Velineni S, Timoney J F
Maxwell H. Gluck Equine Research Center, University of Kentucky, Lexington, USA.
Equine Vet J. 2015 May;47(3):333-8. doi: 10.1111/evj.12272. Epub 2014 Jun 11.
Streptococcus zooepidemicus causes opportunist respiratory and other infections in the horse. Capsule expression is highly variable and known to affect resistance to phagocytosis. Most clinical isolates producing small, dry colonies at 37°C produce mucoid colonies at temperatures below 35°C.
The aim was to understand the molecular basis of increased capsule expression by equine isolates of S. zooepidemicus at temperatures lower than 35°C.
Cross-sectional observational study.
Capsule production by groups of equine S. zooepidemicus strains was determined at 23, 30, 35 and 37°C. Hyaluronidase (HylC) at 23 and 37°C was measured by quantitative enzyme-linked immunosorbent assay. Expressions of hasA and hylC at 23 and 37°C were measured by quantitative reverse transcriptase-PCR. The covRS genes in representative S. zooepidemicus were sequenced and checked for mutations.
Colonies of randomly selected S. zooepidemicus strains became mucoid or showed marked increase in colony mucoidy following the change in temperature to 23°C. Expression of hasA at 23°C was 45- to 700-fold greater than at 37°C. Transcription of hylC at 23°C was 2.5- to 200-fold greater than at 37°C, yet enzyme concentrations in cultures were significantly higher at 37°C (P<0.05), suggesting that production of HylC is regulated post transcriptionally. The covRS gene in S. zooepidemicus was not mutated as seen in isolates of Streptococcus pyogenes with increased capsule production at 25°C.
Sensitivity of capsule expression to temperature above 35°C but not HylC by the general population of equine S. zooepidemicus indicates that capsule is not required for extended colonisation nor for opportunist invasion. Instead, capsule production at lower than body temperature may reflect adaptation to life on skin and mucosal surfaces, where hyaluronic acid contributes to adhesion and resistance to desiccation. Pathogenicity of S. zooepidemicus following opportunist invasion is possibly dependent on factors other than capsule that may be co-regulated with HylC. The Summary is available in Chinese - see Supporting information.
马链球菌兽疫亚种可引起马的机会性呼吸道感染及其他感染。其荚膜表达高度可变，且已知会影响对吞噬作用的抗性。大多数在37°C时产生小而干燥菌落的临床分离株在低于35°C的温度下会产生黏液样菌落。
旨在了解马链球菌兽疫亚种的马分离株在低于35°C的温度下荚膜表达增加的分子基础。
横断面观察性研究。
测定马链球菌兽疫亚种菌株在23、30、35和37°C时的荚膜产生情况。通过定量酶联免疫吸附测定法测量23和37°C时的透明质酸酶（HylC）。通过定量逆转录聚合酶链反应测量23和37°C时hasA和hylC的表达。对代表性马链球菌兽疫亚种中的covRS基因进行测序并检查是否存在突变。
随机选择的马链球菌兽疫亚种菌株的菌落在温度变为23°C后变成黏液样或菌落黏液性显著增加。23°C时hasA的表达比37°C时高45至700倍。23°C时hylC的转录比37°C时高2.5至200倍，但培养物中的酶浓度在37°C时显著更高（P<0.05），这表明HylC的产生在转录后受到调控。马链球菌兽疫亚种中的covRS基因没有像在25°C时荚膜产生增加的化脓性链球菌分离株中那样发生突变。
马链球菌兽疫亚种总体上荚膜表达对高于35°C的温度敏感，但对HylC不敏感，这表明荚膜对于长期定植和机会性侵袭并非必需。相反，低于体温时产生荚膜可能反映了对皮肤和黏膜表面生活的适应性，在这些表面透明质酸有助于黏附并抵抗干燥。马链球菌兽疫亚种机会性侵袭后的致病性可能取决于除荚膜外的其他因素，这些因素可能与HylC共同调控。中文摘要见补充信息。
