Evaluation of Five Selective Media for Isolation of Catalase-Negative Gram-Positive Cocci from Bulk Tank Milk

Abstract

Five selective media including Edwards modified medium, Edwards modified medium supplemented with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L), Streptococcus selective medium, Streptosel agar, and thallium-crystal violet-toxin-ferric citrate medium were evaluated for the isolation of streptococci and streptococci-like organisms from raw milk. The sensitivity and specificity of these selective media for streptococci and streptococci-like organisms were determined by using American Type Culture Collection reference strains. Under experimental conditions Edwards modified medium with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L) showed the highest sensitivity (100%) and specificity (100%) for streptococci and streptococci-like organisms followed by thallium-crystal violettoxin-ferric citrate medium, Edwards modified medium, Streptococcus selective medium, and Streptosel agar. Edwards modified medium supplemented with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L) allowed growth of all streptococci and streptococci-like organisms, while inhibiting growth of the staphylococci and gram-negative reference strains. Bulk tank milk samples from 114 dairy herds were spiral plated onto Edwards modified medium with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L). A total of 344 isolates (at least three isolates from each sample) were randomly selected and identified to their species. This medium permitted growth of 328 streptococci and streptococci-like organisms belonging to genera Aerococcus, Enterococcus, Gemella, Lactococcus, Streptococcus, and Vagococcus. When Edwards modified medium supplemented with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L) was evaluated using bulk tank milk samples, the sensitivity and specificity of this medium for streptococci and streptococci-like organisms were observed to be 100 and 87.5%, respectively. The positive predictive value for streptococci and streptococci-like organisms was observed to be 99.4%. The results of the study indicate that Edwards modified medium supplemented with colistin sulfate (5 mg/L) and oxolinic acid (2.5 mg/L) can be used as a selective medium for the isolation of streptococci and streptococci-like organisms from bulk tank milk.

Bulk tank milk somatic cell count and sources of raw milk contamination with mastitis pathogens

“…In contrast, no standard is available for BTMS culturing for the detection of mastitis pathogen contamination. Various authors were used different media for this purpose (Fenlon et al, 1995;Benda and Vyletelova, 1997a,b;Jayarao and Wang, 1999;Hayes et al, 2001;Sawant et al, 2002;Jayarao et al, 2004;Zadoks et al, 2004;Olde Riekerink et al, 2006). We have used culture media similar to the recommendation of the National Mastitis Council (2005) for the purpose of this study.…”

Incidence of some pathogenic microorganisms in bulk tank milk in some farms of Gharbia governorate

“…The Staphylococci count/ml of milk samples was calculated and recorded. (Sawant et al, 2002) A 0.1 ml of previously prepared dilution was spread onto, the dry surface of modified Edwards agar supported with colisitin sulphate and oxolinic acid. The inoculated plates were incubated at 37ºC for 48 hours.…”

Guidelines for Monitoring Bulk Tank Milk Somatic Cell and Bacterial Counts

“…Plate count agar was used for enumeration of SPC, PIC, and LPC. The numbers of ES and Streptococcus agalactiae (SAG) in BTM samples were estimated using modified Edward's agar supplemented with colistin sulfate and oxolinic acid (Sawant et al, 2002). MacConkey's agar no.…”