在培養液稀釋法(broth dilution susceptibility test)中,偵測methicillin-resistant staphylococci需於Mueller-Hinton培養基中額外添加何物?
2% NaCl
2% \mathrm{MgCl}_{2}
\mathrm{MgCl}_{2}
5% NaCl
5% \mathrm{MgCl}_{2}