Introduction Isolation of Neisserias and other related microorganisms from genital and extra genital sites require the identification of clinically important isolates and represent a challenge in low-complexity clinical microbiology laboratories. A presumptive Neisseria gonorrhoeae (Ng) identification includes the Superoxol test (Spx) among others. Ng produces levels of catalase activity that are stronger than others Neisseria spp. Spx is a simple and inexpensive test that uses 30% hydrogen peroxide as a reagent. Superoxol reaction with Ng is typically ”explosive” compared to weaker reactions of other species. The objective is to report the finding of N. gonorrhoeae superoxol test negative over 25 years in Argentina.
Methods We studied 8047 isolates derived from the GASPP-AR for susceptibility studies between 1990 and 2015. Presumptive identification of isolates was made on the colonies that developed in selective medium. All isolates were confirmed by carbohydrate utilisation and/or coagglutination with monoclonal antibodies and/or mass spectrophotometry (Bruker Daltonik). For Spx a positive result was defined as abundant production of bubbles occurring within two to three seconds of starting emulsification. A negative reaction was defined by weak or delayed bubbling after three seconds. Pulsed field gel electrophoresis (PFGE) was carried out using NheI enzyme.
Results Out of the total isolates studied, 99.9% (8038/8047) showed a positive Spx, however 9 isolates were Spx negative. These isolates came from 5 different regions of the country and have been appearing since 2010. They were characterised as serogroup WII/III with 3 different susceptibility patterns corresponding to three different non-related PFGE profiles.
Conclusion This work confirms the reliability of the Spx for the presumptive identification of Ng. Since several clinical laboratories in developing countries use only presumptive tests for Ng identification, is important to alert about these atypical isolates circulating in our country. It is important to be aware of using complementary tests for identification.
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