International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 1

ISSN 2250-3153

Pathogenicity of Aeromonas hydrophila to blunt

snout bream Megalobrama amblycephala
Ngoc Tuan Tran1, Ze-Xia Gao1,2, James Milton1, Li Lin1,2, Yang Zhou1, Wei-Min Wang1
1
College of Fisheries, Key Lab of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education/Key Lab of
2
Freshwater Animal Breeding, Ministry of Agriculture, Huazhong Agricultural University, Wuhan, Hubei 430070, China Freshwater
Aquaculture Collaborative Innovation Center of Hubei Province, Wuhan 430070, China

Abstract- This study was carried out to confirm whether decade (Citarasu et al. 2011). The existence and pathogenicity of
Aeromonas hydrophila is a main haemorrhagic pathogen in blunt A. hydrophila have been reported in a variety of freshwater
snout bream Megalobrama amblycephala (BSB). The fish was species, comprising Salmo gairdneri (Peters et al. 1988), Clarias
challenged with bacterial concentrations of 1.710 4, 1.7105, batrachus (Angka 1990), tilapia (Liu et al. 1999), Carassius
1.7106 and 1.7107 cfu/fish for 7 days post infection. The auratus (Iqbal et al. 1999; Citarasu et al. 2011), Cyprinus carpio
results showed that mortality was bacterial-dose dependent, with (Chirila et al. 2008; Citarasu et al. 2011), Oreochromis niloticus
100% mortality observed at 1 day at the highest dose level (Ibrahem et al. 2008), and Channa striata (Duc et al. 2013).
(1.7107 cfu/fish). For comparison, control fish exhibited Nevertheless, to date the infection information of BSB in China
cumulative mortalities of 0%. The median lethal dose (LD 50) was is still limited. In present study, the efforts were conducted by a
5105 cfu/fish. A total of 15 bacterial strains of Aeromonas were challenge test to confirm whether A. hydrophila is a main
re-isolated from challenged fish and re-identified based on haemorrhagic pathogen in BSB.
morphological characteristics, biochemical tests and genomic
DNA gene sequencing. No bacteria were isolated from the II. MATERIALS AND METHODS
control group. This study results indicated that A. hydrophila is
A. Bacterial strain and bacterial suspension preparation
capable of causing haemorrhagic septicaemia in BSB. Antibiotic
susceptibility test with two strains D4 and HU201301 was A. hydrophila D4 used in this experiment was isolated from
investigated; both strains showed sensitive to most of the tested BSB with clinical signs of haemorrhagic septicaemia cultured in
drugs. Dongxihu, Hubei, China in 2012 and maintained in the College
of Fisheries, Huazhong Agricultural University. The bacterium
was cultured on the agar medium (including 3 g beef extract, 10
I. INTRODUCTION g peptone, 5 g NaCl, and 15 g agar in 1,000 mL distilled water)
and incubated at 28 oC for 24 hours. In order to harvest bacterial
cells, sterile physiological saline (0.85% NaCl) was added into

B lunt snout bream Megalobrama amblycephala (BSB) or

Wuchang fish is an herbivorous fish species and commonly
the bacterial incubated test tubes, and the surface colonies were
crushed by using a sterile loop to dilute bacterial suspension. The
desired densities of bacteria (1.7105, 1.7106, 1.7107 and
distributes in the middle portion of Yangtze River (Fishbase 1.7108 cfu/mL) were determined by counting on a neubauer
2012). BSB has become a favourable freshwater aquaculture
species in China (Tsao 1960; Zhou et al. 2008). During the past haemocytometer and prepared by ten-fold dilution method. To
culture time, BSB culture industry has suffered problems related confirm the inocula density of bacterial suspension, a method for
to degrading pond environments due to development of plate count by serial dilution was conducted.
intensification which resulted in the odd of stress-induced disease
(Nielsen et al. 2001). Many fish farms have been particularly B. Fish for experiment
infected by epidemics of Aeromonas hydrophila which has been
reported causing haemorrhagic septicaemia clinical signs and For pathogenicity test, healthy BSB weighing 27.18.3 g were
histopathological changes, and causing a great loss in cultured collected in the fish farm in Huanggang, Hubei, China and
BSB (Neilsen et al. 2001; He et al. 2006). transferred to the laboratory of the College of Fisheries,
It has been known for decades that Aeromonas plays a causative Huazhong Agricultural University. All tested fish were
agent role in fish diseases. The wide-spread distribution in acclimatized in 4m3-glass tanks (maintained at 28 oC and pH of
aquatic ecology systems indicates that interactions of Aeromonas 7.5) for 2 week before the artificial injection experiment. During
species with fish are continuous and unavoidable, facilitating the acclimatization period, fish were fed to satiation twice a day
their opportunistic pathogenicity (Ottaviani et al. 2011; Hu et al. (08:00 and 16:00) with commercial pelleted feed.
2012). A. hydrophila were recorded widely infecting freshwater
fish and marine fish species associated with skin lesions, tail and C. Pathogenicity test
fin rot, haemorrhagic septicaemia over the body and tissue Fifty fish without clinical signs by naked eye observation were
destruction, epizootic ulceration and necrosis in the liver and used for intraperitoneal injection experiment. The experiment
kidney of fish (Austin and Adams 1996; Doukas et al. 1998; included 5 groups (n=10 for each), comprising the negative
Janda and Abbott 2010). It was considered as a significant control (physiological saline injection) and four concentrations of
economic problem, particularly in China and India over the past bacterial suspension. Before infection experiment, tested animals

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International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 2
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were slightly anesthetized by MS-222 (Sigma, USA). Inocula 20oC until use. Polymerase Chain Reaction (PCR) was
were set up as intraperitoneal injections at 0.1 mL/fish of performed on all strains. Two universal primers, forward primer
physiological saline or desirable densities of bacterial 27F: 5-agagtttgatcctggctcag-3 and reverse primer 1492R: 5-
suspension. The experiment was conducted in 50 L aquarium tacggctaccttgttacgactt-3 (Sangon Biotech (Shanghai) Co., Ltd.),
with aeration at 28 oC for 7 days. No feed was fed during the were used to amplify 16S genomic DNA gene. The PCR
experiment. amplifications were performed in a final volume of 10 L
The fish were monitored daily and mortality was recorded. The containing 5 U Taq DNA polymerase, 1.0 L 10 buffer (with
cumulative mortality was calculated after challenge test. Mg2+) for Taq DNA polymerase, 0.25 L dNTP, 0.25 L each
Moribund fish was observed for the external and internal clinical primer and 50 ng genomic DNA. A negative control (without
signs. Bacteria were re-isolated and identified by biochemical template DNA) was also carried out. The PCR amplification
tests and sequencing on genomic DNA gene. The median lethal program was set with initial denaturation at 94 C for 5 min, 30
dose (LD50) was finally determined (Reed and Munch 1938). cycles at 94 C for 30 s, 58 C for 45 s, 72 C for 1.5 min, and
followed by final extension step at 72 C for 10 min. The PCR
D. Biochemical tests
products were analysed by using electrophoresis in 1% agarose
Biochemical characteristics of bacterial strains (D4, gels. The PCR products were sequenced in Sangon Biotech
HU201301, HU201302 and HU201304) were performed at 37 oC (Shanghai) Co. Ltd. by the Sangers sequencing method using
unless otherwise specified. Gram staining, motility, catalase ABI 3730. The identity of 16S genomic DNA gene sequences
activity, oxidase activity, carbohydrate fermentation (glucose, was obtained based on BLAST search in GeneBank database
sucrose, lactose, arabinose, mannitol and salicine), Methyl (Altschul et al. 1990).
Red/Voges-Proskauer (MR/VP), citrate utilization, esculine and
starch hydrolysis, indole and hydrogen sulphide (H 2S) III. RESULTS
production and growth on A. hydrophila specific-medium (AHM)
were investigated. Arabinose, aesculin, mannitol, salicin were Clinical signs
carried out by microbial biochemical identification tubes The first-observed mortality time was 8 h after infection. The
(Hangzhou Microbial Reagent Co., Ltd) following to external clinical signs were observed with impaired swimming,
manufactures instruction. Two strains (D4 and HU201301) were exophthalmia and anorexia, swollen eyes, and haemorrhage at
used in tolerance of to salt environment at 28 oC for 24 hours. the site of injection and ventral surface of moribund and dead
E. Antibiotic susceptibility test fish. Internal clinical signs observation showed haemorrhage in
the abdominal cavity, red odiferous fluid, swollen and colour-
The antibiotic susceptibility test was performed by the disk deep spleen, pale liver and sometimes swollen kidney
diffusion method described previously (Bauer et al. 1966). A total recognized. The clinical signs of fish challenged to A. hydrophila
20 antimicrobial agents (Hangzhou Microbial Reagent Co., Ltd) were similar to those of the naturally infected fish recorded (Fig.
including amoxicillin (10 g/disc), florfenicol (75 g/disc), 1).
levofloxacin (5 g/disc), tetracycline (30 g/disc), neomycin (30
g/disc), novobiocin (30 g/disc), doxycycline (30 g/disc), The cumulative mortality
gentamicin (10 g/disc), norfloxacin (10 g/disc), aztreonan (30 The cumulative mortality of BSB challenged with A.
g/disc), fortum (30 g/disc), kanamycin (30 g/disc), hydrophila at 7 days post-inoculation was showed in Fig. 2. The
ceftriaxone sodium (30 g/disc), ofloxacin (5 g/disc), different mortalities were found in different bacterial suspension
piperacillin (100 g/disc), clindamycin (2 g/disc), rifampicin (5 densities. The mortality was recorded as 10, 10, 70 and 100%
g/disc), imipenem (10 g/disc), erythromycin (15 g/disc) and after bacterial intraperitoneal injection with 1.710 4, 1.7105,
chloramphenicol (30 g/disc) were used for investigation. Two 1.7106 and 1.710 7 cfu/fish, respectively. Non-died fish was
strains of bacteria, D4 and HU201301, were used in antibiotic recorded in negative control group during experiment carried out.
susceptibility test. A bacterial suspension (100 L) was spread The median lethal dose (LD50) was 5105 cfu/fish in
onto nutrient agar plates and then chemotherapeutic agent discs intraperitoneal injection of A. hydrophila to BSB.
were placed on. The plates were incubated at 28 oC for 24 h. The
Re-isolation and re-identification
diameter of each inhibition zone (including the diameter of the
disc) was measured and recorded in mm. The responses were A total of 15 bacterial strains were re-isolated from spleen,
illustrated, which is resistant (R), intermediate (I) or sensitive (S) liver and kidney of moribund artificially injected fish with
according to manufacturers recommendation. clinical signs. No evident external lesions or died fish in control
group were recorded and no bacteria were isolated from either
F. Molecular analysis the control experimental fish.
Bacteria were incubated on the agar medium at 28 oC for 24 A similarity was found in biochemical characteristics between
hours. The bacterial suspension was prepared by being diluted in experimental original strain (D4) and re-isolated strains
sterile double-distilled water and centrifuged at 12,000 rpm in 5 (HU201301, HU201302 and HU201303) shown in Table 1. For
min at 4 C. Genomic DNA was extracted using ammonium the morphological characteristics, these bacterial strains grew on
acetate precipitation technique as described previously (Bruford nutrient agar at 28 oC for 24 hours with mucoid yellow colour
et al. 1998) with slight modification. The quality of genomic colonies. All can growth on AHM medium at 28 oC. Microscopic
DNA was evaluated using electrophoresis in 1% agarose gels. observation exhibited a phonotypical homogenization of short
The quantity of genomic DNA samples was measured by using a rod-shaped. All were gram-negative, motile, oxidase-positive and
Nanodrop 2000 (Thermo Scientific, USA). DNA was stored at - catalase-negative. Biochemical testing resulted in positive

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International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 3
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reaction of all tested bacterial strains for production of indole and in amplification of genomic DNA genes and had allowed
H2S, utilization of citrate, hydrolysis of starch and esculin, discriminating of identification up to the species level and typing
fermentation of glucose, lactose, arabinose and mannitol and of other bacteria (Jiang et al. 2006; Sarkar et al. 2012). It has
Methyl Red/Voges-Proskauer. Nevertheless, negative reaction been indicated previously that levels of similarity between
was shown for fermentation of sucrose and salicine in all tested genomic DNA gene sequences higher than 97% suggest that the
strains. strains in question belong to the same species (Stackebrandt and
Goebel 1994), so a 98% identity of sequences of the D4 and
Genomic DNA sequence analysis
HU201301 strains implies that they belong to the same species.
The identification of A. hydrophila based on morphological This challenge test experiment did fulfil Kochs postulates
and biochemical characteristics were carried out. Subsequently, a (Walker et al. 2006).
number of colonies of strains incubated for 24 hours were chosen The high cumulative mortality (100%) of BSB (challenged
for PCR amplification. PCR products of 16S genomic DNA gene with 1.7107 cfu/fish by intraperitoneal injection method) in this
of D4 and HU201301 were sequenced to validate for A. study was comparable to the results previously reported (Mostafa
hydrophila identification. A similarity of identity percentage et al. 2008). They have challenged Heteropneustes fossilis with
(98%) with the nucleotide sequences of genomic DNA gene of A. hydrophila at a dose of 9.6107 cfu/fish using intraperitoneal
two strains was showed; and a high similarity (99% identity) to and intramuscular injection, which also resulted in 100%
other available A. hydrophila sequences in the GenBank database mortality of the tested fish within 1-9 days. Similarly, the
by using BLAST network search. reported mortality of some other fish species challenged by
intraperitoneal injection with lower bacterial density, such as
Antimicrobial susceptibility test walking catfish C. batrachus with 106 cfu/fish (Angka 1990) and
The pattern of antibiotic susceptibility of two strains of A. snakehead C. striata with 106 cfu/fish (Duc et al. 2013) was
hydrophila (D4 and HU201301) is shown in Table 2. This present 100%. Also, several fish species (Labeo rohita, Catla catla and
study found the relevant similarities between the original Cirrhinus cirrhosis) challenged by intramuscular method at a
bacterial strain (D4) used in conducting challenge experiment dose of 2106 cfu/fish had 80 to 100% mortality, while
and the re-isolated strain (HU201301). Both strains showed Hypophthalmichthys molitrix (Valenciennes, 1844) and C. carpio
resistance to amoxicillin, and clindamycin and sensitive to at a dose of 2105 cfu/fish had 60-80% mortality within 2-12
novobiocin, florfenicol, levofloxacin, tetracycline, neomycin, days (Sabur 2006) (cited by Sarkar and Rashid 2012). The LD 50
doxycycline, gentamicin, norfloxacin, aztreonan, fortum, value in this study was 5105 cfu/fish, similar to the LD 50 of A.
kanamycin, ceftriaxone sodium, ofloxacin, piperacillin, hydrophila challenged to snakehead fingerling (Duc et al. 2013),
rifampicin, and chloramphenicol. Interestingly, the D4 strain and lower than for some other fish species, such as Anguilla
showed resistance to imipenem and sensitive to erythromycin, anguilla (106.2 to 107.4 cfu/fish) (Esteve et al. 2004), Channa
while HU201301 showed intermediate to those of antibiotic punctatus (3.42107 cfu/fish) (Yesmin et al., 2004) and Brycon
agents.
amazonicus (6.661011 cfu/fish) (Oliveira et al. 2012), indicating
IV. DISCUSSION that isolates used in challenge test were strongly virulent to BSB.

In this study, a challenge test with A. hydrophila demonstrated Chemotherapeutic agents were previously introduced to treat
similarities in the clinical signs recorded by artificially A. hydrophila infection in cultured fish (Saitanu and Chularak
challenged and naturally infected BSB. The observed symptoms 1983). In this study, the antibiotic sensitivity patterns of two
in the present study resembled those reported in other fish strains (D4 and HU201301) were evaluated and confirmed to be
(Popovic et al. 2000; Nielsen et al. 2001; He et al. 2006; Duc et mostly similar. This test was conducted in order to confirm the
al. 2013). Three among fifteen strains re-isolated from tested fish resemblance of re-isolated strain (HU201301) and experimental
were used to conduct experiment on biochemical tests. Based on inoculated bacterial strain (D4) in sensitive ability to
biochemical characteristics, it was determined that the four antimicrobials, and also to determine the suitable therapeutical
strains (D4, HU201301, HU201302 and HU201303) of bacteria medicines for controlling Aeromonas infection in BSB. Both
were homogenous, which is comparable to previous reports (Lee strains were sensitive to most tested drugs, except for amoxicillin
et al. 2000; Abbott et al. 2003). All four strains grew on the and clindamycin. D4 was also resistant to imipenem, while
previously described AH medium (Kaper et al. 1979), used for HU201301 was only intermediately resistant to this drug. In
species identification, confirming that these bacterial strains are previous studies, A. hydrophila was reported to be sensitive to
A. hydrophila. chloramphenicol, erythromycin, kanamycin, neomycin
Molecular method for detecting of A. hydrophila was (Boonyaratpalin 1989) and resistant to amoxicillin and
introduced and applied in numerous previous studies (Nielsen et clindamycin (Belem-Costa and Cyrino 2006; Adanir and
al. 2001; Swaminathan et al. 2004; Yogananth et al. 2009). The Turutoglu 2007; Jayavignesh et al. 2011). The results from the
genomic DNA was the coding region of ribosomal RNA, which present study were similar to these, but different from the results
was used for phylogenetic studies as it is highly conserved reported by Son et al. (1997, p. 480) and Vivekanandhan et al.
between different species of bacteria and archaea and as (2002, p. 166), who found that A. hydrophila was resistant to
important taxonomic tools (Weisburg et al. 1991; Coenye and chloramphenicol, erythromycin, kanamycin, tetracycline,
Vandamme 2003) such as taxonomy of the genera Aeromonas rifampicin and novobiocin.
(Lee et al. 2002; Chen et al. 2012; Liu and Li 2012; Sarkar et al. The susceptibility of the experimental bacterial strains (D4 and
2012). Two universal primers, 27F and 1492R, were developed HU201301) to some beta-lactam antibiotics was also

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International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 4
ISSN 2250-3153

investigated. In comparison to a previous report (Morita et al. [8] Belem-Costa, A. and J.E.P. Cyrino. 2006. Antibiotic resistence of
Aeromonas hydrophila isolated from Piaractus mesopotamicus (Holmberg,
1994), the results showed the similarity in susceptibility to 1887) and Oreochromis niloticus (Linnaeus, 1758). Sci. agric. (Piracicaba,
aztreonam and imipenem, and difference in resistance to Braz.) 63:281-284.
piperacillin and ceftriaxone. These differences may be related to [9] Boonyaratpalin, S. 1989. Bacterial pathogens involved in the Epizootic
the source of bacterial isolates and the source of antibiotic agents Ulcerative Syndrome of fish in Southeast Asia. Journal of Aquatic Animal
used in the experiment. Moreover, it is known that the bacteria Health 1:272-276.
can receive and transmit antibiotic resistant genes from and to [10] Bruford, M.W., O. Hanotte, J.F.Y. Brookfield and T. Burke. 1998.
Multilocus and single-locus DNA fingerprinting. In: Molecular Genetic
other gram-negative bacteria (Marchandin et al. 2003). Thus, Analysis of Populations: A Practical Approach (ed. A.R. Hoelzel), 2nd
aeromonad-infection in BSB may still be controlled by using edition, IRL Press, Oxford, UK.
correct drugs. Nevertheless, reduction of the use of chemicals in [11] Chen, Y.F., R.S. Liang, X.L. Zhuo, X.T. Wu and J.X. Zou. 2012. Isolation
aquaculture is nowadays considered a good management and characterization of Aeromonas schubertii from diseased snakehead,
Channa maculata (Lacepede). Journal of Fish Diseases 35:421-430.
practice. Certain types of chemicals, especially antibiotics, if
[12] Chirila, F., N. Fit, G. Nadas, O. Negrea and R. Ranga. 2008. Isolation and
used inappropriately, not only cause damages to animals and the characterization of an Aeromonas hydrophila strain in a crap (Cyprinus
environment, but also increase production costs and adverse carpio) toxemia focus. Bulletin UASVM, Veterinary Medicine 65:244-247.
consequences (Tonguthai 2000). Furthermore, the observation of [13] Citarasu, T., D.K. Alfred, S. Velmurugan, V.V. Thanga, T. Kumaran, B.M.
disease odd usually correlates with anorexia (Duc et al. 2013); Michael and T. Selvaraj. 2011. Isolation of Aeromonas hydrophila from
hence the utilization of antibiotics at the disease outbreak time infected ornamental fish hatchery during massive disease outbreak.
International Journal of Current Research 2:037-041.
may not be effective. Also, the extensive use of antibiotic and
[14] Coenye, T. and P. Vandamme. 2003. Intragenomic heterogeneity between
other chemotherapeutics to prevent and treat fish diseases may multiple 16S ribosomal RNA operons in sequenced bacterial genomes.
cause drug-resistance phenomenon in cultured fish (Son et al. FEMS Mircobiol Lett. 228:45-49.
1997). Vaccination treatment was recommended for use in [15] Doukas, V., F. Athanassopoulou, E. Karagouni and E. Dotsika. 1998.
disease prevention in cultured fish (Bakopoulos et al. 1995; Aeromonashydrophila infection in cultured sea bass, Dicentrarchus labrax
Sommerset et al. 2005) and herbal concoction was used in the L., and Puntazzo puntazzo Cuvier from the Aegean Sea. Journal of Fish
Diseases 21:317-320.
therapy of A. hydrophila infection in goldfish (Harikrishnan et al.
[16] Duc, P.M., T.N. Tuan and K. Hatai. 2013. Aeromonas hydrophila infection
2009). in fingerlings of snakehead Channa striata in Viet Nam. Fish Pathology
48:48-51.
V. CONCLUSION [17] Esteve, C., E. Alcaide, R. Canals, S. Merino, D. Blasco, M.J. Figueras and
J.M. Tomas. 2004. Pathogenic Aeromonas hydrophila serogroup O:14 and
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which can cause haemorrhagic septicaemia clinical signs in BSB. 70:5898-5904.
In the antimicrobial susceptibility test, both tested bacterial [18] Fishbase. 2012. http://www.fishbase.org/summary/Megalobrama-
amblycephala.html. Accessed 08 Oct 2012.
strains showed sensitivity to most used drugs.
[19] Harikrishnan, R., C. Balasundaram, Y.G. Moon, M.C. Kim, J.S. Kim and
M.S. Heo. 2009. Use of herbal concoction in the therapy of goldfish
ACKNOWLEDGMENT (Carassius auratus) infected with Aeromonas hydrophila. Bull Vet Inst
Pulawy 53:27-36.
The first author T.N. Tuan would like to thank the China [20] He, L.J., L.K. Liao, J.F. Yuan, H.Y. Tang, Q. Wu and G.W. Zhang. 2006.
Scholarship Council for providing scholarship of doctoral Pathological observation of bacterial septicemia in Megalobrana
program in Huazhong Agricultural University, Wuhan, Hubei, amblycephala. Journal of Southwest Agricultural University (Natural
Science) 28:483-490.
China.
[21] Hu, M., N. Wang, Z.H. Pan, C.P. Lu and Y.J. Liu. 2012. Identity and
virulence properties of Aeromonas isolates from diseased fish, healthy
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International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 6
ISSN 2250-3153

A B
Fig. 1. Clinical signs of BSB (M. amblycephala) intraperitoneally challenged to A. hydrophila (1.7107 cfu/fish). (A)
Haemorrhage at the site of injection and ventral surface; (B) Red odiferous fluid, swollen and colour-deep spleen (arrow)

Fig. 2. Cumulative mortality of BSB (M. amblycephala) challenged with A. hydrophila

Fig. 3. Effect of NaCl concentrations (%) on growth of D4 and HU201301

Table 1. Biochemical profile of D4 and re-isolated strains of A. hydrophila

Biochemical test D4 HU201301 HU201302 HU201303
Gram stain - - - -
Motility + + + +
Oxidase + + + +
Catalase + + + +

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International Journal of Scientific and Research Publications, Volume 5, Issue 7, July 2015 7
ISSN 2250-3153
Glucose + + + +
Sucrose - - - -
Lactose + + + +
Arabinose + + + +
Mannitol + + + +
Salicine - - - -
MR + + + +
VP + + + +
Citrate utilization + + + +
Esculine hydrolysis + + + +
Starch hydrolysis + + + +
Indole production + + + +
H2S production + + + +
AHM + + + +
(+) = positive reaction; (-) = negative reaction

Table 2. Antimicrobial susceptibility testing of experimental original strain (D4) and re-isolated strain of A. hydrophila
HU201301
Antibiotic agents (g/disc) D4 HU201301
Amoxicillin (10) R R
Florfenicol (75) S S
Levofloxacin (5) S S
Tetracycline (30) S S
Neomycin (30) S S
Novobiocin (30) S S
Doxycycline (30) S S
Gentamicin (10) S S
Norfloxacin (10) S S
Aztreonam (30) S S
Fortum (30) S S
Kanamycin (30) S S
Ceftriaxone sodium (30) S S
Ofloxacin (5) S S
Piperacillin (100) S S
Clindamycin (2) R R
Rifampicin (5) S S
Imipenem (10) R I
Erythromycin (15) S I
Chloramphenicol (30) S S
R = resistance; I = Intermediate; S = sensitivity

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