Food-derived Staphylococcaceae species with severe antimicrobial resistance, especially Staphylococcus aureus , is a major threat to public health. Macrococcus caseolyticus (M. caseolyticus) is a member of the Staphylococcaceae family which plays a vital role in fermented products and disease causation in animals. In our previous study, several Staphylococcus aureus antibiotic-resistant island msr (SaRI msr) were found in multidrug-resistant S. aureus. In this study, novel SaRI msr , SaRI msr -III emerged from S. aureus. Another novel SaRI msr -like further emerged in M. caseolyticus from food. These isolates' prevalence and genetic environment were investigated and characterized to understand the distribution and transmission of these novel SaRI msr strains. All SaRI msr -positive S. aureus isolates exhibited a multidrug resistance (MDR) phenotype, within which a series of antimicrobial resistance genes (ARGs) and virulence factor genes (VFs) were identified. In addition, three SaRI msr types, SaRI msr -I (15.1 kb), SaRI msr -II (16–17 kb), and SaRI msr -III (18 kb) carrying mef (D)– msr (F), were identified in these isolates' chromosomes. SaRI msr -(I-III) contains a site-specific integrase gene int and operon mef (D)- msr (F). SaRI msr -III has an additional orf 3- orf 4-IS 30 arrangement downstream of mef (D) and msr (F). Moreover, the SaRI msr -like and macrolide-resistant transposon Tn 6776 forming a novel mosaic structure coexisted in one M. caseolyticus isolate. Within this mosaic structure, the macrolide-resistant genes mef (D)– msr (F) were absent in SaRI msr -like, whereas an operon, mef (F)– msr (G), was identified in Tn 6776. The SaRI msr -(I-III) and SaRI msr -like structure were inserted into the rpsI gene encoding the 30S ribosomal protein S9 in the chromosome. Excision and cyclisation of SaRI msr -III, SaRI msr -like, operon mef (D)- msr (F), and orf 3- orf 4-IS 30 arrangements were confirmed using two-step PCR. This study is the first to report MDR S. aureus harbouring novel SaRI msr -III and M. caseolyticus containing novel mosaic structures isolated from retail foods. Similar SaRI msr -type resistant islands' occurrence and propagation in Staphylococcaceae species require continuous monitoring and investigation. • SaRI msr -(I-III) harbouring mef (D)- msr (F) operon and virulence factors emerged in MDR S. aureus. • Novel SaRI msr -like and Tn 6776 carrying mef (F)- msr (G) operon were located in M. caseolyticus. • Novel SaRI msr -III, mef (D)- msr (F) operon and SaRI msr -like were active. • The transferable SaRI msr , SaRI msr -like and Tn 6776 in Staphylococcus and Macrococcus of food origin should be underscored. [ABSTRACT FROM AUTHOR]