Aeromonas hydrophila subsp. dhakensis subsp. nov., isolated from children with diarrhoea in Bangladesh, and extended description of Aeromonas hydrophila subsp. hydrophila (Chester 1901) Stanier 1943 (approved lists 1980)

A group of 10 Aeromonas hydrophila-like strains referred to as group BD-2, which mainly comprised haemolytic and cytotoxic isolates from diarrhoeal children in Bangladesh, was subjected to a polyphasic taxonomic study including fluorescent amplified fragment length polymorphism (FAFLP) and ERIC-PCR fingerprinting, microplate DNA-DNA hybridization and extensive phenotypic characterization. Comparison of FAFLP and ERIC-PCR genotypic profiles indicated that the group BD-2 isolates constituted a separate taxon that was most closely related to A. hydrophila DNA hybridization group (HG) 1. Determination of DNA-DNA hybridization values with type and reference strains of all known Aeromonas taxa revealed that the BD-2 group represented a homogeneous taxon (internal DNA homology, 77-94%) that exhibited 78-92% DNA relatedness with the type strain of A. hydrophila HG1. These results indicated that the BD-2 group belongs genotypically to A. hydrophila HG1, but examination of 152 phenotypic characteristics revealed that the group BD-2 isolates differed from representatives of HG1 in eight biochemical properties. The diagnostic value of at least three of these tests, namely utilization of urocanic acid and L-arabinose and acid production from L-arabinose, has been confirmed outside this study by other workers. Collectively, the genotypic and phenotypic data reported suggest that the BD-2 group represents a subspecies of A. hydrophila, for which the name Aeromonas hydrophila subsp. dhakensis subsp. nov. is proposed. Its type strain is P21T (= LMG 19562T= CCUG 45377T). An extended description of A. hydrophila subsp. hydrophila (Chester 1901) Stanier 1943 (Approved Lists 1980) is given.

The immune responses of common carp, Cyprinus carpio L., injected with carp interleukin-1beta gene

The function of the common carp, Cyprinus carpio L., interleukin-1beta (IL-1beta) gene was studied by DNA injection. To investigate the immune responses to IL-1beta, a plasmid construct of cytomegalovirus (CMV)-driven carp IL-1beta was injected into the epaxial muscle of carp. IL-1beta protein expressed in serum on 1, 3, and 5 days after plasmid injection was quantified by ELISA and immunohistochemistry. IL1-beta gene injection increased proliferation of the lymphocytes by phytohemagglutinin (PHA). Macrophage functions, such as production of superoxide anion and phagocytosis, also were stimulated by IL-1beta gene injection. Moreover, an increase in resistance to Aeromonas hydrophila infection was recorded in IL-1beta-injected fish compared with control fish. Thus, the cloned homolog of IL-1beta from carp has all the functional similarities to the mammalian IL-1beta gene.

Effects of refrigeration and alcohol on the load of Aeromonas hydrophila in oysters

Members of the bacterial genus Aeromonas are widely distributed throughout the environment and are readily cultured from a variety of foods. One member of this genus, Aeromonas hydrophila, has been reputed to be a significant cause of gastrointestinal disease. In this study, we examined the effects of refrigeration and alcohol on the level of A. hydrophila in oysters. Specifically, vodka was examined because it is used by the food service industry in preparation of Oysters Romanoff. One set of oysters was shucked on receipt, whereas others were refrigerated intact for 7 days at 5 degrees C. The oysters were blended and the numbers of A. hydrophila present determined using starch ampicillin agar. Oysters were also shucked and placed on the half shell with 5 ml of vodka for 10 min. The oysters were then washed and presumptive A. hydrophila levels determined in both the washate and homogenate. On the day of purchase, the average number of presumptive A. hydrophila found was 7.6 x 10(4) CFU/g of oyster meat. After 7 days of refrigeration, the average number had increased to 3.2 x 10(5) CFU/g of oyster meat. In the oysters treated with vodka, the average number of A. hydrophila present internally was 9.9 x 10(4) with high numbers (10(3) to 10(4)) isolated from the oyster surface. From these data, it is clear that refrigeration and alcohol treatment are not sufficient to reduce loads of A. hydrophila in or on oysters.

Aeromonas hydrophila vacuolating activity in the Caco-2 human enterocyte cell line as a putative virulence factor

A non-enterotoxigenic strain of Aeromonas hydrophila isolated from diarrheic stools of an 8-month-old child was found to cause vacuolation in Caco-2 cells. The vacuoles became prominent 60 min after addition of the bacterial culture to the cell monolayers and, after 120 min, a complete disruption of the monolayers was observed. Cell vacuolation was not detected when Caco-2 monolayers were tested with sterile filtrates of overnight cultures of the A. hydrophila vacuolating strain AH14846. This strain produced a diffuse adherence pattern in Caco-2 cell monolayers, but did not produce detectable cytotonic enterotoxin in the suckling mouse test and only produced small quantities of aerolysin. By demonstrating the ability to induce vacuolation in mammalian cells of enterocytic lineage, the current study raises the possibility that such activity might contribute to gastrointestinal symptoms in infections involving Aeromonas strains which do not express well-established enterotoxins.

Childhood gastroenteritis due to Aeromonas hydrophila in Ibadan, Nigeria

This is a prospective study spanning a period of six months where stools of 400 diarrhoeic children and 100 non-diarrhoeic children aged 0-5 years were screened for Aeromonas hydrophila and other enteric pathogens. Out of the 400 diarrhoeic stools only three (0.75%) were positive for Aeromonas hydrophila while none was positive in the control group. No other enteric pathogen was isolated from these positive samples, indicating that Aeromonas hydrophila is responsible for their diarrhoea. Continuous surveillance of this agent of diarrhoea in this environment will further reveal any threat the organism may poise in the nearest future.

Behavior of aeromonas hydrophila in bottled mineral waters

The growth and survival of Aeromonas hydrophila in three types of natural mineral waters were investigated. Mineral waters with different levels of mineral content (low, medium, and high) were experimentally contaminated with A. hydrophila, stored at different temperatures (10 degrees C and 20 degrees C), and analyzed at intervals over a 60-day period. Water samples that were not experimentally contaminated were investigated for indigenous A. hydrophila. The results confirmed that A. hydrophila may occur naturally in mineral waters and showed that the level of mineral content, temperature, length of storage, and, in some cases, the type of container used may favor the growth of A. hydrophila. The greatest proliferation was observed in water with a low mineral content stored in PET bottles at 10 degrees C, in which A. hydrophila peaked at day 28 (4.47 +/- 0.01 log CFU/100 ml). At 20 degrees C, the same load was observed at day 60. The presence of high densities of A. hydrophila in bottled mineral water can constitute a risk for some groups of consumers, such as elderly and immunocompromised persons.

Microbiological quality of drinking water at eight water treatment plants

Eight drinking water treatment plants were sampled monthly during one year to evaluate the removal of bacterial indicators, new indicators and some pathogenic bacteria. Six plants are allocated along the Nile River at Cairo segment and the two others on Ismailia Canal. In this study many parameters were determined; the classical bacterial indicators (total bacterial counts at 22 and 37 degrees C, total coliforms, faecal coliforms and faecal streptococci) show the same trend in all plant intakes except faecal streptococci parameter. The numbers of faecal streptococci in plant intakes on the main stream of Nile River ranged from 8 to 250 MPN/100 ml, but the others ranged from 80 to 2700 MPN/100 ml. With regard to new indicators; total yeasts, Candida albicans, Aeromonas hydrophlia and total staphylococci ranged from 10(1) to 10(5), 10(2) to 10(5), 10(2) to 10(5) and 10(2) to 10(3) cfu/100 ml, respectively. In case of pathogens, salmonellae ranged between 10(2) and 10(3) cfu/100 ml, total vibrios varied between 10(2) and 10(4) and the Listeria group ranged from 10(2) to 10(5) cfu/100 ml from the intake samples. All tested samples from the outlet of water treatment plants, which produce drinking water, were free of classical bacterial indicators. So the produced water has a good quality from the bacteriological point, according to national and international regulations. On the other hand, the drinking water from some tested plants had one or more positive parameters of new indicators and pathogenic bacteria.

Prevalence of enterotoxigenic motile aeromonads in children, fish, milk and ice-cream and their public health significance

Motile aeromonads, which have been implicated as causative agents of human gastroenteritis, meningitis. endocarditis and osteomyelitis, were isolated from fish, pasteurized and flavored milk and ice creams. Forty-five isolates of Aeromonas from diarrheic children (100) and 285 food samples comprising of fish (100), milk (85) and ice creams (100) were identified as A. hydrophila (21), A. sobria (16) and A. caviae (8). Five of these 45 isolates of Aeromonoas (3 A. sobria, 2 A. hydrophila) were from fecal samples of diarrheic children under five years of age. Twenty-six of these 45 isolates were found to be enterotoxin producing by ligated rabbit ileum loop technique. Isolation of enterotoxigenic motile aeromonads from food as well as diarrheic children have great public health significance which will be further discussed.

Surface characters and extracellular toxins involved in the pathogenesis of Aeromonas hydrophila

A small number of serotypically distinct strains of A. hydrophila obtained from diseased freshwater fish were examined for their pathogenic properties comprising of cell surface characteristics and extracellular toxins. Test strains exhibited homogeneity in their cell surface characteristics despite being serologically heterogeneous. Studies on extracellular biological activities revealed qualitative and quantitative differences in production of toxins, probably explaining their antigenic diversity. Three distinct proteases, namely heat stable metallo protease, heat labile serine protease and heat labile metallo protease were identified from the strains.

Is Aeromonas hydrophila the dominant motile Aeromonas species that causes disease outbreaks in aquaculture production in the Zhejiang Province of China?

The significance of Aeromonas hydrophila in association with disease outbreaks in aquaculture production in the Zhejiang province of China was investigated. Bacteriological examination of moribund fish and crabs resulted in 95 bacterial isolates: 88 bacterial isolates from fish and 7 isolates from crabs. PCR and traditional biochemical methods were used for identification of A. hydrophila. Out of 69 motile aeromonads, 35 isolates were identified as A. hydrophila by biochemical tests. However, 6 of those were not identified as A. hydrophila by a species specific PCR method. Serotyping revealed 2 dominant serotypes (O9 and O97) among A. hydrophila isolates. The data presented show that approximately 42% of the motile aeromonads isolated from disease outbreaks among various fish species were A. hydrophila. It is noteworthy that A. hydrophila accounted for more than 50% of the isolated aeromonands isolated from crucian carp Carassius carassius and Wuchang bream Megalobrama amblycephala with haemorrhagic septicaemia. Although this species was the most frequently isolated organism from internal organs of diseased fish and crabs in the present study, other motile Aeromonas spp. were also found. The PCR assay was useful in preventing misidentification of A. hydrophila, which may occur when only phenotypic tests are employed.

Detection of Aeromonas hydrophila in a drinking-water distribution system: a field and pilot study

A 16-month study was conducted on the presence of Aeromonas hydrophila in drinking water in Indiana, U.S.A. Enumeration was conducted in source water, in various sites within a water treatment plant, and in the distribution system in both bulk water and biofilm, as well as in a simulated (annular reactors) drinking-water distribution system. Presumptive Aeromonas spp. counts on source waters regularly approached 10(3)-10(4) CFU/100 mL, during summer months and granular activated carbon - filtered water counts ranged from <1 to 490 CFU/100 mL. In source water, presumptive Aeromonas levels were related to water temperature. Aeromonas hydrophila was never detected in the treatment plant effluent or distributed bulk water, showing disinfectant efficiency on suspended bacteria; however, isolates of A. hydrophila were identified in 7.7% of the biofilm samples, indicating a potential for regrowth and contamination of drinking-water distribution systems.

Rapid iodometric detection of Aeromonas amylase and its diagnostic significance

Twenty-five Aeromonas hydrophila isolates from different sources (Food, 13; Clinical, 6 and Environmental, 6) were studied for the mode of production of Amylase and rapid iodometric detection of the enzyme in vitro. All twenty-five of the isolates produced the enzyme constitutively at 37 degrees C. Amylase producing ability was not dependent on the source of isolation of Aeromonas (F = 0.1069; p > 0.05). Using iodometric technique, in a microtitration tray, the enzyme was fully demonstrated in 10(40%) of the isolates within 30 min, in 22(88%) within 60 min and in all (25 or 100%) within 90 min. The rapid detection of Aeromonas amylase will, no doubt, be of great value in routine diagnostic microbiology.

Role of bacteria in the epizootic ulcerative syndrome (EUS) of fishes

Bacteriological examination of certain water bodies and fishes carrying EUS was carried out. As a whole, 17 species of bacteria were isolated from the investigated water bodies and EUS affected fishes. The species of bacteria isolated from fishes are common to those isolated from water. Experimental infection trials conducted suggested that Aeromonas hydrophila in association with Pseudomonas fluorescens, may be playing the role of primary aetiological agent in producing EUS in fishes.

Aeromonas hydrophila and its relation with drinking water indicators of microbiological quality in Argentine

In Argentine, water municipal supplies disinfection is carried out by chlorine. We have isolated Aeromonas hydrophila from a chlorinated water supply in Buenos Aires that fulfilled Argentinean microbiological quality standards. It is an aquatic organism that could produce cytotoxins and enterotoxins associated with acute gastroenteritis and wound infections in human and hemorrhagic septicaemia of fish, reptiles and amphibians. The isolated strain produced protein bands at isoelectric point in the range of 4.6-5.3 lightly labile at 56 degrees C and heat labile at 100 degrees C non cholera antitoxin reactive in electrofocusing assay (IEF) and showed hemolytic activity thermolabile at 56 degrees C and 100 degrees C in 5% rabbit erythrocytes in phosphate buffered saline. A cytotoxic effect thermolabile at 56 degrees C and 100 degrees C and a cytotonic activity were demonstrated in Vero cell cultures. Survival assay of A. hydrophila and indicator organisms would show no correlation between their contamination sources. Biofilms production could explain the persistence of this gram negative pathogen organism in chlorinated tap water. A water system supply maintenance program and pasteurisation may be performed in spite of water chlorination.

Case report: recovery of Calliphora vicina first-instar larvae from a human traumatic wound associated with a progressive necrotizing bacterial infection

Human myiasis caused by Calliphora vicina is rare in Europe. Here we report a case of C. vicina infection occurring in the traumatic leg wound of a healthy 21-year-old man. Firstly, a progressive necrotizing infection developed in the wound despite administration of antibiotics. Aeromonas hydrophila was isolated from the wound samples. Secondly, during debridement, C. vicina first-instar larvae were isolated from the wound. To our knowledge, this is the first European case of C. vicina wound myiasis associated with severe A. hydrophila infection.

Fulminant pneumonia due to Aeromonas hydrophila in a man with chronic renal failure and liver cirrhosis

A 40-year-old man on hemodialysis was admitted due to dyspnea and chest pain and was diagnosed with pneumonia and pericarditis. Ampicillin was administered, but thereafter severe septic shock developed. The fulminant type of pneumonia progressed rapidly, and he died only 48 hours after the onset of symptoms. The autopsy and sputa culture revealed pneumonia due to Aeromonas hydrophila. The source of this infection remained unkown. Interestingly, there were two types of A. hydrophila found during such a short period. The physician should suspect this disease by questioning the patient's history. Early treatment with adequate antibiotics is the only means of saving such a patient's life.

Rapidly progressive pneumonia due to Aeromonas hydrophila shortly after near-drowning

An 87-year-old woman died of rapidly progressive pneumonia due to Aeromonas hydrophila shortly after a near-drowning event. Autopsy showed necrotizing pneumonia and postmortem cultures of both blood and lung revealed the organism. Fulminant pneumonia should be considered in patients of a near-drowning event.

Virulence profiles and other biological characters in water isolated Aeromonas hydrophila

Thirty water isolates of A. hydrophila were tested for potential virulence profiles, antibiotic resistance and Bacteriocin-Like Substances (BLS) production. Cytotoxic activity was present in all strains tested, 87% were hemolytic and 70% adhesive. Lysine decarboxylase reactions (LDC) positivity was correlated with virulence factors: 100% versus cytotoxicity, 84% versus adherence, 76% versus hemolytic activity. The correlation was also present in the LDC-negative strains. Hemolytic and cytotoxic activities were frequently associated: high cytotoxicity, corresponding to high hemolytic activity and vice versa. The in vitro susceptibility of A. hydrophila to 28 antibacterial agents showed that cefotaxime was the most active beta-lactam antibiotic, and Cefuroxime inhibited 90% of the strains. Isolates were resistant to Penicillin G, Ampicillin, Carbenicillin, Amoxicillin, Cephalotin and Cefaclor. Tetracycline, Chloramphenicol, Nitrofurantoine, the quinolones and the aminoglycosides (except Streptomycin) were consistently active. BLS production never emerged against closely-related microorganisms. On the contrary A. hydrophila presented a heteroinhibitory activity against non-taxonomically related genera such as Listeria spp. (L. seeligeri NCTC 11856, L. welshimeri NCTC 11857, L. ivanovii NCTC 11846) and S. aureus ATCC 25923. Although a large number of strains showed virulence determinants together with other biological characters such as antibiotic resistance and BLS production, it was not possible to relate these factors to the observed plasmids.

Prevalence of enterotoxin genes in Aeromonas spp. isolated from children with diarrhea, healthy controls, and the environment

Aeromonads are causative agents of a number of human infections. Even though aeromonads have been isolated from patients suffering from diarrhea, their etiological role in gastroenteritis is unclear. In spite of a number of virulence factors produced by Aeromonas species, their association with diarrhea has not been clearly linked. Recently, we have characterized a heat-labile cytotonic enterotoxin (Alt), a heat-stable cytotonic enterotoxin (Ast), and a cytotoxic enterotoxin (Act) from a diarrheal isolate of Aeromonas hydrophila. Alt and Ast are novel enterotoxins which are not related to cholera toxin; Act is aerolysin related and has hemolytic, cytotoxic, and enterotoxic activities. We studied the distribution of the alt, ast, and act enterotoxin genes in 115 of 125 aeromonads isolated from 1, 735 children with diarrhea, in all 27 aeromonads isolated from 830 control children (P = 7 x 10(-4) for comparison of rates of isolation of aeromonads from cases versus those from controls), and in 120 randomly selected aeromonads from different components of surface water in Bangladesh. Aeromonas isolates which were positive only for the presence of the alt gene had similar distributions in the three sources; the number of isolates positive only for the presence of the ast gene was significantly higher for the environmental samples than for samples from diarrheal children; and isolates positive only for the presence of the act gene were not found in any of the three sources. Importantly, the number of isolates positive for both the alt and ast genes was significantly higher for diarrheal children than for control children and the environment. Thus, this is the first study to indicate that the products of both the alt and ast genes may synergistically act to induce severe diarrhea. In 26 patients, Aeromonas spp. were isolated as the sole enteropathogen. Analysis of clinical data from 11 of these patients suggested that isolates positive for both the alt and ast genes were associated with watery diarrhea but that isolates positive only for the alt gene were associated with loose stools. Most of the isolates from the three sources could be classified into seven phenospecies and eight hybridization groups. For the first time, Aeromonas eucrenophila was isolated from two children, one with diarrhea and another without diarrhea.

Aeromonas hydrophila isolated from wild freshwater fish in Croatia

Aeromonas hydrophila was recovered from fish living in lake Vrana on the Croatian island of Cres. The occurrence of the bacterium in the fish was assessed and related to gross signs of disease and findings at necropsy as a potential health hazard for fish. Isolated bacteria were subjected to morphological, physiological, biochemical and antibiotic susceptibility tests. A total of 26 A. hydrophila isolates were obtained. There was a clear seasonality, as no isolates were recovered in the summer months. Most of the isolates were sensitive to all the antimicrobials used in the study except novobiocin and penicillin G. Affected fish manifested haemorrhages over the skin, in the liver, kidney and swim bladder, spleen infarcts, fatty liver, ascitic fluid and swollen haemopoietic tissues. A. hydrophila does not appear to pose a major threat for the fish in the lake at present but under unfavourable and stressful conditions it could seriously compromise fish health.

Necrotizing fasciitis caused by Aeromonas hydrophila

Aeromonas Hydrophila is a gram-negative bacillus commonly found in soil, sewage, and fresh or brackish water in many parts of the United States. In healthy people, the most common clinical manifestations attributed to Aeromonas are diarrhea and soft tissue infections. In people with suppressed immune systems or liver disease, A hydrophila can cause meningitis, endocarditis, peritonitis, hemolytic-uremic syndrome, or septicemia. We present the first known case of fulminant necrotizing fasciitis from A hydrophila that is not associated with trauma, liver disease, or immunosuppression.

Survey for psychrotrophic bacterial pathogens in minimally processed lettuce

A total of 120 minimally processed, cut and packaged lettuce samples were purchased from retail supermarkets or provided by a salad production facility over an 8-month period. The samples were tested for total aerobic plate counts and for the presence of potentially pathogenic species belonging to the genera of Listeria, Aeromonas and Yersinia. The aerobic plate counts ranged from 103 to 109 colony forming units (cfu) g-1. Most samples (76%) contained between 105 and 107 cfu g-1 total aerobic bacteria. Listeria monocytogenes was isolated from three samples, Aeromonas hydrophila or Aeromonas caviae from 66 samples, and Yersinia enterocolitica from 71 samples. The pathogenic potential of Y. enterocolitica isolates was determined by screening for an array of biochemical, serological and genetic traits (heat-stable enterotoxin gene, the attachment and invasion gene locus, the invasin gene locus and the virulence plasmid). The Y. enterocolitica isolates lacked many of the phenotypic and genetic markers associated with virulence in primary pathogenic strains. As the roles of the reputed virulence factors of Aeromonas spp. in human infection are uncertain, the pathogenic potential of the Aeromonas isolates in lettuce remains unclear.

Isolation of Aeromonas hydrophila in children with diarrhea

Aeromonas species are gram-negative bacilli that lead to a wide spectrum of infectious diseases in human. In the present study, these bacilli were reviewed to assess their significance as enteric pathogens in this area. During the years of 1994 to 1998, the clinical microbiology laboratory received 2150 stool specimens of children with diarrhea. Medical charts of patients who had positive culture for Aeromonas hydrophila were reviewed. A. hydrophila were isolated from 50 (2.3%) of 2150 children with diarrhea. Most patients were outpatients with ages ranging from 5 months to 16 years old (mean age 3.5 years). The male to female ratio was 0.85:1. All patients suffered from watery or loose diarrhea, some with blood-tinged stool. Whether or not they received medication, all patients had uneventful recoveries. The results of antibiotic susceptibility testing revealed that all strains were not susceptible to ampicillin. In summary, A. hydrophila may be considered as a causative agent of gastrointestinal illness in children.