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Memórias do Instituto Oswaldo Cruz
Fundação Oswaldo Cruz, Fiocruz
ISSN: 1678-8060 EISSN: 1678-8060
Vol. 91, Num. 4, 1996, pp. 499-500
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Mem Inst Oswaldo Cruz, Rio de Janeiro, Vol. 91(4),
pp. 499-500. Jul/Aug 1996
Received 17 October 1995. Accepted 18 April 1996
Research note
Behaviour of Aeromonas spp. after Animal Passage
VC Almeida^+ , MP Nunes
Laboratorio de Zoonoses, Departamento de Microbiologia Medica,
Instituto de Microbiologia, CCS-UFRJ,Caixa Postal 68040,
21941-590 Rio de Janeiro, RJ, Brasil
^+Corresponding author. Fax:55-21-270.8793
Code Number: OC96095
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[TABLES AND FIGURES AT END OF TEXT]
Key words: Aeromonas - biological
characteristics - animal passage
The Aeromonas genus have been considered as important
infectious agents in humans and animals (JM Janda 1991 Clin
Microbiol Reviews 4: 397-410). The biological
characteristics such as, toxins production (e. g. hemolysins,
cytotoxins and enterotoxins) and also cell-associated
features, that appear to play important role in infectious
processes in humans and animals, have been studied in the
attempt of elucidate patogenicity of the different
Aeromonas species (Janda loc. cit.). Evidences
indicate that the animal passage may influence in the
expression of biological characteristics in many organisms
such as, Plesiomonas shigelloides (SC Sanyal et al.
1980 J Med Microbiol 13: 401-409) and Vibrio cholera
O1 biotype El Tor (A Tikoo et al. 1994 J Med Microbiol
40: 246-251). DV Singh and SC Sanyal (1992 J Med
Microbiol 37: 262-267) reported that passage
through rabbit instestines may control the expression of the
genes responsible for toxins production in Aeromonas
spp.
In this communication we report on the alteration of the
hemolytic and enterotoxigenic character and also surface
characteristics in one strain of Aeromonas isolated
from environment, after animal passage by endovenous route.
Four samples of Aeromonas were used in this study,
three from polluted estuary water (A. caviae - 030,
Aeromonas sp. - 057, A. trota - 058) and one
from drain treatment station supplyed by Fundac o Oswaldo
Cruz, Rio de Janeiro (A. hydrophila - T336). Those
strains were maintend in nutrient agar (NA) with 1% of NaCl
(FW Hickman-Brenner et al. 1987 J Clin Microbiol 25:
900- 906) at room temperature.
All samples were tested with regar to hemolysin production,
through b hemolysis zones around the colonies in rabbit blood
agar with 5% (v/v) of eritrocytes and the haemolitic activity
was analyzed with the metodology described by M Cumberbatch et
al. (1979 Infect Immun 23: 829-837). The suckling mouse
test (WA Dean et al. 1972 Infect Dis 125: 407), was
used for enterotoxin detection, the autoagglutination capacity
for self pelleting (SP) and for preciptation after boiling
(PAB) as described by JM Janda et al. (1987 Infect Immun
55: 3070-77). The hidrofobic profile by phase partitioning
with hydrocarbon solvents described by M Rosenburg et al.
(1980 Fems Microbiol Lett 9: 29-33).
Strains for animal experiments were cultivated in 5ml of BHI
(OXOID) at 28^oC for 5 hr. After this period, samples were
centrifugated at 3000 x g by 10 min and ressuspended in
sterile saline (0.85%).
Six groups of two male albinic mouses BALB/C, 4-6 weeks old,
were inoculated by endovenous route with 0.5 ml of the
bacterial suspension with 10^10 cells per ml.The control
group received 0.5 ml of sterile saline (0.85%). All strains
were recovered from spleen 24 hr after inoculation.
It was observed that, from the four enviroment strains, just
A. hydrophila T336, from the drain water station
treatment, that had not produced toxins in the early tests,
became hemolytic with high titre and produced enterotoxin
after inoculation in mouse (Table). The autoagglutination
capacity expressed by SP^- PAB^+ phenotype (did not make self
pellet and precipitate after boiling) considered by Janda
(loc. cit.) as a virulence marker for Aeromonas
was observed in A. hydrophila T336 over the increase
of it's hidrofobic capacity after animal passage.
According to Singh (loc. cit.) strains of Aeromonas
which did not produce toxins during the initial
experiments became toxigenic after one to three consecutive
passages through rabbit intestines, thus suggesting that
Aeromonas are potentially enterotoxic and hemolytic
despite the species and origin of strain. Such behaviour may
be a result from the existence of a repression-derepression
phenomenon controlling expression of a toxin gene, depending
on a passage through the gut of a susceptible host. However,
according to our experiments, the changes in the hemolytic and
enterotoxigenic behaviour also occurs after intravenous
inoculation together with alterations in the autoagglutination
capacity and hidrofobicity, as seen with A. hydrophila
T336. It was observed that the animal passage may
influence in the expression of those characteristics despite
of the inoculation route.
This work was supported by grants from CAPES (Coordenac o de
Aperfeicoamento de Pessoal de Nivel Superior) and FINEP
(Financiadora de Estudos e Projetos).
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Table. Characteristics of Aeromonas spp. strains
before and after animal passage
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Strains Hemolitic Entero- Autoagglu- Hidrofobic
activity toxin tination capacity (%)
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A. caviae -/- -/- SP^-PAB^-/SP^-PAB^- 58.0/62.5
(030)
Aeromonas sp. -/- -/- SP^+PAB^+/SP^+PAB^+ 58.0/58.5
(057)
A. hydrophila -/1024 -/+ SP^-PAB^-/SP^-PAB^+ 70.0/10.5
(T336)
A. trota 8/8 -/- SP^-PAB^-/SP^-PAB^- 12.0/22.5
(058)
- negative results ; + positive results; SP: self pelleting ;
PAB: preciptation after boiling; %: adherence percentage face
to xilen apolar solvent
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Copyright 1996 Fundacao Oswaldo Cruz
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