofloxacin; D004338:Drug Combinations; D005839:Gentamicins; D013419:Sulfamethizole; D013752:Tetracycline; D014295:Trimethoprim; C029078:trimethoprim sulfamethizole; D000096926:Benzenesulfonamides