Serratia ficaria: a misidentified or unidentified rare cause of human infections in fig tree culture zones

Abstract

Serratia ficaria, an enterobacterium involved in the fig tree ecosystem, has been isolated from human clinical samples in rare instances, and its role as a pathogen is unclear. In 7 years, we have isolated S. ficaria from seven patients; it was the only pathogen in 4 patients, including a patient with septicemia described previously and three patients with gallbladder empyemas described in the present report. From March 1995 to July 1997, the incidence of biliary infections due to S. ficaria was 0.7%. We discuss the digestive carriage of this bacterium and its epidemiology with respect to the fig tree life cycle. Since fig trees grow around the Mediterranean as well as in the United States (California, Louisiana, Hawaii), S. ficaria should be more frequently isolated. In our experience, various strains have been misidentified or unidentified by commercial systems. Incorrect identification could be an additional explanation for the paucity of reported cases. S. ficaria produces nonpigmented, lactose-negative colonies which give off a potatolike odor. This odor is the primary feature of S. ficaria and must prompt reexamination of the identifications proposed by commercial systems. We tested 42 novel strains using three commercial systems: Vitek gram-negative identification (GNI) cards and API 20E and ID 32E strips (bioMérieux, Marcy-l'Etoile, France). The percentages of positivity that we have obtained were lower than those published previously for the following characteristics: lipase, gelatinase, DNase, and rhamnose. The best system for the recognition of S. ficaria is ID 32E, which correctly identified 27 of 42 strains. The API 20E system gave correct identifications for only two strains. S. ficaria was not present in the Vitek GNI card system database.