Five years of experience with a national external quality control program for the culture and identification of Neisseria gonorrhoeae

Abstract

In response to a need for monitoring the proficiency of public health laboratories in isolating and identifying Neisseria gonorrhoeae, a national external quality control program was developed. Essentially, three types of freeze-dried samples, representing different levels of challenge for identification, were sent to laboratories for testing. The quality of the samples was confirmed by external reference laboratories, and stability of the samples was confirmed by thermal degradation tests before the samples were sent to laboratories enrolled in the program. By analyzing laboratory results, we identified common errors and chronic problems in testing samples. As a group, laboratories testing small numbers of actual patient specimens did not perform as well in the program as did laboratories testing large numbers of specimens; however, the performance of laboratories testing small numbers of specimens improved over time. Overall, laboratories experienced the most difficulty with samples containing N. gonorrhoeae mixed with other microbial species. Laboratories that performed confirmatory tests committed fewer errors than did laboratories that performed presumptive tests only, but the failure to use pure cultures of gonococci for inoculation of cystine tryptic digest agar appeared to be a chronic problem in confirmatory carbohydrate testing. A review of the use of different plating media and confirmatory tests showed that the use of certain media and tests changed over time.

Fluorescent monoclonal antibody for confirmation of Neisseria gonorrhoeae cultures

“…Acid reactions from sugars and nitrate reduction are the standards to which other methods of culture confirmation are compared (7). However, these methods are occasionally compromised by limited or unpredictable growth of N. gonorrhoeae in broth or semisolid media (1,3,10). More rapid methods for identification based on serological reactions and detection of preformed enzymes have been developed but often require subculture of isolates to provide adequate cellular mass for testing (4,9).…”

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

“…In addition to typical strains of N. gonorrhoeae, samples included carbon dioxide-dependent strains, penicillinase-producing strains, and a vancomycin-susceptible strain. Microbial species other than N. gonorrhoeae included in some samples have been described previously (4 Cultures of N. gonorrhoeae were propagated from previously freeze-dried preparations by restoring each of eight vials with 2 ml of Todd Hewitt broth (Difco Laboratories, Detroit, Mich.); the contents of each vial were pooled, and the resulting cell suspension was mixed and diluted to 32 ml with sterile 0.85% NaCl. Each of the eight 75-cm2 tissue culture flasks (Corning Glass Works, Corning, N.Y.), containing 50 ml of Thayer-Martin agar (5) without hemoglobin, was inoculated with 4 ml of the cell suspension.…”

“…During the period 1976 to 1980, 16 lots of samples containing N. gonorrhoeae were sent to laboratories for testing. Of the laboratories reporting results with 4,922 freeze-dried preparations from the 16 lots, there were only 39 (0.8%) reports of no growth of gonococci (4). In such instances it was difficult to state with absolute certainty that the gonococci were nonviable or that unsatisfactory laboratory practices were responsible for these results.…”