Dr. Strangemilk or: How I Learned to Stop Worrying and Love the Pseudomonas - Sam Reichler, Ph.D. Candidate, Wiedmann Lab, Cornell University

Sam Reichler

Ph.D. Candidate, Wiedmann Lab, Cornell University

Dr. Strangemilk or: How I Learned to Stop Worrying and Love the Pseudomonas

Human consumption of domesticated ruminant milk began over 10,000 years ago during the Neolithic Revolution. The extremely perishable nature of fresh milk has remained a persistent challenge from these prehistoric times to the present day. Bacteria present in and on the udder, in the farm environment, and on the hands and implements of milkers contaminate the milk and rapidly proliferate in its nutrient-rich conditions. For this reason, untreated fresh milk spoils within hours at ambient temperatures. This changed with the dual advents of mechanical refrigeration and pasteurization in the 19th century. Although the primary purpose of pasteurization is to reduce the foodborne pathogen population of milk to an acceptable risk level, pasteurization also drastically reduces the population of nonpathogenic vegetative bacterial cells responsible for spoilage. For this reason, refrigerated contemporary high-temperature, short-time pasteurized milk has an optimum shelf life of approximately 21 days. The largest obstacle to achieving this optimum is recontamination of milk with heat-labile bacteria during processing following pasteurization, a phenomenon called post-pasteurization contamination (PPC).

The 4 studies I will present advance our knowledge of PPC in several relevant areas: (1) The prevalence and identity of post-pasteurization contaminant Gram negative bacteria in large Northeastern United States fluid milk processing plants; (2) an assessment of plant sanitation and employee training interventions for the reduction of PPC rates in fluid milk; (3) a single gene sequencing-based subtyping technique for Pseudomonas spp., currently the most common post-pasteurization contaminant; and (4) genotypic and phenotypic characterization of 2 Pseudomonas spp. responsible for blue and gray color defects in dairy products. The results of these studies emphasized several high-level conclusions regarding the present state of PPC and our knowledge thereof.