Quantitation of viableCoxiella burnetiiin milk products using a liquid medium-based MPN-PCR assay

Abstract

This Technical Research Communication describes a new method by which thermally treatedCoxiellain milk products may be grown in a liquid growth medium and quantitated using an MPN-PCR assay.Coxiellais generally not used in studies on thermal and non-thermal processing of milk due to the need for specialized and highly laborious techniques such as animal assays and tissue culture for determining viability. Recently, a liquid growth medium (ACCM-2) and modified atmosphere were used to growCoxiellafrom pure cultures, infected mouse tissues, and clinical samples, however, the ability to growCoxiellafrom a food such as milk has not been shown. The potential ability to enrichCoxielladirectly from contaminated milk presents a new avenue for conducting pasteurization research in which the viability of heat-treated or injured cultures could be more easily determined through direct enrichment ofCoxiellain ACCM-2. ACCM-2 medium allowed enrichment ofCoxiellafrom bovine whole milk and cream, whole goat, and whole camel milks but not whole water buffalo milk. Enrichment was possible from whole bovine milk containing as few as 6Coxiellage/ml of milk. The applicability of this ACCM-2 enrichment method was shown when using an MPN-PCR assay to quantitate the number of viableCoxiellaremaining in whole bovine milk after 64 °C thermal treatment for up to 10 min.