Compositions and Methods for the Enrichment and Isolation of Campylobacter Pylori and Related Organisms From Biological Specimens and the Environment

C. pylori is a slow growing, fastidious organism and therefore cannot be easily isolated from biologic specimens which contain other contaminating bacteria. The contaminating bacteria in such specimens grow quickly and overgrow any C. pylori which may be present. For this reason, C. pylori cannot be cultured from the usual specimens such as stool, although it may be isolated from stomach biopsies and gastric juice. These latter two specimens require an expensive endoscopy and biopsy of the stomach. There is a need therefore for a method which might enable C. pylori to be isolated from a stool specimen, vomitus, oral secretions, contaminated gastric biopsies or other patient specimens, or specimens from the environment.

We have discovered that C. pylori can survive in an acid medium, provided that urea is present. Other bacteria are killed by acid even when urea is present, but C. pylori breaks down the urea to generate ammonia. Ammonia is alkaline and protects the organism from acid attack. This protection comes in two phases. When large amounts of C. pylori are inoculated into solutions containing urea with a pH greater than approximately 2.5, the organism is able to modify the pH of the solution and raise it to a more comfortable environment, e.g. pH 6.5. Secondly, if the pH of the solution is less than 2.5, C. pylori does not raise the pH of the total solution but still survives, presumably by the action of urease within the organism. C. pylori maintains an intracellular or pericellular microenvironment that protects its viability against the surrounding acidic environment.

Utilizing this principle it is possible to isolate C. pylori from heavily contaminated specimens such as stool. The sample to be cultured is first homgenized in a small volume of water and then diluted with a solution of urea in acid. This step will obtain an aqueous suspension of the sample in a highly acidic environment in the presence of urea. As an example, in a recent experiment we homogenized five grams of stool in 20 mls of normal saline. The suspension was then inoculated with 0.5mls of saline to which a colony of C. pylori had been added. After 10 minutes, the stool/C. pylori mixture was added to 4.5 mls of 5 mmolar urea solution which had been acidified to a pH of 1.6 with sulfuric acid. The specimen was then incubated at room temperature for 5 minutes. Samples of the solution were then plated onto non-selective blood agar and cultured in a micro-aerophilic environment for three days. After three days there were very few contaminating organisms on the plate but the C. pylori had survived and colonies of the organism were present.

This general principle may be used to isolate any urease producing organism from the environment. The incubation of the specimen in the presence of strong acid and urea is an "enrichment" process which markedly decreases the ratio of contaminating organisms to the urease producing organism. A further enhancement is to plate the specimen after incubation, onto a medium which contains antibiotics inhibitory to organisms which survive the incubation step, but which are not inhibitory to the organism being sought.

We have observed that the urease enzyme of C. pylori is immediately denatured in strong acid. This process is irreversible. Many other bacterial irease enzymes are also denatured in this way. We have observed that when a specimen that contains C. pylori is plated onto a urea detection agar (for example CLOtest agar), there is enough preformed urease in the specimen to react with the agar and produce a color change, even if no bacterial growth occurs. Similarly, a normal stool sample contains some active preformed bacterial urease which causes a color change after some hours in contact with such a urease detection gel. However, if the specimen is ground or homogenized and then acid-treated as in part one of this invention, pre-formed extra cellular urease is destroyed. The specimen may then be plated onto a urea-detecting culture medium. At this point the only active urease will be in live, intact organisms. As the bacteria grow in the selected urease detecting medium, new urease will be produced and will escape from the bacteria within a short time, (less than 48 hours). A bacterial colony producing urease is then visible on the medium by the presence of a color change in the underlying gel. Thus a urease producing organism is detected well before the slow-growing colonies are large enough to see with the naked eye (in the case of C. pylori the culture usually takes 3 days). A single colony is easily picked off and sub-cultured. An way to make such a urease detection culture medium is to start with a clear agar on which C. pylori grows, such as Brucella or GC agar with the addition of 1% fetal calf or horse serum and 1% corn starch (Buck G. E., Smith J. S. Medium Supplementation for growth of C. pyloridis. J Clin Microbiol 1987; 25: 597-99). A suitable addition to this medium is urea in a concentration of between 1-100 mmols per liter, and a pH indicator such as phenol red or thymol blue. A buffer may be added to adjust the final pH of the agar to between 3.0 and 7.0. An example of a suitable buffer is 45 mls of 0.1 molar disodium citrate plus 55 mls of 0.1N HCl as described in Ciba Geigy scientific tables. Acidification of the agar would further enhance the selection of urease positive organisms but may affect the stability of the medium.

An example of this method would be the isolation of C. pylori from a gastric biopsy specimen. If the fresh specimen is plated immediately into the urease detecting culture agar, there is enough urease in the specimen to change the color of the medium generally, and prevent the early isolation of a single colony. However, if the biopsy is ground and treated with acid and urease solution for between 1 and 30 minutes and then plated onto the urease detection medium, the only urease present is within live organisms. Very early colonies are then detected by a color change. Similar pre-treatment would enable early isolation of C. pylori or other urease producing organisms from a contaminated biological specimen such as stool, sputum, or vaginal secretion, or from the environment. The early detection and subsequent isolation of C. pylori would be very useful to enable specific etiologic diagnosis of this infection and rapid determination of antibiotic sensitivities (a process which now takes approximately 7 days in most laboratories).