Possibility of application of the disk diffusion method for studying the sensitivity of coagulase-negative staphylococcus to ceftaroline

Ceftaroline is a modern broad-spectrum antibiotic (generation V of cephalosporin), an active metabolite of ceftaroline fosamil. The bactericidal effect of the drug is due to its high affinity of penicillin-binding protein PSP2a (mecA gene), which is responsible for the resistance of staphylococcus strains to methicillin. To determine the antibiotic sensitivity of microorganisms in the bacteriological laboratories of the Russian Federation, the disk diffusion method is widely used, which determines the sensitivity categories as resistant, moderately resistant, or sensitive. However, for several antibacterial drugs, including ceftaroline, criteria for assessing the efficiency only for Staphylococcus aureus are regulated, although coagulase-negative staphylococci (CoNS) are capable to cause various nosocomial infections and are a reservoir of mobile genetic elements determining staphylococci resistance to beta-lactam antibiotics. In cases of testing the sensitivity of CoNS to ceftaroline without established criteria for sensitivity/resistance, doctors cannot interpret the results reliably. In our study, we analyzed the sensitivity of 227 strains of seven CoNS species to ceftaroline. In 93.4% of cases, Staphylococcus epidermidis cultures were identified, and Staphylococcus saprophyticus and Staphylococcus lungdunensis were detected in 3.1% and 2.2% of cases, respectively. Based on the difference in the control points for cefoxitin for S. aureus and S. epidermidis, we proposed options for evaluating the sensitivity/resistance to ceftaroline for CoNS strains. In accordance with these criteria, 88.4% of the cultures selected demonstrated sensitivity to the drug. Moreover, 97.5% of the strains of methicillin-sensitive S. epidermidis were sensitive to ceftaroline, and only 2.5% were moderately resistant. Resistance to ceftaroline was demonstrated by 4.5% of methicillin-resistant S. epidermidis isolates, which in turn were characterized by poly- and pan-resistance. Representatives of the other six species being studied were sensitive to ceftaroline in 100% of cases. The results confirm the high activity of ceftaroline against CoNS. The proposed evaluation criteria interpreted the results more accurately, supplemented the existing antibioticograms, and used ceftaroline in treatment of infections caused by such bacteria.