Evaluation of an acriflavine disk assay for differentiating Staphylococcus aureus from other staphylococci isolated from bovine milk.
OBJECTIVE
To develop an acriflavine disk assay for identification of Staphylococcus aureus and to test whether the acriflavine disk assay could be used to differentiate S aureus from other staphylococci isolated from bovine milk samples.


METHODS
Prospective study.


METHODS
882 staphylococcal isolates from bovine milk samples and 3 S intermedius isolates from dogs.


METHODS
Paper disks saturated with various amounts of acriflavine were used in a growth inhibition assay to determine the amount of acriflavine that would most reliably differentiate S aureus from other staphylococci. For all isolates, hemolytic pattern, results of tube coagulase tests after 4 and 24 hours of incubation, growth on acriflavine-supplemented media, results of an acriflavine disk assay, and results of an automated identification system were determined.


RESULTS
10 micrograms of acriflavine/disk was determined to be the most appropriate concentration for use in the assay. All 112 isolates identified as S aureus by the automated identification system were resistant to this concentration of acriflavine, and only 1 of 236 isolates identified as non-S aureus staphylococci was resistant. There was substantial agreement between results of using the acriflavine disk assay as a diagnostic criterion for differntiating S aureus isolates from non-S aureus staphylococci and results of the automated identification system. Agreement between results of determining hemolytic pattern and results of other diagnostic tests was only moderate.


CONCLUSIONS
The acriflavine disk assay, using 10 micrograms of acriflavine/disk, was a practical, accurate method for differentiating S aureus isolates from non-S aureus staphylococci.
Department of Veterinary Preventive Medicine, College of Veterinary Medicine, Ohio State University, Columbus 43210, USA.
R L
RL
Wallace
W G
WG
Queen
K H
KH
Hoblet
J S
JS
Hogan
D000167:Acriflavine / Q000494:pharmacology*; D000818:Animals; D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D002417:Cattle; D003470:Culture Media; D004352:Drug Resistance, Microbial; D008892:Milk / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000302:isolation & purification*
D000891:Anti-Infective Agents, Local; D003470:Culture Media; D000167:Acriflavine