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Infect Immun, August 1998, p. 3841-3847, Vol. 66, No. 8
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Production of Stabilized Virulence Factor-Negative Variants by Group A Streptococci during Stationary Phase

B. A. B. Leonard,dagger M. Woischnik, and A. Podbielski*

Department of Medical Microbiology and Hygiene, University of Ulm Clinic, 89081 Ulm, Germany

Received 8 January 1998/Returned for modification 9 April 1998/Accepted 4 May 1998

Many of the virulence factors associated with fulminant group A streptococci (GAS) infection are expressed under in vitro exponential growth conditions. However, the survival of GAS in tissue and intracellularly, as well as colonization of asymptomatic carriers, has been reported for GAS. The bacteria associated with these niches may encounter high-density, low-nutrient-flowthrough conditions that may more closely mimic in vitro stationary-phase conditions than exponential growth. Therefore, the behavior of GAS in stationary-phase culture was examined. We observed that after 24 h in stationary phase, GAS serotypes M49 and M2 developed a unstable colony dimorphism of typical large and atypical small colonies. Between days 4 and 5, we isolated stabilized atypical small colonies which remained stable for up to nine passages (approximately 200 generations) on fresh medium before fully reverting to the large-colony phenotype. Upon analysis, the small colonies showed no difference in cell number per colony, growth rate, survival in prolonged stationary-phase culture, or antibiotic sensitivity. However, the small colonies showed decreased transcription of hyaluronic acid capsule, the global positive virulence factor regulator gene mga, the mga-regulated emm mRNA (M-protein structural gene), and speB (cysteine protease). Accordingly, the small colonies were completely sensitive in a traditional phagocytosis assay. The production of virulence factors and phagocytosis resistance of the small-colony isolates was recovered when, after several passages on fresh medium, the colony morphology began to revert.

* Corresponding author. Mailing address: Department of Medical Microbiology and Hygiene, University of Ulm Clinic, Robert-Koch Str. 8, 89081 Ulm, Germany. Phone: 49-731-5024615. Fax: 49-731-5024619. E-mail: andreas.podbielski{at}medizin.uni-ulm.de.

dagger Present address: Temple University School of Medicine, Department of Microbiology and Immunology, Philadelphia, PA 19140.

Infect Immun, August 1998, p. 3841-3847, Vol. 66, No. 8
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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