BACTERIAL ISOLATES FROM PATIENTS WITH CHRONIC OTITIS MEDIA AND CHANGES IN THEIR ANTIMICROBIAL SUSCEPTIBILITY WITH ASSAY INOCULUM SIZE
1978 Volume 81 Issue 9 Pages 899-906
Details
1978 Volume 81 Issue 9 Pages 899-906
Bacterial counts in otorrhea from 20 patients with chronic otitis media were studied.
Samples of aural discharge were collected using a platinum loop with an inner diameter of 2 mm, each loopful of liquid measuring 0.01 ml. And antimicrobial susceptibility test was performed on 36 strains of six bacterial species isolated from otorrhea in patients with chronic otitis media. The inoculum size were 106 and 108 cells per ml.
The results were as follows:
1) The bacterial counts of otorrhea ranged from 107 to 109 per ml for Staph. aureus, Corynebacterium, Pseudomonas aeruginosa, Proteus mirabilis and Proteus inconstans.
2) The Staph. epidermidis count showed a biphasic distribution with ranges from 105 to 106 cells per ml and from 103 cells per ml downward.
3) Staph. aureus and Staph. epidermidis strains proved resistant to penicillin G as well as to aminobenzylpenicillin when assayed using suspension of 108 cells per ml and susceptible to those drugs as assessed using suspensions of 106 cells per ml.
4) With one of the five strains of Proteus inconstans tested, the reactivity to aminobenzylpenicillin and to cefazolin was noted to vary from susceptible to resistant with the concentration of bacterial cells in the MIC assay suspension.
5) The results of the present study indicate that it is advisable to use an assay suspension of a bacterial isolate from chronic otitis media at concentration of 108 cells/ml rather than 106 cells/ml in the antimicrobial susceptibility test so that discrepancy often encountered between the results of the laboratory test and the clinical response to antimicrobial chemotherapy may be minimized.
