Helicobacter pylori was thought to cause gastritis and gastric ulcers. A team of brave, lucky, and extremely dedicated scientists proved that hypothesis. Without a certain amount of luck, or serendipity, the bacterium now known as Helicobacter pylori may never have come to be understood so clearly, nor would the investigators have connected the bacterium so convincingly to a range of medical conditions such as gastritis, gastric ulcers, peptic ulcers and gastric cancer.
Robert Koch’s postulates
For a bacterium to be officially recognised as being the causative agent of a disease, it must fulfill the four criteria set out by Robert Koch, a German physician and bacteriologist, in 1890:
- The bacteria must be present in every case of the disease.
- The bacteria must be isolated from the host with the disease and grown in pure culture.
- The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host.
- The bacteria must be recoverable from the experimentally-infected host.
Robert Koch was awarded the Nobel prize in Physiology or Medicine in 1905 for his investigations and discoveries on the infectious disease Tuberculosis.
Discovery of Helicobacter pylori
Two Australian medical doctors, Barry Marshall and Robin Warren, first identified Helicobacter pylori, when large numbers of curved or spiral bacteria were observed within the gastric biopsies of patients suffering from chronic gastritis. The bacteria were found within the gastric mucosa, closely associated with the surface of the gastric epithelium (Warren, 1983).
Isolating the bacterium
In order to provide evidence for the second of Koch’s postulates, Marshall and Warren, after some difficulties, eventually succeeded in culturing H. pylori from biopsy specimens of patients with active chronic gastritis. Their successful method for gaining pure cultures of H. pylori was to grow the bacterium on moist chocolate agar in a micro-aerobic environment after a prolonged incubation period (Marshall, 1983).
It is said that their success in culturing the bacterium was due to a bit of good luck, or serendipity. Apparently the laboratory closed early for a celebration on a Friday evening. The plates, which had shown no growth after the standard incubation period, were due for disposal and were left in the micro-aerobic environment for an extra two days. When the scientists returned to the laboratory the following week, they found that bacteria had grown and colonies were visible. It turns out that H. pylori is just a slow starter, and requires a longer incubation period than bacteria such as E. coli.
Proof of Pathogenicity of Helicobacter pylori
The strongest evidence for H. pylori as a causative agent of type B gastritis was provided by Marshall et al (1985). This required healthy human volunteers to ingest a culture of the bacterium, in order to fulfil the third of Koch’s postulates. The first healthy non-infected human volunteer to demonstrate the development of symptomatic gastritis was Barry Marshall himself.
Marshall and Warren were awarded the Nobel Prize for Physiology or Medicine in 2005 for their discovery of the link between H. pylori and peptic ulcers. They were awarded this prize exactly 100 years after Robert Koch, the man who set out the criteria which were the back bone of their research.