Comparative in vitro antibiotic resistance of surface-colonizing coagulase-negative staphylococci

Abstract

The MBCs of nafcillin, vancomycin, gentamicin and daptomycin (LY146032) were determined for three clinical isolates of coagulase-negative staphylococci grown in suspension and adherent to biomaterials. Strains studied were the slime-producing strain Staphylococcus epidermidis RP-12 (ATCC 35983), S. hyicus SE-360, and the non-slime-producing strain S. hominis SP-2 (ATCC 35982). All three strains were allowed to colonize surgical-grade disks of stainless steel, polymethylmethacrylate, and ultrahigh-molecular-weight polyethylene for 24 h, and the disks were then exposed to various concentrations of antibiotics for 24 h. Surviving adherent bacteria were mechanically dislodged from the disks and quantitated by standard broth dilution plating techniques. Biomaterial-adherent RP-12 and SE-360 yielded approximately 10 times more CFU per disk than non-slime-producing SP-2 did. For all organisms, 10 times more bacteria bound to polymethylmethacrylate disks than to the other biomaterials. In general, bacteria adherent to biomaterials exhibited greater resistance to antibiotics than the same strains in suspension did. Resistance was independent of bacterial slime-producing characteristics and was related to the biomaterial colonized.Biomaterial-centered infections are characterized by the following features: (i) a biomaterial or damaged tissue substratum; (ii) adhesive, frequently polymicrobial bacterial colonization; (iii) persistence of infection until the substratum is removed; (iv) resistance to host defense mechanisms and antibiotic treatment; (v) specificity of materials, organisms, and location; and (vi) transformation of autochthonous or opportunistic organisms to virulent pathogens (18).Mechanisms of antibiotic resistance have not been well characterized. A biofilm barrier effect has been proposed (4,5,7,16,30). Studies have shown that when organisms are grown in suspension they are susceptible to lower concentrations of antibiotics than when they are in surface-adherent, biofilm-enclosed populations (4,5,16,20,24). The selection of therapeutic antibiotics is usually based on standard suspension culture MIC and MBC studies. In this study, antibiotic susceptibilities of organisms grown in suspension and on biomaterials were examined.The ability of antibiotics to kill coagulase-negative staphylococci is clinically important, since studies have shown that staphylococci are major colonizers of surgical biomaterials, including heart valves, intravascular catheters, and orthopedic appliances (la, 6). Prosthetic infections are generally resistant to antibiotic therapy and frequently require removal of the implant before eradication of the infection is possible (12-19).Both coagulase-positive and coagulase-negative staphylococci have been reported as causes of biomaterial-centered infections, with a tendency for coagulase-negative species to be associated with polymer-sited infections (2,12,15,26 (2,21). RP-12 is an adherent slime producer, whereas strain SP-2 has been reported to be nonadherent to smooth, inert surfaces a...

Correlation between In Vivo and In Vitro Efficacy of Antimicrobial Agents against Foreign Body Infections

“…Ciprofloxacin again had the lowest activity. Gristina et al [29] had similar findings with another method. They recently showed that adherent coagulase-negative staphylococci have generally higher MBCs than do planktonic bacteria.…”

Genetic determinants and biofilm formation of clinicalStaphylococcus epidermidisisolates from blood cultures and indwelling devises

“…The comparison between the different specimens is not equivalent, since 64 isolates were from blood cultures and only 13 isolates were recovered from implants. The isolates in our study and elsewhere, which produced biofi lm, were less susceptible toward a number of antibiotics [32][33][34][35][36]. A possible reason for the higher antibiotic resistance may be the reduced growth of the bacteria within the biofi lm or the insuffi cient uptake of antibiotics [37].…”

Cortical allograft as a vehicle for antibiotic delivery

“…The inoculum used in this study (0.6 × 10 5 CFU) is comparable to that used in other surface-colonizing infection models (Gristina et al 1989, Zimmerli et al 1994). According to our in vitro study, the peak ciprofloxacin concentration was approximately 150 times the MIC for S. aureus ATCC 25923 when ciprofloxacin was eluted from bone impregnated for 10 h. By comparison, the peak concentrations of netilmicin, vancomycin and rifampicin were 7,700, 360 and 24,000 times the respective MICs for S. aureus ATCC 25923, respectively.…”