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. 2014 Jul;52(7):2340-5.
doi: 10.1128/JCM.00487-14. Epub 2014 Apr 23.

Mechanical homogenization increases bacterial homogeneity in sputum

Affiliations

Mechanical homogenization increases bacterial homogeneity in sputum

Joshua R Stokell et al. J Clin Microbiol. 2014 Jul.

Abstract

Sputum obtained from patients with cystic fibrosis (CF) is highly viscous and often heterogeneous in bacterial distribution. Adding dithiothreitol (DTT) is the standard method for liquefaction prior to processing sputum for molecular detection assays. To determine if DTT treatment homogenizes the bacterial distribution within sputum, we measured the difference in mean total bacterial abundance and abundance of Burkholderia multivorans between aliquots of DTT-treated sputum samples with and without a mechanical homogenization (MH) step using a high-speed dispersing element. Additionally, we measured the effect of MH on bacterial abundance. We found a significant difference between the mean bacterial abundances in aliquots that were subjected to only DTT treatment and those of the aliquots which included an MH step (all bacteria, P = 0.04; B. multivorans, P = 0.05). There was no significant effect of MH on bacterial abundance in sputum. Although our results are from a single CF patient, they indicate that mechanical homogenization increases the homogeneity of bacteria in sputum.

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Figures

FIG 1
FIG 1
Flow chart of the experimental design. Tubes with large dots represent sputum without mechanical homogenization. Filled tubes represent sputum with mechanical homogenization.
FIG 2
FIG 2
Effect of MH on heterogeneity of total bacterial abundance and B. multivorans abundance among aliquots of nine sputum samples. Comparison of A1 (without MH) aliquots to A2 (with MH) aliquots from fraction A shows a significant difference in the means of abundance in all bacteria (P = 0.04) (A) and in B. multivorans (P = 0.05) (C). Comparison of B1 aliquots to B2 aliquots (both with MH) from fraction B shows no significant difference in the means of abundance in all bacteria (P = 0.76) (B) and in B. multivorans (P = 0.99) (D).
FIG 3
FIG 3
The effect of mechanical homogenization on the abundance of total bacteria (A) and of B. multivorans (B). The abundances were measured by qPCR for paired groups of aliquots with and without MH, as described in Materials and Methods. The columns represent the Hedges d effect sizes of mechanical homogenization on bacterial recovery. The error bars were determined by the SEM of the effect size (δ). Error bars that cross zero indicate no effect.
FIG 4
FIG 4
The overall effect of mechanical homogenization on the abundance of total bacteria and B. multivorans in sputum. The abundances were measured by qPCR for paired groups of aliquots with and without MH. The columns represent the effect sizes of mechanical homogenization on bacterial recovery. The error bars were determined by the SEM of the overall effect size (δ). Error bars that cross zero indicate no effect.

References

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