Characterization of Staphylococcus caprae Clinical Isolates Involved in Human Bone and Joint Infections, Compared with Goat Mastitis Isolates

Abstract

Staphylococcus caprae is an emerging microorganism in human bone and joint infections (BJI). The aim of this study is to describe the features of S. caprae isolates involved in BJI (H for human) compared with those of isolates recovered in goat mastitis (A for animal). Fourteen isolates of each origin were included. Identifications were performed using a Vitek 2 GP ID card, tuf gene sequencing, and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) Vitek MS. Molecular typing was carried out using pulsed-field gel electrophoresis (PFGE) and DiversiLab technology. The crystal violet method was used to determine biofilm-forming ability. Virulence factors were searched by PCR. Vitek MS technology provides an accurate identification for the two types of isolates compared to that of gold-standard sequencing (sensitivity, 96.4%), whereas the Vitek 2 GP ID card was more effective for H isolates. Molecular typing methods revealed two distinct lineages corresponding to the origin despite few overlaps: H and A. In our experimental conditions, no significant difference was observed in biofilm production ability between H and A isolates. Nine isolates (5 H isolates and 4 A isolates) behaved as weak producers while one A isolate was a strong producer. Concerning virulence factors, the autolysin atlC and the serine aspartate adhesin (sdrZ) genes were detected in 24 isolates (86%), whereas the lipase gene was always detected, except in one H isolate (96%). The ica operon was present in 23 isolates (82%). Fibrinogen-binding (fbe) or collagen-binding (cna) genes were not detected by using primers designed for Staphylococcus aureus or Staphylococcus epidermidis, even in low stringency conditions. Although S. caprae probably remains underestimated in human infections, further studies are needed to better understand the evolution and the adaptation of this species to its host. Since Staphylococcus caprae was first described by Devriese et al. in 1983 based on a strain isolated from goat's milk (reference strain CCM3573) (1), its involvement in veterinary medicine has been well described (2-5). This coagulase-negative species is considered to be a commensal organism of the skin and mammary glands of goats, but it can also cause mastitis. S. caprae is the main species isolated from goat's milk. Surprisingly, this species also has been reported as a human hospital-acquired pathogen, mostly implicated in bone and joint infections (BJI) (6-8). In this context and also in the veterinary environment, it remains difficult to differentiate between contamination, colonization, and infection. S. caprae may be misidentified when using old phenotypic methods, leading to an underestimation of its pathogenic role.In this study, we compared three methods for S. caprae identification with isolates recovered from BJI or goat mastitis. The phylogenetic relationship between human (H) S. caprae isolates recovered from BJI and animal (A) S. caprae isolates recovered from goat mastitis were analyzed using two different typing methods: ...

Staphylococcus caprae bacteraemia and native bone infection complicated by therapeutic failure and elevated MIC: a case report

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