Beyond the Usual Suspects: Weeksella virosa as a Potential Human and Animal Pathogen

Weeksella virosa (W. virosa) is a rare, non-saccharolytic Gram-negative bacterium initially described in the 1970s, later proposed as a distinct genus in 1986. The genus Weeksella currently contains two species, namely W. virosa and W. massiliensis. Although primarily considered non-pathogenic, recent evidence has linked W. virosa to a limited number of clinical infections, mostly in immunocompromised patients. This review aims to consolidate the current body of knowledge on W. virosa, encompassing its microbiological and biochemical characteristics, involvement in human and animal infections, antimicrobial susceptibility profiles, and a critical evaluation of existing diagnostic methodologies. This review includes 13 case reports detailing 16 human cases retrieved from multiple databases, highlighting diagnostic inconsistencies and a lack of standardized antimicrobial susceptibility testing. Although W. virosa is generally susceptible to most antibiotics with the exception of aminoglycosides, recent reports seem to suggest a possible emerging resistance trend. The presence of this organism in hospital environments raises concerns about its potential transmission within healthcare settings. While biochemical testing appears to offer reasonably accurate identification of W. virosa, molecular confirmation may be warranted in some cases mainly due to the organism's rarity. The reliability of MALDI-TOF MS for the identification of W. virosa remains currently uncertain. Further studies, including electron microscopy and genome-wide analysis, are urgently needed to clarify the pathogenic potential of this bacterium and guide clinical management. This review underscores the necessity for awareness among clinicians and microbiologists regarding this underrecognized pathogen.