DIAGNOSTIC REAGENTS 333 



susceptibility of 10 Shigella strains and one Proteus strain to bacitracin, dihydro- 

 streptomycin, penicillin, Chloromycetin and terramycin. They reported this 

 method could be used to determine if an organism is sensitive, moderately sensi- 

 tive or resistant and concluded that the test was adaptable to a field laboratory 

 or mobile unit. Christensen and Lipsett^^ reported that Bacto-Sensitivity Disks 

 could be satisfactorily used to show the relative sensitivity of a variety of micro- 

 organisms to six antibiotics, using Bacto-Heart Infusion Agar, with or without 

 blood as a test medium. Mitchell, Arnold and Lett^* used Bacto-Sensitivity Disks 

 in their study of the sensitivity of Pseudomonas aeruginosa isolated from external 

 otitis. They reported this method as a quick aid to the physician in his choice of 

 therapy, since the test could be run directly, using the specimen as inoculum. 

 Spaulding and Anderson^^ called attention to the necessity for the determination 

 of the susceptibility of microorganisms to various antibiotics in treating certain 

 types of infections. They described and evaluated a disk technique which is 

 readily performed and within the scope of any laboratory capable of culturing 

 clinical material. The test gives information which is a valuable and often an in- 

 dispensable guide to successful treatment of severe, refractory or relapsing infec- 

 tions. They state that disks are presently available that may be transferred 

 directly to the inoculated plate and are admirably suited to the needs of the 

 clinical laboratory. Bacto-Sensitivity Disks are of this type, containing known 

 amounts of the various antibiotics, thus eliminating the need of making standard- 

 ized solutions of the antibiotics. 



Pike, Schulze and McCullough^^ using Bacto-Tryptose Agar and Bacto-Sensi- 

 tivity Disks determined the sensitivity of Mima polymorpha, isolated from a 

 patient, and reported prompt recovery upon administration of the selected anti- 

 biotic. Lind and Swanton^^ reported that the Disk method of determining 

 whether an organism is sensitive to one or more antibiotics is reliable, relatively 

 inexpensive, rapid and when used as a guide to therapy is of definite value to the 

 physician and patient. Trafton and Lind^^ in a study of urinary infections pointed 

 out that sensitivity testing by the Disk method permitted a rapid, accurate and 

 inexpensive determination of the susceptibility of microorganisms to the various 

 antibiotics. They suggested that physicians should be encouraged to use these 

 tests routinely and reported clinical data showing that the Disk method gives a 

 fairly reliable guide to prognosis when selecting an antibiotic. Fusillo and 

 Kuhns,^^ using Bacto-Sensitivity Disks described a method for antibiotic sensi- 

 tivity testing using one concentration of each antibiotic with a single plate of 

 medium to give the entire antibiotic sensitivity spectrum thereby saving time, 

 media and equipment. Broom, Martineau and Young^o used Bacto-Sensitivity 

 Disks in determining the sensitivity of organisms in their evaluation study of the 

 Disk Method in treating 100 clinical cases. Their results showed the indispensa- 

 bility of sensitivity testing from the clinical standpoint and demonstrated the 

 practicability of the disk technique in routine diagnosis. Koch and Bourgeoises- 

 reported increased resistance of staphylococci to penicillin as well as aureomycin 

 and terramycin. They used Bacto-Sensitivity Disks in determining the resistance 

 of staphylococci and showed that the Disk Method correlated in every instance 

 with results obtained by the two fold tube dilution technique. Gould and Bowlegs 

 in a study of the determination of bacterial sensitivity to antibiotics reported the 

 Disk technique to be more accurate than "ditch and cylinder" methods, and less 

 tedious. They pointed out that the serial dilution tube method is much more 

 laborious than the Disk method, and subject to more errors. Closely similar re- 

 sults were obtained when the Disk method was carried out in parallel with the 

 serial dilution tube method and reported that the Disk technique is as accurate 

 as the more complicated tube dilution method for all purposes. They expressed 

 their results as "sensitive, relatively resistant and resistant," and stated this suffices 



