Long term freeze storage of Campylobacter pyloridis

Maintenance of Helicobacter pylori cultures in agar stabs

BACKGROUND

Helicobacter pylori requires frequent passage at 37 °C with reduced oxygen tension to maintain viability, and recovery from frozen stocks can be unpredictable and slow. Agar stab cultures were assessed as a possible means of maintaining viability without the need to passage every 4-7 days.

MATERIALS AND METHODS

Agar stabs prepared from either Brucella or Brain Heart Infusion media were inoculated deeply with H. pylori strains or H. felis and grown under varying conditions for up to 13 weeks. Subcultures were prepared from these stabs at various intervals to test for viability.

RESULTS

Established cultures in agar stabs failed to survive at room temperature but did survive at 37 °C with 10% CO₂ for up to 56 days. H. felis remained viable for up to 28 days. No difference was observed between the two media formulations.

CONCLUSION

H. pylori grown in agar stabs remains viable for prolonged periods of time without the need to subculture and may represent an improved method for storing H. pylori for infrequent use.

Helicobacter pylori is a fragile bacteria when stored at low and ultra-low temperatures

BACKGROUND AND AIM

Usually, bacteria are cryopreserved for short-term storage at low and ultra-low temperatures. There are no reports as to whether Helicobacter pylori is a fragile bacteria when stored at low and ultra-low temperatures as compared with other intestinal bacteria. A study was done on seven H. pylori strains and other intestinal bacteria to compare different temperatures for storage of organisms in saline solution.

METHODS

Seven H. pylori strains, specifically American Type Culture Collection (ATCC) strains 43504 and TN2GF4, and five strains isolated from the present patients were grown on a modified Skirrow's agar for H. pylori. Escherichia coli and Bacteroides distasonis, both representing isolates from the present patients, were grown on trypticase soy blood agar for E. coli, and EG agar for B. distasonis. Culture was for 4-5 days under microaerobic, aerobic and anaerobic conditions at 37 degrees C. Cells were harvested by scraping growth from the solid medium and into sterile saline. The cells were adjusted to concentrations of 109 viable cells/mL in saline and preserved at 4 degrees C, -20 degrees C, or -80 degrees C for 3 weeks before reculture under microaerobic, aerobic and anaerobic conditions at 37 degrees C for 7 days. After incubation, morphologically distinct colonies were counted, isolated, and identified by standard bacteriologic techniques. The H. pylori were morphologically analyzed by electronic microscopy before and after preservation. Mongolian gerbils were inoculated with the cryopreserved H. pylori to evaluate the bacterial infectivity.

RESULTS

Six of the seven H. pylori strains failed to culture after being preserved at 4 degrees C, -20 degrees C, or -80 degrees C. Only ATCC 43504 could be cultured after freezing at -80 degrees C. The number of H. pylori ATCC 43504 before preservation was 9.0 +/- 0.5 (log10 no. organisms/mL) and decreased to 5.7 +/- 0.6 after preservation. Morphologically, all H. pylori except ATCC 43504 strains transformed from a bacillary to a coccoid form after preservation. In addition, none of the H. pylori strains could infect Mongolian gerbils after preservation. Escherichia coli and B. distasonis were recovered. Titers before and after 4 degrees C, -20 degrees C, and -80 degrees C, respectively, were 9.1 +/- 0.2, 8.9 +/- 0.5, 8.6 +/- 0.3, and 8.7 +/- 0.3 for E. coli and 9.1 +/- 0.4, 8.7 +/- 0.6, 8.6 +/- 0.5, and 8.8 +/- 0.3 for B. distasonis.

CONCLUSIONS

Helicobacter pylori is a fragile bacteria for storage at low and ultra-low temperatures in comparison with other intestinal bacteria.

Bacteriology of Helicobacter pylori

The discovery and first isolation of H. pylori in pure culture from gastric biopsies in 1982 provided the basis for a completely new area of microbiology. Since then, H. pylori has been an intensively pursued topic world-wide, and extensive data have been acquired on all aspects of its basic microbiology, both at the conventional phenotypic level and at the molecular level. H. pylori is a remarkable microorganism because of its ability to readily colonize a major proportion of human population worldwide and to persist successfully for long periods (probably decades) in a hostile environment. At the same time it interacts with the host immune system in such a way as to permit long-term survival. Blaser (1993) proposed a model in which both host and parasite adapt to down regulate inflammatory phenomena to promote survival. Urease production by H. pylori (an important factor in that process) is one of its most distinct features with a key role in its success as an infective agent. Another less obvious yet highly significant feature of H. pylori is the ability to achieve a high degree of interstrain diversity in genomic DNA nucleotide sequences, while maintaining overall genetic homology and phenotypic homogeneity amongst strains. The selective advantage this diversity provides the bacterium is not understood. A key objective of future microbiological studies should be to understand the population genetic structure of H. pylori. Most species of bacteria are clonal in natural population structure, yet all genomic data suggest the contrary is true for H. pylori. Furthermore, it is not clear if all strains of H. pylori are equally pathogenic, and that some subsets may possess additional pathogenicity factors that are responsible for the development of different disease pathologies. A phylogenetic framework of the genetic relationships of the clones within H. pylori would enable an examination of the total genetic diversity, with respect to ethnic or geographical population and the nature of the disease caused. A second aim would be to understand the mode of transmission of H. pylori from individual to individual. Although there is some evidence for either an oral-oral or a faecal-oral route, no reliable microbiological protocols exist for the isolation of H. pylori from non-gastric sites. There is therefore, considerable scope for the development of microbiological media and test methods for isolation from faeces and dental plaque, and possibly even food and environmental sources. To conclude, the availability of new information on the above aspects would greatly facilitate the monitoring of therapy; would enable more accurate epidemiological studies on the age of acquisition and spread of H. pylori infection; and would provide a basis for future prevention of disease by identification of individuals at high risk of infection with a particular pathogenic strain type.

Transport and storage of Helicobacter pylori from gastric mucosal biopsies and clinical isolates

Various transport and storage conditions for the recovery of Helicobacter pylori from gastric biopsies were evaluated. Gastric mucosal biopsies from 16 Helicobacter pylori-infected patients were stored in cysteine-Albimi medium containing 20% glycerol in a refrigerator (4 degrees C) for 1 and 2 weeks and in a -20 degrees C laboratory freezer for 4 and 12 weeks. Two clinical isolates were stored in saline, Stuart's transport media, cysteine-Albimi broth with 20% glycerol, brucella broth with 20% glycerol and skim milk with 17% glycerol at room temperature, 4 degrees C, -20 degrees C and -70 degrees C. Storage at 4 degrees C for 1 and 2 weeks resulted in Helicobacter pylori recovery from 81% and 19% of biopsies, respectively. Storage at -20 degrees C yielded Helicobacter pylori recovery in 100% and 57% after 4 and 12 weeks, respectively. At room temperature after 6 h, the Helicobacter pylori titer was reduced. The best storage media for frozen isolates were skim milk/glycerol, brucella broth/glycerol and cysteine-Albimi/glycerol (in descending order). Recovery was better at -70 degrees C than -20 degrees C.

Selected cryopreservatives for long term storage of Helicobacter pylori at low temperatures

To meet the need for information on cryopreservation, a study was done on 32 Helicobacter pylori strains, comparing different cryopreservative media. Sheep blood, horse blood, horse serum with and without glycerol, and mineral oil media were used for long term storage of H pylori at -70 degrees C or in liquid nitrogen. Procedures were developed which permitted recovery of 87.5% of the strains included in the study after they had been stored for 24 months. Of those strains stored for more than three years, 60% were recovered. It is concluded that most strains of H pylori can be stored for up to one year or longer, under refrigeration, at -70 degrees C or in liquid nitrogen.

Evaluation of techniques for isolation, subcultivation, and preservation of Helicobacter pylori

With sheep blood agar (SBA), Belo Horizonte medium, and Brussels campylobacter charcoal agar, 104 strains of Helicobacter pylori were detected in 309 gastric biopsies. Each medium revealed only 69 to 71% of the strains. Ten strains grew solely on SBA, and four strains each grew on Belo Horizonte medium and Brussels campylobacter charcoal agar. Subculturing of 50 fresh H. pylori isolates on SBA revealed a progressive reduction in growth with increasing passage. Thirty strains stopped growing between passages two and seven. Four strains survived more than 20 passages. The preservation of fresh H. pylori isolates at -193 and -70 degrees C and by lyophilization was compared by use of 10% porcine mucin solution, fetal calf serum, and a commercial cryopreservative fluid. Of 30 strains, 77 to 90% could be recultivated on SBA after preservation at -70 degrees C in all three storage media. The data indicate that for the primary isolation of H. pylori, not only one selective medium but several selective media with different antibiotic supplements plus at least one nonselective medium should be used to yield the highest culture rates. Frequent subculturing of H. pylori on SBA selects strains which may not be representative of clinical isolates. Storage of fresh H. pylori isolates at -70 degrees C in 10% mucin solution is a simple and effective preservation procedure.

Microbiological aspects of Helicobacter pylori (Campylobacter pylori)

The human gastric pathogen Campylobacter pylori has recently been reclassified as Helicobacter pylori, and a related spiral bacterium found in the stomach of ferrets has been designated Helicobacter mustelae. The general microbiological features of Helicobacter pylori are delineated here, with details of phenotypic differences between Helicobacter pylori and Helicobacter mustelae; comparisons are made with Wolinella succinogenes and Campylobacter jejuni. The Helicobacter organisms possess an external glycocalyx which can be visualised by electron microscopy, and which may be involved in bacterial adherence. The finding of soluble and cell-associated haemagglutinins of Helicobacter pylori is reported. Detection of Helicobacter pylori in clinical specimens, susceptibility of the organism to antibacterial agents, and other aspects of practical and clinical significance are briefly reviewed.