Enumeration of respiring Pseudomonas spp. in milk within 6 hours by fluorescence in situ hybridization following formazan reduction

Respiring Pseudomonas spp. in milk were quantified within 6 h by fluorescence in situ hybridization (FISH) with vital staining. FISH with an oligonucleotide probe based on 16S rRNA sequences was used for the specific detection of Pseudomonas spp. at the single cell level. 5-Cyano-2,3-ditolyl tetrazolium chloride (CTC) was used to estimate bacterial respiratory activity. The numbers of respiring Pseudomonas cells as determined by FISH with CTC staining (CTC-FISH) were almost the same or higher than the numbers of CFU as determined by the conventional culture method.