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. 2018 Oct 11;13(10):e0205603.
doi: 10.1371/journal.pone.0205603. eCollection 2018.

Rapid antibiotic susceptibility testing on blood cultures using MALDI-TOF MS

Marlène Sauget  1   2   3 , Xavier Bertrand  1   3 , Didier Hocquet  1   2   3
Affiliations

Rapid antibiotic susceptibility testing on blood cultures using MALDI-TOF MS

Marlène Sauget et al. PLoS One. .

Abstract

Antibiotic resistance is a major public health problem requiring the early optimization of antibiotic prescriptions. Matrix-Assisted Laser Desorption Ionization-Time Of Flight Mass Spectrometry (MALDI-TOF MS) has been shown to accurately identify bacteria from positive blood culture. Here, we developed a rapid detection of Escherichia coli resistance to amoxicillin (AMX) and cefotaxime (CTX) from positive blood culture based on MALDI-TOF MS. Potential sparing of broad-spectrum antibiotics was also evaluated. We tested 103 E. coli-positive blood cultures. Blood cultures were subculture 1-hour in antibiotic-free rich liquid media before further incubation with and without AMX for 2.5 h or CTX for 2 h. Protein extracts associated with an internal control were spotted on a MALDI-TOF target and spectra were analyzed with the MBT-ASTRA prototype software (Bruker Daltonik GmbH, Bremen, Germany). Bacterial growth ratio was calculated from the AUC spectra obtained in the presence and absence of the antibiotic and compared to a threshold which classified E. coli as susceptible or resistant. Results were interpreted with MICs determined using agar dilution method as reference technique. MBT-ASTRA recognized 95% and 84% of the AMX- and CTX-susceptible isolates, respectively. Overall, quantitative analysis of mass spectra allows susceptibility testing within 4 hours after the positivity of blood culture with E. coli. At the first report of positive blood culture, MALDI-TOF MS would then provide the prescribers with the bacterial identification and the susceptibility to AMX and CTX, thus limiting the use of broad-spectrum compounds.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Susceptibility of E. coli to AMX and CTX revealed by m/z 2000–10000 AUC with MS-ASTRA (Bruker Daltonik GmbH).
The red rectangle indicate one peak of the internal standard (m/z 6,800) used for the quantitative comparaison of the spectra. (A, B) Spectra acquired after 2-h incubation of a CTX-susceptible E. coli isolate at 37°C with (A) and without (B) 20 mg/l of CTX. (C, D) Spectra acquired after 2-h incubation of a CTX-resistant E. coli isolate at 37°C with (C) and without (D) 20 mg/l of CTX. The spectra obtained with AMX-S and AMX-R E. coli incubated 2.5 h at 37°C with 8 mg/l of AMX are stricly superposable.
Fig 2
Fig 2. Spectra analysis with MBT-ASTRA prototype software (Bruker Daltonik GmbH).
(A) The area under the curve (AUC) of spectra of 2 E. coli isolates Susceptible (S) and resistant (R) to CTX, with (Control_S_CTX, Control_R_CTX) and without the antibiotic (Control_S_BHI, Control_R_BHI), respectively. The AUC, normalized with an internal control, was calculated automatically by the software through a “calculation window” m/z 2000–10000. (B) A bacterial growth ratio (GR) was automatically calculated by the software from the AUC spectra obtained in the presence and absence of CTX and compared to a threshold which classified E. coli as susceptible (GR ≤ 0.4 for Control_S.CTX:BHI) or resistant (GR > 0.4 for Control_R.CTX:BHI).
See this image and copyright information in PMC

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