Smith Amanda J, Ward Philip N, Field Terence R, Jones Catherine L, Lincoln Ruth A, Leigh James A
Institute for Animal Health, Compton Laboratory, Compton, Newbury, Berks RG20 7NN, United Kingdom.
Infect Immun. 2003 Sep;71(9):4842-9. doi: 10.1128/IAI.71.9.4842-4849.2003.
A mutant strain of Streptococcus uberis (AJS001) that was unable to grow in bovine milk was isolated following random insertional mutagenesis. The level of growth in milk was restored to that of the parental strain (strain 0140J) following addition of MnSO(4) but not following addition of other metal ions. The mutant contained a single insertion within mtuA, a homologue of mtsA and psaA, which encode metal-binding proteins in Streptococcus pyogenes and Streptococcus pneumoniae, respectively. Strain AJS001 was unable to infect any of eight quarters on four dairy cows following intramammary challenge with 10(5) CFU. Bacteria were never recovered directly from milk of these animals but were detected following enrichment in Todd-Hewitt broth in three of eight milk samples obtained within 24 h of challenge. The animals showed no inflammatory response and no signs of mastitis. Three mammary quarters on two different animals simultaneously challenged with 600 CFU of the parental strain, strain 0140J, became colonized, shed high numbers of S. uberis organisms in milk, displayed a marked inflammatory response to infection, and showed overt signs of mastitis. These data indicate that mtuA was required for efficient uptake of Mn(2+) during growth in bovine milk and infection of the lactating bovine mammary gland.
通过随机插入诱变分离出一株乳房链球菌突变株（AJS001），该菌株无法在牛乳中生长。添加硫酸锰后，其在牛奶中的生长水平恢复到亲代菌株（0140J菌株）的水平，但添加其他金属离子后则未恢复。该突变体在mtuA内有一个单一插入，mtuA是mtsA和psaA的同源物，它们分别在化脓性链球菌和肺炎链球菌中编码金属结合蛋白。用10⁵CFU进行乳房内攻毒后，AJS001菌株无法感染四头奶牛的八个乳腺中的任何一个。从未直接从这些动物的乳汁中分离到细菌，但在攻毒后24小时内采集的八个乳汁样本中有三个在托德-休伊特肉汤中富集后检测到了细菌。这些动物没有炎症反应，也没有乳腺炎的迹象。用600CFU亲代菌株0140J同时攻毒两只不同动物的三个乳腺，这些乳腺被定殖，乳汁中排出大量乳房链球菌，对感染表现出明显的炎症反应，并出现明显的乳腺炎迹象。这些数据表明，mtuA是在牛乳中生长和感染泌乳期奶牛乳腺过程中有效摄取锰离子所必需的。
