Vulnerability of Bacillus spores and of related genera to physical impaction injury with particular reference to spread-plating

Aerobiology: Experimental Considerations, Observations, and Future Tools

Understanding airborne survival and decay of microorganisms is important for a range of public health and biodefense applications, including epidemiological and risk analysis modeling. Techniques for experimental aerosol generation, retention in the aerosol phase, and sampling require careful consideration and understanding so that they are representative of the conditions the bioaerosol would experience in the environment. This review explores the current understanding of atmospheric transport in relation to advances and limitations of aerosol generation, maintenance in the aerosol phase, and sampling techniques. Potential tools for the future are examined at the interface between atmospheric chemistry, aerosol physics, and molecular microbiology where the heterogeneity and variability of aerosols can be explored at the single-droplet and single-microorganism levels within a bioaerosol. The review highlights the importance of method comparison and validation in bioaerosol research and the benefits that the application of novel techniques could bring to increasing the understanding of aerobiological phenomena in diverse research fields, particularly during the progression of atmospheric transport, where complex interdependent physicochemical and biological processes occur within bioaerosol particles.

Optimization of single plate-serial dilution spotting (SP-SDS) with sample anchoring as an assured method for bacterial and yeast cfu enumeration and single colony isolation from diverse samples

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SP-SDS forms a simple tool for bacterial cfu estimation for samples with unknown cfu.

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Prime recommendation of anchoring specimens to fixed initial OD or a standard base.

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Six serial dilutions of 20 μl each applied per 9-cm plate followed by manual counting.

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Suits pure and mixed bacterial stocks, spores, yeasts and composite samples.

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Superior to alternate techniques like track-dilution, drop-plating or drop-spotting.

We propose a simple technique for bacterial and yeast cfu estimations from diverse samples with no prior idea of viable counts, designated as single plate-serial dilution spotting (SP-SDS) with the prime recommendation of sample anchoring (10⁰ stocks). For pure cultures, serial dilutions were prepared from 0.1 OD (10⁰) stock and 20 μl aliquots of six dilutions (10¹–10⁶) were applied as 10–15 micro-drops in six sectors over agar-gelled medium in 9-cm plates. For liquid samples 10⁰–10⁵ dilutions, and for colloidal suspensions and solid samples (10% w/v), 10¹–10⁶ dilutions were used. Following incubation, at least one dilution level yielded 6–60 cfu per sector comparable to the standard method involving 100 μl samples. Tested on diverse bacteria, composite samples and Saccharomyces cerevisiae, SP-SDS offered wider applicability over alternative methods like drop-plating and track-dilution for cfu estimation, single colony isolation and culture purity testing, particularly suiting low resource settings.