2025 Volume 42 Issue 2 Pages 34-43
Selective broths for Escherichia albertii have been developed for its selective enrichment and efficient isolation. Here, we evaluated E. albertii-selective media, CTD-TSB and NCT-mTSB, for the efficiency of detection and isolation using wild raccoon fecal specimens. CTD-TSB culture yielded comparable detection rate (71.5%) to and higher isolation rate (34.3%) than non-selective enrichment with TSB (71.4% and 5.0%, respectively). While detection rate of NCT-mTSB culture was lower (55.6%) than the other broths, it yielded much higher isolation rate (79.8%). PCR-based intra-specimen diversity analysis of E. albertii isolates identified 2 or more genotypes in 38.7% of raccoon specimens from which this bacterium was isolated. Both the selective broths contributed to catching the heterogeneic E. albertii from each specimen as well as increasing the isolation efficiency. However, in several raccoon specimens, certain E. albertii genotypes identified in non-enriched samples were not identified when selective enrichment broths were used, especially in the NCT-mTSB. The discrepancies were more noticeable in specimens with low E. albertii load, where it could not be detected without prior enrichment. Growth test with selected isolates revealed that the bacterial load required for successful growth in NCT-mTSB varied significantly among isolates (101 to 107 CFU). Some isolates which could not be isolated from NCT-mTSB required more E. albertii to grow in this medium than number of E. albertii initially present in the fecal samples, suggesting that they were not isolated from selective broths because their numbers were low. These findings suggest that combination of at least two media for enrichment is necessary to avoid false-negative results and for comprehensive isolations.
