title: Activation of persistent Streptococcus equi subspecies zooepidemicus in mares with subclinical endometritis.
abstract: Endometritis in horses caused by Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) may be underdiagnosed due to traditional diagnostic methods lacking sensitivity and specificity. We serendipitously identified a bacterial growth medium (bActivate) that appeared capable of inducing growth of dormant S. zooepidemicus, which subsequently allowed detection by standard diagnostics. To assess the effect of bActivate we compared its ability to activate dormant S. zooepidemicus in a group of potentially infected subfertile mares with phosphate-buffered saline (PBS). All mares had to test negative for S. zooepidemicus on a low-volume uterine lavage, be negative on endometrial cytology and without clinical signs of endometritis to be included in the investigation. The mares were instilled with bActivate or PBS in the uterus. Growth of S. zooepidemicus was induced by bActivate in 64% (16/25) and PBS in 8% (1/12) of the mares, respectively (p<0.002). In vitro studies supported that some strains of S. zooepidemicus were able to form persister cells tolerating 32-times of the minimal inhibitory concentration of penicillin compared to normal growing cells. Persister cells had not acquired penicillin resistance, but seemed to tolerate the antimicrobial due to dormancy. This is, to our knowledge, the first description of controlled growth induction of dormant bacteria from a subclinical infection. Moreover we demonstrated how endometritis can origin from a reservoir of dormant bacteria residing within the endometrium, and not only as an ascending infection. Further studies should aim at determining the prevalence of dormant S. zooepidemicus, impact of activation on diagnostic and treatment efficacy, uterine health and mare fertility.
authors.affiliation: The Fertility Clinic, Rigshospitalet, Section 4071, University Hospital of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark. Electronic address: morten.petersenr@gmail.com.
authors.forename: M R
authors.initials: MR
authors.lastname: Petersen
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Stigboejlen 4, DK-1870 Frederiksberg C, Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Skive
authors.affiliation: Section of Veterinary Reproduction and Obstetrics, Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlaegevej 68, DK-1870 Frederiksberg C, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Christoffersen
authors.affiliation: Hagyard Equine Medical Institute, Lexington, Kentucky, USA.
authors.forename: K
authors.initials: K
authors.lastname: Lu
authors.affiliation: Ansager Large Animal Hospital, Gartnerhaven 5, 6823 Ansager, Denmark.
authors.forename: J M
authors.initials: JM
authors.lastname: Nielsen
authors.affiliation: Maxwell H. Gluck Center for Equine Research, University of Kentucky, Lexington, USA.
authors.forename: M H T
authors.initials: MH
authors.lastname: Troedsson
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Stigboejlen 4, DK-1870 Frederiksberg C, Denmark.
authors.forename: A M
authors.initials: AM
authors.lastname: Bojesen
mesh_terms: D000818:Animals; D058345:Asymptomatic Infections; D004716:Endometritis / Q000175:diagnosis / Q000382:microbiology / Q000662:veterinary*; D004717:Endometrium / Q000382:microbiology; D005260:Female; D006734:Horse Diseases / Q000175:diagnosis* / Q000382:microbiology; D006736:Horses; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D012680:Sensitivity and Specificity; D013290:Streptococcal Infections / Q000175:diagnosis / Q000382:microbiology / Q000662:veterinary*; D018502:Streptococcus equi / Q000254:growth & development* / Q000302:isolation & purification
keywords: Activation; Dormancy; Endometritis; Horse; Persister cells; Streptococcus equi subsp. zooepidemicus