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Open Access Research article

A comparison of conventional methods for the quantification of bacterial cells after exposure to metal oxide nanoparticles

Hongmiao Pan1, Yongbin Zhang2, Gui-Xin He3, Namrata Katagori3 and Huizhong Chen1*

Author Affiliations

1 Division of Microbiology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson 72079, AR, USA

2 Nanotechnology Core Facility, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson 72079, AR, USA

3 Department of Clinical Laboratory and Nutritional Sciences, University of Massachusetts Lowell, Lowell 01854, MA, USA

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BMC Microbiology 2014, 14:222  doi:10.1186/s12866-014-0222-6

Published: 21 August 2014

Abstract

Background

Due to potential interference of nanoparticles on bacterial quantification, there is a challenge to develop a fast, accurate and reproducible method for bacterial quantification. Currently various bacterial quantification methods are used by researchers performing nanoparticles study, but there has been no efficacy evaluation of these methods. Here we study interference of nanoparticles on three most commonly used conventional bacterial quantification methods, including colony counting to determine the colony-forming units (CFU), spectrophotometer method of optical density (OD) measurement, and flow cytometry (FCM).

Results

Three oxide nanoparticles including ZnO, TiO2, and SiO2 and four bacterial species including Salmonella enterica serovar Newport, Staphylococcus epidermidis, Enterococcus faecalis, and Escherichia coli were included in the test. Results showed that there is no apparent interference of the oxide nanoparticles on quantifications of all four bacterial species by FCM measurement; CFU counting is time consuming, less accurate and not suitable for automation; and the spectrophotometer method using OD measurement was the most unreliable method to quantify and detect the bacteria in the presence of the nanoparticles.

Conclusion

In summary, FCM measurement proved to be the best method, which is suitable for rapid, accurate and automatic detection of bacteria in the presence of the nanoparticles.

Keywords:
Nanoparticles; Bacterial quantification; Flow cytometry (FCM); Colony-forming units (CFU); Optical density (OD)