Activities of Ceftobiprole and Other Cephalosporins against Extracellular and Intracellular (THP-1 Macrophages and Keratinocytes) Forms of Methicillin-Susceptible and Methicillin-ResistantStaphylococcus aureus

Abstract

Restricted to the hospital setting for many years, the methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) epidemic is now reaching an increasing variety of other environments (12), such as patients in the community in various parts of the world (16,35,41) and animals (21, 40). Beyond its spectacular ability to adapt and to develop resistance to most antimicrobial agents (9), including drugs of last resort, such as vancomycin, linezolid, and daptomycin (5, 28, 31), the capacity of S. aureus to invade, sojourn, and thrive intracellularly (8, 23, 34) creates an additional challenge since intracellular forms tend to be poorly susceptible to most available antibiotics (38). Evaluations of new antistaphylococcal agents directed against resistant S. aureus strains must therefore include an assessment of their ability to control intracellular infections. While animal models of staphylococcal infection are being developed (32), models of cultured cells remain useful because they offer the possibility to explore in detail the pharmacological parameters governing the response of the intracellular bacteria to the drug in the absence of host factors (7,38). In this context, we observed that, contrary to most original assumptions (36), the poor accumulation of ␤-lactams in phagocytic cells does not preclude the observation of significant activity against intracellular methicillin-susceptible S. aureus (MSSA). This is actually dependent on the time of exposure (12 to 24 h) and whether the extracellular concentration is maintained at a sufficiently large but still clinically pertinent level (7,20). We previously reported that intraphagocytic MRSA isolates regain almost full susceptibility to penicillins and carbapenems, due to the acidic pH prevailing in phagolysosomes (19). This finding has been rationalized by the observation that acidic pH improves the accessibility to and the acylation of PBP 2a by penicillins within a time frame relevant to the growth rate of MRSA through protein conformational changes (17). This triggered us to study ceftobiprole in this context. Ceftobiprole, also known as BAL9141 and Ro 63-9141 (4), is the first clinically developed cephalosporin that shows almost similar activities against MRSA and MSSA isolates in conventional in vitro tests (15,42). It has now been approved for clinical use in some countries and has been studied in a large array of preclinical and clinical settings (see references 3 and 43 for recent reviews).

Interaction of Ceftobiprole with the Low-Affinity PBP 5 of Enterococcus faecium

“…The membrane fractions were subjected to SDS-PAGE and fluorography. ), produced and purified in our laboratory (14). The sPBP 5fm-ceftobiprole adduct was very stable.…”

Importance of Relating Efficacy Measures to Unbound Drug Concentrations for Anti-Infective Agents

“…The ability of an antibiotic to accumulate intracellularly is studied in vitro by using specific target cells (e.g., macrophages, polymorphonuclear neutrophils, and lung parenchyma cells) and/or in vivo, for example, by using a murine peritonitis infection model (64)(65)(66)(67). In vivo studies provide an opportunity to evaluate drug distribution to the target site and the immune system's response to an infection.…”

Activity of Ceftaroline against Enterococcus faecium PBP5

“…3, the secondorder rate constant k ϩ2 /K for ceftaroline was 950 Ϯ 70 M Ϫ1 s Ϫ1 , i.e., 50 to 100 times higher than the value reported for benzylpenicillin (15 to 24 M Ϫ1 s Ϫ1 ), which indicates that ceftaroline inactivates sPBP5 much faster than benzylpenicillin (5) and faster than ceftobiprole, another anti-MRSA cephalosporin (k ϩ2 /K ϭ 110 Ϯ 10 M Ϫ1 s Ϫ1 [13]). While the inhibitory activity of ceftaroline for E. faecium PBP5 is significant, the k ϩ2 /K rate constant for sPBP5 is 15 to 25 times lower than those determined for MRSA PBP2a (23,600 Ϯ 2,000 M Ϫ1 s Ϫ1 [unpublished data]) produced and purified in our laboratory (19) and for the penicillin-resistant Strep- tococcus pneumoniae PBP2x (12,600 M Ϫ1 s Ϫ1 ) (20). The sPBP5-ceftaroline adduct was very stable.…”