Table 1.
Yersinia enterocolitica isolation methods used by local, state, and federal laboratories during an investigation of Y. enterocolitica infections associated with improperly pasteurized milk products – southwest Pennsylvania, March–August, 2011
| Laboratory | Samples | Enrichment | Incubation | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Broth or Buffer | Temperature | Time (days) | Potassium hydroxide | Inoculation day | Agar plates | Temperature | Time (days) | ||
| ACHD | |||||||||
| Method 1 | Dairy A products | PSBB | 5°C | 21 | 0·5% to agar plates | 10, 21 | MacConkey, CIN | ±25°C | 1–2 |
| Method 2* | Dairy A products | PSBB | 5°C, 25°C | 1, 2 | 0·25% to broth after 1 day cold enrichment | 3, 4 | MacConkey, CIN | ±25°C | 1–2 |
| PDA | |||||||||
| Method 1 (FDA BAM) [27] | Dairy A products and environmental | PSBB | 10°C | 10 | 0·5% to agar plates† | 10 | MacConkey, CIN | 30°C | 1–2 |
| PADOH | |||||||||
| Method 1 (FDA BAM) | Dairy A products and environmental | PSBB | 10°C | 10 | 0·5% to agar plates† | 10 | MacConkey, CIN | 30°C | 1–2 |
| Method 2 | Dairy A products and environmental | PSBB | 4°C | 21 | 0·5% to agar plates† | 7, 14, 21 | MacConkey, CIN | 30°C | 1–2 |
| CDC | |||||||||
| Method 1 | Environmental | n.a. | n.a. | n.a. | n.a. | Direct plating | MacConkey, CIN | 25°C, 30°C | 2 |
| Method 2 | Environmental | PBS | 4°C | 21 | Broth treated with 0·25% for 2 min, then 0·5% for 15 s before plating | 21 | MacConkey, CIN | 25°C, 30°C | 2 |
| Method 3 | Environmental | n.a. | 25°C | 2 | Broth treated with 0·25% for 2 min, then 0·5% for 15 s before plating | 1, 2 | MacConkey, CIN | 25°C, 30°C | 2 |
ACHD, Allegheny County Health Department; PSBB, peptone sorbitol bile broth; CIN, cefsulodin-irgasan-novobiocin agar; PDA, Pennsylvania Department of Agriculture; FDA, Food and Drug Administration; BAM, Bacterial Analytical Manual [27]; PADOH, Pennsylvania Department of Health; CDC, Centers for Disease Control and Prevention; PBS, phosphate buffered saline; n.a., not applicable.
In this method, dairy A product was added to 225 ml peptone sorbitol bile broth and refrigerated at 5°C for 1 day. On day 2, the broth was alkalinized by using 1 ml of 0·25% potassium hydroxide (KOH) and incubated at room temperature (25°C) for 2 days. MacConkey and cefsulodin-Irgasan-novobiocin agar plates were inoculated with the room temperature broth on days 3 and 4, and incubated at ± 25°C for 1–2 days.
1:10 dilution of enrichment without potassium hydroxide also plated on agar per BAM guidelines.