So should we be worried? CC398 is less harmful to humans than the MRSA strain that kills about 300 people in UK hospitals annually but the article notes that it is highly resistant to antibiotics and can be particularly dangerous to those with compromised immune systems. Fire is hot, water is wet. In fact, human infection is very rare and relatively mild. Good hygiene and thorough cooking will eliminate pretty much all risk.
If we go beyond the senationalist headlines, the real story is the threat of antibiotic resistant organisms is a real worry. Antibiotic use in farming helps promote resistant organisms that – if they infect us – are hard to treat due to lack of effective drugs. MRSA is such an organism and can be fatal if a hospital patient gets a bloodstream infection but these livestock-associated strains seem to be less virulent wehn it comes to infecting humans than other MRSA strains in the past.
Yes, they could mutate but so long as we continue to cook meat properly and observe proper food hygiene practices the risk remains very low.