PROLONGED MAINTENANCE OF SPIROCHETES AND FILTRABLE VIRUSES IN THE FROZEN STATE

Long-term preservation of Leptospira spp.: challenges and prospects

Preservation of leptospiral cultures is tantamount to success in leptospiral diagnostics, research, and development of preventive strategies. Each Leptospira isolate has imperative value not only in disease diagnosis but also in epidemiology, virulence, pathogenesis, and drug development studies. As the number of circulating leptospires is continuously increasing and congruent with the importance to retain their original characteristics and properties, an efficient long-term preservation is critically needed to be well-established. However, the preservation of Leptospira is currently characterized by difficulties and conflicting results mainly due to the biological nature of this organism. Hence, this review seeks to describe the efforts in developing efficient preservation methods, to discover the challenges in preserving this organism and to identify the factors that can contribute to an effective long-term preservation of Leptospira. Through the enlightenment of the previous studies, a potentially effective method has been suggested. The article also attempts to evaluate novel strategies used in other industrial and biotechnological preservation efforts and consider their potential application to the conservation of Leptospira spp.

Re-evaluating the sensitivity of the rabbit infectivity test for Treponema pallidum in modern era

BACKGROUND

The rabbit infectivity test (RIT) was previously described as a highly-sensitive method for clinically detecting Treponema pallidum. But our primary study indicated this result may have changed in current antibiotics era.

METHODS

By inoculating rabbits testis with cerebrospinal fluid (CSF) (n=63) and exudate from hard chancre lesions (n=13), we re-evaluated the sensitivity of RIT in modern era. All isolated T. pallidum strains from the RIT were performed for the strain type based on "CDC subtype/tp0548" method. Chi-square and Fisher's exact tests were used to determine the statistical significance of differences across data sets.

RESULTS

Result indicated that 2 of 63 CSF (2/63, 3.17%) and 5 of 13 lesion exudate samples (5/13, 38.47%) were positive in the RIT, with a much longer time to detection for CSF samples. Only 1 of 28 samples from patients who admitted treatment with antibiotics prior to clinical exam was positive in the RIT; while 6 of 48 patients, who admitted no recent exposure to antibiotics or was unclear about the medical history, were positive in RIT. DNA sequence analysis revealed 6 strains of 14d/f subtype and one strain of 14a/f subtype.

CONCLUSIONS

In conclusions, RIT is no longer a highly sensitive method for detecting T. pallidum in clinical samples as before, and is not inadequately considered to be a reference method for measuring the sensitivity of other new methods, such as the PCR. These data represent the first reexamination of the sensitivity of RIT in the post-antibiotic era with a large clinical sample.

THE ACTION OF EXTREME COLD ON LEUKEMIC CELLS OF MICE

Suspensions of leukemic cells of mice from three different strains of leukemia were subjected to rapid or slow freezing and rapid or slow thawing. Suspensions rapidly frozen to –196°C. were in all cases innocuous, whereas those frozen slowly were capable of transmitting leukemia. The infectivity of slowly frozen material varied from an estimated 0.0001 per cent to 1 per cent of that of fresh material, and this figure probably represents the percentage of surviving leukemic cells. Particles of spleen and lymph node reacted to slow and rapid freezing in the same manner as suspensions prepared from them. For one of the strains rapid thawing was less injurious than slow thawing; for the other two the rate of thawing seemed to be immaterial. Infectivity was equally well preserved after freezing to –21°C. whether freezing occurred spontaneously after supercooling or was initiated near the freezing point by inoculation with ice, or whether thawing was slow or rapid. Suspensions already slowly frozen at temperatures of –2° or lower, whether spontaneously or by inoculation with ice, could no longer be completely inactivated by subsequent rapid cooling to –196°C. Unfrozen suspensions initially above the freezing point or supercooled to –2°C. or –8°C. and then rapidly cooled to –196°C. were inactivated. This protective action of previous slow freezing was most marked when the initial temperature of the frozen suspension was –15°C. or lower; when it was –2°C. protection was barely detected. These observations indicate that the changes which are peculiar to rapid freezing alone and lead to complete inactivation take place during rapid transition from the liquid to the solid state, in a range of temperature lying between –15°C. and the freezing point. Temperature measurements carried out in this range showed that suspensions were about equally infections whether the temperature at their centers dropped from 0°C. to –15°C. in 30 minutes or in 1 minute; when the drop occurred in 12 seconds or less, the suspensions became innocuous.

FURTHER LABORATORY STUDIES ON THE CLASSIFICATION OF PSITTACOSIS-LIKE AGENTS

1. It was demonstrated by pathogenicity and latency tests in mammals and birds that variations exist among a group of viruses, isolated from several sources and producing coccoid elementary bodies resembling those of psittacosis. 2. Active cross immunity tests emphasized these differences and confirmed their significance. 3. On the basis of the present experimental evidence the psittacosis-like viruses causing atypical pneumonia in man may be classified into three groups: psittacosis, ornithosis, and human pneumonitis (strain S-F) of undetermined origin.

THE ANTIGENIC RELATIONSHIP OF THE VIRUSES OF MENINGOPNEUMONITIS AND LYMPHOGRANULOMA VENEREUM

Animals recovered from infection with the viruses of lymphogranuloma venereum, meningopneumonitis, and psittacosis, were reinoculated in crossimmunity tests with these viruses. In mice immunized by intracerebral or intranasal inoculation a reciprocal partial cross-immunity between the viruses of lymphogranuloma venereum and meningopneumonitis was demonstrated. In preliminary experiments, similar cross-immunity between the agents of lymphogranuloma venereum and psittacosis was not definitely demonstrated. Hamsters, white rats, and kangaroo rats recovered from intracerebral or intranasal infection with the virus of lymphogranuloma venereum were more resistant than normal controls to inoculation with the virus of meningopneumonitis. Sera of animals immunized with the viruses of lymphogranuloma venereum and meningopneumonitis showed cross-reactions by complement fixation with antigens of these viruses. The results indicate an antigenic relationship between the viruses of lymphogranuloma venereum and meningopneumonitis.

Storage of pathogenic leptospires in liquid nitrogen

The virulence and viability of various serovars of Leptospira interrogans were successfully preserved by storage in liquid nitrogen. Dimethyl sulphoxide at a final concentration of 2.5% (v/v) was added as cryoprotectant to a culture of leptospires grown in Ellinghausen-McCullough-Johnson-Harris medium. Ampoules were cooled at a controlled rate of 1 degree-3 degrees C/min to -70 degrees C, then transferred to the liquid phase of a liquid nitrogen storage unit. Glycerol was discounted as a cryoprotectant as it was found to be approximately 10 times more toxic than dimethyl sulphoxide to four of five serovars used in this study. The viability of nine strains has so far been observed over a period of 8-22 months storage in liquid nitrogen and full viability of all strains has been preserved over this period. Virulence of strains of serovars pomona and hardjo was well preserved, as demonstrated by challenge tests in guinea pigs and domestic pigs.