The Survival of Escherichia coli sprayed into Air and into Nitrogen from Distilled Water and from Solutions of Protecting Agents, as a Function of Relative Humidity

Abstract

SUMMARYThe survival in air as a function of relative humidity (RH) and aerosol age is reported for Escherichia coli (strains B and Jepp) and for Serratia marcescens (strain U K 8 ) sprayed from suspensions in distilled water and in solutions of dextran and of raffinose. The survival in nitrogen ( > 99.9 yo) of E . coli (strains B, Jepp and commune) is given as a function of RH, when sprayed from suspension in distilled water and in raffinose solution. The results show that E . coli in the aerosol was subject to at least three stresses, an air stress, an RH stress, and a collection stress. The air stress accounted for loss of viability at low RH and the RH stress occured a t high RH and is expressed as RH ranges in which E . coli rapidly lost viability. The survival, especially a t high RH, depended upon the composition of the collecting fluid. At high RH a range of RH was found in which the bacteria were unstable when collected in phosphate buffer. Addition of raffinose (chosen as a typical protecting agent) to the spray fluid and the addition of M-sucrose to the collecting fluid eliminated the instability for E . coli (commune) and decreased it for the other two strains.

Survival of virulentLegionella pneumophilain aerosols

“…Oxygen is known to be toxic to many bacterial aerosols, but often the effect may only be apparent at low r.h. (Hess, 1965;Cox, 1966;Benbough, 1967Benbough, , 1969Webb, 1967); it is possible that the poorer survival of L. pneumophila in drier air may be due in part to oxygen toxicity. One disadvantage of assessing microbial aerosol stability at only three representative r.h. values is that for many bacteria zones of relative instability exist at certain r.h. values (Anderson, 1966;Benbough, 1967;Cox, 1966Cox, , 1969Cox, , 1971) and similar zones of instability have been found for freeze-dried bacteria (Bateman et al 1961;Dewald et al 1967). The survey of the viability of L. pneumophila 74/81 aerosols held for 15 min showed that this organism survives poorly at 55 % r.h. compared with its stability at r.h. values slightly above and below this (65 and 40 % respectively); this suggests that such zones of instability also exist for legionella.…”

“…Samples were recovered from aerosols for 1 min, using raised impingers with a flow rate of 10-5 1/min (May & Harper, 1957). Impingers contained 10 ml of one of the following sterile fluids; distilled water, Page's saline (Page, 1967), PBMA (Cox, 1966) or GPMA (gelatine, 0-2 % w/v in PBMA).…”

The Toxic Effect of Oxygen Upon the Aerosol Survival of Escherichia coli B

“…Amongst these was the nature of the atmosphere, in that at low relative humidity (RH), but not at high RH, survival was much greater in nitrogen than in air (Cox, 1966a;Cox & Baldwin, 1966). The previous suggestion that this survival difference was owing to the toxic action of oxygen (Cox, 1966a) is now examined.…”

“…The methods used were as previously reported (Cox, 1966a) except that in all experiments a rotating dnm container (Goldberg, Watkins, Boerk & Chatigny, 1958) was used for storing the aerosol cloud, and only Escherichia coli B sprayed from distilled water was studied. The drum apparatus used for the present work was similar to that used by Cox (1966a).…”

Methods for the Assessment of Microbial Populations Recovered from Enclosed Aerosols

“…niger have been used extensively as a biological tracer (Harper & Morton, 1952;Harper et al 1958;Anderson, 1966;Cox, 1966;Benbough, 1969;Hambleton, 1970), but there is evidence that a proportion of the spores may die in the aerosol (Harper et al 1958;Anderson, 1966;Cox, 1966 B) and results with populations of small bacteria with long generation times (e.g. Pasteurella tularensis, live vaccine strain) are unreliable.…”