Skylab Environmental and Crew Microbiology Studies

GERALD R. TAYLOR, RICHARD C. GRAVES, ROYCE M. BROCKETT, J. KELTON FERGUSON, AND BEN J. MIESZKUC

THE OBJECTIVES of the Skylab microbiology studies were to detect the presence of potentially pathogenic micro-organisms on the crewmembers and their spacecraft and to obtain data which would contribute to an understanding of the response of the crew’s microbial flora to the space flight environment. These data were interpreted in light of the theories of microbial simplification, intercrew transfer of medically important micro-organisms, important micro-organisms, in-flight autoinfections, and postflight microbial shock, which have been proposed by various authors (ref. 1).

Before and after each flight, the 12 areas outlined in table 8-I were sampled from each astronaut. Two calcium alginate swabs, wetted in phosphate buffer, were used to sample the nostrils and each external body surface area. A single, dry alginate swab for virological analysis was used to sample the throat. Phosphate buffer was used to wash the oropharyngeal cavity. Additionally, a midstream urine sample was collected from the first void of the day and fecal specimens were collected at the convenience of the subject. In-flight crew samples, as noted on table 8-I, were collected 16 days before termination of each Skylab mission and returned under chilled conditions for analyses.

Samples were collected before, during, and after each Skylab mission, as shown in figure 8-1. The Orbital Workshop was sampled up to 10 times, including one preflight sample set. In-flight air samples were collected 2 days before the end of each mission. The Command Module was sampled on launch and recovery days for each mission. In all cases samples collected in-flight were stored differently, and for a longer time than were pre-flight and postflight samples. Therefore, direct correlation of the resulting data is not always applicable.

In excess of ten thousand selected microbial isolates were analyzed by quantitation, identification, and characterization. For this report, the effects of space flight conditions on microbial populations will be examined only to the first level of complexity. That is, only alterations affecting the total autoflora will be evaluated. More detailed analyses conducted at increasing  degrees of complexity will be published elsewhere.

Results and Discussion

Changes in the Habitability of the Skylab Environment.—Microbial Content of In-flight Skylab Air.—The concentration of bacteria recovered from air samples obtained 2 days before return from each Skylab visit are displayed in figure 8-2. Low levels of in-flight bacterial contamination were observed on the first two missions, whereas the recovery from Skylab 4 was considerably higher. These higher counts were due entirely to an influx of Serratia marcescens, a micro-organism which has been shown to produce various infections in man (ref. 2). Whereas this species was not recovered from any preflight crew sample analysis, it was recovered from multiple sites from all three Skylab 4 astronauts immediately upon recovery. Further, this species persisted in the nasal cavity of the Pilot throughout the postflight quarantine period. Subsequent investigation demonstrated several potential sources of this micro-organism in the Skylab environment. However, these potential sources could not be sampled in-flight and, therefore, a direct correlation could not be made. By active microbial monitoring, the release of this microbial contamination into the Orbital Workshop was traced from possible sources, was detected in the Skylab air, was subsequently recovered as a new species from all three crewmembers, and was ultimately shown to colonize the nasal passages of one astronaut.

Bacterial Recovery from Sample Sites within the Skylab Orbital Workshop.—The total concentrations of viable bacterial cells recovered from the Skylab spacecraft surface sites at various sampling periods are presented in figure 8-3. These in-flight samples were collected to evaluate the level of microbial contamination occurring in the Orbital Workshop. The results of analyses of samples collected prior to launch are typical of a clean (although obviously not sterile) environment. The reduction of aerobic bacteria recovered from the Skylab 2 in-flight samples is probably a reflection of the thermal problems experienced in the Orbital Workshop after launch. Although there was a simultaneous tenfold increase in the presence of anaerobic bacteria, the Skylab 2 crew apparently entered a very clean environment, which remained relatively clean during the mission.

The recovery of both aerobic and anaerobic bacteria from the Skylab 3 mission increased another 1 to 2 log[10] units, with no apparent reason except for increased length of habitation by the crew-members. During the 84-day Skylab 4 mission the total concentration of aerobic bacteria remained nearly constant although anaerobe recovery decreased significantly. This drop was due to the loss of Propionibacterium acnes which contributed strongly to the anaerobe population of the other two Skylab missions. This loss of P. acnes reflects a similar loss of anaerobic bacteria from the skin surfaces of the astronauts (these data will be presented later in this paper). Therefore, this decrease in anaerobic bacterial contamination of the Skylab, was shown to directly reflect a decrease in these same microbes in the contaminating reservoir, the skin of the astronauts.

The recovery of aerobic bacteria from 15 sites within the Apollo Command Modules, sampled immediately before and after each mission to the Skylab, are summarized in figure 8-4. Whereas there was some variation in the contamination level of the different Command Modules, there were no major differences between preflight and postflight values for a particular Command Module. Therefore, the variations noted in the Orbital Workshop could not be shown to affect population levels in the Command Modules.

Fungal Recovery from Sample Sites within the Skylab Orbital Workshop.—It had been suggested that molds would present problems on long-term space flights, especially if high humidities were experienced (ref. 3). Figure 8-5 shows the number of fungal isolations from the Skylab vehicle before launch and during each mission. These numbers were low until the Skylab 4 mission. Although overall humidity was low on the Skylab 4 mission, local areas of high humidity cannot be entirely eliminated. The reasons for the large increase in fungal isolations on Skylab 4 have been well established. Early in the Skylab 4 mission, it was discovered that "mildew" was present on the liquid-cooled garments which had been previously stowed aboard. A sample was taken off this growth, and one liquid cooled garment was returned for additional sampling. In general, the species of fungi isolated from surface samples and air samples were the same species isolated from the liquid cooled garment. These same micro-organisms also contaminated the Petri dishes of the ED31 experiment flown on Skylab 4. It is apparent that the liquid-cooled garments were the source of spore contamination since some of these garments had not previously been removed from their original containers, but were subsequently found to harbor these micro-organisms.

This contamination was also reflected in the recovery of fungi from the crew samples collected 16 days before return from Skylab. For Skylab 2 and Skylab 3, a total of two and zero filamentous fungi, respectively, was isolated from the crew in-flight. On Skylab 4 a total of 11 fungi were isolated, including a significant contamination to the astronauts. It is important to note that this contamination to the crew was demonstrated 62 days after the first exposure to the liquid-cooled garments, indicating either continued contamination from inanimate sources, abnormally slow return to normal levels, or both.

The number of fungal species isolated from the 15 Command Module sites before and after each Skylab mission is shown in Figure 8-6. These data illustrate that the fungal contamination of the Orbital Workshop during the Skylab 4 mission did not affect the Command Module samples collected on recovery day. Although the Command Module was attached to the Orbital Workshop during this period of contamination, it was a separate entity, out of the area of heavy use, and away from the contaminating space suits. This relatively clean Command Module probably contributed to the low level of fungal contamination of the crew post-flight.

Postflight Variation in the Major Components of the Autoflora.—Aerobic Bacteria.—Prior to the Skylab missions, several authors had theorized that major microflora changes might occur during space flight and that these changes might not be compatible with man’s health and welfare on extended missions (refs. 4, 5, 6, 7, 8, 9,10,11,12,13, 14, 15). The theoretical change which was most often proposed called for a "microbial simplification" which may be defined as a major decrease in the number of different types of micro-organisms in the autoflora. To evaluate this hypothesis, the variations of the aerobic bacterial portion of the total autoflora within sample collection sites were analyzed as shown in Figure 8-7. This analysis shows that the frequency with which recovery day values lie outside the preflight range is similar for the 10-day Apollo 14 mission and the three Skylab missions. More specifically, the total number of viable cells recovered was frequently higher post-flight whereas the number of genera and species decreased in all missions except Skylab 4. Therefore, it is possible to make the following observations concerning recovery of aerobic bacteria following these space flights. Values obtained from immediate postflight sample analyses are frequently outside of the established preflight range. When different, these values most often reflect an increase in total number of viable cells and a decrease in the number of different genera and species recovered.

Anaerobic Bacteria.—A similar analysis of the anaerobic bacterial portion of the total autoflora is shown in Figure 8-8. The analysis presented in this figure illustrates that the anaerobic portion of the autoflora behaves quite differently than the aerobic portion. The frequency and direction of postflight change is different from each Skylab mission, but apparently is not related to mission duration (as the 10-day Apollo 14 and the 84-day Skylab 4 results are most similar). Following the Apollo 14, Skylab 2 and Skylab 4 missions, fewer viable anaerobic cells and fewer genera and species were recovered from up to 70 percent of the sites sampled. However, this is not a universal event as all of these values increased in some sample areas following Skylab 3 mission. These post-flight increases were due to an unusually high level of contamination with Propionibacterium acnes on the skin of the Skylab 3 astronauts which matched exactly the increased contamination of Skylab surfaces mentioned earlier.

The summaries presented in figures 8-7 and 8-8 indicate that, whereas the trends are not inviolate, the following conclusions may be stated. Gross numerical changes in the autoflora cannot be correlated with mission duration up to 84 days. Total numbers of viable bacterial cells tend to increase for aerobes and decrease for anaerobes. The number of different aerobic genera and species change little, whereas there is generally a decrease in the number of different anaerobic types recovered.

Yeasts and Filamentous Fungi.—We have previously shown, as demonstrated in Figure 8-9, that for the Apollo missions there was, typically, a significant reduction in the number of isolated fungal species up to the launch day. This was taken to be indicative of severely restricting opportunities of contamination to the crew for 3 weeks before flight. Analysis of postflight Apollo data indicated that exposure to the space flight environment for up to 2 weeks resulted in an even greater reduction with a relative increase in incidence of the potential pathogen, Candida albicans (ref. 16).

Essentially the same pattern may be demonstrated from the Skylab 2 and Skylab 3 data, as shown in Figure 8-10. However, fungal recovery was not depressed following the 59-day mission of Skylab 3, indicating increased exposure to fungi within the Skylab. Results of the same analyses for Skylab 4 are also shown in figure 8-10 where essentially the same pattern is again demonstrated. This is an important observation in light of the previously mentioned in-flight contamination of the Orbital Workshop and Skylab 4 crew and the fact that the Skylab 4 Pilot Sustained a "rash" in-flight which was presumed to be a mycotic infection and responded to treatment with Tinactin. In spite of the gross contamination, the probable mycotic infection, and the epic length of the space flight, approximately the same number of fungal isolates were recovered from the Skylab 4 crew-members throughout the 17-day postflight quarantine period. This indicates that with adequate preparation, monitoring, and treatment (if necessary) it is possible to control mycological problems in space for missions of this length where the humidity is generally low.

Behavior of Medically Important Components of the Autoflora.—Opportunity for Postflight Microbial Shock.—A summary of the numerical means of recovered isolates of medically important micro-organisms from all nine prime Skylab crewmembers is presented in Fgure 8-11. This summary indicates that the incidence of these species on the body decreased during the preflight quarantine period, to establish a low point the morning of launch. This event no doubt reflects decreased contact with these species during this quarantine period. The largest number of medically important micro-organisms is recovered from the immediate postflight sample set after which the value returns to its near normal pre-quarantine value.

Several authors have warned that returning space travelers may experience a "Microbial Shock" and may respond negatively to renewed contact with potentially pathogenic micro-organisms which are absent in the space flight environment (refs. 7, 12, 17, 18, 19, 20).

This warning is based on the assumption that contact with potential pathogens during space flight would be limited, resulting in a reduction of immunocompetence. However, these data show that there is an increase in the distribution of potential pathogens immediately following space flight. This result supports earlier findings reported for shorter duration space flights (refs. 14, 17, 21, 22, 23). Therefore, if a reduction in total immunocompetence was to occur during these missions, it is difficult to see how this reduction would be in response to decreased contact with medically important components of the autoflora. As with the Apollo missions, there was no clinical or microbiological evidence of any "Microbial Shock" following any of the Skylab missions.

Intercrew Transfer of Potentially Pathogenic Micro-organisms.—Transfer of pathogenic micro-organisms between crewmembers during space flight has previously been reported for missions up to 18 days (refs. 17, 21, 22, 24). During the Skylab series it was possible to demonstrate in-flight cross-contamination, colonization, and in-flight infection with Staphylococcus aureus. Most strains of this species, which is one of the most infectious of the common inhabitants of man’s autoflora, may be distinguished by their reaction with specific bacteriophages. This allows us to monitor the exchange of these microbes with greater resolution. The phage-type pattern of S. aureus recovery for Skylab 2 is shown on table 8-II. These data show that the same S. aureus phage type was repeatedly recovered from the nasal passages of the Pilot, indicating that this crewmember was a carrier of this micro-organism. Although spread to the Orbital Workshop was demonstrated, there was apparently no transfer to the other crewmembers in-flight. Therefore, being restricted to a confined space for 28 days with an S. aureus carrier does not necessarily result in cross infection.

A more complex situation is outlined in table 8-III. The data summarized in this table indicate that the Skylab 3 Commander and Pilot were both nasal carriers of S. aureus, carrying phage type 3A and 29/79, respectively. Prior to the flight, S. aureus was not recovered from any of the Scientist Pilot samples. Analyses of in-flight-collected samples show that the workshop became contamined with both phage types and that type 29/79 was temporarily transferred to the Scientist Pilot. Postflight analyses show that type 3A had spread to the Pilot but, as could be expected (ref. 25), did not colonize this subject who was already a carrier of another phage type. Phage type 3A was repeatedly isolated from the post-flight specimens of the Scientist Pilot, indicating actual colonization. This is a clear demonstration of in-flight intercrew transfer of a pathogenic species where the contaminant could be shown to have established itself as a member of the autoflora of the new host.

It is important at this point to relate these observations to crew in-flight illness events during the Skylab 3 mission. The Pilot, a 29/79 carrier, developed a hordeolum (sty) which was successfully treated with Neosporin. The Commander, a 3A carrier, developed auxiliary swellings of a furuncle (boil) type which were treated with warm compresses. As neither of these infections were draining, in-flight contingency samples were not taken, so we do not know for sure the identity of the causative agent. However, we do know that the causative agent of both of these maladies is usually S. aureus, and both of these individuals were carriers of this micro-organism. Therefore, it is accurate to say that we have traced the development of a pathogenic micro-organism from its preflight carrier state in two crewmembers through in-flight contamination of the Orbital Workshop, and colonization on the third crewmember. Also, it is highly probable that this species was responsible for the active in-flight infections of the two S. aureus carriers.

Conclusions

A general overview of some of the general contamination of the Skylab vehicle and of the major activities of the microbial autoflora of the Skylab astronauts has been presented. These data show that, while gross contamination of the Skylab environment was demonstrated and there were several in-flight disease events (presumably of microbial origin), such events were not shown to be limiting hazards for long-term space flight. Evaluation of the major groups of micro-organisms comprising the microbial populations tested, tended to support the theory of microbial simplification for anaerobic bacteria, but not for other microbes. Intercrew transfer of pathogens was demonstrated. The data mediate against the theory of postflight microbial shock. The question of in-flight autoinfection remains unanswered because none of the in-flight disease events were evaluated microbiologically.Further general evaluations of the dynamics of the autoflora as a whole, and specific analyses of selected species and groups, will be published separately.

Acknowledgments

The authors wish to thank all of the many individuals who contributed to this study. Special thanks go to every member of the Northrop Services, Inc., Microbiology Team at the Johnson Space Center for their indispensable support. In particular, the following people are recognized: Theron O. Groves, Mary R. Henney, C. J. Hodapp, Kathryn D. Kropp, Florence J. Pipes, and Charles P. Truby.

References

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