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SUSCEPTIBILITY TESTING WITH DISC DIFFUSION FOR NEW CEPHALOSPORINS: PRE‐DIFFUSION REVISITED
Author(s) -
FrimodtMØLler NIELS,
Hvass ERIK,
HØJbjerg TOVE,
MØLler SUSANNE,
Mortensen IDA,
Thomsen VILLY FRØLUND
Publication year - 1986
Publication title -
acta pathologica microbiologica scandinavica series b: microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.909
H-Index - 88
eISSN - 1600-0463
pISSN - 0108-0180
DOI - 10.1111/j.1699-0463.1986.tb03036.x
Subject(s) - diffusion , cephalosporin , ceftriaxone , ceftazidime , effective diffusion coefficient , agar diffusion test , chemistry , dilution , agar dilution , agar , microbiology and biotechnology , bacteria , minimum inhibitory concentration , antibiotics , biology , medicine , physics , thermodynamics , antibacterial activity , genetics , radiology , magnetic resonance imaging , pseudomonas aeruginosa
The purpose of the present study was to investigate the effect of 20‐hour pre‐diffusion, i.e. placing the antibiotic‐containing discs on the agar for 20 hours prior to inoculation, as compared to direct diffusion, i.e. placing the discs on the agar immediately after inoculation, for the newer 3. generation cephalosporins as represented by ceftazidime and ceftriaxone. Regression lines (zone sizes vs. inhibitory concentrations, as measured by plate‐dilution) were constructed for three groups of bacteria chosen because of their differences in growth characteristics on agar: E. coli (n = 50), Enterobacter sp. (n = 35), and streptococci (n = 51). The results for both cephalosporins were: 1) 20‐hour pre‐diffusion produced larger zones than direct diffusion, 2) regression studies for 20‐hour pre‐diffusion as compared to direct diffusion resulted in greater variation in zone sizes, numerically lower slopes, lower residual variances and higher correlation coefficients, and 3) regression lines were significantly different for the 3 groups of bacteria with direct diffusion but not so with 20‐hour pre‐diffusion. Considering the interpretation of zone sizes with disc diffusion for the cephalosporins tested, 20‐hour pre‐diffusion was superior to direct diffusion.