This is a story typical in the history of inventors, an individual who is determined to follow their belief in their idea. This is the story of the history of Petrifilm.

In 1967 Robert L Nelson was hired into the 3M division called Medical Products which had a small group of 10 people working in the product development lab. One of his first ideas was to develop a biological indicator for sterilisation but he was not encouraged to pursue this line of development.

Bob was new to the company and not considered to be a team player since he pressed on with his idea. In the 1880’s, Robert Koch became the first to use bacterial spores as biological indicators (BI), as they are known today. Koch conducted a series of experiments in which a roll of flannel contaminated with spores was exposed to dry heat. The problem was it took 7 days to get a result and required excellent aseptic technique. After some effort, in 1971 Bob developed a self-contained biological indicator which had the spore strip and nutrient medium within a single container, requiring minimal handling by the end user and with results in 24 – 48 hours. The product was known as Attest™ and is widely used today to validate autoclaves. In 1973 Bob moved to the new Health Care division. His next assignment was to develop a microbial profile system that incorporated a different species of bacteria into an Attest Indicator package. The first species were to be controls used to run a Kirby-Bauer test for antibiotic testing. The standard test was to inoculate Tryptic soy broth and incubate for 4-6 hours. The inoculum was then diluted to a 0.1 McFarland standard. This turbidity yields 100 million bacteria/mL. Mueller-Hinton agar plates are streaked and antibiotic discs are placed on the agar. Incubation is over night. Zones of inhibition are measured. While developing this product, Bob realized that a medium could be developed that would grow the bacteria to the desired number. By 1978 Bob helped produce the Inocupac™ system. By 1980, while developing a pickup wand for the Inocupac system, Bob observed that the initial pickup was always within a 1/2 log. He then developed a new wand that would pick up 100 million bacteria/mL so it could be an inoculation system for preparation of standardized bacterial inocula. It was sold as the Prompt™ system. About the same time, Bob was utilising 15% of his work time to research, which was something 3M was renowned for to encourage new ideas, to developing an agar plate that would have a longer shelf life. He visited the University of Minnesota hospital labs and found that the majority of their budget was spent on media. He tried encapsulating the media and placing the capsules into a polyvinyl alcohol. This design did not work well. One day, in the men's bathroom, Bob was talking to Chuck Roberts, a chemist. Chuck was developing a geriatric diaper, using a polysaccharide powder called Super Slurper, a corn starch based superabsorbent polymer invented by Agricultural Research Service (ARS) scientists in 1973. They placed a small amount in a beaker and added water. This swelled and produced a firm gel. So Bob coated some 3M Scotch® tape with the Super Slurper, added some Tryptic soy broth and inoculated the gel with E. coli. The next day colonies were growing. Sue McAllister and Paul Hanson soon joined the project and contributed much to assure a successful birth of a new product, Petrifilm™. The invention received U.S. Pat. No. 4,565,783 on January 21 1986. Dr Rich Matner joined the group about 1986 to help develop the Aerobic Count and Hemorrhagic EC Petrifilm plates. Bob’s next project was to develop a Yeast and Mold Petrifilm plate. Whilst playing tennis with Paul Hansen, he suggested that Bob try a nonwoven in the plate as Paul was manager of the nonwoven technology centre. The nonwoven was used and proved successful. Rich Matner and Marlys Lund also made major contributions in the development of this plate. Mary Ramos was assigned to work on the High Sensitivity plate. She discovered some gums that absorb more water which allowed us to place more than 1mL of sample/20 sq. cm. Mary decided to join professional services and Bob continued the development of the High Sensitivity Coliform Count plate. He decided to dissolve the nutrients in a latex adhesive so that powder could be coated on both sides. All the latex adhesives proved to be toxic. Mike Crandall in Specialty adhesives developed a non-toxic latex adhesive which is currently being used. From my last counts, Bob Nelson has over 10 patents in microbiology products. As you can tell from this story, many people have been responsible for Petrifilm's successful development for a lonely beginning. The beauty of the product is that it looks simple, but in reality is quite complex.

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