Epidemiological cutoff values for a 96-well broth microdilution plate for high-throughput research antibiotic susceptibility testing of M. tuberculosis
Authors:   The CRyPTIC Consortium, Fowler Philip W , Barilar Ivan , Battaglia Simone , Borroni Emanuele , Brandao Angela Pires , Brankin Alice , Cabibbe Andrea Maurizio , Carter Joshua , Cirillo Daniela Maria , Claxton Pauline , Clifton David A , Cohen Ted , Coronel Jorge , Crook Derrick W , Dreyer Viola , Earle Sarah G , Escuyer Vincent , Ferrazoli Lucilaine , Gao George Fu , Gardy Jennifer , Gharbia Saheer , Ghisi Kelen Teixeira , Ghodousi Arash , Gibertoni Cruz Ana Luíza , Grandjean Louis , Grazian Clara , Groenheit Ramona , Guthrie Jennifer L , He Wencong , Hoffmann Harald , Hoosdally Sarah J , Hunt Martin , Iqbal Zamin , Ismail Nazir Ahmed , Jarrett Lisa , Joseph Lavania , Jou Ruwen , Kambli Priti , Khot Rukhsar , Knaggs Jeff , Koch Anastasia , Kohlerschmidt Donna , Kouchaki Samaneh , Lachapelle Alexander S , Lalvani Ajit , Lapierre Simon Grandjean , Laurenson Ian F , Letcher Brice , Lin Wan-Hsuan , Liu Chunfa , Liu Dongxin , Malone Kerri M , Mandal Ayan , Mansjö Mikael , Matias Daniela , Meintjes Graeme , de Freitas Mendes Flávia , Merker Matthias , Mihalic Marina , Millard James , Miotto Paolo , Mistry Nerges , Moore David , Musser Kimberlee A , Ngcamu Dumisani , Nhung Hoang Ngoc , Niemann Stefan , Nilgiriwala Kayzad Soli , Nimmo Camus , Okozi Nana , Oliveira Rosangela Siqueira , Omar Shaheed Vally , Paton Nicholas , Peto Timothy EA , Watanabe Pinhata Juliana Maira , Plesnik Sara , Puyen Zully M , Rabodoarivelo Marie Sylvianne , Rakotosamimanana Niaina , Rancoita Paola MV , Rathod Priti , Robinson Esther , Rodger Gillian , Rodrigues Camilla , Rodwell Timothy C , Roohi Aysha , Santos-Lazaro David , Shah Sanchi , Kohl Thomas Andreas , Smith Grace , Solano Walter , Spitaleri Andrea , Supply Philip , Surve Utkarsha , Tahseen Sabira , Thuong Nguyen Thuy Thuong , Thwaites Guy , Todt Katharina , Trovato Alberto , Utpatel Christian , Van Rie Annelies , Vijay Srinivasan , Walker Timothy M , Walker A Sarah , Warren Robin , Werngren Jim , Wijkander Maria , Wilkinson Robert J , Wilson Daniel J , Wintringer Penelope , Xiao Yu-Xin , Yang Yang , Yanlin Zhao , Yao Shen-Yuan , Zhu Baoli 
Published: March 2021

Drug susceptibility testing of M. tuberculosis is rooted in a binary susceptible/resistant paradigm.

Whilst there are considerable advantages in measuring the minimum inhibitory concentrations (MICs) of a panel of drugs for an isolate it is n ecessary to measure the epidemiological cutoff values (ECOFF/ECVs) to permit comparison with qualitative data. Here we present ECOFF/ECVs for 13 anti-TB compounds, including bedaquiline and delamanid, derived from 20,637 clinical isolates collected by 14 laboratories based in 11 countries on five continents. Each isolate was incubated for 14 days on a dry 96-well broth microdilution plate and then read. Resistance to most of the drugs due to prior exposure is expected and the MIC distributions for many of the compounds are complex and therefore a phenotypically wild-type population could not be defined. Since a majority of samples also underwent genetic sequencing, we defined a genotypically wild-type population and measured the MIC of the 99th percentile by direct measurement and via fitting a Gaussian using interval regression.

The proposed ECOFF/ECV values were then validated by comparing to the MIC distributions of high-confidence genetic variants that confer resistance and to qualitative drug susceptibility tests obtained via Mycobacterial Growth Indicator Tube and the Microscopic-Observation Drug-Susceptibility assay.

These ECOFF/ECV values will inform and encourage the more widespread adoption of broth microdilution – this is a cheap culture-based method that tests the susceptibility of 12-14 antibiotics on a single 96-well plate and so could help personalise the treatment of tuberculosis.