Pennsylvania Animal Diagnostic Laboratory System
PADLS Conferences Spring 2001 11. Isolation of Organisms
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A total of 5 selective media including Colistin sulphate (10mg/L) and oxolinic acid (5mg/L) supplemented tryptic soy agar with 5% sheep blood (COBA), Edwards modified medium (EM), Edwards modified medium with colistin sulphate (5mg/L) and oxolinic acid (2.5mg/L) (EMCO), Streptosel (S), and Thallium-crystal violet-toxin-Ferric Citrate medium (TKTFC) were evaluated for their ability to support growth of streptococci and streptococci like organisms (SSLO; Aerococcus, Enterococcus, Lactococcus, Streptococcus) and inhibit growth of organisms belonging to genus Staphylococcus and Gram-negative organisms reported to occur in bulk tank milk. The 5 selective media were inoculated with 32 species of bacteria that belong to the genera aerococci, enterococci, lactococci, streptococci, gram-negative bacteria, and staphylococci. It was observed that, under laboratory conditions. EMCO allowed the growth of SSLO, while inhibiting growth of all staphylococci and gram-negative bacteria. While COBA, EM, S and TKTFC media either inhibited growth of SSLO or allowed growth of Gram-negative bacteria or Staphylococcal organisms on them. The sensitivity and specificity of EMCO media was determined by plating 50 bulk tank milk samples from 9 counties in Pennsylvania. Three to five colonies from EMCO media from each bulk tank milk sample were identified to species level. Out of two hundred isolates screened, 186 (catalase negative) were identified as SSLO (Aerococcus, n=55; Enterococcus, n=13; Lactococcus, n=7; Streptococcus, n=110; and Gemella sp, n=1). Twelve isolates were identified as non-SSLO (catalase positive) and 2 isolates (catalase negative) could not be identified. The sensitivity and specificity of EMCO was observed to be 100% and 86% respectively. The results of this study suggest that EMCO can be used for selective isolation of streptococci and streptococci like organisms.

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