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

Clinical Microbiology and Infection, vol. 28, pp. 1615–1623

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.

Authors 17

1. Bieke Tack corresponding

   Instituut voor Tropische Geneeskunde · KU Leuven

   Affiliation as printed

   Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium; Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium. Electronic address: btack@itg.be

   Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium

   Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium

2. Marie-France Phoba

   National Institute of Biomedical Research

   Affiliation as printed

   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

   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. Thong Phe

   Sihanouk Hospital Center of HOPE

   Affiliation as printed

   Sihanouk Hospital Center of Hope, Phnom Penh, Cambodia

4. Palpouguini Lompo

   Institut de Recherche en Sciences de la Santé · Clinical Research Unit Nanoro

   Affiliation as printed

   IRSS/Clinical Research Unit of Nanoro, Nanoro, Burkina Faso

5. Charlien Hupko

   KU Leuven

   Affiliation as printed

   Faculty of Medicine, KU Leuven, Leuven, Belgium

6. Stefanie Desmet

   Universitair Ziekenhuis Leuven · KU Leuven

   Affiliation as printed

   Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium; Clinical Department of Laboratory Medicine, University Hospitals Leuven, Leuven, Belgium

   Clinical Department of Laboratory Medicine, University Hospitals Leuven, Leuven, Belgium

   Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium

7. Delphine Martiny

   University of Mons · Université Libre de Bruxelles

   Affiliation as printed

   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

   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. Wesley Mattheus

   Sciensano (Belgium)

   Affiliation as printed

   Division of Human Bacterial Diseases, Sciensano, Uccle, Belgium

9. María Pardos de la Gándara

   Institut Pasteur · Université Paris Cité

   Affiliation as printed

   Institut Pasteur, Université Paris Cité, Unité des Bactéries Pathogènes Entériques, Centre National de Référence des Escherichia coli, Shigella et Salmonella, Paris, France

10. Lisette Mbuyi-Kalonji

    National Institute of Biomedical Research

    Affiliation as printed

    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

    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

11. Laura Maria Francisca Kuijpers Aachen Department of Infectious Diseases

    Leiden University Medical Center

    Affiliation as printed

    Department of Infectious Diseases, Leiden University Medical Center, Leiden, the Netherlands

12. Barbara Barbé

    Instituut voor Tropische Geneeskunde

    Affiliation as printed

    Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium

13. Olivier Vandenberg

    Université Libre de Bruxelles · University College London

    Affiliation as printed

    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

    Center for Environmental Health and Occupational Health, School of Public Health, Université Libre de Bruxelles, Brussels, Belgium

    Division of Infection and Immunity, Faculty of Medical Sciences, University College London, London, United Kingdom

    Innovation and Business Development Unit, Laboratoire des Hôpitaux Universitaires de Bruxelles, Universitaire Laboratorium Brussel (LHUB-ULB), Bruxelles, Belgium

14. Octavie Lunguya

    National Institute of Biomedical Research

    Affiliation as printed

    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

    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

15. Joaquı́m Ruiz

    Universidad Científica del Sur

    Affiliation as printed

    Grupo de Investigación en Dinámicas y Epidemiología de la Resistencia a Antimicrobianos - "One Health," Universidad Cientifica del Sur, Lima, Peru

    Grupo de Investigación en Dinámicas y Epidemiología de la Resistencia a Antimicrobianos - “One Health,” Universidad Cientifica del Sur, Lima, Peru

16. Jan A. Jacobs

    Instituut voor Tropische Geneeskunde · KU Leuven

    Affiliation as printed

    Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium; Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium

    Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium

    Department of Microbiology, Immunology and Transplantation, KU Leuven, Leuven, Belgium

17. Liselotte Hardy

    Instituut voor Tropische Geneeskunde

    Affiliation as printed

    Department of Clinical Sciences, Institute of Tropical Medicine, Antwerp, Belgium