Comparative virulence studies and transcriptome analysis of Staphylococcus aureus strains isolated from animals

Staphylococcus aureus can infect a wide range of animals and pose as a serious threat to public health by transferring via animals or animal-derived food stuff. Even more importantly, multiple drug resistance development in the bacteria has resulted in therapeutic failure of a number of antibiotics. Therefore by realizing the need of time, this study was designed to investigate the underlying mechanisms of virulence and resistance in S. aureus. After screening through in vivo and in vitro virulence assays and susceptibility test, a highly virulent and multidrug resistant MRSA strain was selected for differential analysis by RNA-seq technology and gene expression results were verified by RT-qPCR. Up-regulation of crucial regulators like sarA and KdpDE seemed to play role in decreased expression of many exotoxin genes while enhanced the adhesion and cell wall protein expression, leading to strong biofilm production in the presence of inactivated agr system. In addition to resistance genes like blaZ, ermC and femA, up-regulation of vraS and multidrug ABC transporter genes contributed to the multidrug resistance in MRSA. Fluoroquinolone resistance was attributed to mutational changes in gyrA and parC genes. Our findings suggested that many virulence and resistance determinants in S. aureus are controlled by complex network of various regulators, and sarA is the most important of those as it adds to pathogenicity of the bacteria and ensures its survival in diverse environment. Further investigations are required to unveil these mechanisms in S. aureus. Overall design: Four samples were analysed including 2 MRSA1679a test strain and 2 reference strain ATCC1 samples with two replicates of each.