30 
Excerpt from a letter by Roy Curtiss III to Donald S. Fredrickson, 
April 12, 1977. 
In terms of communicability of J2. coli K-12, we know that enteric 
diseases caused by enteropathogenic JS. coli and various strains of 
Shigella, Salmonella and Vibrio are transmitted by contaminated food and 
water and that manifestation of disease symptoms requires consumption of 
approximately one million bacteria. Such enteric diseases are seldom 
spread by aerosols. Indeed, it is well known, for example, that cages of 
mice infected with Salmonella can be housed in the same room with uninfect- 
ed mice which remain uninfected. The finding that I!, coli cells can be 
recovered from the nasopharynx of approximately five percent of those 
humans tested might suggest that aerosol spread could occur. Such _E. 
coli cells, however, are only intermittently present in the nasopharynx 
and are usually found at concentrations too low to initiate an infection 
even if they were representative of a pathogenic strain. They most likely 
get into the nasopharynx due to poor personal hygiene. After learning 
of these observations quite some years ago, I monitored my nostrils and 
skin for the presence of those 12. coli K-12 strains I was working with. I 
was successful in detecting these strains about ten percent of the time 
when the monitoring was done at the end of the work day, but never obtained 
positive results when the monitoring was done the next morning. I should 
hasten to add that my research with E!. coli K-12 at that time involved 
mouth pipetting and other aerosol-generating procedures on an open lab 
bench: procedures and conditions which are not permitted by the NIH 
Guidelines. These results, preliminary as they are, nevertheless suggest 
that E^. coli K-12 does not colonize the nasopharynx. Based on these 
observations, the fact that E. coli ' s normal ecological niche is the colon 
and the fact that transmission of enteric diseases is by ingestion of 
contaminated water and food, I doubt that 12. coli K-12 could be converted 
to an air-borne "infectious" agent by introduction of recombinant DNA. In 
terms of the more usual means for spread of enteric pathogens, it is 
evident that enteric diseases are very well controlled in the United 
States by sanitary engineering, even though there have been reports of 
poor water quality in some parts of the country and higher-than-desired 
levels of pollution of rivers, streams, etc. There is, however, a con- 
certed effort to improve biological waste water treatment and thus lessen 
pollution and improve water quality. Even if there were a natural catas- 
trophe such as caused by an earthquake, tornado, hurricane, etc., it is 
unlikely that 12. coli K-12 containing recombinant DNA could initiate or 
sustain an epidemic in view of K-12's inability to colonize and overcome 
host defense mechanisms. 
