Aeromonas Veronii Biovar Sobria Research Articles

Characterization and Pathology of Aeromonas veronii Biovar Sobria from Diseased Sheatfish Silurus glanis in China

Aeromonas spp., is an important opportunistic pathogen responsible for great economic losses in aquaculture. In this paper, we report our study of an Aeromonas infection that occurred in cultured sheatfish Silurus glanis in May 2016 in a farm in Tianjin city. Typical external symptoms included petechial skin hemorrhages, ascitic distension of the abdomen, redness and swelling of the anus. The isolate SAV-165 from the diseased fish was identified as A. veronii biovar sobria by biochemical properties and molecular techniques. Experimental challenge showed that a 50% lethal dose (LD50) of SAV-165 was 1.59 × 106 CFU/ml in zebrafish Danio rerio. The antimicrobial susceptibility test indicated that the isolate was susceptible to aminoglycosides and chloramphenicol, but resistant to penicillins and sulphonamides. Histopathological examination showed fatty changes and swelling of hepatocytes in the liver, congestion in the submucosa of intestine and the renal veins of the kidney. This is the first report of A. veronii biovar sobria infection in S. glanis in China.

Effect of dietary selenium on immuno-biochemical plasticity and resistance against Aeromonas veronii biovar sobria in fish reared under multiple stressors

The present investigation aims to study role of dietary selenium (Se) on growth performance, oxidative stress markers (catalase, superoxide dismutase and glutathione-s-transferase), stress biomarkers [blood glucose, cortisol and heat shock protein (HSP 70) and immunological status, Nitro blue tetrazolium (NBT), total protein, albumin, globulin, A/G ratio, total immunoglobulin and vitamin C] and survival of fish after Aeromonas veronii biovar sobria challenged. Pangasianodon hypophthalmus was treated with lead (Pb, 4 ppm), and high temperature (34 °C) for 60 days. The growth performance was reduced with declined in feed intake, growth rate and feed efficiency in case of group exposed with Pb alone and concurrent exposure to Pb high temperature (34 °C). The Se has immunomodulatory properties however, supplementation of the dietary Se @ 1 and 2 mg/kg diet has been realistically improved growth performance up to 240%, elevated antioxidative status in different tissues, and immunological status were also improved significantly in the P. hypophthalmus. The bacterial challenged with A. veronii biovar sobria in the P. hypophthalmus resulting in less cumulative mortality (%) and high relative (%) survival has been observed with supplementation of dietary Se @ 1 and 2 mg/kg diet. The bioaccumulation of Pb in muscle tissue has been also drastically reduced with supplementation of dietary Se in feed. Hence, overall results indicated that, dietary Se @ 1 and 2 mg/kg have ability to enhanced overall performance and alleviated multiple stresses in P hypophthalmus.

Immuno-protective role of biologically synthesized dietary selenium nanoparticles against multiple stressors in Pangasinodon hypophthalmus

An environment friendly and sustainable approach is being emerged in the area of nanotechnology for accelerated growth and development of culturable aquatic animals hence green chemistry is gaining momentum in recent years. The present study has been carried out to delineate the effects of selenium nanoparticles (Se-NPs) on growth performance, antioxidative status and immunity of fish reared under lead (Pb) and high temperature (34 °C). Three hundred and fifteen fish were equally distributed in seven treatments in triplicates. Three isocaloric and isonitrogenous experimental diets viz. control (Se-NPs-0 mg/kg), Se-NPs at 1 mg/kg and Se-NPs at 2 mg/kg were formulated. The fish were reared under lead (Pb, 1/21st of LC50 (4 ppm)) and high temperature (34 °C) stress and fed with or without dietary Se-NPs. The effects of dietary Se-NPs were studied in terms of growth performance (Weight gain %, feed conversion ratio, protein efficiency ratio and specific growth rate), antioxidative status (catalase, superoxide dismutase, glutathione-S-transferase and glutathione peroxidase), neurotransmitter enzymes (AChE), stress biomarkers (heat shock protein 70, serum cortisol, blood glucose, vitamin C), immunological status (total protein, A/G ratio and respiratory burst activity) in Pangasinodon hypophthalmus post challenge with Aeromonas veronii biovar sobria. Results of the investigation demonstrated significant improvement of growth performance, antioxidative status, neurotransmitter enzyme activity, stress markers and more importantly enhanced immunity of the fish with dietary incorporation of Se-NPs at 1 mg/kg. In addition, post bacterial infection, the relative % survival increased and cumulative mortality % decreased in the group fed with Se-NPs at 1 mg/kg diet. Pb and high temperature treated and fed with control diet group showed devastating impact on the growth performance, antioxidative status, stress markers and immunity of the fish. Similarly, application of Se-NPs at 2 mg/kg showed poor growth performance and elevated level of oxidative stress and other stress biomarkers including other biochemical attributes. Inclusive results indicated that, Se-NPs at 1 mg/kg has capability to enhance overall performance and alleviate multiple stresses in P. hypophthalmus. Hence, Se-NPs at optimum level have ability to develop green chemistry in feed industry for better growth performance of the fish.

Isolation and characterization of a novel, T7-like phage against Aeromonas veronii.

A virulent Aeromonas veronii biovar sobria and the corresponding novel, lytic bacteriophage (VTCCBPA5) were isolated from village pond water. The phage was found to belong to family Podoviridae. PCR analysis of major capsid protein gene confirmed its classification to T7-like genus. The protein profiling by SDS-PAGE indicated the major structural protein to be~45kDa. The phage (VTCCBPA5) is host specific and is stable over a range of pH (6-10) and temperatures (4-45°C). On the basis of restriction endonuclease analysis combined with prediction mapping, it was observed to vary significantly from previously reported podophages of Aeromonas sp., viz. phiAS7 and Ahp1. The phylogenetic analysis on the basis of PCR-amplified segment of DNA polymerase gene of phage revealed it being an outgroup from podophages of Klebsiella sp. and Pseudomonas sp. though a small internal fragment (359bp) showed the highest identity (77%) with Vibrio sp. phages. Thus, this is the first report of a novel Podoviridae phage against A. veronii. It expands the assemblage of podophages against Aeromonas sp. and BPA5 could be potentially useful in biocontrol of environmentally acquired Aeromonas veronii infections.

Dietary zinc promotes immuno-biochemical plasticity and protects fish against multiple stresses

The abiotic and biotic stress is an episode that effect on regulatory, neuro-endocrine and immune systems of animals including fish. The stress creates stimulatory and suppressive of immune system resulting in increases the incidence of infection. In view of these points, we have conducted an experiment to mitigate the stress through a nutritional approach through Zinc (Zn) supplementation in Pangasius hypophthalmus (initial weight-3.65 ± 0.75 g). Three isocaloric and isonitrogenous diets with graded levels of zinc 0, 10 and 20 mg/kg were prepared and fed to seven different groups with each in triplicate. The experimental group as follows as normal water with control diet (Ctr/Ctr), lead (Pb) exposed and fed with control diet (Ctr/Pb), control diet and exposed to Pb and temperature (Ctr/Pb-T), Zn 10 mg/kg fed without stressors (Zn- 10 mg/kg), Zn 20 mg/kg fed without stressors (Zn-20 mg/kg), Zn 10 mg/kg fed and Pb and temperature exposed (Pb-T/Zn 10 mg/kg) and Zn 20 mg/kg fed and exposed to Pb and temperature (Pb-T/Zn 20 mg/kg). The Pb in treated water was maintained at the level of 1/20th of LC50 (4 ppm) and temperature at 34 °C in exposure groups. The neutraceuticals role of dietary Zn was studied in terms of antioxidative enzymes (catalase, superoxide dismutase, glutathione-S-transferase), stress markers (Heat shock protein 70, cortisol, acetylcholine esterase, blood glucose, Vitamin C), immunological parameters (Total protein, albumin, globulin, A/G ratio and NBT) and subsequent challenge with Aeromonas veronii biovar sobria. The antioxidative enzymes, stress markers, albumin were significantly (p < 0.01) elevated, brain AChE and immuno-hematological parameters were significantly (p < 0.01) decreased due to lead (Pb) and temperature exposure. The relative survival (%) was reduced due to the concurrent effect of Pb, high temperature stress and bacterial challenge. Zinc at the rate of 10 and 20 mg/kg was found to be restore the biochemical and immunological parameters against concurrent exposure to lead (Pb), temperature and pathogenic infection. Results obtained in the present study indicate that supplementation of 10 and 20 mg/kg of Zn in the diet has a definitive role in the mitigation of lead (Pb) and temperature exposure along with pathogenic infection in P. hypophthalmus.

Infection status and virulent genes of Aeromonas in diarrhea patients in Pudong New Area, Shanghai

To investigate the infection status and virulent genes of Aeromonas in patients with acute diarrhea in Pudong New Area, Shanghai. In 2012, stool samples were collected from diarrhea patients in 12 sentinel hospitals in Pudong for the detections of 13 pathogens causing diarrhea, and the detections of 5 diarrhea related virulent genes were conducted for Aeromonas isolates. A total of 101 patients were infected with Aeromonas in 2533 patients (4.0%). A total of 101 Aeromonas strains were isolated, including 17 Aeromonas hydrophila strains (18.8%), 44 Aeromonas veronii biovar sobria strains (52.5%) and 12 Aeromonas caviae strains (29.7%). And 44 coinfections with other pathogens were detected. Aeromonas infection mainly occurred in summer and in people aged ≥20 years. Among the patients infected with Aeromonas, 71 (70.3%) had watery diarrhea, 20 (19.8%) had vomiting and 11 (10.9%) had fever. Virulent genes detection showed that 95.0% of the Aeromonas. strains carried virulent genes, and the detection rates of hlyA, aerA, act, alt, and ast genes were 5.9%, 6.9%, 67.3%, 42.6% and 13.9%, respectively. High incidence of Aeromonas infection was found in the patients with acute diarrhea in Pudong, and a high proportion of coinfections with other pathogens was detected too. Most Aeromonas strains carried virulent genes, and the distribution varied.

Detection and Characterization of Antimicrobial Resistance and Putative Virulence Genes inAeromonas veroniiBiovar Sobria Isolated from Gilthead Sea Bream (Sparus aurataL.)

The purposes of this study were to investigate the antimicrobial resistance of Aeromonas veronii biovar sobria isolated from gilthead sea bream and to characterize the virulence-implicated genes. Fish samples (n=365) were collected from wholesale and retail markets in Aljouf, Saudi Arabia between 2013 and 2014. A total of 45 A. veronii biovar sobria isolates (12.3%) from those samples were tested for resistance to a range of antimicrobial agents. All strains exhibited 100% resistances to nalidixic acid, carbenicillin, cephalothin, erythromycin, kanamycin, tetracycline, and trimethoprim-sulfamethoxazole. Additionally, the highest susceptibility encountered was to ciprofloxacin (100%). In the present study, we examined the presence of several genes, including aerolysin, elastase, lipase, flagellin, enterotoxin, and DNases, that code for putative virulence factors that may play important roles in bacterial infection. It was found that all of these genes were common in these strains. Several strains isolated from diseased gilthead sea bream were tested for virulence in gilthead sea bream by intraperitoneal injections. The median lethal dose values ranged from 5×10(3) to 5.2×10(9) colony-forming units per fish. These data suggest that commercial gilthead sea bream fish may act as the reservoir for multiresistant A. veronii biovar sobria and facilitate the dissemination of virulence genes.

Tissue distribution, expression, and antimicrobial activity of Anas platyrhynchos avian β-defensin 6

In this study, a novel avian β-defensin (AvBD) was isolated from the Chaohu duck. The complete nucleotide sequence of the gene contained a 204-bp open reading frame that encoded 67 amino acids (aa), including a signal peptide of 20 aa, a propiece of 5 aa, and a mature peptide of 42 aa. The homology, characterization, and comparison of this gene with AvBD from other avian species confirmed that it was duck AvBD6. Also, the preproprotein of AvBD6 from chicken, goose, and duck was highly conserved with 100% aa homology. The AvBD6 mRNA was widely expressed in the investigated tissues of healthy 5-mo-old ducks, with the exception of the skin, kidney, and bursa. The AvBD6 mRNA was highly expressed in the spleen, lung, stomach, tongue, and egg yolk, successively; moderately expressed in the bone marrow and liver; and expressed to lower degrees in the trachea, heart, intestine, muscle, esophagus, and testis. We produced recombinant AvBD6 by expressing the gene in Escherichia coli. The yield of soluble glutathione S-transferees (GST)-AvBD6 in the inclusion bodies increased significantly as the incubation temperature was decreased from 37 to 30°C. As expected, the GST-AvBD6 exhibited strong bactericidal properties [minimum inhibitory concentration (MIC) = 0.5 to 2 μM] against the Aeromonas veronii biovar sobria strain BJCP-5, E. coli, and Enterococcus faecalis [ATCC 29212); it possessed medium bactericidal properties (MIC = 4 to 8 μM) against Staphylococcus aureus, Salmonella enteritidis, Pseudomonas aeruginosa (ATCC 27853), and Bacillus subtilis (CMCC 63501;; and it possessed low bactericidal properties (MIC = 16 μM) against Candida albicans (ATCC 10231). Additionally, the antimicrobial activity of GST-AvBD6 proved to be the same as that of synthetic AvBD6. The A. veronii biovar sobria strain BJCP-5 cells that were treated with GST-AvBD6 showed lysis and shrinkage under scanning electron microscopy. The mechanisms of AvBD6-mediated killing of A. veronii biovar sobria involved both cell lysis and nonlysis. Our results indicate that AvBD6 plays an important role in the innate immunity of the Chaohu duck.

Infections following the application of leeches: two case reports and review of the literature

IntroductionSince the 1980s, leeches have been ingeniously used in the management of venous flap congestion. The presence of anticoagulative substances in their saliva improves the blood drainage. Their digestive tract contains several bacterial species, the main ones being Aeromonas hydrophila and Aeromonas veronii biovar sobria, which contribute to the digestion of ingested blood. These bacteria can be the cause of infections.Case presentationWe report two cases of septicemia related to Aeromonas veronii biovar sobria that presented after leeches had been applied to congested transverse rectus abdominis myocutaneous flaps for delayed mammary reconstructions.Patient number 1 was a 55-year-old Caucasian woman who underwent a delayed breast reconstruction procedure. On the sixth postoperative day she showed a clinical presentation of septicemia. Aeromonas veronii biovar sobria was identified in the patient’s skin and blood bacteriological samples. Her fever ceased after 4 days of antibiotic treatment.Patient number 2 was a 56-year-old Caucasian woman who underwent a delayed breast reconstruction procedure. On the seventh postoperative day we noticed that she showed a clinical presentation of septicemia. Aeromonas veronii biovar sobria was identified in the patient’s blood cultures and local bacteriological samples. An antibiogram showed resistance to amoxicillin/clavulanic acid. Her fever ceased on the eleventh postoperative day after 4 days of antibiotic treatment.ConclusionThe rate of infection after application of leeches is not negligible. The concentration of Aeromonas inside the digestive tracts of leeches largely decreases when the patient is under antibiotic therapy. These germs are sensitive to third-generation cephalosporins and fluoroquinolones and resistant to amoxicillin/clavulanic acid. We recommend preventive treatment based on classical measures of asepsis and on oral antibioprophylaxy with a fluoroquinolone during the whole period of treatment by leeches.

Gastrointestinal Colonization Rates for Human Clinical Isolates of Aeromonas Veronii Using a Mouse Model

A variety of environment-associated gastrointestinal infections have been associated with the Aeromonas group of bacteria which contain both non-virulent strains as well as virulent strains within a particular species. This study monitors the colonization rates of colon tissue in a mouse-streptomycin dose/response model involving isolates of Aeromonas veronii biovar sobria obtained from human clinical specimens. The ability to successfully colonize mouse colon tissues by the human clinical isolates was then compared with the rates achieved in a previous study of Aeromonas isolates obtained from environmental drinking water samples. Results suggest that strains of Aeromonas isolated from drinking water environmental samples contain pathogenic and virulence capabilities similar to those seen in Aeromonas veronii clinical isolates from human infections.

Complex Evolutionary History of the Aeromonas veronii Group Revealed by Host Interaction and DNA Sequence Data

Aeromonas veronii biovar sobria, Aeromonas veronii biovar veronii, and Aeromonas allosaccharophila are a closely related group of organisms, the Aeromonas veronii Group, that inhabit a wide range of host animals as a symbiont or pathogen. In this study, the ability of various strains to colonize the medicinal leech as a model for beneficial symbiosis and to kill wax worm larvae as a model for virulence was determined. Isolates cultured from the leech out-competed other strains in the leech model, while most strains were virulent in the wax worms. Three housekeeping genes, recA, dnaJ and gyrB, the gene encoding chitinase, chiA, and four loci associated with the type three secretion system, ascV, ascFG, aexT, and aexU were sequenced. The phylogenetic reconstruction failed to produce one consensus tree that was compatible with most of the individual genes. The Approximately Unbiased test and the Genetic Algorithm for Recombination Detection both provided further support for differing evolutionary histories among this group of genes. Two contrasting tests detected recombination within aexU, ascFG, ascV, dnaJ, and gyrB but not in aexT or chiA. Quartet decomposition analysis indicated a complex recent evolutionary history for these strains with a high frequency of horizontal gene transfer between several but not among all strains. In this study we demonstrate that at least for some strains, horizontal gene transfer occurs at a sufficient frequency to blur the signal from vertically inherited genes, despite strains being adapted to distinct niches. Simply increasing the number of genes included in the analysis is unlikely to overcome this challenge in organisms that occupy multiple niches and can exchange DNA between strains specialized to different niches. Instead, the detection of genes critical in the adaptation to specific niches may help to reveal the physiological specialization of these strains.

Development of imipenem resistance in an Aeromonas veronii biovar sobria clinical isolate recovered from a patient with cholangitis

Several imipenem-susceptible and -resistant Aeromonas veronii biovar sobria isolates with different morphologies and antimicrobial susceptibilities recovered from bile samples of a patient with cholangitis were analysed. These isolates belonged to the same clone and the imipenem-resistant strains showed overexpression of the imiS gene, encoding a chromosomal carbapenemase. These results should make clinicians aware of the possible emergence of multidrug-resistant A. veronii biovar sobria, perhaps as a consequence of previous treatment of a urinary tract infection with amoxicillin plus clavulanic acid.

Characterization of Vibrio cholerae isolated from the aquatic basins of the State of Pernambuco, Brazil

Through a continuous bacteriological monitoring programme carried out by the Health Secretariat of the State of Pernambuco, Brazil, two isolates of Vibrio cholerae O1 El Tor Ogawa were discovered in an endemic area in 2001, during a cholera inactive period, along with six V. cholerae non-O1/non-O139 strains and two Aeromonas veronii biovar sobria strains showing an unusual characteristic of agglutination with O1 antiserum. Between that time and 2005, eight other O1 isolates were found. The virulence genes present in the V. cholerae differed among strains, with only three O1 strains harboring the ctxA gene. The O1 and some non-O1/non-O139 strains displayed identical patterns of amplification of the 16S-23S intergenic spacer region. RAPD of the 10 V. cholerae O1 strains, with the two primers used, revealed heterogeneity. The presence of V. cholerae carrying virulence genes in the aquatic basins examined confirms that they constitute a vibrio reservoir during a cholera inactive period, thus strengthening the argument for a continuous monitoring programme and preventative measures for cholera, mainly in the areas where the supply of drinking water is deficient.

Aeromonas–Acanthamoeba interaction and early shift to a viable but nonculturable state of Aeromonas by Acanthamoeba

To investigate the hypothesis that amoeba may comprise a significant environmental reservoir for Aeromonas, Acanthamoeba-Aeromonas interaction experiments were performed. Acanthamoeba were grown in monoculture and co-cultures with three different species of Aeromonas. Survival, invasion and viable but nonculturable state experiments were performed. We showed that at a low initial bacterial cell density, growth of Aeromonas spp. was inhibited by Acanthamoeba castellanii, while A. castellanii growth was unaffected. In contrast, a high initial bacterial cell density, Aeromonas hydrophila AEW44 and Aeromonas veronii biovar sobria AEW104 suppressed the growth of A. castellanii. Fluorescent and phase-contrast microscopic observations of GFP tagged Aer. hydrophila AEW44 demonstrated that the bacterial cells aggregated on A. castellanii cells after 15 min of incubation and internalized. Aeromonas hydrophila AEW44 cells were found to be actively moving. Interestingly, Aer. hydrophila AEW44 cells shifted more rapidly to a viable but nonculturable form when co-cultured with A. castellanii than in monoculture. We demonstrated that Aeromonas spp. are able to interact with and to infect the protozoan A. castellanii under laboratory conditions. Free-living amoeba might play a role as reservoir for Aeromonas, and thus may increase the transmission of Aeromonas by acting as a vehicle.

A Distinct Cause of Necrotizing Fasciitis: Aeromonas veronii Biovar Sobria

Aeromonas veronii biovar sobria (veronii var. sobria) has not been implicated in the pathogenesis of necrotizing fasciitis in North America. Case report and literature review. An 80-year-old man with diabetes mellitus and acute myeloblastic leukemia developed a rapidly spreading skin and soft tissue infection of the right lower extremity pathognomonic for necrotizing fasciitis with signs of sepsis. Cultures grew Aeromonas veronii biovar sobria. Despite aggressive management, including an urgent right below-knee amputation, this patient died of multiple organ dysfunction syndrome. A. veronii var. sobria should be recognized as one of the causative organisms for necrotizing fasciitis in immunocompromised patients. Early administration of proper antibiotics and aggressive surgical treatment may reduce morbidity and mortality rates in such infections.

The role of c-di-GMP signaling in anAeromonas veroniibiovarsobriastrain

Aeromonas is a ubiquitous gram-negative bacterium that persists in the environment. It is shown that all isolates of persistent Aeromonas clones show strong biofilm formation ability. C-di-GMP regulates biofilm formation in many bacteria. To investigate the impact of c-di-GMP signaling, we introduced heterologous GGDEF and EAL domain proteins from Salmonella Typhimurium to an Aeromonas veronii biovar sobria strain. Overexpression of the GGDEF domain protein AdrA increased c-di-GMP concentration and biofilm formation and reduced motility. Production of the quorum-sensing signaling molecule C4-homoserine lactone and adhesion to aquatic plant duckweed and amoeba surfaces were enhanced. On the other hand, overexpression of the EAL domain protein YhjH decreased biofilm formation and increased motility.

Induction of apoptosis in Vero cells byAeromonas veroniibiovarsobriavacuolating cytotoxic factor

Recently, a cytotoxin named vacuolating cytotoxic factor (VCF) in Aeromonas sobria and Aeromonas veronii biovar sobria was described. We have now purified this factor using ion metallic affinity chromatography. The VCF is a nonhemolytic enterotoxin that acts as a serine protease. The toxin can be partially neutralized by serum antiaerolysin and it induced not only cytoplasmatic vacuole formation, but also mitochondrial disorders that must be signaling the apoptotic pathways, leading to Vero (African green monkey kidney) cell death. These results suggest that the VCF is a virulence factor of these bacteria, participating in the processes of human disease provoked by preformed toxins in food and infection.

Postoperative Infektion eines epigastrischen Hämatoms mit Aeromonas veronii biovar sobria

A 52-year-old man with a gastric signet-ring cell carcinoma but without acute symptoms was admitted for reconstructive surgery of the gastrointestinal tract. Before the present surgery all functional and radiological tests merely confirmed the previously known disease. Except for mild anemia and abnormal electrolytes all laboratory tests were within normal limits. COURSE, DIAGNOSIS AND TREATMENT: The patient underwent reconstructive surgery of the gastrointestinal tract, namely an ascending sigmoidostomy and resection of an enterocutaneous fistula. For a few days the postoperative development was as expected and the drain, placed during surgery, was removed at the expected time. 9 days postoperatively the patient developed signs of an infection (fever up to 38.8 degrees C, increased WBC and raised C-reactive protein levels). Computed tomography (CT) of the abdomen revealed an epigastric tumor measuring 6 x 5 cm. CT-guided needle aspiration of this lesion showed macroscopic signs of an infected hematoma. A pigtail catheter was successfully implanted for continuous drainage. Both the fluids obtained from CT-guided aspiration and the pigtail drain grew Aeromonas veronii biovar sobria when cultured on standard blood agar. Administration of both cefotaxim and metronidazole for 10 days produced a decrease in the inflammatory parameters. The abdominal CT at that time showed a noticeable regression of the epigastric mass so that the patient was discharged from hospital 3 weeks after surgery. This case emphasizes the importance of adequately dosed antibiotic therapy, also for unusual bacteria such as species of Aeromonas.

Hemolytic and Proteolytic Activities of Aeromonas hydrophila and Aeromonas veronii Biovar sobria in Broth and Salmon Extract at Different Temperatures

Expression of hemolytic and proteolytic activities throughout the growth cycle was investigated with two enterotoxic aeromonad strains assigned to the species Aeromonas hydrophila and Aeromonas veronii biovar sobria. Although growth kinetic data were dependent on strain, temperature, and substrate, maximum populations attained were higher than 9 log CFU/ml in aerated tryptone soya broth plus yeast extract (TSBYE) and salmon extract within the range 4 to 28°C. For both strains in TSBYE, variable amounts of hemolytic activity were first detected at any temperature when aeromonad counts were over 9 log CFU/ml. Afterwards, this activity increased up to similar levels (109 to 112 hemolytic units per ml) without a significant increase in populations. Salmon extract supported hemolysin synthesis at 28 but not 4°C. Proteolytic activity of the A. hydrophila strain was only expressed in salmon extract at 28°C, whereas A. veronii biovar sobria did at 28°C in both substrates and at 10°C in TSBYE.

Virulence markers in Aeromonas hydrophila and Aeromonas veronii biovar sobria isolates from freshwater fish and from a diarrhoea case.

To evaluate the public health significance of representative strains of two Aeromonas spp., mainly from freshwater fish, on the basis of production of virulence-associated factors and presence of the haemolytic genes aerA and hlyA. Eleven strains of Aer. hydrophila, three strains of Aer. veronii biovar sobria (all from freshwater fish) and one strain of Aer. hydrophila from human diarrhoea were tested for potential virulence traits and for the presence of the haemolytic genes aerA and hlyA. Ten Aer. hydrophila isolates were aerA(+)hlyA(+) and two aerA(+)hlyA(-). Aeromonas veronii biovar sobria isolates were aerA(-)hlyA(-). Strains from the three genotypes showed enterotoxic activity in the suckling mouse assay. At 28 degrees C, four Aer. hydrophila fish strains could be considered as potentially virulent (possessing at least two of these characteristics: haemolytic, cytotoxic and enterotoxic). One Aer. veronii biovar sobria strain and the clinical isolate were cytotoxic on Vero cells. When grown at 4 degrees C, these six isolates fulfilled virulence criterion, but at 37 degrees C, only one fish strain, an Aer. hydrophila, did. The potential health risk derived from the presence of Aer. hydrophila and Aer. veronii biovar sobria in ice-stored freshwater fish should not be underestimated. Expression of virulence factors is affected by temperature incubation and not always related to the presence of haemolytic genes.