The use of the oxidase test for enumerating psychrophilic bacteria in cottage cheese

The 75 samples of Cottage cheese secured from manufacturers and retail outlets in Tennessee over a period of six months were analyzed to determine whether the oxidase count of the Standard Plate Count was a true reflection of the Psychrophilic Plate Count obtained by the standard procedure. The purpose of this investigation was also aimed to consider the feasibility of the oxidase test as a substitute to standard procedure for enumerating psychrophilic bacteria.

Analysis of the data with paired t test indicated the presence of a highly significant difference between the oxidase test and the standard procedure. Observations revealed that oxidase positive organisms constituted only 38 percent of the Standard Plate Count and 17 percent of the Psychrophilic Plate Count. Some of the psychrophilic plates containing more than one million psychrophiles per gram of cheese were negative for oxidase test.

The study gave an impression that oxidase test was not giving a true representation of psychrophilic microorganisms involved in the spoilage of Cottage cheese. This investigation also raised the question whether all Pseudomonas organisms involved in the spoilage of Cottage cheese are capable of showing the oxidase positive characteristic.