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A unique siderophore from Aeromonas hydrophila : Is it a major virulence factor for fish?
Vol. Ii, No. 2
ISDCI ECTOTHERM SYMPOSIUM
A UNIQUE SIDEROPHORE FROM AEROMONAS V I R U L E N C E F A C T O R F O R FISH?
441
H Y D R O P H I L A : IS IT A M A J O R
A. D e u t e r , S. Bargouthi, R. Byers and L.W. C l e m D e p a r t m e n t of Microbiology, University of Mississippi Medical C e n t e r , Jackson, MS USA
C e r t a i n strains of the fish opportunistic p a t h o g e n A e r o m o n a s hydrophila produce a unique p h e n o l a t e siderophore (designated AHS) t h a t m a y r e p r e s e n t the m e c h a n i s m by which this m i c r o o r g a n i s m obtains iron f r o m the host during disease. In vitro growth of these strains was not inhibited by physiologic c o n c e n t r a t i o n s of t r a n s f e r r i n ~iron free); although significantly higher t r a n s f e r r i n levels were inhibitory, such inhibition could be r e v e r s e d by d e f e r r i AHS. P r e l i m i n a r y in vivo studies showed AHS-producing strains of A. hydrophila to be virulent for fingerling channel catfish. F u r t h e r m o r e , this virulence w"as enhanced by s i m u l t a n e o u s injections of AHS. It was also observed t h a t fingerling fish f r o m d i f f e r e n t b r e e d e r s exhibited d i f f e r e n c e s in susceptibility to the AHS-producing strains. C u r r e n t l y ongoing studies are a i m e d a t d e t e r m i n i n g a) the i m m u n o g e n i c i t y of AHS and b) the virulence of t r a n s p o s o n - i n d u c e d m u t a n t s of A. hydrophila s p e c i f i c a l l y lacking the ability to produce AHS.
P H Y L O G E N Y OF L Y M P H O C Y T E HETEROGENEITY: THE THYMUS OF THE CHANNEL CATFISH C a t h e r i n e F. Ellsaesser, Jan E. BIF and L.W. Clem D e p a r t m e n t of Microbiology, U n i v e r s i t y of Mississippi Medical C e n t e r , Jackson, MS USA
Studies of the t h y m u s of the channel c a t f i s h r e v e a l e d t h a t , although it was p r e s e n t in fingerling channel c a t f i s h less than one y e a r old, it r e a c h e d its p e a k size about a y e a r a f t e r hatching. The n u m b e r of t h y m o c y t e s ( a p p r o x i m a t e l y 3 x 107) t h a t were r e c o v e r a b l e f r o m fingerling channel catfish r e m a i n e d c o n s t a n t from about S e p t e m b e r to March following h a t c h i n g (catfish h a v e only one s p a w n / y e a r and hatching occurs in April or May). B e t w e e n March and April of the second y e a r , the thymus d r a m a t i c a l l y i n c r e a s e d in size (up to 3 x 109 t h y m o c y t e s ) and r e m a i n e d enlarged throughout t h a t s u m m e r . In S e p t e m b e r , the thymus began to involute to a point such t h a t by N o v e m b e r no thymus tissue could be found m a c r o s c o p i c a l l y . This n a t u r a l involution could be a c c e l e r a t e d by subjecting the fish to t r a n s p o r t or handling stress. Analysis of the cells found in the t h y m u s e s of fish aged 4 to 18 months r e v e a l e d t h a t t h e y were p r i m a r i l y T cells (as defined by a n t i - T cell monoclonal antibodies); few if any s u r f a c e immunoglobulin p o s i t i v e B cells were p r e s e n t . The cells in the thymus responded to the m i t o g e n c o n c a n a v a l i n A only in the p r e s e n c e of added a c c e s s o r y cells (monocytes) or a m o n o c y t e - d e r i v e d s u p e r n a t a n t (presumably containing IL-I) a t p e r m i s s i v e t e m p e r a t u r e s (ZToC). T h y m o c y t e s could also be induced to divide at n o n - p e r m i s s i v e (17oc) as well as p e r m i s s i v e t e m p e r a t u r e s when i n c u b a t e d in the p r e s e n c e of the following c o m b i n a t i o n s of s t i m u l a n t s : a) the phorbol e s t e r TPA ( I Z - o - t e t r a d e c a n o y l p h o r b o l - 1 3 - a c e t a t e ) and the c a l c i u m ionophore AZ3187, b) TPA and Con A or c) AZ3187 and Con A. In those cases where TPA or AZ3187 were used, a c c e s s o r y cells or their p r o d u c t s were not needed. These results support the notion t h a t channel c a t f i s h t h y m o c y t e s functionally m i m i c those cells in the p e r i p h e r a l blood previously d e s i g n a t e d as T cells.
ISDCI ECTOTHERM SYMPOSIUM
A UNIQUE SIDEROPHORE FROM AEROMONAS V I R U L E N C E F A C T O R F O R FISH?
441
H Y D R O P H I L A : IS IT A M A J O R
A. D e u t e r , S. Bargouthi, R. Byers and L.W. C l e m D e p a r t m e n t of Microbiology, University of Mississippi Medical C e n t e r , Jackson, MS USA
C e r t a i n strains of the fish opportunistic p a t h o g e n A e r o m o n a s hydrophila produce a unique p h e n o l a t e siderophore (designated AHS) t h a t m a y r e p r e s e n t the m e c h a n i s m by which this m i c r o o r g a n i s m obtains iron f r o m the host during disease. In vitro growth of these strains was not inhibited by physiologic c o n c e n t r a t i o n s of t r a n s f e r r i n ~iron free); although significantly higher t r a n s f e r r i n levels were inhibitory, such inhibition could be r e v e r s e d by d e f e r r i AHS. P r e l i m i n a r y in vivo studies showed AHS-producing strains of A. hydrophila to be virulent for fingerling channel catfish. F u r t h e r m o r e , this virulence w"as enhanced by s i m u l t a n e o u s injections of AHS. It was also observed t h a t fingerling fish f r o m d i f f e r e n t b r e e d e r s exhibited d i f f e r e n c e s in susceptibility to the AHS-producing strains. C u r r e n t l y ongoing studies are a i m e d a t d e t e r m i n i n g a) the i m m u n o g e n i c i t y of AHS and b) the virulence of t r a n s p o s o n - i n d u c e d m u t a n t s of A. hydrophila s p e c i f i c a l l y lacking the ability to produce AHS.
P H Y L O G E N Y OF L Y M P H O C Y T E HETEROGENEITY: THE THYMUS OF THE CHANNEL CATFISH C a t h e r i n e F. Ellsaesser, Jan E. BIF and L.W. Clem D e p a r t m e n t of Microbiology, U n i v e r s i t y of Mississippi Medical C e n t e r , Jackson, MS USA
Studies of the t h y m u s of the channel c a t f i s h r e v e a l e d t h a t , although it was p r e s e n t in fingerling channel c a t f i s h less than one y e a r old, it r e a c h e d its p e a k size about a y e a r a f t e r hatching. The n u m b e r of t h y m o c y t e s ( a p p r o x i m a t e l y 3 x 107) t h a t were r e c o v e r a b l e f r o m fingerling channel catfish r e m a i n e d c o n s t a n t from about S e p t e m b e r to March following h a t c h i n g (catfish h a v e only one s p a w n / y e a r and hatching occurs in April or May). B e t w e e n March and April of the second y e a r , the thymus d r a m a t i c a l l y i n c r e a s e d in size (up to 3 x 109 t h y m o c y t e s ) and r e m a i n e d enlarged throughout t h a t s u m m e r . In S e p t e m b e r , the thymus began to involute to a point such t h a t by N o v e m b e r no thymus tissue could be found m a c r o s c o p i c a l l y . This n a t u r a l involution could be a c c e l e r a t e d by subjecting the fish to t r a n s p o r t or handling stress. Analysis of the cells found in the t h y m u s e s of fish aged 4 to 18 months r e v e a l e d t h a t t h e y were p r i m a r i l y T cells (as defined by a n t i - T cell monoclonal antibodies); few if any s u r f a c e immunoglobulin p o s i t i v e B cells were p r e s e n t . The cells in the thymus responded to the m i t o g e n c o n c a n a v a l i n A only in the p r e s e n c e of added a c c e s s o r y cells (monocytes) or a m o n o c y t e - d e r i v e d s u p e r n a t a n t (presumably containing IL-I) a t p e r m i s s i v e t e m p e r a t u r e s (ZToC). T h y m o c y t e s could also be induced to divide at n o n - p e r m i s s i v e (17oc) as well as p e r m i s s i v e t e m p e r a t u r e s when i n c u b a t e d in the p r e s e n c e of the following c o m b i n a t i o n s of s t i m u l a n t s : a) the phorbol e s t e r TPA ( I Z - o - t e t r a d e c a n o y l p h o r b o l - 1 3 - a c e t a t e ) and the c a l c i u m ionophore AZ3187, b) TPA and Con A or c) AZ3187 and Con A. In those cases where TPA or AZ3187 were used, a c c e s s o r y cells or their p r o d u c t s were not needed. These results support the notion t h a t channel c a t f i s h t h y m o c y t e s functionally m i m i c those cells in the p e r i p h e r a l blood previously d e s i g n a t e d as T cells.