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The survival in
transport medium of different auxotypes of N. gonorrhoeae
varied significantly.
Survival of six
auxotypes of Neisseria gonorrhoeae in transport media.
Wade JJ, Graver MA.
Journal of Clinical
Microbiology 2003;41:1720-1721.
Summary:
Question
Do various auxotypes of N. gonorrhoeae differ in their abilities to
survive in plain and charcoal-containing transport media?
Design
The survival of five distinguishable strains of each of six auxotypes of N.
gonorrhoeae was determined for eight combinations of inoculum-transport
medium-time.
Participants
Thirty strains of N. gonorrhoeae, including 5 prototype strains and
5 strains each of auxotypes requiring proline and arginine, arginine and
hypoxanthine, proline, hypoxanthine, and arginine, were tested.
Description of Tests and Diagnostic
Standard
A McFarland no. 1 standard suspension of each N. gonorrhoeae strain
was diluted 1:10 in PBS and in nutrient broth. Swabs were inoculated with
100 μl of each suspension. Eight swabs were prepared for each strain
to test all combinations of conditions, which included PBS and broth
inocula, plain and charcoal-containing Amies transport media, and storage
at room temperature for 24 and 48 hours. Survival was determined for each
strain under each condition by vortexing the swab in 1 ml of PBS and
plating in triplicate on chocolate agar.
Main Outcome Measures
The median of the 3 colony forming units (CFU) counts was calculated for
each of the 8 conditions of inoculum-medium-time for each strain. The
median of the five CFU values for an auxotype was compared to those of the
other auxotypes for each condition.
Main Results
In plain medium at 24 h, the auxotype proline/arginine survived best, the
auxotypes proline and hypoxanthine survived least well, and the other 3
groups showed intermediate rates of survival. Survival at 24 h in plain
medium was reduced when the inoculum was prepared in broth compared to
PBS. Survival rates in charcoal-containing medium were improved at 24 h
for all groups compared to plain medium and were similar for both inocula.
Survival rates in charcoal-containing medium were improved at 48 h for all
groups except the auxotypes hypoxanthine and arginine.
Authors' Conclusions
The results show marked differences in
survival of auxotypes in plain transport medium and the value of charcoal
both for reducing this variability for up to 24 h and for improving
recovery of some groups at 48 h. Swabs processed after 24 h are
increasingly unlikely to yield isolates representative of those causing
infection in the population sampled.
Source of funding: None given.
For correspondence: J. J. Wade, South
London Public Health Laboratory, King's College Hospital, Denmark Hill,
London SE5 9RS, UK. E-mail address: jimwade@btinternet.com.
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