Genetic Characterization and Role in Virulence of the Ribonucleotide Reductases of Streptococcus sanguinis

Streptococcus sanguinis is a cause of infective endocarditis and has been shown to require a manganese transporter called SsaB for virulence and O2 tolerance. Like certain other pathogens, S. sanguinis possesses aerobic class Ib (NrdEF) and anaerobic class III (NrdDG) ribonucleotide reductases (RNRs) that perform the essential function of reducing ribonucleotides to deoxyribonucleotides. The accompanying paper (Makhlynets, O., Boal, A. K., Rhodes, D. V., Kitten, T., Rosenzweig, A. C., and Stubbe, J. (2014) J. Biol. Chem. 289, 6259–6272) indicates that in the presence of O2, the S. sanguinis class Ib RNR self-assembles an essential diferric-tyrosyl radical (FeIII2-Y•) in vitro, whereas assembly of a dimanganese-tyrosyl radical (MnIII2-Y•) cofactor requires NrdI, and MnIII2-Y• is more active than FeIII2-Y• with the endogenous reducing system of NrdH and thioredoxin reductase (TrxR1). In this study, we have shown that deletion of either nrdHEKF or nrdI completely abolishes virulence in an animal model of endocarditis, whereas nrdD mutation has no effect. The nrdHEKF, nrdI, and trxR1mutants fail to grow aerobically, whereas anaerobic growth requires nrdD. The nrdJgene encoding an O2-independent adenosylcobalamin-cofactored RNR was introduced into the nrdHEKF, nrdI, and trxR1 mutants. Growth of the nrdHEKF and nrdI mutants in the presence of O2 was partially restored. The combined results suggest that MnIII2-Y•-cofactored NrdF is required for growth under aerobic conditions and in animals. This could explain in part why manganese is necessary for virulence and O2 tolerance in many bacterial pathogens possessing a class Ib RNR and suggests NrdF and NrdI may serve as promising new antimicrobial targets

Presence of <i>Rickettsia</i> Species in Ticks Collected from Companion Animals in Northeastern Georgia, United States

Tick-borne diseases are a major threat to both humans and their pets; therefore, it is important to evaluate the prevalence of pathogens carried by ticks on companion animals. In this study, attached and unattached Ixodid ticks were removed from companion animals by a veterinary practice in Hall County, Georgia. DNA was extracted from unengorged adult ticks and each was screened for the presence of Rickettsia spp. by polymerase chain reaction (PCR) and sequenced to determine the species present. Two hundred and four adult hard-bodied ticks were identified to species and Rickettsia spp. were found in 19.6% (n = 38) of the 194 analyzed DNA extracts. Rickettsia montanensis was found in Dermacentor variablis (14.7%; n = 25), Amblyomma maculatum (33.3%; n = 2), and Rhipicephalus sanguineus s.l. ticks (25%; n = 4). One Amblyomma americanum tick contained Rickettsia amblyommatis, while Rickettsia felis was found in one Dermacentor variablis tick, serving as the first report of Rickettsia felis in a tick in this region and within this tick vector. This study suggests that there is a risk of companion animals contracting a species of Rickettsia from a tick bite in northeastern Georgia, indicating a need for more investigation and highlighting the importance of tick prevention on pets

Evaluating Trends in Strangles Outbreaks Using Temperature and Precipitation Data in the United States of America for 2018–2022

Strangles is a highly contagious upper respiratory infection of equids that is globally distributed. The causative agent of strangles, Streptococcus equi subspecies equi, can be spread through indirect contact with infected fomites, and studies have shown this microbe to live well in varying environmental conditions. The purpose of this study was to analyze strangles case numbers across the United States of America from 2018 to 2022 to investigate potential temporal or weather patterns associated with outbreaks. Diagnosed case records were obtained from the Equine Disease Communication Center, university databases, government agencies, or veterinary diagnostic labs, and geographic information systems (GISs) were used to map cases and to acquire relevant meteorological data from outbreak areas. These data were analyzed using logistic regression to explore trends that occur between outbreaks and changes in temperature and precipitation. Initial review of weather data suggested monthly changes in strangles case numbers corresponded with changing seasons. Logistic regression indicated that changes in monthly average temperature and minimum temperature were significantly associated with increased or decreased odds of strangles outbreaks, respectively. Future analyses should focus on weather data isolated within a smaller region or state to better resolve trends in strangles outbreaks throughout the continental USA

Disulfide-Mediated Oligomer Formation in Borrelia burgdorferi Outer Surface Protein C, a Critical Virulence Factor and Potential Lyme Disease Vaccine Candidate▿

Borrelia burgdorferi OspC is an outer membrane lipoprotein required for the establishment of infection in mammals. Due to its universal distribution among B. burgdorferi sensu lato strains and high antigenicity, it is being explored for the development of a next-generation Lyme disease vaccine. An understanding of the surface presentation of OspC will facilitate efforts to maximize its potential as a vaccine candidate. OspC forms homodimers at the cell surface, and it has been hypothesized that it may also form oligomeric arrays. Here, we employ site-directed mutagenesis to test the hypothesis that interdimeric disulfide bonds at cysteine 130 (C130) mediate oligomerization. B. burgdorferi B31 ospC was replaced with a C130A substitution mutant to yield strain B31::ospC(C130A). Recombinant protein was also generated. Disulfide-bond-dependent oligomer formation was demonstrated and determined to be dependent on C130. Oligomerization was not required for in vivo function, as B31::ospC(C130A) retained infectivity and disseminated normally. The total IgG response and the induced isotype pattern were similar between mice infected with untransformed B31 and those infected with the B31::ospC(C130A) strain. These data indicate that the immune response to OspC is not significantly altered by formation of OspC oligomers, a finding that has significant implications in Lyme disease vaccine design