Epidemiological cut-off value and antibiotic susceptibility test methods for azithromycin in a collection of multi-country invasive non-typhoidal Salmonella

Bieke Tack; Marie-France Phoba; Phe Thong; Palpouguini Lompo; Charlien Hupko; Stefanie Desmet; Delphine Martiny; Wesley Mattheus; Maria Pardos de la Gandara; Lisette Mbuyi-Kalonji; Laura Kuijpers; Benoit Prevost; Barbara Barbé; Olivier Vandenberg; Octavie Lunguya; Joaquim Ruiz; Jan Jacobs; Liselotte Hardy

doi:10.1016/j.cmi.2022.06.009

Epidemiological cut-off value and antibiotic susceptibility test methods for azithromycin in a collection of multi-country invasive non-typhoidal Salmonella

Clin Microbiol Infect. 2022 Dec;28(12):1615-1623. doi: 10.1016/j.cmi.2022.06.009. Epub 2022 Jun 20.

Authors

Bieke Tack¹, Marie-France Phoba², Phe Thong³, Palpouguini Lompo⁴, Charlien Hupko⁵, Stefanie Desmet⁶, Delphine Martiny⁷, Wesley Mattheus⁸, Maria Pardos de la Gandara⁹, Lisette Mbuyi-Kalonji², Laura Kuijpers¹⁰, Benoit Prevost¹¹, Barbara Barbé¹², Olivier Vandenberg¹³, Octavie Lunguya², Joaquim Ruiz¹⁴, Jan Jacobs¹⁵, Liselotte Hardy¹²

Affiliations

¹ Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium; Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium. Electronic address: [email protected].
² Department of Microbiology, National Institute for Biomedical Research, Kinshasa, Democratic Republic of the Congo; Department of Microbiology, University Teaching Hospital of Kinshasa, Kinshasa, Democratic Republic of the Congo.
³ Sihanouk Hospital Center of Hope, Phnom Penh, Cambodia.
⁴ IRSS/Clinical Research Unit of Nanoro, Nanoro, Burkina Faso.
⁵ Faculty of Medicine, KU Leuven, Leuven, Belgium.
⁶ Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium; Clinical Department of Laboratory Medicine, University Hospitals Leuven, Leuven, Belgium.
⁷ Department of Microbiology, Laboratoire des Hôpitaux Universitaires de Bruxelles, Universitaire Laboratorium Brussel (LHUB-ULB), Bruxelles, Belgium; Faculté de Médecine et Pharmacie, Université de Mons (UMONS), Mons, Belgium.
⁸ Division of Human Bacterial Diseases, Sciensano, Uccle, Belgium.
⁹ Institut Pasteur, Université Paris Cité, Unité des Bactéries Pathogènes Entériques, Centre National de Référence des Escherichia coli, Shigella et Salmonella, Paris, France.
¹⁰ Department of Infectious Diseases, Leiden University Medical Center, Leiden, the Netherlands.
¹¹ Department of Microbiology, Laboratoire des Hôpitaux Universitaires de Bruxelles, Universitaire Laboratorium Brussel (LHUB-ULB), Bruxelles, Belgium.
¹² Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.
¹³ Center for Environmental Health and Occupational Health, School of Public Health, Université Libre de Bruxelles, Brussels, Belgium; Innovation and Business Development Unit, Laboratoire des Hôpitaux Universitaires de Bruxelles, Universitaire Laboratorium Brussel (LHUB-ULB), Bruxelles, Belgium; Division of Infection and Immunity, Faculty of Medical Sciences, University College London, London, United Kingdom.
¹⁴ Grupo de Investigación en Dinámicas y Epidemiología de la Resistencia a Antimicrobianos - "One Health," Universidad Cientifica del Sur, Lima, Peru.
¹⁵ Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium; Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium.

PMID: 35738320
DOI: 10.1016/j.cmi.2022.06.009

Abstract

Objective: Azithromycin is an alternative to treat invasive non-typhoidal Salmonella (iNTS) infections. We determined its epidemiological cut-off (ECOFF) and compared azithromycin susceptibility testing methods for iNTS.

Methods: We used EUCAST ECOFFinder to determine the minimum inhibitory concentrations (MIC; obtained by broth microdilution) ECOFF and corresponding disk zone diameters of 515 iNTS from blood cultures in Democratic Republic of Congo, Burkina Faso, Rwanda, and Cambodia. Transferable resistance mechanisms were determined by polymerase chain reaction. We compared azithromycin susceptibility testing by semi-automated broth microdilution (customized Sensititre panel; reference), agar dilution, gradient tests (bioMérieux, Liofilchem, HiMedia; read at 80% (MIC80%) and 100% inhibition (MIC100%)), and disk diffusion (Rosco, Oxoid, BD, Liofilchem) for 161 wild- and 198 non-wild-type iNTS.

Results: Azithromycin MIC ECOFF was 16 mg/L corresponding to a 12 mm zone diameter; mphA was detected in 192/197 non-wild- and 0/47 wild-type iNTS. Categorical agreement was excellent (≥98%) for all methods. Essential agreement was very good for agar dilution (>90%) but moderate for gradient tests (MIC80%: 52% to 71% and MIC100%: 72% to 91%). Repeatability was good for all methods/brands. Interreader agreement was high for broth microdilution and agar dilution (all ≤1 twofold dilution difference) and disk diffusion (>96% ≤3 mm difference) but lower for gradient tests (MIC80% & MIC100%: 83% to 94% ≤1 twofold dilution difference).

Discussion: Azithromycin ECOFF of iNTS was 16 mg/L, i.e. equal to Salmonella Typhi. Disk diffusion is an accurate, precise, and user-friendly alternative for agar dilution and broth microdilution. Reading gradient tests at 100% instead of 80% inhibition improved accuracy and precision.

Keywords: Agar dilution; Antibiotic susceptibility testing; Azithromycin; Broth microdilution; Disk diffusion; Epidemiological cut-off; Gradient test; Non-typhoidal Salmonella; Performance.

MeSH terms

Agar
Anti-Bacterial Agents / pharmacology
Azithromycin / pharmacology
Humans
Microbial Sensitivity Tests
Salmonella
Salmonella Infections*
Typhoid Fever*

Substances

Azithromycin
Agar
Anti-Bacterial Agents