Genotypic versus phenotypic methods in detection of Listeriamonocytogenes prosthetic joint infection

An uncommon case of a severe prosthetic joint infection (PJI) in a 71-year-old immunocompetent woman is presented. Listeria monocytogenes was identified in two consecutive samples using broad-range PCR and sequencing, whereas cultivation remained negative in the first sample and streptococci of a non-GAS, non-GBS type were detected in the second one. This report demonstrates that the phenotypic approach may lead to misidentification of L. monocytogenes in a routine clinical setting. Molecular methods of pathogen detection might be useful when a rare and/or unexpected microorganism is present or the sample is collected during antibiotic treatment.