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Date of Award


Document Type


Degree Name

Master of Science (M.S.)


Graduate School

First Advisor

Fuad Nahhas

First Committee Member

Kishori Chaubal

Second Committee Member

Richard Tenaza

Third Committee Member

Alice Hunter


Susceptibility of 112 strains of Staphylococcus aureus obtained from Dameron Hospital, Stockton, California was tested with 18 antimicrobials . The MIC method was used with the following antimicrobials : tetracycline, oxacillin, penicillin, ampicillin, vancomycin, cefazolin, erythromycin, clindamycin, gentamycin, rifampin, trimethoprimsulfamethoxazole, chloramphenicol, and cefotaxime . The standard Kirby-Bauer disc diffusion method was used to test neomycin, tobramycin, and amikacin . Methicillin, oxacillin, and nafcillin were tested with a modified Kirby-Bauer method, which included the addition of a 4% salt supplement to the media, incubation at 32C, and readings at both 24 and 48 hours. Comparing results of this study with those of Hall (1975), suggested that resistance to the following antibiotics has increased: penicillin, ampicillin, erythromycin, neomycin, gentamycin, methicillin, oxacillin, nafcillin, cefazolin, and clindamycin . Resistance to tetracycline has decreased. No resistance to chloramphenicol or vancomycin was encountered in either study . Of the 112 strains studied, 13 . 4% were susceptible to all antibiotics tested. Twelve patterns of resistance were identified : 0 . 9% were resistant to neomycin only, 1.8% to erythromycin only, 63.9% to both penicillin and ampicillin, and 20 . 0% were multiply- resistant . Nine patterns of multiple-resistance were found, involving a minimum of three antibiotics and a maximum of nine . Three MRSA strains were identified from out-patient isolates; no in-patient isolates were methicillin-resistant . The study suggests that MRSA strains are not a problem at Dameron Hospital, but identification of this group would be more accurate if incubation of the MIC panels is maintained for at least 24 hours at ~35C . It was found that the MIC method of antimicrobial susceptibility testing is more reliable than the Kirby-Bauer disc diffusion method for detection of methicillin-resistance. Problems involved in identification of heteroresistant staphylococci are discussed .





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