How Jane Hinton cultivated gonorrhea and saved us from antibiotic resistant bugs
My scientific education was replete with figures of white men: portly and slim; bearded and shock haired; they bent over microscopes, they forgot moldy plates. But, as I’m learning, that version of history elides the presence of intelligent, capable women, especially those of color. I first learned of Jane Hinton in Hilda Bastian’s excellent blog post on the lack of images of women African American scientists. Jane Hinton was one of the first African-American women to become a Doctor of Veterinary Medicine. Before she joined the University of Pennsylvania School of Veterinary Medicine, she was a laboratory technician at Harvard. While there, she worked on cultivating gonococcus, the causative agent of gonorrhea. What I didn’t realize when I began reading her ground-breaking paper is that the medium she devised is still saving lives today. The medium that bears her name, Mueller-Hinton agar is used in laboratories around the world to cultivate pathogenic microbes, determine treatment plans and prevent food borne illness. So what is this medium, and how did it reshape microbiology?
In 1941, the year Jane Hinton and her colleague J. Howard Mueller devised their medium, the world was in the midst of World War II. The loss of life from the violence was staggering, but to add to the misery, a number of diseases such as gonorrhea and meningitis were also rampant. In 1939, 80% of venereal diseases cases among soldiers were due to gonorrhea. Luckily, with the invention of sulfa drugs, it was possible to cure these infections. But, treatment by the correct medication required correct diagnosis, which meant successfully culturing the bacterium that caused the disease, Neisseria gonorrhoeae (gonococcus). Culturing these microbes also helped in efforts to improve detection and generate vaccines against these diseases.
Previously, gonococcus was cultivated on different kinds of medium, each of which had its own disadvantages. For example, Difco Proteose Chocolate Agar was dark, hence measuring the size and number of bacterial colonies was difficult. Media that contained serum could not be heated under pressure, which risked the survival of hardy bacterial cysts that could later contaminate the plates. In order to solve these problems, Hinton and Mueller took a methodical approach to determine which ingredients helped in bacterial growth, and reported their efforts in the paper “A Protein-Free Medium for Primary Isolation of the Gonococcus and Meningococcus”.
They took as their starting point, the Gordon and Hine Pea Meal Extract Agar. This had previously been used to culture meningococcus, the causative agent of meningitis, and could also be used to grow gonococcus. It had three main ingredients: meat extract, agar and pea flour extract. When they isolated starch, protein and fat from pea flour and tested each separately, they were surprised to discover that starch, not protein, aided in the growth of microbes. They hypothesized that starch acts as a sponge to soak up chemicals that might be toxic to the bacteria. This surmise has since been confirmed, and starch is now commonly used in microbiological media as a detoxifying agent. They also substituted the arduous meat extract with simpler meat products. In their own words, the authors found that:
“The results have been highly satisfactory. Colonies are frequently larger on the starch medium than on the chocolate. They are easily recognizable, particularly with the aid of the oxidase reagent. “
They also tested growing meningococcus on the medium and found that it grew well. The ability to grow these microbes made the medium a huge step forward in microbiology. But the true utility of the medium was yet to be uncovered.
Together with the development of antibiotics came a challenge: the spread of antibiotic resistance. As soon as Penicillin was used widely to treat soldiers in WW2, resistance to the drug developed. Thus grew the need to check for antibiotic resistance. Varying approaches gave widely differing results, making it hard to rely on the data, and adding to the confusion of the medical professionals. Therefore, scientists were in search of an assay that could be reproduced identically in different laboratories. In 1966, Kirby and Bauer refined the process of determining antibiotic resistance by using the zone of clear growth around a paper disc steeped in a specified amount of antibiotic as a measure of resistance. The other important decision they had to make was the choice of culture media on which the bacteria would grow. The ideal medium would allow for the growth of a wide range of organisms, would not degrade antibiotics by virtue of being too acidic or basic, and allow the easy penetration of antibiotics placed on its surface. They chose Mueller-Hinton agar.
The strengths of Mueller-Hinton agar come from how it was devised: since Mueller and Hinton had focused on paring the medium down to its most basic components, there was less batch to batch variation in the medium. The simplicity also minimized the presence of antibiotic inhibitors, which could reduce the effect of antibiotics on the bacteria. This is also a loose agar, meaning the particles are not packed cheek by jowl, allowing the antibiotics space to move through the medium. And finally, the magic ingredient of starch, which acts to prevent bacterial toxins from interfering with the test results, and serves as a source of energy. After labs around the world had weighed in with their own positive experiences, the Clinical and Laboratory Standards Institute (CLSI), a global body establishing the best laboratory standards adopted the Kirby-Bauer technique using Mueller-Hinton agar as the world-wide standard for antibiotic testing. Now, the demand for standardized medium is so great, there are companies that make and sell tons of Mueller-Hinton agar.
That Jane Hinton’s work has become central to basic microbiology points to the importance of methodical, logical science. And she succeeded in this field in an age when her ability to pursue it to the utmost was severely limited. It is important that we celebrate her achievements so that we finally see the edifice of scientific knowledge being built by all of the peoples who contributed. So that when future generations of scientists are trained, they will know that whether they are brown or black, male, female or neither, they too, will be given their due.
