Infections caused by anaerobes are common in children. However, limited data are available on bloodstream infections caused by these bacteria in Europe. A multicentre retrospective observational study was conducted over a 4-year period (2020-2023) across 44 European hospitals to analyze all anaerobes isolated from blood cultures. The study examined the epidemiology and antimicrobial resistance profiles of anaerobes identified in paediatric patients, comparing the findings with those observed in adults. Among the 14,527 total anaerobic isolates, 186 (1.3%) were detected from paediatric patients. These were predominantly Gram-positive (70%) and Gram-negative (22%) bacilli. The most prevalent species in paediatric patients were Cutibacterium acnes (24.7%), Schaalia odontolytica (9.7%), Actinomyces oris (8.1%), and Bacteroides fragilis (7.5%). Relative feature importance based on the mean SHAP (SHapley Additive exPlanations) values distinguished paediatric patients and adults based on their antibiotic resistance patterns with high accuracy. Compared to those from adult patients, Gram-positive bacilli detected in paediatric samples displayed higher resistance rates for meropenem (15% vs. 9%), metronidazole (52% vs. 24%), and vancomycin (27% vs. 6%), and lower resistance to benzylpenicillin (11% vs. 17%), amoxicillin/clavulanate (9% vs. 17%), and clindamycin (30% vs. 36%). Gram-negative bacilli in paediatric samples displayed lower resistance to benzylpenicillin (18% vs. 29%), piperacillin/tazobactam (26% vs. 33%), and clindamycin (20% vs. 27%), and they were highly susceptible to imipenem, meropenem, and metronidazole as those detected in adult patients. Bacteroides species detected in paediatric and adult patients displayed high resistance to piperacillin/tazobactam (33% vs. 39%) and clindamycin (38% vs. 29%), while they were highly susceptible to metronidazole. Compared to those from adult samples, Cutibacterium acnes in paediatric patients displayed lower resistance to benzylpenicillin (none vs. 15%) and clindamycin (17% vs. 29%). The comparison of species and susceptibility profiles of anaerobes detected in paediatric and adult patients highlighted the importance of reporting antimicrobial susceptibility surveillance data by age group.

Amsterdam UMC Department of Medical Microbiology and Infection Prevention Amsterdam The Netherlands

BIOSS Centre for Biological Signaling Studies University of Freiburg 79104 Freiburg Germany

CIBER de Enfermedades Infecciosas Instituto de Salud Carlos 3 Madrid Spain

Clinical Department for Clinical Microbiology Prevention and Control of Infectious Diseases University of Zagreb School of Medicine University Hospital Centre Zagreb Kispatic Street 12 10000 Zagreb Croatia

Clinical Microbiology Department of Translational Medicine Faculty of Medicine Lund University Malmö Sweden Clinical Microbiology Laboratory Medicine Skåne Lund Sweden

Clinical Microbiology Division Antoni Jurasz University Hospital No 1 in Bydgoszcz 9 Skłodowska Curie St Bydgoszcz 85 094 Poland

Department of Biomedical and Biotechnological Sciences University of Catania 95123 Catania Italy

Department of Clinical Microbiology and Microbial Pathogenesis University Hospital of Heraklion 711 10 Crete Greece

Department of Clinical Microbiology Cliniques Universitaires Saint Luc Brussels Belgium

Department of Clinical Microbiology Copenhagen University Hospital Rigshospitale Copenhagen Denmark

Department of Clinical Microbiology Copenhagen University Hospital Rigshospitalet Copenhagen Denmark Department of Clinical Medicine Faculty of Health and Medical Sciences University of Copenhagen Copenhagen Denmark

Department of Clinical Microbiology University Hospital Antwerp Edegem Belgium

Department of Clinical Microbiology University Hospital of Split Split Croatia

Department of Clinical Microbiology Vall d'Hebron Barcelona Hospital Campus Barcelona Spain

Department of Clinical Pathology Centro Hospitalar Universitário de Lisboa Central Lisbon Portugal

Department of Dental Microbiology Medical University of Warsaw Warsaw Poland Microbiological Laboratory University Center of Laboratory Medicine Medical University of Warsaw Warsaw Poland

Department of Experimental Medicine University of Salento Via Provinciale Monteroni N 165 73100 Lecce Italy

Department of Genetics and Microbiology Universitat Autònoma de Barcelona Bellaterra Spain

Department of Medical and Clinical Pharmacology Toulouse University Hospital Toulouse France

Department of Medical and Surgical Sciences University of Bologna 40126 Bologna Italy

Department of Medical Microbiology 2nd Faculty of Medicine Charles University and Motol University Hospital Prague Czech Republic

Department of Medical Microbiology and Immunology Prof Dr Elissay Yanev Faculty of Medicine Medical University of Plovdiv 4002 Plovdiv Bulgaria

Department of Medical Microbiology and Infectious Diseases Erasmus Medical Center Rotterdam The Netherlands

Department of Microbiology and Infection Control Akershus University Hospital Lørenskog Norway

Department of Microbiology and Laboratory Medical Immunology Medical University of Lodz Lodz Poland

Department of Microbiology Ludwik Rydygier Collegium Medicum in Bydgoszcz Nicolaus Copernicus University in Toruń 9 Skłodowska Curie St 85 094 Bydgoszcz Poland

Department of Microbiology Medical Faculty Commenius University and University Hospital Bratislava Bratislava Slovakia

Department of Microbiology Medical School University of Patras Patras Greece

Department of Microbiology Oslo University Hospital Oslo Norway

Department of Microbiology St Vincent's University Hospital Elm Park Dublin D04 T6 F4 Ireland

Department of Microbiology University of Oslo Oslo Norway

Department of Molecular Medical Microbiology Faculty of Medicine Jagiellonian University Medical College Krakow Poland

Department of Paediatrics Agios Nikolaos General Hospital 721 00 Crete Greece

Department of Pharmaceutical Microbiology Faculty of Pharmacy Jagiellonian University Medical College Krakow Poland Department of Microbiology University Hospital Krakow Poland

Department of Public Health and Paediatrics University of Torino Turin Italy

Division of Medicine and Laboratory Sciences Institute of Clinical Medicine Faculty of Medicine Department of Microbiology and Infection Control University of Oslo Oslo Norway

Faculdade de Medicina Universidade de Lisboa Lisbon Portugal

Infectious Diseases Service Lausanne University Hospital Lausanne Switzerland

INSERM Immunology and New Concepts in ImmunoTherapy INCIT UMR 1302 Nantes Université Nantes France

Institut de Biologie des Hôpitaux de Nantes Service de Bactériologie et des Contrôles Microbiologiques CHU de Nantes 9 Quai Moncousu 44093 Nantes Cedex 01 France

Institut Micalis UMR 1319 Université Paris Saclay INRAe AgroParisTech Châtenay Malabry France

Institute for Medical Microbiology Immunology and Hygiene University Hospital Cologne and Faculty of Medicine University of Cologne Cologne Germany

Institute of Hygiene and Medical Microbiology Medical University of Innsbruck 6020 Innsbruck Austria

Institute of Laboratory Medicine Semmelweis University Budapest Hungary

Institute of Medical Microbiology and Hygiene Medical Center Univerity of Freiburg Faculty of Medicine 79104 Freiburg Germany

Institute of Medical Microbiology and Virology Carl Von Ossietzky University Oldenburg Oldenburg Germany

Institute of Medical Microbiology and Virology Klinikum Oldenburg Oldenburg Germany

Institute of Medical Microbiology Jena University Hospital Friedrich Schiller University Jena Germany

Institute of Medical Microbiology University of Zurich Zurich Switzerland

Institute of Microbiology and Immunology Faculty of Medicine University of Ljubljana Ljubljana Slovenia

Institute of Microbiology Lausanne University Hospital and University of Lausanne Lausanne Switzerland

Laboratoire de Bactériologie Hygiène CHU de Toulouse Université de Toulouse Toulouse France

Laboratory of Microbiology University Hospital St George Plovdiv 4000 Bulgaria

Microbiological Laboratory University Center of Laboratory Medicine Medical University of Warsaw Warsaw Poland

Microbiology and Virology Unit University Hospital Città Della Salute E Della Scienza Di Torino Turin Italy

Microbiology Department Multidisciplinary Research Center On Antimicrobial Resistance Microbiology Laboratory Pius Branzeu' Emergency Clinical County Hospital 'Victor Babes' University of Medicine and Pharmacy Timisoara Romania

Microbiology Service University Clinical Hospital of Valencia Valencia Spain

Microbiology Unit IRCCS Azienda Ospedaliero Universitaria di Bologna Bologna Italy

Neonatal Intensive Care Unit IRCCS AOU Bologna 40139 Bologna Italy

Regional Department of Clinical Microbiology University Hospital Waterford Waterford Ireland

Service de Microbiologie Clinique Hôpitaux Saint Joseph and Marie Lannelongue Paris France

Service of Microbiology Hospital Universitario de Gran Canaria Dr Negrín Las Palmas Spain

Servicio de Microbiología Hospital Universitario Ramón y Cajal and Instituto Ramón y Cajal de Investigaciones Sanitarias Madrid Spain

Serviço de Patologia Clínica Centro Hospitalar Universitário Lisboa Norte Lisbon Portugal

U O C Laboratory Analysis Unit A O U Policlinico San Marco Via S Sofia 78 95123 Catania Italy

Université Limoges INSERM CHU Limoges UMR 1092 Limoges France

Vall d'Hebron Institut de Recerca Barcelona Spain

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