Tgp chi Khoa hgc Tru&ng Dgi hgc Cdn Tha PhdnB: Ndng nghiip. Tliuy san vd Cdng nghi Sinb hoc. 26(2(113/ 96-103
Tap chl Khoa hpc Tri/dng Oai hpc Can Thd website: sj.ctu.edu.vn
STREPTOCOCCUS INIAE, TAC ^fHAN GAY BENH "DEN THAN"
TREN CA RO DONG (ANABAS TESTUDINEUS) Tir Thanh Dung', Huynh Thi Nggc Thanh va Nguyen Khuong Duy ' Khoa Thuy sdn, Truang Bgi hgc Cdn Tha
Thdng tin chung:
Ngdy nhgn: 19/12/2012 Ngdy chdp nhdn. 20 062013 Title:
Streptococcus iniae, the causative agent of "dark body"disease in climbing perch (Anabas lesludineus) in the Mekong Delta Tukhoa:
Cd rd ddng (Anabas lesludineus), benh "den thdn ", LDsii, Streptococcus iniae
Keywords:
Climbing perch (Anabas testudineus), "dark bodv"
disease. Streptococcus iniae, LD^g
ABSTRACT
This study describes the first isolation Streptococcus iniae as causative agent of "dark body" disease in climbing perch (Anabas testudineus). A total of 114 diseased climbing perch samples with darkened body colour and lethargy was collected from different commercial farms in the Mekong Delta. Diseased fish showed external signs of dark coloration and eyes with corneal opacity. Internally, ascites, hepatomegaly, and splenomegaly were observed. All potential agents were considered. Small, opaque and pure colonies isolated from fish liver, kiney, spleen, blood, eyes and brain on brain heart infusion agar (BHI) and blood agar (BA) were observed in pure culture after 24-36 hours incubating at 28°C. Colonies were chain-forming and Gram positive cocci Conventional and rapid identification systems and 16S rRNA gene partial sequencing were used to identify the train isolated from "dark body" disease as Streptococcus iniae. LDso tiials was carried out with two S. iniae isolates, al concentrations from 1& to Iff CFU/mL, in healthy climbing perch (3-6g body weight), with values of 3,73^1(f CFU/mL crfter 120h and 2,43^1(f CFU/mL after 144h. An experimental injection challenge study fulfilled Koch's postulates. Experimented showed similar clinical signs to the natural infection.
TOM TAT
Nghiin cuu md td ldn ddu tien phdn lap vi khudn Streptococcus iniae la tdc nhdn gdy binh "den thdn" trin cd ro ddng (Anabas testudineus). Nghiin cuu da thu dugc 114 mdu cd rd ddng binh cd ddu hieu den thdn a cdc ao nuoi thdm canh khdc nhau a cdc tinh ddrig bdng sdng Ciru Long. Cd b^nh cd ddu hiiu khdp vimg lung mdu den. mdt cd md due, xudt huyet ngi quan.
gan. than vd tiiy tgng sung to Cdc mdu cd dugc kiim tdng qudt cdc tdc nhdn gdy binh Sau thdi gian ii 24-36 gid & 28°C, cdc khudn lac thudn dang nho li ti trang due dugc phdn lap tir cdc mdu gan, thdn. ty tang mdu, mat va ndo cd binh xudt hien nhieu trin mdi truang brain heart infusion agar (BHI) vd thgch mdu (BA). Quan sdt ti bdo vi khudn nhudm Gram cd hinh cau, dgng chudi. Gram duong Ket qud kiim tia dac diim hinh thdi sinh Iv, smh hoa, kit API 20Strep vd gidi trinh tic gen 16S rRNA da xdc dinh vi khuan phdn lap trin cd rd ddng binh "den thdn" Id Streptococcus iniae Hai Chung v, kliudn S. iniae diin hinh dugc sir dung di gdy thi nghiim cdm nhiem tren cd rd ddng giong khde (trgng luang 3-6 g) bdng phuang phdp 3 3^^W CFU/mL sau 120 h vd 2A3^I(f CFU/ml sau 144li. Kit qud cdm nluem da thoa man dinh de Kochs Cd ro ddng nhiim benh sau khi gdy cdm nhiem co dau hieu ldm sdng gidng voi bjnh "den thdn " ngodi ao nudi
Tap cbi Khoa hgc Tnr&ng Dgi hgc Cdn Tha Phdn B: Ndng nghiep. Thuy si 1 GlOfI THIEU
Ca rd ddng {Anabas testudineus) la loai ca phan bd rdng, cd the sdng d cac thuy vuc nudc nggt va mrdc Ig. Chung phan bo nhieu quoc gia tren thi gidi nhu Uc, An Do, Trung Qudc, Philippin, Thai Lan, Lao, Campuchia, Viet Nam va nhieu qudc gia chau A khac (Fishbase.
2010). O nudc ta, viec img dung cac tien bd khoa hgc ky thuat, tham canh va da dang hda cdc ddi tugng nudi chu luc nhu ca tra, basa, rd phi, dieu hdng,... da gdp phan nang cao hieu qua trong nudi udng thuy san. Gin day, ca rd dong dang la ddi tugng nudi chu yeu d cac tinh nhu Hau Giang, Can Tha, Dong Thdp, Tien Giang... Tuy nhien, viec md rdng dien tich nudi cung nhu viec tham canh hda ddi tugng nudi nay da phat sinh nhieu vin de can dugc quan tam. dac biet la dich benh do vi khuan. Trong dd, benh do nhdm vi khuan Streptococcus hien dang gay nguy hiem tren nhieu loai ca nudi va thiet hai cho nghe nudi trdng thuy san tren the gidi hang nam len den 150 Uieu dd la (Romalde et al, 2009).Trong nhdm vi khuan nay. Streptococcus iniae gay benh tren nhieu loai cd nudc nggt va Ig. Th«>
mdt sd nghien cuu gan day da tim thay it nhat 27 loai ca nudi va tu nhien da nhiem benh do vi khudn S. iniae (Agnew va Barnes, 2007).
Tuy nhien cho den nay chua cd tai lieu nao cdng bd ve benh do S. iniae uen cd rd ddng.
Benh "den than" tren cd rd dong hien nay gay Uiiet hai Idn cho ngudi nudi. vdi ti le hao hut Uen 50%. Chinh vi thi, viec xac dinh tac nhan S. iniae gay benh "den than" Uen cd rd la van dl cip thilt va dugc thuc hien Uong nghien cuu nay.
2 PHU'ONG PHAP NGHIEN C i r u 2.1 Kiem tra benh ca
Mlu ca rd dong benh "den than" dugc thu rir 20 ao nudi tham canh d mdt sd tinh ddng bing sdng Cim Long, Tdng sd miu bao gdm 114 mau ca rd ddng cd bieu hien benh "den than" vd 26 cd khde trgng lugng 6-200 g. dugc thu tu cac ao nudi tham canh d tinh Hau Giang. Dong Thap, Cin Tho va Tiln Giang, cd dugc thu sudt tu thdng 2/2011^/2012. Cdc thdng sd v l ky thuat nudi. dieu kien cham sdc,
ng nghe Sinh hgc: 2612013). 96-103 quan ly ao nudi ciing nhu dau hieu lam sang dugc ghi nhan. Mlu dugc gift lanh va dua ve phan lich phdng dii nghiem Bg mdn Benh hgc Thiiy san, Khoa Thuy san.Trudng Dai hgc c i n Tha.
Mdu ca dugc kiem tra sue khde tdng qudt bao gdm ky sinh triing. nam va vi khuan. Ky sinh Uung dugc kiem tra dua theo md ta Noga (2010), lay mau nhdt Uen da va mang cd va quan sat mau dudi kinh hien vi vdi do phdng dai 4-40X. Kiem Ua nam Uen ca dua theo md ta cua Hatai and Egusa (1979), quan sat sgi nam Uen tieu bdn tuai, mau benh sau do dugc rua vdi nudc mudi sinh Iy va dugc cay tren mdi trudng GYA (Glucose 1%, Yeast extract 0,25% va Agar 1,5%) da them Sueptomycin vd Ampicillin 500 pg/ml, cac dta dugc li 2-4 ngay d 28-30''C. Kiem ua vi sinh dugc tien hdnh dua theo cam nang cua Frerichs va Millar (1993), mau gan, than, ty tang, mdu. mat va nao cd benh "den than" dugc ca\' uen mdi trudng brain heart inflision agar (BHIA.
Merck) va thach mau (BA: Blood agar, Nam Khoa), dugc u sau 24 - 36h, d 28°C.
2.2 Phan lap va dinh danh vi khuan Vi khuan phat uien uen mdi trudng BHI agar va BA dugc kiem ua cac chi tieu ca ban nhu: nhudm Gram, Iinh di ddng. oxidase, catalase, phan ung O/F. kha nang dung huyet.
Dinh danh vi khuan dugc dua cac chi tieu hinh thai, sinh ly, sinh hda theo cam nang ciia Cowan va Steel (1993), Frerichs va Millar (1993) va Buller (2004) ddng thdi su dung bd kit API 20SUep (BioMerieux, Phap) vdi cac budc thuc hien theo hudng dan cua nha san xuat va gidi uinh ttr gen 16S rRNA tra ciiu uen ngan hang Gen bang chuang trinh Blast Search tai phdng thi nghiem Nam Khoa Biotek.
2 3 Thi nghiem cam nhiem xac djnh LD50 (Lethal Dose) vi khuan ga}' benh Ca thi nghiem: Ca rd ddng gidng khde cd trgng lugng 6 - 1 0 gram/con, dugc su dung thi nghiem gay cdm nhilm tren he thdng bl nhua (60L). Cdc be sau khi dugc liet trimg va nia sach. cho nudc vao be (40L). sue khi lien luc vai ngay de loai het chlorine. Trudc khi ga\
Tgp chi Khoa hgc Tnrang Dgi hgc Cdn Tha PhdnB-Ndng nghiip. Thuy san vd Cong nghe Smh hgc. 26(2013). 96-103 cam nhilm, ca dugc kiem tra siic khde de dam
bao hoan toan khdng nhiem benh. Cd dugc thuan dudng Uong dieu kien thi nghiem 2 tudn vdi mat do 10 con/be, Suot thdi gian thi nghiem dugc bd sung sue khi va cho an thdc an cua cdng ly Cargill Viet Nam. Thi nghiem dugc tien hanh d phdng thi nghiem udt tai Khoa Thiiy san-Trudng Dai hoc Can Tha.
Vi khuan gay cdm nhiem: Hai chung 5.
iniae S2FC4 va S8FCI phan lap txt ca ro benh
"den than" tai ao nudi su dung cho thi nghiem
cam nhiem. Sau khi vi khuin dugc nudi tang sinh trong Brain-Heart infusion broth (BHIB) tren may lie d 28°C 18-24h, tien hanh ly lam 13000 vong d 4°C Uong 10 phut, sau dd rua lEti vdi dung djch vdi nudc mudi sinh Iy (0,85%
NaCl), ldp lai Uong 2 lin. Mat do vi khudn dugc xdc dinh bang do d budc sdng 620 nm (0D=1 ± 0,02) luang duong mat do vi khuin Id 10* CFU/mL. Sau do pha loSng tren thach mdu va dem khuin lac sau 36 h d 28°C. Cac mat dp vi khuan gay cam nhiem trong nghiSn cuu nay dugc trinh bay d Bang 1:
Bang 1: Mat d$ vi khuan sir dung tfai ngfaiem cam nfaiem
Chiing vi khuan Mat do vi khuan (CFU/mL)
T03M0'y2^03M0V2^03^^T0V2i03M^
5. iniae S2FC4
S. iniae S%¥C\ l,4xl0\ 1,4>=I0^ l,4xl0^ 1,4^10*
Phirang phdp cdm nhiim: Ca thi nghiem dugc tiem vao xoang bung lieu 0.1 mL/cd vdi mat do vi khuan d Bang I. Rieng nghiem thdc doi chung dugc tiem nudc muoi sinh ly tiet trung (0,85% NaCt) cung vdi lieu nay. Tit ca cac Ihl nghiem dugc bd ui ngau nhien vdi 3 lan lap lai. Sd lugng, thdi diem ca chit va cac dau hieu lam sang dugc ghi nhan trong qua trinh thi nghiem. Nudc dugc thay mdi ngay va nhiet do nudc dugc biln ddng Irong khoang 28 - 3 r C . Ca Id dd hay vua mdi chit dugc phan lap vi khuan d gan, than trudc. ty tang, mdu, mat va nao tren mdi trudng BHI agar va BA.
Cd sau khi gay cam nhiem theo doi trong suot 14 ngay. Khi kit thiic thi nghiem, gia tri LDso dugc xac dmh theo phuang phap ciia Reed va
Muench (1938). Sd lieu cam nhiem dugc phan tich bdng chuang Uinh Microsoft Excel.
3 K E T QUA 3.1 Dau hieu benh ly
Bieu hien ben ngodi: Ca benh co bieu hi^n giam an, bai Id dd tren mat ao, ca thi cd co mau den bit thudng (Hinh IA). Ca b6nh nang thudng cd bieu hien co giat, bai lgi bat thudng tren mat nudc. Mit ca ldi va due, bung truang to (Hinh 1 A), nhilu trudng hgp ca benh xuat huyet d hau mdn, xung quanh mit va cac gdc vay.
Biiu hi4n ben trong: Xoang byng cd dich mau; gan, th^n va ty tang stmg lo va xudt huylt (Hinh IB).
Hinh 1: A: Ca ro benh bilu hi^n than den sSm, mSt due yk bung to (mui ten). B: Xoang chua dich m^u, gan va ty tang sung to (mfli ten)
T^ chi Khoa 1^ Tnr&ng Dgi hgc Cdn Tha Phdn B: Nong nghiip. Thuy san vd Cdng nghe Sinh hpc: 26'2013> 96-103 m Phan lap va dinh danh tac nhan gay benh
Ket qua kiem tra ngoai va ndi kV sinh triing khdng thiy su khac biet gida ca benh "den than" va ca khde. Dien hinh nhu cac mau cd rd kiem tra thudng xuit hi^n trung banh xe.
Henneguya va san la 16 mdc Dactylogyrus sp d muc do cam nhiem thdp ( 1 - 4 con/lame). Ca ro ddng nudi nhiem ndi ky sinh Camallanus sp. vdi mat do thip ( 1 - 2 triing/ca). Nhu vay, ky sinh trung tren mang va da ca rd dong khdng la tac nhan gay nen benh "den than".
Tucmg tu, ket qua quan sat mlu tucri khdng tim thay sgi nam hay khuan t\- tren mau da va mgt sd ca quan ngi tang.
Tdng cdng 97 chung \ i khudn dugc phan lap tu gan, than. t> tang, mdu mat va nao cua
^
ca benh "den than" uen mdi trudng BHI va BA, Hau het deu xuat hien vi khuan thuan sau 24 - 36 h ii d nhiet do 28°C. Vi khudn phan lap dugc deu la cdc le bao \ i khuan Gram duong (Hinh 2B). dang chum Uen mdi trudng thach va dang chudi hoac dan cau Uen mdi trudng Idng hay cac mdu mau (Hinh 2A). Kit qua nghien cuu nay tim thay vi khuan trong cdc mau phan lap thudc nhdm Streptococcus. Vi khuan phat uien uen mdi trudng BHI agar va BA sau 24 - 36 h d 28°C, dudng kinh khuin lac khoang 1 mm, mau tring due, b l mat uon Idng. Vi khuan cd kha nang dung huyet dang p tren mdi trudng thach mau (Hinh 3B) va phdt Uien trong mdi trudng NaCl 6.5%, am tinh vdi Catalase. Oxidase. O T . khdng phat trien d pH 9.6 hay d nhiet do dOT (Bang 2).
•^ I
Hinh 2: A: .Miu man ca nhiem S. iniae pfaecb tren lame, cac te bao vi khuau fainfa cau va chuoi t^p trung quanh te bao mau (40X), B: Vi khuan S. iniae Gram duong hinh cau Bang 2: D^c diem hinh thai, sinh ly, sinh hda \1 kfauan gay bfnfa "den than" tren ca ro
Chi Tiea Gram Hbihd^ng Kidt thuoc khuan lac Sd ngay phat trien Dung htiySt Catalase Oxidase ADH O/F NaCl 6.5%
pH9.6 dOX
S. iniae (BuUer, 2004) + Cau, chuoi
1 mm 24-18 gid
S. iniae phan lap (/r= 97) Cau. chuoi
1 mm 24 gid
rap chi Khct, hoc Tnnmg Bai»«- Can Tha Phin B Sdng ngliiip. Thin, .on vo Cdiig nghi Sinh ftpc. 26 (20131 96-103
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^ B W ^
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Hinh 3: A: Ket qua djnh danh bing kit API 20 Strep, B: Khuin lac 5; iniae tren m6i trirdng BA, (dimg fauyet d a n g ^
Kit qud dinh danh bing kit API20 SUep (BIOMERIEUS. Phap) cho tiidy, til ca vi khuin cho phan iing Voges-Proskauer (VP), hippurate (HIP), and a-galactosidase (a-GAL) am tinh. Trong khi do, cho phan ung duang tinh vdi esculine degradation (ESC), pyrolidonylamidase (PYRA), p-glucuronidase (P-GUR). alkaline phosphatase (PAL), leucine arylamidase (LAP). Dac biet. ddi vdi ribose (RIB), mannitol (MAN), uehalose (TRE).
amygdalin (AMD) va glycogen (GLY) bi a-xit hoa (duong linh) bdi cdc chung vi khuan ndy.
Trong khi hau bet cdc chiing phan lap khdng the oxy hoa cac loai dudng cdn lai nhu:
arabinose (ARA), sorbitol (SOR), lactose (LAC), inuline (INU) va raffinose (RAF). Dac diem hinh thdi, sinh ly va sinh hda cua cdc chung Uong nghien cuu nay gidng vdi chiing vi khuan Streptococcus iniae trong nghien cuu cua Buller (2004) tru chi tieu arginine hydrolysis (AHD) co the thay ddi (+/-) tiiy theo cdc chung phdn lap (Hinh 3A). Ddng thdi ket hgp ung dung sinh hgc phan tu gidi uinh tu gen 16S rRNA dugc tra cuu Uen ngan hang Gen bang chuang trinh Blast Search da khing dinh dugc \ i khuan hinh cau la Streptoccus iniae cd trinh tu gen tuong ddng la 100%.
Z.i Ket qua thi nghiem cam nhilm LD50 K e t q u a cdm nhilm nhdn iao 2 chting vi
khuan Streptococcus iniae S2FC4 va S8FC1 tren ca rd da xuat hien cdc dau hieu lam sdng gidng vdi ca rd benh "den than" ngoai ao nudi.
Sau 18 gid cam nhiem, cd thi nghiem cd dau hieu benh den than, bai Id dd va cd chet da dugc ghi nhan sau 27 gid gay cam nhiem d cac mat do 10^ CFU/mL. Sau 36 gid, cd bit diu xuat hien bung truang to, xuat huyet cac goc nguc, vay dudi va vay hau mdn. Sau do, ca co bieu hien mat md due vd Idi, gan, than, ty tang sung va xuat huyet da dugc ghi nhan d tit cd cdc Id cam nhiem. Sau 7 ngdy gay cdm nhiem, cd d cac nghiem thuc deu chet vdi li le td 20- 80%. Sau 14 ngay cam nhiem, ti le ca chet tren cac chiing vi khuan cam nhilm S. iniae S2FC4 vd S8FCld mat do 10^ CFU/ml lin lugt la 60% va 80%. Trong khi do. Id ddi chdng (khong tiem vi khuin S.iniae), cd vdn boat ddng binh thudng frong sudt thdi gian thi nghiem. Vi khuan phan lap dugc tir cd thi nghiem cdm nhiem nay dugc tai djnh danh cho kit qua giong vdi kit qua vi khuin gay benh
"den than" ngoai ttr nhien. Nhu vay. loai vi khuin Gram duang, hinh ciu S. iniae la tdc nhan gay benh "den than" tren ca rd dong. Qua thi nhiem nay. gia Ui LD50 tren 2 chung vi khudn cam nhiem 5. iniae S2FC4 va S8FCI dugc xac dinh ldn lugt la 3,73^10^ CFU/mL sau I20h va 2.43x10'CFU/mL sau 144h.
Tgp chi Khoa hgc Tnr&ng Dgi hoc Cdn Tha Phan B: Ndng nghiip. Thin sdn vd Cdng nghe Sinh hgc. 26 (2013). 96-103
I M I I M
Hinfa 4: Oo tfai ti le ehit gay cam vdi 2 chung S.iniae S2FC4 va S8FC1 (tir trai qua) 4 THAO LUAN
Trong nudi frdng thiiy san, nhdm vi khuin Streptococcus la tdc nhan gay benh cua hau het cac loai cd nudi va tu nhien d vung nudc nggt, lg va man (Agnew va Barnes, 2007 vd Pasnik et al., 2009). O Nhat, vi khuan nay gay benh Uen cd hdi Oncorhynchus mykiss dugc bao cdo dau tien nam 1958 do Hoshina at al. Nam 1976, Pier va Madin lan dau phan lap S. iniae tu cac vet thuang tren ca heo Inia geqffrensis.
Sau dd, vi khuan nguy hiem nay gdy benh tren nhieu lodi cd lam tdn that ldn ve kinh te (Creeper va Buller, 2006 va Noga, 2010). Tren ca rd ddng, trong nghien cuu nay lan dau tien phan lap dugc S. iniae Uen ca rd ddng benh
"den than".
Vi khuan S. iniae cd kha nang dung huyet dang p. am tinh vdi Catalase, Oxidase, O/F, khdng phdt trien d pH 9.6 va d nhiet do 6 0 ^ . Ket qua nay hoan toan phii hgp vdi nhieu nghien ciru trudc day theo cam nang Cowan va Steel (1993). Ferguson, (1994) vd Buller (2004). Ngoai ra, S. iniae phan lap uen ca rd benh "den than" phat frien d ndng do mudi 6.5%, Day la mdt dac diem sinh hgc rat dac biet ciia nhdm vi khuan nay, cd lien quan den kha nang ga\ benh uen nhieu ddi tugng nudi d ca vung nudc nggt va man (Nagatsugawa.
1983 va Humphrey e/a/., 1987),
Mac du S. iniae cd cac dac diem rat dac tnmg uong nhdm Streptococcus, nhieu tac gid
da phat hien da so dac diem cua S. iniae rat gidng vdi S. dysgalactiae subsp. equisimilis (Lau et al, 2003 va Buller, 2004). Hem niia, cho den nay cdc dac diem de djnh danh S iniae khdng cd frong ca sd dd lieu ciia cdc bd kit dinh danh vi khuin nhu API 20 Strep, Rapid ID 32 Suep. Vi the, chi dua vao kit qua kit nay de dinh danh vi khuan 5. iniae la chua phti hgp. Tuy nhien, cac chi lieu trong cdc phan ung sinh hoa Uong bd kit van cd the dugc su dung de so sdnh vdi ket qua ciia nhieu cdng trinh nghien cuu trudc day (Lau et al, 2003 va Agnew va Barnes, 2007). Do dd, cac ket qua dinh S. iniae Uong nghien cuu nay phii hgp vdi cdc ket qud ciia Buller (2004) va nhieu tac gia khac. Viec ung dung sinh hpc phan tu gidi trinh lu gen 16S rRNA la each tot nhit trong viec dinh danh loai vi khuan nay (Roach et al, 2006 va EI Aamri el al, 2010).
Trong thi nghiem gay cdm nhiem, cd d cdc nghiem thuc ddi chung vdn hoat dgng binh thudng. Trong khi cac nghiem thuc cd tiem chung vi khuan S. iniae, ca rd giong nhilm benh va chet cd dau hieu lam sang gidng vdi benh "den than" ngoai ao nuoi. Ket qud nay da thda man dinh de Kochs. Trong thdi gian thi nghiem. nhiet do nudc cao (28 - 29''C) la mgt Uong nhung yeu to lam ca de man cdm vdi S.
iniae vd tang ti le ca chet. Dieu nay cung dugc tim thay qua nghien cuu cua Agnew va Barnes (2007). Trong thi nghiem nay, gia tri LD50 fren 2 chiing vi khuan tren cd rd ddng tuang ddi
Tgp chi Khoa hgc Truang Dgi hgc Cdn Tba PhdnB-Ndng nghiip. Thuy san vd Cdng nghi Sinb hoc 26(2013) 96-103 cao 10^ vd 10^ CFU/mL. Dilu nay phii hgp vdi
nhieu nghien ctm trudc do Uen cd ro phi (3.18x10* CFU) (Perera et al, 1997) vd ca chem (2.0x|0^ CFU) (Bromage va Owens 2002). Trong nghien cuu nay, tit ca cac chung diu gdy cd chet sau 48 gid tiem. Dieu nay phu hgp vdi thi nghiem trudc day cua Bromage et al (1999), tac gia gay cam nhiem uen cd chem Lates calcarifer, vi khuan S. iniae gay ca chet sau 18-24 gid. Trong khi dd, nghien cuu cua El Aamri et al (2010) cho thiy, ca frap bien Pagruspagrus nhiem vi khuan S. iniae cd bieu hien Id dd va chit sau 72 gid d 10* CFU/mL.
Su khdc nhau thdi gian ca chet giua cac nghien cuu tiiy thupc vdo su man cdm khdc nhau cua timg loai ca, ddc luc ciia vi khuan cung nhu cac ylu mdi trudng, dac biet la nhiet dd (Agnew va Barnes, 2007).
S KETLU^N
Vi khuan Streptococcus iniae Gram duang, hinh cdu la tac nhan gay benh "den than" tren ca rd dong {Anabas testudineus). Cd benh co dau hieu benh ly: ca the ca cd mau den bat thudng, mil md due vd loi, cdc ca quan ngi tang sung va xuit huyet. Kit qua cdm nhiem xdc dinh LD50 fren 2 chiing vi khuin cam nhiem 5. iniae S2FC4 va S8FC1 la 3.73x10^ CFU/mL sau 120h va 2,43x 10* CFU/mL sau 144h.
L d i CAM TA
Nhdm nghien cuu chan thanh cam an su tai trg kinh phi cua de tdi Khoa hgc va Cdng nghe cip Bd (Ma so: B2012-16-16) 6k hoan thanh nghien cuu nay.
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Cambridge University Press. 351pp.
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Identification Manual. CABI Publishing.
390pp.
4. Bromage, S. E, A. Thomas and L. Owens, 1999. Streptococcus iniae, a bacterial infection in barramundi Lates calcarifer. Disease of aquatic Organisms. 36: 177-181.
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199-205.
6. Creeper, H.J and N.B, Buller, 2006. An outbreak of Streptococcus iniae in barramundi {Lates calcarifera) in freshwater cage culture.
Australian Veterinary Journal. 84: 408-411.
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