Human Wound Infection with Mannheimia glucosida following Lamb Bite

Abstract

e Mannheimia spp. are veterinary pathogens that can cause mastitis and pneumonia in domestic cattle and sheep. While Mannheimia glucosida can be found as normal flora in oral and respiratory mucosa in sheep, there have been no reported cases of human infection with this organism. CASE REPORTA 64-year-old man sustained a bite on the right thumb from a 10-month-old lamb. The lamb's teeth punctured his thumbnail while he was holding the lamb's mouth open during anthelminthic treatment with a malfunctioning dosing device. He applied epoxy resin to the nail to prevent the shattered edges from catching. Following this application, he developed pain around the wound, and 10 days after the injury, he presented to the hospital. On examination, the nail was discolored, with localized wound tenderness but no discharge, and there was erythema tracking from the right thumbnail up to the axilla. The wound was explored surgically, the nail plate was removed, and pus was washed out and sent to the laboratory for microscopy and culture. The patient was treated with intravenous flucloxacillin for 24 h, followed by oral cephalexin for 7 days. On review 1 week later, the erythema had resolved and the wound had healed well.Microscopy revealed large numbers of polymorphonuclear cells, but no organisms were seen on Gram staining. After 1 day of incubation on horse blood agar, there was heavy growth of a Gram-negative bacillus that was catalase positive, oxidase positive, and indole negative. It was hemolytic on 5% horse blood agar and Mueller-Hinton agar containing 5% sheep blood. After a second day of incubation, a lighter growth of Escherichia coli, Enterococcus faecalis, coagulase-negative staphylococci, and mixed anaerobes was apparent.With the use of the Vitek 2 GN card (bioMérieux, Marcy l'Etoile, France), the Gram-negative bacillus was identified as Sphingomonas paucimobilis (97% match). Notably, the trehalose reaction was negative, the beta-glucosidase reaction was positive, and the ornithine decarboxylase reaction was negative on the Vitek card. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS)-based identification was performed using the Microflex LT mass spectrometer (Bruker Daltonik), and the results were analyzed using the MALDI Biotyper software program (version 4.0.0.1). The top score for this Gram-negative organism was Mannheimia haemolytica, with a score of 2.177 and the accompanying comment "species of this genus have very similar patterns, therefore distinguishing their species is difficult." Other Mannheimia species appeared in the top 10 identifications listed, including Mannheimia glucosida, the highest score for which was 1.305. Partial 16S rRNA gene sequencing was performed using the MicroSeq 500 bacterial identification kit (Perkin-Elmer/Applied Biosystems, Foster City, CA), with sequence analysis performed on 500 nucleotides using MicroSeq 500 (version 2.2). A result for M. haemolytica was reported, with a specimen score of 43 and a 98.4% match (consensus length of 48...

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