Frequency and mechanisms of spontaneous fosfomycin nonsusceptibility observed upon disk diffusion testing of Escherichia coli

Aaron E. Lucas, Ryota Ito, Mustapha M. Mustapha, Christi L. McElheny, Roberta T. Mettus, Sarah L. Bowler, Serena F. Kantz, Marissa P. Pacey, A. William Pasculle, Vaughn S. Cooper, Yohei Doi

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

Fosfomycin maintains activity against most Escherichia coli clinical isolates, but the growth of E. coli colonies within the zone of inhibition around the fosfomycin disk is occasionally observed upon susceptibility testing. We aimed to estimate the frequency of such nonsusceptible inner colony mutants and identify the underlying resistance mechanisms. Disk diffusion testing of fosfomycin was performed on 649 multidrug-resistant E. coli clinical isolates collected between 2011 and 2015. For those producing inner colonies inside the susceptible range, the parental strains and their representative inner colony mutants were subjected to MIC testing, whole-genome sequencing, reverse transcription-quantitative PCR (qRT-PCR), and carbohydrate utilization studies. Of the 649 E. coli clinical isolates, 5 (0.8%) consistently produced nonsusceptible inner colonies. Whole-genome sequencing revealed the deletion of uhpT encoding hexose-6-phosphate antiporter in 4 of the E. coli inner colony mutants, while the remaining mutant contained a nonsense mutation in uhpA. The expression of uhpT was absent in the mutant strains with uhpT deletion and was not inducible in the strain with the uhpA mutation, unlike in its parental strain. All 5 inner colony mutants had reduced growth on minimal medium supplemented with glucose-6-phosphate. In conclusion, fosfomycin-nonsusceptible inner colony mutants can occur due to the loss of function or induction of UhpT but are rare among multidrug-resistant E. coli clinical strains. Considering that these mutants carry high biological costs, we suggest that fosfomycin susceptibility of strains that generate inner colony mutants can be interpreted on the basis of the zone of inhibition without accounting for the inner colonies.

Original languageEnglish
Article numbere01368
JournalJournal of clinical microbiology
Volume56
Issue number1
DOIs
Publication statusPublished - 01-01-2018

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Fosfomycin
Escherichia coli
Genome
Antiporters
Polymerase Chain Reaction
Glucose-6-Phosphate
Hexoses
Nonsense Codon
Growth
Reverse Transcription
Phosphates
Carbohydrates
Costs and Cost Analysis
Mutation

All Science Journal Classification (ASJC) codes

  • Microbiology (medical)

Cite this

Lucas, Aaron E. ; Ito, Ryota ; Mustapha, Mustapha M. ; McElheny, Christi L. ; Mettus, Roberta T. ; Bowler, Sarah L. ; Kantz, Serena F. ; Pacey, Marissa P. ; Pasculle, A. William ; Cooper, Vaughn S. ; Doi, Yohei. / Frequency and mechanisms of spontaneous fosfomycin nonsusceptibility observed upon disk diffusion testing of Escherichia coli. In: Journal of clinical microbiology. 2018 ; Vol. 56, No. 1.
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abstract = "Fosfomycin maintains activity against most Escherichia coli clinical isolates, but the growth of E. coli colonies within the zone of inhibition around the fosfomycin disk is occasionally observed upon susceptibility testing. We aimed to estimate the frequency of such nonsusceptible inner colony mutants and identify the underlying resistance mechanisms. Disk diffusion testing of fosfomycin was performed on 649 multidrug-resistant E. coli clinical isolates collected between 2011 and 2015. For those producing inner colonies inside the susceptible range, the parental strains and their representative inner colony mutants were subjected to MIC testing, whole-genome sequencing, reverse transcription-quantitative PCR (qRT-PCR), and carbohydrate utilization studies. Of the 649 E. coli clinical isolates, 5 (0.8{\%}) consistently produced nonsusceptible inner colonies. Whole-genome sequencing revealed the deletion of uhpT encoding hexose-6-phosphate antiporter in 4 of the E. coli inner colony mutants, while the remaining mutant contained a nonsense mutation in uhpA. The expression of uhpT was absent in the mutant strains with uhpT deletion and was not inducible in the strain with the uhpA mutation, unlike in its parental strain. All 5 inner colony mutants had reduced growth on minimal medium supplemented with glucose-6-phosphate. In conclusion, fosfomycin-nonsusceptible inner colony mutants can occur due to the loss of function or induction of UhpT but are rare among multidrug-resistant E. coli clinical strains. Considering that these mutants carry high biological costs, we suggest that fosfomycin susceptibility of strains that generate inner colony mutants can be interpreted on the basis of the zone of inhibition without accounting for the inner colonies.",
author = "Lucas, {Aaron E.} and Ryota Ito and Mustapha, {Mustapha M.} and McElheny, {Christi L.} and Mettus, {Roberta T.} and Bowler, {Sarah L.} and Kantz, {Serena F.} and Pacey, {Marissa P.} and Pasculle, {A. William} and Cooper, {Vaughn S.} and Yohei Doi",
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Lucas, AE, Ito, R, Mustapha, MM, McElheny, CL, Mettus, RT, Bowler, SL, Kantz, SF, Pacey, MP, Pasculle, AW, Cooper, VS & Doi, Y 2018, 'Frequency and mechanisms of spontaneous fosfomycin nonsusceptibility observed upon disk diffusion testing of Escherichia coli', Journal of clinical microbiology, vol. 56, no. 1, e01368. https://doi.org/10.1128/JCM.01368-17

Frequency and mechanisms of spontaneous fosfomycin nonsusceptibility observed upon disk diffusion testing of Escherichia coli. / Lucas, Aaron E.; Ito, Ryota; Mustapha, Mustapha M.; McElheny, Christi L.; Mettus, Roberta T.; Bowler, Sarah L.; Kantz, Serena F.; Pacey, Marissa P.; Pasculle, A. William; Cooper, Vaughn S.; Doi, Yohei.

In: Journal of clinical microbiology, Vol. 56, No. 1, e01368, 01.01.2018.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Frequency and mechanisms of spontaneous fosfomycin nonsusceptibility observed upon disk diffusion testing of Escherichia coli

AU - Lucas, Aaron E.

AU - Ito, Ryota

AU - Mustapha, Mustapha M.

AU - McElheny, Christi L.

AU - Mettus, Roberta T.

AU - Bowler, Sarah L.

AU - Kantz, Serena F.

AU - Pacey, Marissa P.

AU - Pasculle, A. William

AU - Cooper, Vaughn S.

AU - Doi, Yohei

PY - 2018/1/1

Y1 - 2018/1/1

N2 - Fosfomycin maintains activity against most Escherichia coli clinical isolates, but the growth of E. coli colonies within the zone of inhibition around the fosfomycin disk is occasionally observed upon susceptibility testing. We aimed to estimate the frequency of such nonsusceptible inner colony mutants and identify the underlying resistance mechanisms. Disk diffusion testing of fosfomycin was performed on 649 multidrug-resistant E. coli clinical isolates collected between 2011 and 2015. For those producing inner colonies inside the susceptible range, the parental strains and their representative inner colony mutants were subjected to MIC testing, whole-genome sequencing, reverse transcription-quantitative PCR (qRT-PCR), and carbohydrate utilization studies. Of the 649 E. coli clinical isolates, 5 (0.8%) consistently produced nonsusceptible inner colonies. Whole-genome sequencing revealed the deletion of uhpT encoding hexose-6-phosphate antiporter in 4 of the E. coli inner colony mutants, while the remaining mutant contained a nonsense mutation in uhpA. The expression of uhpT was absent in the mutant strains with uhpT deletion and was not inducible in the strain with the uhpA mutation, unlike in its parental strain. All 5 inner colony mutants had reduced growth on minimal medium supplemented with glucose-6-phosphate. In conclusion, fosfomycin-nonsusceptible inner colony mutants can occur due to the loss of function or induction of UhpT but are rare among multidrug-resistant E. coli clinical strains. Considering that these mutants carry high biological costs, we suggest that fosfomycin susceptibility of strains that generate inner colony mutants can be interpreted on the basis of the zone of inhibition without accounting for the inner colonies.

AB - Fosfomycin maintains activity against most Escherichia coli clinical isolates, but the growth of E. coli colonies within the zone of inhibition around the fosfomycin disk is occasionally observed upon susceptibility testing. We aimed to estimate the frequency of such nonsusceptible inner colony mutants and identify the underlying resistance mechanisms. Disk diffusion testing of fosfomycin was performed on 649 multidrug-resistant E. coli clinical isolates collected between 2011 and 2015. For those producing inner colonies inside the susceptible range, the parental strains and their representative inner colony mutants were subjected to MIC testing, whole-genome sequencing, reverse transcription-quantitative PCR (qRT-PCR), and carbohydrate utilization studies. Of the 649 E. coli clinical isolates, 5 (0.8%) consistently produced nonsusceptible inner colonies. Whole-genome sequencing revealed the deletion of uhpT encoding hexose-6-phosphate antiporter in 4 of the E. coli inner colony mutants, while the remaining mutant contained a nonsense mutation in uhpA. The expression of uhpT was absent in the mutant strains with uhpT deletion and was not inducible in the strain with the uhpA mutation, unlike in its parental strain. All 5 inner colony mutants had reduced growth on minimal medium supplemented with glucose-6-phosphate. In conclusion, fosfomycin-nonsusceptible inner colony mutants can occur due to the loss of function or induction of UhpT but are rare among multidrug-resistant E. coli clinical strains. Considering that these mutants carry high biological costs, we suggest that fosfomycin susceptibility of strains that generate inner colony mutants can be interpreted on the basis of the zone of inhibition without accounting for the inner colonies.

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