The use of radiation to estimate the numbers of micro-organisms in air-borne particles

Abstract

The form of the killing curve obtained by bombaring micro-organisms with high energy electrons enables an estimate to be made of the numbers of individual viable organisms present in the aggregates or clumps comprising the sample. Samples of Staph. aureus collected from the air of two hospital wards have been found to consist of aggregates containing, on the average, only about four viable cocci per air-borne particle. These samples were taken during quiet periods and during periods of active dispersion of the organism but there was no active spread of staphylococcal disease at any time.The work on the linear accelerator was carried out with the aid of grants provided by the Treasurer and the Board of Governors from the Discretionary Fund of St Bartholomew's Hospital, to whom we wish to express our gratitude.

Size‐resolved emission rates of airborne bacteria and fungi in an occupied classroom

“…The wide dispersion of single taxa across multiple size ranges (Figure 4) also suggests that bacteria were mostly not present in particles as single cells. That indoor airborne bacteria may be found in aggregates has been previously reported by Lidwell et al (1959). The size distribution observed in this study is consistent with recent outdoor measurements of bioaerosol particle concentration determined by an ultraviolet aerodynamic particle sizer that demonstrated a pronounced peak at 3.2 lm geometric mean diameter, which the authors attributed to unicellular fungal spores and agglomerated bacteria (Huffman et al, 2010).…”

“…The wide dispersion of single taxa across multiple size ranges (Figure 4) also suggests that bacteria were mostly not present in particles as single cells. That indoor airborne bacteria may be found in aggregates has been previously reported by Lidwell et al. (1959).…”

Dispersal of skin microorganisms

“…Although on average only 4 viable Staph. aureus cells appeared to make up each airborne particle (Lidwell, Noble & Dolphin, 1959) the particles were shown to be about 14 ^m in equivalent diameter; a particle big enough to be composed of some hundreds of cocci (Noble, Lidwell & Kingston, 1963). It should perhaps be emphasized that, for reasons of mathematical convenience, airborne particles are best considered as spheres having unit density.…”

The effect of surface charge, negative and bipolar ionization on the deposition of airborne bacteria

“…It has been estimated that the amount of skin squamae shed from hospital staff, visitors and patients equals approx. 3 × 10 8 per day, and an average of four viable bacteria per skin scale has been found in hospital wards (Lidwell et al. 1959; Noble 1981).…”

“…It has been estimated that the amount of skin squamae shed from hospital staff, visitors and patients equals approx. 3 · 10 8 per day, and an average of four viable bacteria per skin scale has been found in hospital wards (Lidwell et al 1959;Noble 1981). Duguid showed as early as 1945 that a sneeze can release hundreds of thousands of droplets into the air at speeds in excess of 200 miles per hour; and a cough, although producing only about 1% of the amount of airborne droplets as a sneeze, occurs much more often (Duguid 1945).…”