Alcohols as solution for delaying microbial degradation of biological evidence on cotton swabs

Abstract

Poor storage of biological evidence on cotton swabs is known to lead to fungal and bacterial growth. However, there are often situations where it is inconvenient to dry the swabs without running the risk of contamination, or where only plastic bags are the best option for packaging material. This study aims to investigate the effectiveness of using 70% ethanol (v/v) and 100% isopropanol (v/v) to prevent or delay microbial growth on cotton swabs containing biological evidence and their effects on the subsequent STR analysis. The alcohols was applied on cotton swabs as moistening agent prior to collection of dried saliva stains. The cotton swabs were then packaged immediately in sealable plastic bags and stored at room temperature (27–29°C) for up to 5days to simulate improper storage conditions. DNA was extracted and then amplified using AmpFLSTR® Identifiler® Plus PCR Amplification kit to obtain STR profiles. The results showed no observable fungal growth on any of the swabs moistened with 70% ethanol (v/v) or 100% isopropanol (v/v), and full STR profiles could be obtained from these swabs, while the growth was observed on swabs moistened with sterile deionised water after 5days. The outcome of this study could be used to suggest an alternative DNA evidence collection and storage method in remote areas where samples must be transported in non-ideal conditions to central labs for analysis.