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Malthusian Parameters as Estimators of the Fitness of Microbes: A Cautionary Tale about the Low Side of High Throughput.

Concepción-Acevedo J, Weiss HN, Chaudhry WN, Levin BR - PLoS ONE (2015)

Bottom Line: The maximum exponential growth rate, the Malthusian parameter (MP), is commonly used as a measure of fitness in experimental studies of adaptive evolution and of the effects of antibiotic resistance and other genes on the fitness of planktonic microbes.Thanks to automated, multi-well optical density plate readers and computers, with little hands-on effort investigators can readily obtain hundreds of estimates of MPs in less than a day.This leads us to question the reliability of estimates of MP obtained with these high throughput devices and the utility of these estimates of the maximum growth rates to detect fitness differences.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Emory University, Atlanta, Georgia, United States of America.

ABSTRACT
The maximum exponential growth rate, the Malthusian parameter (MP), is commonly used as a measure of fitness in experimental studies of adaptive evolution and of the effects of antibiotic resistance and other genes on the fitness of planktonic microbes. Thanks to automated, multi-well optical density plate readers and computers, with little hands-on effort investigators can readily obtain hundreds of estimates of MPs in less than a day. Here we compare estimates of the relative fitness of antibiotic susceptible and resistant strains of E. coli, Pseudomonas aeruginosa and Staphylococcus aureus based on MP data obtained with automated multi-well plate readers with the results from pairwise competition experiments. This leads us to question the reliability of estimates of MP obtained with these high throughput devices and the utility of these estimates of the maximum growth rates to detect fitness differences.

No MeSH data available.


Related in: MedlinePlus

Variation in estimated MP attributable to the age of the culture and replica.Each color represents a different replica and the values represent the average OD from 10 different wells. (A and B) respectively, Pseudomonas aeruginosa WT in LB and glucose limited minimal medium. (C and D) respectively E. coli WT in LB and glucose-limited minimal medium. (E) S. aureus Newman, WT, in MHII. For statistics refer to S2 Table.
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pone.0126915.g002: Variation in estimated MP attributable to the age of the culture and replica.Each color represents a different replica and the values represent the average OD from 10 different wells. (A and B) respectively, Pseudomonas aeruginosa WT in LB and glucose limited minimal medium. (C and D) respectively E. coli WT in LB and glucose-limited minimal medium. (E) S. aureus Newman, WT, in MHII. For statistics refer to S2 Table.

Mentions: In their protocol, Hall and colleagues [23] recommend careful control of the preparation, and in particular the age of the inoculum introduced into the microtiter wells. They suggest there will be variation in estimated MPs between runs and within microtiter plates. To explore the magnitude of this variation, and thereby the robustness and reliability of microtiter plate reader estimates of the MP, we estimated this parameter with suspensions of wild type cells of each species initiated from cultures maintained for 24, 48, and 72 hours at 37°C, in their respective media. We repeated this experiment four times to determine the extent to which estimates of MP vary between runs. We also examined the extent of variation within plates by inoculating 50 wells with the same cell mixture (E. coli B/6 in LB). We restricted this consideration to the Bioscreen data. The results of these experiments are presented in Fig 2. Finally, to determine the effects of the wave-length of the plate reader and the extent of shaking, using the Bioscreen we estimated the MPs for wild type strains of all three species in broth and minimal medium at a wavelength of 540nm and with shaking for 10 seconds before reading the ODs, rather than continuously between readings.


Malthusian Parameters as Estimators of the Fitness of Microbes: A Cautionary Tale about the Low Side of High Throughput.

Concepción-Acevedo J, Weiss HN, Chaudhry WN, Levin BR - PLoS ONE (2015)

Variation in estimated MP attributable to the age of the culture and replica.Each color represents a different replica and the values represent the average OD from 10 different wells. (A and B) respectively, Pseudomonas aeruginosa WT in LB and glucose limited minimal medium. (C and D) respectively E. coli WT in LB and glucose-limited minimal medium. (E) S. aureus Newman, WT, in MHII. For statistics refer to S2 Table.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4482697&req=5

pone.0126915.g002: Variation in estimated MP attributable to the age of the culture and replica.Each color represents a different replica and the values represent the average OD from 10 different wells. (A and B) respectively, Pseudomonas aeruginosa WT in LB and glucose limited minimal medium. (C and D) respectively E. coli WT in LB and glucose-limited minimal medium. (E) S. aureus Newman, WT, in MHII. For statistics refer to S2 Table.
Mentions: In their protocol, Hall and colleagues [23] recommend careful control of the preparation, and in particular the age of the inoculum introduced into the microtiter wells. They suggest there will be variation in estimated MPs between runs and within microtiter plates. To explore the magnitude of this variation, and thereby the robustness and reliability of microtiter plate reader estimates of the MP, we estimated this parameter with suspensions of wild type cells of each species initiated from cultures maintained for 24, 48, and 72 hours at 37°C, in their respective media. We repeated this experiment four times to determine the extent to which estimates of MP vary between runs. We also examined the extent of variation within plates by inoculating 50 wells with the same cell mixture (E. coli B/6 in LB). We restricted this consideration to the Bioscreen data. The results of these experiments are presented in Fig 2. Finally, to determine the effects of the wave-length of the plate reader and the extent of shaking, using the Bioscreen we estimated the MPs for wild type strains of all three species in broth and minimal medium at a wavelength of 540nm and with shaking for 10 seconds before reading the ODs, rather than continuously between readings.

Bottom Line: The maximum exponential growth rate, the Malthusian parameter (MP), is commonly used as a measure of fitness in experimental studies of adaptive evolution and of the effects of antibiotic resistance and other genes on the fitness of planktonic microbes.Thanks to automated, multi-well optical density plate readers and computers, with little hands-on effort investigators can readily obtain hundreds of estimates of MPs in less than a day.This leads us to question the reliability of estimates of MP obtained with these high throughput devices and the utility of these estimates of the maximum growth rates to detect fitness differences.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Emory University, Atlanta, Georgia, United States of America.

ABSTRACT
The maximum exponential growth rate, the Malthusian parameter (MP), is commonly used as a measure of fitness in experimental studies of adaptive evolution and of the effects of antibiotic resistance and other genes on the fitness of planktonic microbes. Thanks to automated, multi-well optical density plate readers and computers, with little hands-on effort investigators can readily obtain hundreds of estimates of MPs in less than a day. Here we compare estimates of the relative fitness of antibiotic susceptible and resistant strains of E. coli, Pseudomonas aeruginosa and Staphylococcus aureus based on MP data obtained with automated multi-well plate readers with the results from pairwise competition experiments. This leads us to question the reliability of estimates of MP obtained with these high throughput devices and the utility of these estimates of the maximum growth rates to detect fitness differences.

No MeSH data available.


Related in: MedlinePlus