The prevalence of proline iminopeptidase negative Neisseria gonorrhoeae throughout England and Wales

Evaluation of the utility and cost of secondary confirmatory testing for Neisseria gonorrhoeae identification from culture

Current guideline recommends the use of two identification methods for Neisseria gonorrhoeae. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) is now used for primary identification and may be sufficient for definitive identification of N. gonorrhoeae. The performance of three secondary tests (BactiCard, RapID NH and NET test) were compared using 45 bacterial isolates, including 37 Neisseria species. These secondary tests demonstrated diminished specificity (67% - 88%) for N. gonorrhoeae compared with MALDI-TOF. Additionally, data from six clinical microbiology laboratories was used to compare confirmatory test costs and the agreement of results with MALDI-TOF. Discrepancies were documented for 9.4% of isolates, though all isolates (n= 288) identified by MALDI-TOF as N. gonorrhoeae were confirmed by the reference laboratory. These data demonstrate that MALDI-TOF alone is sufficient for N. gonorrhoeae identification, as secondary did not add diagnostic value but do add costs to the testing process.

Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry for the identification of Neisseria gonorrhoeae

Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS) was compared with the API NH biochemical method for the identification of Neisseria gonorrhoeae in routine clinical samples. A retrospective review of laboratory records for 1090 isolates for which both biochemical and MALDI-TOF MS identifications were available was performed. Cases of discrepant results were examined in detail for evidence supportive of a particular organism identification. Of 1090 isolates, 1082 were identified as N. gonorrhoeae by API NH. MALDI-TOF MS successfully identified 984 (91%) of these after one analysis, rising to 1081 (99.9%) after two analyses, with a positive predictive value of 99.3%. For those isolates requiring a repeat analysis, failure to generate an identifiable proteomic signature was the reason in 76% of cases, with alternative initial identifications accounting for the remaining 24%. MALDI-TOF MS identified eight isolates as N. gonorrhoeae that were not identified as such by API NH-examination of these discrepant results suggested that the MALDI-TOF MS identification may be the more reliable. MALDI-TOF MS is at least as accurate and reliable a method of identifying N. gonorrhoeae as API NH. We propose that MALDI-TOF MS could potentially be used as a single method for N. gonorrhoeae identification in routine cases by laboratories with access to this technology.

Identification of prolyliminopeptidase-negative Neisseria gonorrhoeae strains in Canada

Neisseria gonorrhoeae strains that fail to produce the enzyme prolyliminopeptidase have been identified in Canada. Commercial test panels use prolyliminopeptidase activity for identification and to avoid the misdiagnosis of gonorrhea, at least 2 distinct methods for the confirmatory identification of N. gonorrhoeae is imperative.

Prevalence, phenotypic and genetic characteristics of prolyliminopeptidase-negative Neisseria gonorrhoeae isolates in Sweden during 2000-2007

In Neisseria gonorrhoeae culture diagnostics, species confirmation is commonly performed using commercial biochemical tests relying on prolyliminopeptidase (PIP) activity. It was previously shown that one PIP-negative strain was mainly globally transmitted during 2000-2004. The aims were to investigate the prevalence and phenotypic and genetic characteristics of PIP-negative N. gonorrhoeae isolates in Sweden during 2000-2007. Gonococcal isolates (n = 1230) cultured in Sweden during 2000-2007 were characterized using PIP screening, antibiogram, serovar determination, pip and porB gene sequencing, and N. gonorrhoeae multiantigen sequence typing (NG-MAST). Fifteen (1.2%) of the isolates were PIP-negative. Of those, 13 (87%) were indistinguishable to the previously described globally transmitted strain, i.e. displayed serovar IB-4 (Bpyvut), similar antibiograms, ST210 (n = 10)/ST292 (n = 3) and contained an identical single nucleotide pip gene deletion. Wherever high reliance is placed on PIP activity for N. gonorrhoeae species confirmation, changes in the diagnostic strategies may need to be considered and/or monitoring of the PIP activity is crucial.