Storage Effects on Sample Integrity of Environmental Surface Sampling Specimens with Bacillus anthracis Spores

Abstract

The effect of packaging, shipping temperatures and storage times on recovery of Bacillus anthracis. Sterne spores from swabs was investigated. Macrofoam swabs were pre-moistened, inoculated with Bacillus anthracis spores, and packaged in primary containment or secondary containment before storage at -15°C, 5°C, 21°C, or 35°C for 0-7 days. Swabs were processed according to validated Centers for Disease Control/Laboratory Response Network culture protocols, and the percent recovery relative to a reference sample (T₀) was determined for each variable. No differences were observed in recovery between swabs held at -15° and 5°C, (p ≥ 0.23). These two temperatures provided significantly better recovery than swabs held at 21°C or 35°C (all 7 days pooled, p ≤ 0.04). The percent recovery at 5°C was not significantly different if processed on days 1, 2 or 4, but was significantly lower on day 7 (day 2 vs. 7, 5°C, 10², p=0.03). Secondary containment provided significantly better percent recovery than primary containment, regardless of storage time (5°C data, p ≤ 0.008). The integrity of environmental swab samples containing Bacillus anthracis spores shipped in secondary containment was maintained when stored at -15°C or 5°C and processed within 4 days to yield the optimum percent recovery of spores.

Keywords: Bacillus anthracis; Environmental sampling; Shipping integrity; Swab; qPCR.

Figure 1

%R of BA from macrofoam swabs with dust and 104 spores and stored in (1) primary and (2) secondary containment. Bars represent 95% confidence intervals, n=120 for each containment, n=30 for each bar. Bars correspond with the following days: Day 1 , Day 2 , Day 4 , and Day 7 . A: Inoculum 10⁴ CFU/swab, B: Inoculum 10² CFU/swab.