β-lactam Antibiotics Stimulate the Pathogenicity of Methicillin-resistant Staphylococcus aureus Via SarA-controlled Tandem Lipoprotein Expression

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a leading cause of nosocomial infections worldwide. MRSA resists nearly all {beta}-lactam antibiotics that have a bactericidal activity and a signal inducer effect. However, studies have yet to clarify whether the inducer effect of empirically used {beta}-lactams stimulates MRSA pathogenicity in vivo. Here, we showed that a new cluster of tandem lipoprotein genes (tlpps) was upregulated in MRSA in response to the subinhibitory concentrations of {beta}-lactam induction. The increased Tlpps significantly altered immune responses by macrophages with high IL-6 and TNF levels. The deletion of the tlpps mutant (N315{Delta}tlpps) significantly decreased the proinflammatory cytokine levels in vitro and in vivo. The bacterial loads of N315{Delta}tlpps in the mouse kidney were also reduced compared with those of the wild type N315. The {beta}-lactam-treated MRSA exacerbated cutaneous infections with increased lesion size, extended illness, and flake-like abscess-formation compared with those of the nontreatment. The {beta}-lactam antibiotics that promoted the MRSA pathogenicity were SarA dependent, and the increasing expression of tlpps after {beta}-lactam treatment was directly controlled by the global regulator SarA. Overall, our findings suggested that {beta}-lactams should be used carefully because it might lead to a worse outcome of MRSA infection than inaction in the treatment.\n\nAuthor summary{beta}-lactams are widely used in practice to treat infectious diseases, however, {beta}-lactams worsening the outcome of a certain disease is poorly understood. In this study, we have identified a new cluster of tandem lipoprotein genes (tlpps) that is upregulated in the major clinically prevalent MRSA clones in response to the subinhibitory concentrations of {beta}-lactams induction. The major highlight in this work is that {beta}-lactams induce SarA expression, and then SarA directly binds to the tlpp cluster promoter region and upregulates the tlpp expression in MRSA. Moreover, the {beta}-lactam stimulated Tlpps are important virulence factors that enhance MRSA pathogenicity. The deletion of the tlpps mutant significantly decreases the proinflammatory cytokine levels in vitro and in vivo. The {beta}-lactam induced Tlpps enhance the host inflammatory responses by triggering the expression of IL-6 and TNF, thereby promoting bacterial colonization and abscess formation. These data elucidate that {beta}-lactams can worsen the outcome of MRSA infection through the induction of tlpps that are controlled by the global regulator SarA.