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.
March 30, 2021
Zoom Recording ID: 98225343013
UUID: yuhMBhPnR8ijcT4KejwTsA==
Meeting Time: 2021-03-30T19:30:28Z