Present Address: Center for Molecular and Cellular Biosciences, The University of Southern Mississippi, 118 College Drive # 5018, Hattiesburg, MS, 39406, USA.
Department of Orthopaedics, University of Mississippi Medical Center, Jackson, MS, USA.
BMC Microbiol. 2020 Oct 27;20(1):324. doi: 10.1186/s12866-020-01964-8.
The msaABCR operon regulates several staphylococcal phenotypes such as biofilm formation, capsule production, protease production, pigmentation, antibiotic resistance, and persister cells formation. The msaABCR operon is required for maintaining the cell wall integrity via affecting peptidoglycan cross-linking. The msaABCR operon also plays a role in oxidative stress defense mechanism, which is required to facilitate persistent and recurrent staphylococcal infections. Staphylococcus aureus is the most frequent cause of chronic implant-associated osteomyelitis (OM). The CA-MRSA USA300 strains are predominant in the United States and cause severe infections, including bone and joint infections.
The USA300 LAC strain caused significant bone damage, as evidenced by the presence of severe bone necrosis with multiple foci of sequestra and large numbers of multinucleated osteoclasts. Intraosseous survival and biofilm formation on the K-wires by USA300 LAC strains was pronounced. However, the msaABCR deletion mutant was attenuated. We observed minimal bone necrosis, with no evidence of intramedullary abscess and/or fibrosis, along reduced intraosseous bacterial population and significantly less biofilm formation on the K-wires by the msaABCR mutant. microCT analysis of infected bone showed significant bone loss and damage in the USA300 LAC and complemented strain, whereas the msaABCR mutant's effect was reduced. In addition, we observed increased osteoblasts response and new bone formation around the K-wires in the bone infected by the msaABCR mutant. Whole-cell proteomics analysis of msaABCR mutant cells showed significant downregulation of proteins, cell adhesion factors, and virulence factors that interact with osteoblasts and are associated with chronic OM caused by S. aureus.
This study showed that deletion of msaABCR operon in USA300 LAC strain lead to defective biofilm in K-wire implants, decreased intraosseous survival, and reduced cortical bone destruction. Thus, msaABCR plays a role in implant-associated chronic osteomyelitis by regulating extracellular proteases, cell adhesions factors and virulence factors. However additional studies are required to further define the contribution of msaABCR-regulated molecules in osteomyelitis pathogenesis.
msaABCR 操纵子调节多种葡萄球菌表型，如生物膜形成、荚膜产生、蛋白酶产生、色素沉着、抗生素耐药性和持久细胞形成。msaABCR 操纵子通过影响肽聚糖交联来维持细胞壁完整性。msaABCR 操纵子在氧化应激防御机制中也发挥作用，这对于促进葡萄球菌的持续和反复感染是必需的。金黄色葡萄球菌是慢性植入物相关骨髓炎（OM）最常见的原因。CA-MRSA USA300 株在美国占主导地位，引起严重感染，包括骨和关节感染。
USA300 LAC 株引起明显的骨损伤，表现为严重的骨坏死，伴有多个病灶的死骨和大量多核破骨细胞。USA300 LAC 株在 K 线内的存活和生物膜形成明显。然而，msaABCR 缺失突变体则减弱。我们观察到最小的骨坏死，没有证据表明骨髓内脓肿和/或纤维化，同时减少骨髓内细菌种群和显著减少 K 线内的生物膜形成msaABCR 突变体。受感染骨的 microCT 分析显示，USA300 LAC 和互补株的骨丢失和损伤明显，而 msaABCR 突变体的作用则降低。此外，我们观察到在 K 线周围感染骨的成骨细胞反应增加和新骨形成。msaABCR 突变体细胞的全细胞蛋白质组学分析显示，与成骨细胞相互作用并与金黄色葡萄球菌引起的慢性 OM 相关的蛋白质、细胞粘附因子和毒力因子的表达显著下调。
本研究表明，USA300 LAC 株中 msaABCR 操纵子的缺失导致 K 线植入物中的生物膜缺陷、减少骨髓内存活和减少皮质骨破坏。因此，msaABCR 通过调节细胞外蛋白酶、细胞粘附因子和毒力因子在植入物相关慢性骨髓炎中发挥作用。然而，需要进一步的研究来进一步确定 msaABCR 调节的分子在骨髓炎发病机制中的作用。
