Minimum Inhibitory Concentration: Salivary Staphylococci from Hospital and Community

Objectives: To compare in vitro Minimum Inhibitory Concentration (MIC) of 6 antibiotics against Staphylococcus spp. The antibiotics analyzed were Oxacillin (OX), Vancomycin (VA), Amoxicillin / Clavulanic acid (XL); Azithromycin (AZ), Cefotaxime (CT), Imipenem (IP). Methods: The Etest system (AB BIODISC, Solna, Sweden) comprises an inert and non-porous plastic strip with a predefined antibiotic gradient which was used to determine the MIC (mg/mL) against 80 staphylococci isolated from saliva of 40 patients hospitalized in an Intensive Therapy Unit (ITU) and 40 community individuals as control group. The microbial suspension equivalent to a 0.5 McFarland scale was inoculated onto Petri plates (15x150mm) with Muller Hinton Agar and the fluid excess was removed and the surface was completely dry before applying the 6 different Etest strips in each Petri plate. The incubation was realized at 35ºC for 18-24 hours considering MIC as the lowest dilution of the antibiotics that inhibited the microbial growth. Results: The results submitted to statistical analysis revealed the great difference between hospital and community staphylococci. From 40 hospital staphylococci, 25 (62.5%) were resistant to OX; 17 (42.5%) to XL; 22 (55.0%) to AZ; 20 (55.0%) to CT and 18 (45.0%) to IP. However, from 40 community staphylococci, only 11 (27.0%) were resistant to AZ. There were no antimicrobial resistance to OX, XL, CT and IP. No Staphylococcus spp. from hospital or community was resistant to vancomycin. Conclusions: Saliva can be source of multiresistant microorganisms. Moreover, the hospital staphylococci were more resistant to antibiotics than those from the community.