Preparation and stability of freeze-dried Neisseria gonorrhoeae cultures used for external quality control

Abstract

In 1976, the Centers for Disease Control initiated an external quality control program for the isolation and identification of Neisseria gonorrhoeae. This program required microbial samples of sufficient stability for shipment to laboratories throughout the United States. The Centers for Disease Control undertook studies to determine the most appropriate media for the propagation of strains for freeze-drying, the cell-suspending media that would afford protection during and after freeze-drying, the most favorable growth conditions, the proper times and methods for harvesting cells, the appropriate lyophilization conditions, the critical residual moisture content, and the stability of samples. These studies resulted in the development of methods for preparing and testing freeze-dried samples suitable for shipment.

Survival Rate of Microbes after Freeze-Drying and Long-Term Storage

“…This method satisfied most of the conditions for good freeze-drying survival rates (i.e., preservation of fluids, culture age, etc.) (2,4,5). Drying ampoules were sealed with a gas burner, and the vacuum was checked with a high-frequency spark tester.…”

Centers for Disease Control performance evaluation program in bacteriology: 1980 to 1985 review

“…The results of thermal degin PE samples were reported previously (5). The results radation testing (11) showed that the concentration of reported by participants for seven selected samples of gram-gonococci was >106 CFU/ml after exposure of freeze-dried negative cocci are presented in Table 4. The percentage of vials to 35°C for 7 days.…”

“…Samples for PE. All samples were prepared by CDC personnel and freeze-dried (6,11). Samples were planned on an annual basis to contain species representative of six major groups of bacteria.…”

“…Quality control of PE samples. The methods used for the quality control of the bacteriology PE samples have been reported elsewhere (6,11). After internal testing at CDC, representative vials of all lots or batches of samples were sent first to a group of 8 to 10 reference laboratories for validations of their quality before samples were sent to regular participants.…”

Relationship between performance in three of the Centers for Disease Control microbiology proficiency testing programs and the number of actual patient specimens tested by participating laboratories

“…After freeze-drying, representative vials of each lot of samples were subjected to quality control testing. Testing consisted of (i) checking the vacuum in the vials; (ii) determining the CFU per milliliter with appropriate noninhibitory and selective media, if applicable; (iii) conducting thermal degradation tests (11); (iv) performing characterization tests; and (v) determining residual moisture content. Thermal degradation tests were conducted by placing samples at elevated temperatures (e.g., 35 to 55°C) to simulate deleterious shipment conditions and to ensure the quality of the samples upon receipt by participant laboratories.…”