The restricted number of human hosts on an Antarctic research station, and the infrequency of visitors introducing new genetic material, provides a unique environment for elucidating the mechanisms controlling population changes in commensal micro-organisms. This is a field in which substantive scientific advances can be made by utilising Antarctic staff.

Since the Antarctic microbiological work began a number of typing techniques have been used to analyse the collections. One of the first studies was carried out at Halley Research Station using polyacrylamide gel electrophoresis (PAGE) and Western blotting to conduct a population genetic study of Staphylococcus capitis. This was the first study of any coagulase negative species by a universally applicable typing system, and the first to show simultaneous carriage of multiple clones (strains) on single individuals. This study also produced evidence that Staphylococcus intermedius is part of the normal human flora and not, as was previously thought, restricted to domestic animals. Pioneer work on the systematics, of coagulase-negative staphylococci isolated at Faraday Research Station showed that the analysis of ribosomal RNA restriction patterns was a particularly useful technique for speciation.

Escherichia coli in the human gut is known to be genetically very variable. In order to determine whether host to host transmission or, alternatively, recombination produced the genetic variability, the small enclosed over-wintering population at Signy research station were sampled over one year, and multilocus enzyme electrophoresis was used to characterise the electropherotype patterns within the whole population. The results of the analysis supported the hypothesis that the bowel flora is quite stable, changes being due to immigration rather than recombination.

Another group of gut commensals, the Enterococci, formerly thought to be Streptococci were examined from a group of over-wintering human hosts. The taxonomy of this group of organisms required higher resolution typing methods. This was achieved by developing a rapid, small scale method of extracting pure enterococcal DNA, cutting the DNA into fragments using restriction enzymes, and separating the fragments by agarose gel electrophoresis. DNA fingerprinting has become one of the standard methods of typing micro-organisms and represents a considerable advance over indirect techniques for investigating population genetic structure.

The advantages of these newer DNA-based methods were demonstrated in a study of the genus Micrococcus - common commensal species of which are carried on human skin. A collection of Micrococcus spp. from overwintering staff on Faraday Research Station was examined using three typing methods. The first was an extensive biochemical analysis commonly used for clinical typing, the second was polyacrylamide gel electrophoresis of cell proteins and the third was DNA restriction enzyme analysis. To the latter was added rRNA restriction enzyme pattern analysis. A taxonomic scheme emerged from this extensive study. Comparisons of the scheme with standard strains from the National Collection of Type Cultures revealed shortcomings in the current classification of Micrococcus. This work is potentially of importance for distinguishing Micrococci from the more clinically important Staphylococci.

Concomitantly with the Micrococccus study, the European Space Agency funded an international pilot study to collect and analyse Staphylococcus epidermidis from French, Australian and British Antarctic personnel (Pennington and Haston, 1992). This study had two aims. The first was to test the feasibility and practicability of using isolated Antarctic communities for research into problems related to space exploration. International collaboration was seen as particularly desirable in order to increase the sample sizes available for study. The second aim was to test the hypothesis that the population structure of this important human pathogen was clonal. An additional interest was to determine the global distribution of identified clones. The study achieved both the logistic and scientific aims.

Haemophilus spp., although normal colonists of the upper respiratory tract, can be significant pathogens causing a spectrum of disease including epiglottitis, otitis media and meningitis caused by the capsulate strain type b (Hib) against which a recently introduced conjugate vaccine is proving effective. Non-capsulate strains, unaffected by this vaccine, commonly cause non-invasive infections of the upper respiratory tract but can cause significant invasive disease in susceptible groups. This long term study was jointly funded by the MRC and aimed to determine the mechanisms which control the extreme genetic diversity of this important group of organisms.

All of the typing methods described above have used biological amplification whereby a few colonies are isolated from the original sample after culture, sub-cultured to increase the material available for analysis and then subjected to either biochemical or genomic identification procedures. Study of the Antarctic community by these methods found two carriers of H. influenzae out of 15 individuals which agreed with other published work showing that H. influenzae constitutes only 2.2% of the total Haemophilus flora. It is relatively easy to culture this organism along with all the other species in the throat but identification may be obscured because of the high background of related organisms.

An alternative way to amplify up the species of interest is to use in vitro DNA amplification such as the polymerase chain reaction (PCR). PCR has already been shown to be useful in the detection of micro-organisms where culture, extraction and identification are difficult or time consuming. A novel approach has been taken by Hobson et al {859#} by extracting all of the DNA from a mixed bacterial sample. The presence of a particular species is then identified using PCR amplification of a marker gene and then indentifying strain types using restriction endonuclease digestion patterns of the PCR products. This has been shown to be a quick and sensitive method for the determination of H. influenzae carriage. Using this method, a carriage rate of 52% was demonstrated for Antarctic staff overwintering at Signey research station for a seven month period.

Certain bacterial species do not seem to have particularly extensive genetic diversity between different isolates and in these cases it is necessary to use much more sensitive strain typing techniques. Pulsed-field gel electrophoresis (PFGE) is probably more sensitive because it detects changes in very long restriction enzyme DNA fragments which are probably more susceptible to mutational changes. PFGE was used on a two winter study of Staphylococcus aureus at Halley in 1994-95. These studies found that carriage of S. aureus strains in individuals was generally very stable, even over periods of 2y. Similarly the yeast Candida albicans was stably carried over a period of at least half a year with no transfer between individuals being detected, even to those with no resident strains of their own.

Human contamination of Antarctic environments is a sensitive issue and has been the focus of many research articles over the past 35 years. The majority of these studies have targeted waste materials and various hydrocarbons, with assessment of microbial contaminants being largely restricted to sewage outfalls. This study used highly sensitive molecular methods to detect bacteria of human origin in the area surrounding Halley research station. It was apparent from both molecular and culture methods that bacteria of human origin were extremely difficult to detect outside the immediate surrounding of the buildings, though recommendations are made for increasing the probability of determining the presence of organisms in the environment. The results also indicate that molecular methods are more sensitive than cultural techniques, in that the only evidence for organisms in the environment surrounding the building came from positive PCR reactions. PCR would appear to be a useful method for studying the microbial ecology of Antarctic environments.