Aeromonas species in fish, fish-eggs, shrimp and freshwater

Clinical Features, Genome Epidemiology, and Antimicrobial Resistance Profiles of Aeromonas spp. Causing Human Infections: A Multicenter Prospective Cohort Study

Background

The genus Aeromonas is increasingly implicated in human infections, but knowledge of its clinical characteristics and antimicrobial resistance profiles has been limited owing to its complex taxonomy.

Methods

We conducted a multicenter prospective cohort study of patients with Aeromonas infections at hospitals across Japan. Patients were eligible for inclusion if they had an Aeromonas spp. strain in a clinical culture and were considered infected at the culture site. Clinical data were collected, and isolates underwent susceptibility testing and whole-genome sequencing.

Results

A total of 144 patients were included. Hepatobiliary infection accounted for a majority of infections (73% [105 of 144]), which mostly occurred in elderly patients with comorbid conditions, including hepatobiliary complications. The all-cause 30-day mortality rate was 10.0% (95% confidence interval, 4.9%-14.8%). By whole-genome sequencing, 141 strains (98%) belonged to 4 Aeromonas species-A caviae, A hydrophila, A veronii, and A dhakensis-with significant intraspecies diversity. A caviae was predominant in all infection sites except skin and soft tissue, for which A hydrophila was the prevailing species. The genes encoding chromosomally mediated class B, C, and D β-lactamases were harbored by 92%-100% of the isolates in a species-specific manner, but they often lacked association with resistance phenotypes. The activity of cefepime was reliable. All isolates of A hydrophila and A dhakensis carried an mcr-3-like colistin resistance gene and showed reduced susceptibility to colistin.

Conclusions

Hepatobiliary tract was the most common infection site of Aeromonas spp., with A caviae being the dominant causative species. The resistance genotype and phenotype were often incongruent for β-lactam agents.

The difference in the composition of gut microbiota is greater among bats of different phylogenies than among those with different dietary habits

Bats have a very long evolutionary history and are highly differentiated in their physiological functions. Results of recent studies suggest effects of some host factors (e.g., phylogeny and dietary habit) on their gut microbiota. In this study, we examined the gut microbial compositions of 18 different species of bats. Results showed that Firmicutes, Gammaproteobacteria, and Actinobacteria were dominant in all fecal samples of bats. However, the difference in the diversity of gut microbiota among bats of different phylogenies was notable (p = 0.06). Various species of Firmicutes, Actinobacteria, and Gammaproteobacteria were found to contribute to the majority of variations in gut microbiota of all bats examined, and Aeromonas species were much more abundant in bats that feed on both insects and fish than in those of insectivores. The abundance of various species of Clostridium, Euryarchaeota, and ancient bacterial phyla was found to vary among bats of different phylogenies, and various species of Vibrio varied significantly among bats with different dietary habits. No significant difference in the number of genes involved in various metabolic pathways was detected among bats of different phylogenies, but the abundance of genes involved in 5 metabolic pathways, including transcription; replication, recombination, and repair; amino acid transport and metabolism; and signal transduction mechanisms, was different among bats with different dietary habits. The abundance of genes in 3 metabolic pathways, including those involved in stilbenoid, diarylheptanoid, and gingerol biosynthesis, was found to be different between insectivorous bats and bats that feed on both insects and fish. Results of this study suggest a weak association between dietary habit and gut microbiota in most bats but a notable difference in gut microbiota among bats of different phylogenies.

Genetic characterization and virulence determinants of multidrug-resistant NDM-1-producing Aeromonas caviae

The emergence of carbapenemase significantly threatens public health. It is prevalent worldwide but rare in Aeromonas caviae. Unlike most bacterial species, A. caviae has two distinct flagella systems, which are closely related to biofilm formation. The ability to form biofilms on host tissues or inert surfaces constitutes an important cause of many persistent infections, which causes difficulties in clinical treatment. Here, we report on a multidrug-resistant (MDR) A. caviae carrying bla _NDM-1 with a novel sequence type 1,416. The strong ability of biofilm formation of FAHZZU2447 was verified by a crystal violet assay. The resistome profile and location of the bla _NDM-1 gene were determined by antimicrobial susceptibility testing, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE), and Southern blot analysis. Moreover, the strain underwent whole-genome sequencing to identify its genomic characteristics. In addition, the bla _NDM-1 gene was located on a ∼243 kb plasmid with genetic context IS1R-bla _NDM-1-ble-trpF-dsbD-hp-sul1-qacE. Phylogenetic analysis indicated the transmission of A. caviae in China, Japan, and Thailand. Our study aimed to elucidate the genomic features of bla _NDM-1-producing A. caviae, thereby clarifying the distribution of A. caviae worldwide and emphasizing the harmfulness of biofilm formation to the clinic. Further comprehensive surveillance of this species is needed to control further dissemination.

Synthesis of the Aeromonas veronii strain Bs8 disaccharide repeating unit

Presented herein is the synthesis of the Aeromonas veronii disaccharide repeating unit which has been achieved in 11 steps starting from d-fucose and d-galactosamine.

Virulence and antimicrobial resistance potential of Aeromonas spp. associated with shellfish

Aeromonas spp. are associated with seafood-related outbreaks worldwide. In seafood industry, shellfish play a major role in global seafood production. With this emerging trend of shellfish consumption, shellfish-related bacterial infections are being reported frequently. Aeromonas spp. are natural contaminants found in shellfish. Although 36 species have been identified, some species including Aeromonas hydrophila, Aeromonas caviae and Aeromonas veronii biotype sobria have dragged major attention as foodborne pathogenic bacteria. The ability to elaborate a variety of virulence factors of Aeromonas spp. contributes to the pathogenic activities. Also, emerging antimicrobial resistance in Aeromonas spp. has become a huge challenge in seafood industry. Furthermore, multidrug resistance increases the risk of consumer health. Studies have supplied pieces of evidence about the emerging health risk of Aeromonas spp. isolated from seafood. Therefore, the present review was intended to highlight the prevalence, virulence and antimicrobial resistance of Aeromonas spp. isolated from various types of shellfish.

First report of isolation of Aeromonas taiwanensis from India

Genus Aeromonas consists of facultative anaerobic, Gram negative Bacilli which are primary environmental inhabitants worldwide. A recently reported strain of the genus, Aeromonas taiwanensis, was found while studying the presence of infectious marine microbes in a lacustrine wetland in India, making this the first isolation report from the country.

The use of the so-called 'tubs' for transporting and storing fresh fishery products

On-land transport/storage of fresh fishery products (FFP) for up to 3 days in 'tubs' of three-layered poly-ethylene filled with freshwater and ice was compared to the currently authorised practice (fish boxes of high-density poly-ethylene filled with ice). The impact on the survival and growth of biological hazards in fish and the histamine production in fish species associated with a high amount of histidine was assessed. In different modelling scenarios, the FFP are stored on-board in freshwater or seawater/ice (in tubs) and once on-land they are 'handled' (i.e. sorted or gutted and/or filleted) and transferred to either tubs or boxes. The temperature of the FFP was assumed to be the most influential factor affecting relevant hazards. Under reasonably foreseeable 'abusive' scenarios and using a conservative modelling approach, the growth of the relevant hazards (i.e. Listeria monocytogenes, Aeromonas spp. and non-proteolytic Clostridium botulinum), is expected to be < 0.2 log10 units higher in tubs than in boxes after 3 days when the initial temperature of the fish is 0°C ('keeping' process). Starting at 7°C ('cooling-keeping' process), the expected difference in the growth potential is higher (< 1 log10 for A. hydrophila and < 0.5 log10 for the other two hazards) due to the poorer cooling capacity of water and ice (tub) compared with ice (box). The survival of relevant hazards is not or is negligibly impacted. Histamine formation due to growth of Morganella psychrotolerans under the 'keeping' or 'cooling-keeping' process can be up to 0.4 ppm and 1.5 ppm higher, respectively, in tubs as compared to boxes after 3 days, without reaching the legal limit of 100 ppm. The water uptake associated with the storage of the FFP in tubs (which may be up to 6%) does not make a relevant contribution to the differences in microbial growth potential compared to boxes.

Aeromonas Isolates from Fish and Patients in Tainan City, Taiwan: Genotypic and Phenotypic Characteristics

The present study aimed to isolate Aeromonas from fish sold in the markets as well as in sushi and seafood shops and compare their virulence factors and antimicrobial characteristics with those of clinical isolates. Among the 128 fish isolates and 47 clinical isolates, Aeromonas caviae, A. dhakensis, and A. veronii were the principal species. A. dhakensis isolates carried at least 5 virulence genes, more than other Aeromonas species. The predominant genotype of virulence genes was hlyA lip alt col ela in both A. dhakensis and A. hydrophila isolates, alt col ela in A. caviae isolates, and act in A. veronii isolates. A. dhakensis, A. hydrophila, and A. veronii isolates more often exhibited hemolytic and proteolytic activity and showed greater virulence than A. caviae isolates in Caenorhabditis elegans and the C2C12 cell line. However, the link between the genotypes and phenotypes of the studied virulence genes in Aeromonas species was not evident. Among the four major clinical Aeromonas species, nearly all (99.0%) A. dhakensis, A. hydrophila, and A. veronii isolates harbored bla _CphA, which encodes a carbapenemase, but only a minority (6.7%, 7/104) were nonsusceptible to carbapenem. Regarding AmpC β-lactamase genes, bla _AQU-1 was exclusively found in A. dhakensis isolates, and bla _MOX3 was found only in A. caviae isolates, but only 7.6% (n = 6) of the 79 Aeromonas isolates carrying bla _AQU-1 or bla _MOX3 exhibited a cefotaxime resistance phenotype. In conclusion, fish Aeromonas isolates carry a variety of combinations of virulence and β-lactamase resistance genes and exhibit virulence phenotypes and antimicrobial resistance profiles similar to those of clinical isolates.IMPORTANCE Aeromonas species can cause severe infections in immunocompromised individuals upon exposure to virulent pathogens in the environment, but the characteristics of environmental Aeromonas species remain unclear. Our study showed that several pathogenic Aeromonas species possessing virulence traits and antimicrobial resistance similar to those of Aeromonas isolates causing clinical diseases were present in fish intended for human consumption in Tainan City, Taiwan.

Biofilm and Sediment are Major Reservoirs of Virulent Aeromonas hydrophila (vAh) in Catfish Production Ponds

The genus Aeromonas comprises more than 60 recognized species that include many important fish pathogens such as the causative agents of furunculosis and motile Aeromonas septicemia (MAS). Although MAS is typically considered a secondary infection, a new virulent A. hydrophila (vAh) strain has been causing devastating losses to the catfish industry in Alabama since 2009. The objective of this study was to characterize the spatiotemporal distribution of Aeromonas sp. and, specifically, vAh in a commercial catfish farm in western Alabama. We sampled biofilm, sediment, and water from three ponds during four consecutive months during the growing season. Total aerobic counts were between 8.8 × 10⁵ and 1.5 × 10⁶  CFU/mL but were significantly higher in biofilm and sediment than in water throughout the sampling period. Total Aeromonas counts in water samples significantly increased in all three ponds after the month of August and ranged from 7.8 × 10³ to 4.9 × 10⁴  CFU/mL. A similar trend was observed in biofilm and sediment samples for which total Aeromonas counts increased in samples taken in late summer to early fall. Over time, the concentration of Aeromonas in water samples decreased by one order of magnitude, while there was a significant increase in sediments as temperature dropped. The virulent vAh was detected in 35.4% of biofilm samples and 22.9% of sediment samples, suggesting that both environments serve as the major reservoir for this pathogen. Future monitoring efforts should focus on targeting sediment and biofilms since samples of these appear to naturally enrich for the presence of vAh and other Aeromonas species.

Quality assessment of Zeus faber (Peter's fish) ovaries regularly commercialized for human consumption

In the last few years, the consumption of fish eggs has increased rapidly, finding widespread use also in mass catering. This increase has involved also those of the Peter's fish (Zeus faber). Females of this species, by their reproductive characteristics, have highly developed gonads in different periods of the year, making the raw material easy to find. The aim of the present study was to perform a quality assessment of Zeus faber ovaries regularly commercialized for human consumption. A total number of 34 samples, divided in fresh (11) and frozen (23), were processed for microbiological characterization, parasitological and histological evaluations. Fresh and frozen samples have significant (P<0.01) differences in total bacterial charge, with values of 4.75±0.5 Log CFU/g and 3.65±0.7 Log CFU/g respectively. The mean value of Enterobacteriaceae was 2.58±0.7 Log CFU/g in fresh products, while 52.17% (12) of frozen samples reported loads of <1 Log CFU/g. No Salmonella spp. and Listeria monocytogenes were found. Aeromonas spp. was detected in two frozen sample (with loads of 2.2 and <1 Log CFU/g) and in 5 fresh ovaries with value ranged from 1.70 to 3.48 Log CFU/g. Vibrio spp. was found in 4 (36.36%) and 3 (13.04%) of fresh and frozen samples respectively, with loads always <1 Log CFU/g. All 31 Vibrio strains isolated, were identified as Vibrio alginolyticus, and 61.29% (19) of them was positive for the ToxRS factor and 6.45% (2) for ToxR. The 47.06% (16) of total samples showed infestations by larvae of Anisakis Type 1 in the serous and inside the ovary. In this last case, histologically it was found to be free larvae. This study attested satisfactory hygiene conditions for Zeus faber ovaries currently marked for human consumption. The presence of potentially pathogenic strains of V. alginolyticus and Aeromonas spp., but above all the frequent infestation by Anisakis larvae, represent a potentially hazard for the consumer.

Etiology and Risk Factors of Acute Gastroenteritis in a Taipei Emergency Department: Clinical Features for Bacterial Gastroenteritis

BACKGROUND

The causative pathogen is rarely identified in the emergency department (ED), since the results of cultures are usually unavailable. As a result, antimicrobial treatment may be overused. The aim of our study was to investigate the pathogens, risk factors of acute gastroenteritis, and predictors of acute bacterial gastroenteritis in the ED.

METHODS

We conducted a matched case-control study of 627 stool samples and 612 matched pairs.

RESULTS

Viruses (41.3%) were the leading cause of gastroenteritis, with noroviruses (32.2%) being the most prevalent, followed by bacteria (26.8%) and Giardia lamblia (12.4%). Taking antacids (adjusted odds ratio [aOR] 4.10; 95% confidence interval [CI], 2.57-6.53), household members/classmates with gastroenteritis (aOR 4.69; 95% CI, 2.76-7.96), attending a banquet (aOR 2.29; 95% CI, 1.64-3.20), dining out (aOR 1.70; 95% CI, 1.13-2.54), and eating raw oysters (aOR 3.10; 95% CI, 1.61-5.94) were highly associated with gastroenteritis. Elders (aOR 1.04; 05% CI, 1.02-1.05), those with CRP >10 mg/L (aOR 2.04; 95% CI, 1.15-3.62), or those who were positive for fecal leukocytes (aOR 2.04; 95% CI, 1.15-3.62) or fecal occult blood (aOR 1.97; 95% CI, 1.03-3.77) were more likely to be hospitalized in ED. In addition, presence of fecal leukocytes (time ratio [TR] 1.22; 95% CI, 1.06-1.41), abdominal pain (TR 1.20; 95% CI, 1.07-1.41), and frequency of vomiting (TR 0.79; 95% CI, 0.64-0.98) were significantly associated with the duration of acute gastroenteritis. Presence of fecal leukocytes (aOR 2.08; 95% CI, 1.42-3.05), winter season (aOR 0.45; 95% CI, 0.28-0.74), frequency of diarrhea (aOR 1.69; 95% CI, 1.01-2.83), and eating shrimp or crab (aOR 1.53; 95% CI, 1.05-2.23) were highly associated with bacterial gastroenteritis. The area under the receiver operating characteristic curve of the final model was 0.68 (95% CI, 0.55-0.63).

CONCLUSIONS

Acute bacterial gastroenteritis was highly associated with season, frequency of diarrhea, frequency of vomiting, and eating shrimp or crab.

Aeromonas in Arab countries: 1995-2014

The aim of this review is to provide information on the prevalence, clinical syndromes, and antimicrobial resistance and therapy of Aeromonas spp. infections in Arab countries. The data were obtained by an English language literature search from 1995 to 2014 of Medline and PubMed for papers using the search terms "Aeromonas+name of Arab country (i.e. Algeria, Egypt, etc.)". Additional data were obtained from a Google search using the aforementioned terms. The organisms have been reported from diarrheal children, patients with cholera-like diarrhea, an outbreak of acute gastroenteritis and from different types of animals, foods and water source in several Arab countries in the Middle East and North Africa with predominance of A. hydrophila, A. caviae and A. sobria. Using molecular techniques few studies reported genes encoding several toxins from aeromonads isolated from different sources. Among the antimicrobials examined in the present review third generation cephalosporins, fluoroquinolones and aminoglycosides showed excellent activity and can be employed in the treatment of Aeromonas-associated human infections in Arabic countries. Whenever possible, treatment should be guided by the susceptibility testing results of the isolated organism. In the future, studies employing molecular testing methods are required to provide data on circulating genospecies and their modes of transmission in the community, and on their mechanisms of resistance to antimicrobials. Microbiology laboratories and research centers are encouraged to look for these organisms in clinical, food and water sources to attain a better understanding of the public health risks from these organisms in Arab countries.

Isolation and Seroprevalence of Aeromonas spp. Among Common Food Animals Slaughtered in Nagpur, Central India

Aeromonads are ubiquitous foodborne pathogens with a global distribution. Animal-origin foods and contaminated animals are the main sources of Aeromonas infection to humans. So far little is known about the occurrence of Aeromonas spp. in food-producing animals in India. The present study was conducted to determine the prevalence and seroprevalence of Aeromonas species from 50 each of meat, blood, and sera samples collected from cattle, buffaloes, goats, and pigs slaughtered in and around Nagpur, Central India. Alkaline peptone water and ampicillin dextrin agar were used to isolate Aeromonas spp. An indirect enzyme-linked immunosorbent assay (ELISA) was standardized by use of whole-cell antigen (WC) and outer membrane protein (OMP) of Aeromonas hydrophila (MTCC 646). Aeromonads were isolated from 44 (22%) of the meat samples, and 1 (0.5%) from the blood samples. Seroprevalence by indirect ELISA-based WC antigen was estimated as 68% in cattle, 44% in buffaloes, 60% in goats, and 30% in pigs. OMP-based ELISA yielded a seroprevalence of 56%, 48%, 52%, and 22% in cattle, buffaloes, goats, and pigs, respectively. The results revealed that OMP-based ELISA and WC-based ELISA were in agreement with one another. Isolation along with high seropositivity demonstrates the presence of foodborne Aeromonas spp. in the Nagpur city of Central India.

Aeromonas species: an opportunistic enteropathogen in patients with inflammatory bowel diseases? A single center cohort study

BACKGROUND

The role of Aeromonas species as an enteropathogen in patients with and without inflammatory bowel disease (IBD) is still debated. The aim was to explore the significance of positive Aeromonas stool cultures in IBD and patients without IBD.

METHODS

Observational retrospective study including all patients with a stool culture positive for Aeromonas between January 2011 and October 2013 at the Leuven University Hospitals. Demographics, clinical, and endoscopic outcomes and laboratory results were analyzed.

RESULTS

A total of 77 patients (11 IBD) were identified. In 37 cases, Aeromonas caused a mild self-limited gastrointestinal infection. Among the 40 patients needing antibiotics, 22 presented a mild-to-moderate gastrointestinal infection; 4 suffered from extraintestinal complications; and 4 were coinfected by Campylobacter spp. A. veronii caused more frequently severe infection than the other species (25% versus 5%; P = 0.046). In 2 patients with ulcerative colitis, Aeromonas triggered a moderate-to-severe flare and 2 cases appeared in the context of de novo Crohn's disease. In contrast, in 1 patient with ulcerative colitis and 2 patients with Crohn's disease, Aeromonas caused a mild gastrointestinal infection not worsening the disease activity and in 4 patients with Crohn's disease, it presented in the context of active disease with no clear pathogenic role. Patients with IBD were treated more often with antibiotics (82 versus 41%, P = 0.012) and had more complications (46 versus 14%, P = 0.024).

CONCLUSIONS

Aeromonas caused mostly mild infections but also moderate and severe infections. A. veronii was more prevalent in patients with IBD and was associated with worse clinical outcomes. Aeromonas caused milder infections in patients without IBD. Other risk factors for severe infection were not found.

Microbial community assembly and succession on lake sturgeon egg surfaces as a function of simulated spawning stream flow rate

We investigated microbial succession on lake sturgeon (Acipenser fulvescens) egg surfaces over the course of their incubation period as a function of simulated stream flow rate. The primary objective was to characterize the microbial community assembly during succession and to examine how simulated stream flow rate affect the successional process. Sturgeon eggs were reared under three flow regimes; high (0.55 m/s), low (0.18 m/s), and variable (0.35 and 0.11 m/s alternating 12 h intervals). Eggs were collected from each flow regime at different egg developmental stages. Microbial community DNA was extracted from egg surface and the communities were examined using 16S rRNA gene-based terminal restriction fragment length polymorphism and 454 pyrosequencing. Analysis of these datasets using principal component analysis revealed that microbial communities were clustered by egg developmental stages (early, middle, and late) regardless of flow regimes. 454 pyrosequencing data suggested that 90-98 % of the microbial communities were composed of the phyla Proteobacteria and Bacteroidetes throughout succession. β-Protebacteria was more dominant in the early stage, Bacteroidetes became more dominant in the middle stage, and α-Proteobacteria became dominant in the late stage. A total of 360 genera and 5,826 OTUs at 97 % similarity cutoff were associated with the eggs. Midway through egg development, the egg-associated communities of the low flow regime had a higher diversity than those communities developed under high or variable flow regimes. Results show that microbial community turnover occurred during embryogenesis, and stream flow rate influenced the microbial succession processes on the sturgeon egg surfaces.

Effect of Modified Atmosphere with Varying O2 Concentrations on the Quality of Packed Pacific White Shrimp (Penaeus vannamei) during Cold Storage

The purpose of this study was to evaluate the effect of modified atmosphere packaging (MAP) with varying O2concentrations on the quality changes of Pacific white shrimp during cold storage at (4±1)°C by using the quality indices such as Total viable counts (TVC), TVB-N, pH, firmness, whiteness and sensory evaluation. Results showed that MAP inhibited the microbial growth and the spoilage which was confirmed by the lowered TVC and TVB-N. Among the four MAP groups, shrimp packaged in bags 40%CO2\55%O2\5%N2showed the lowest level of TVC and TVB-N, and shrimp in 40%CO2\5%O2\55%N2had the best appearance with lighter blackspots during storage. Low O2concentration packaging exhibited the ability to retard melanosis, but weakening the ability to impede the spoilage. Extremely high O2concentration with low CO2concentration packaging inhibit the microbial growth compared to the CK, but improved the melonasis of shrimp and reduced its sensory quality rapidly.

Ocorrência de Aeromonas sp. e microrganismos psicrotróficos e estimativa do prazo de validade comercial de filé de pintado (Pseudoplatystoma coruscans) mantidos sob refrigeração

Verificou-se a ocorrência de bactérias do gênero Aeromonas e estimou-se o prazo de validade comercial de filés de pintado (Pseudoplatystoma coruscans) com pele, durante estocagem em refrigeração por meio da quantificação de microrganismos heterotróficos aeróbios psicrotróficos e análises físico-químicas para determinação do pH e detecção de amônia e gás sulfídrico. Foram utilizadas 45 amostras de filé de pintado, com aproximadamente 100 gramas cada, embaladas individualmente em polietileno de alta densidade e armazenadas em câmara frigorífica entre 0ºC e 3ºC. A cada dois a três dias de estocagem, três unidades de filés foram submetidas a análises microbiológicas e físico-químicas, totalizando 15 análises durante o período de estocagem. As contagens de Aeromonas sp. e microrganismos heterotróficos aeróbios psicrotróficos variaram de 1,89 a 9,47logUFC/g e 0 a 6,54logUFC/g, respectivamente. A variação do pH foi de 6,20 a 6,97, e as análises de amônia e gás sulfídrico foram negativas durante todo o período. O pH dos filés de pintado atingiu o limite máximo de 6,4 aos 23 dias de estocagem, e estimou-se o seu prazo de validade comercial.

Aeromonas and Pseudomonas: antibiotic and heavy metal resistance species from Iskenderun Bay, Turkey (northeast Mediterranean Sea)

We studied the susceptibility patterns to 15 different antibiotics and six heavy metals in Aeromonas spp. and Pseudomonas spp. isolated from Iskenderun Bay, Turkey (northeast Mediterranean Sea). A high percentage of Aeromonas isolates showed resistance to cefazolin (66.6%) and trimethoprim-sulphamethoxazole (66.6%). Amongst the Pseudomonas isolates, there was a high incidence of resistance to nitrofurantoin (86.2%), cefazolin (84.8%) and cefuroxime (71.7%). Most isolates showed tolerance to different concentrations of heavy metals, and minimal inhibition concentrations ranged from 25 to >3,200 microg/ml. The Aeromonas spp. and Pseudomonas spp. showed high resistance to copper of 98.3% and 75.4%, respectively, and low resistance to lead of 1.7% and 7.2%, respectively. Our results show that antibiotic and heavy metal resistant Aeromonas spp. and Pseudomonas spp. were widespread in Iskenderun Bay in 2007 and 2008. The increasing presence of antibiotic and heavy metal resistant Aeromonas spp. and Pseudomonas spp. may become a potential human health hazard.

Characterization of Aeromonas species isolated from an estuarine environment

Thirty water samples were collected, at two week intervals, from the estuary of the River Cocó. The aim was to characterize the presence, distribution and types of Aeromonas spp, in the estuary of the River Cocó, Ceara, Brazil (03°46’28.83’’S e 38°26’36.52’’S). Aeromonas were identified in 19 (63%) samples analyzed by plating and CFU counts. Presence/absence tests were positive for 11 (37%) of the samples resulting in the detection of Aeromonas in a total of 23 (77%) of samples. CFU counts varied from < 10 to 1.4 x 10⁴ CFU mL^-1. From the isolated strains seven species of Aeromonas were identified: A. caviae (29/69), A. veronii bv. sobria (13/69), A. veronii bv. veronii (8/69), A. trota (6/69), A. media (5/69), A. sobria (4/69) and A. hydrophila and Aeromonas sp. (2/69). Of the 38 strains tested, 23 (60%) showed resistance to at least one of the eight antimicrobials. Multiple resistance to antibiotics was observed in A. caviae, A. media , A. sóbria and A. veronii bv. sobria. Aeromonas caviae showed the highest multiple resistance, being resistant to four antibiotics. The presence of those microorganisms may contribute to the occurrence of gastroenteritis, mainly in children, since they are considered opportunists.

Distribution of virulence factors and molecular fingerprinting of Aeromonas species isolates from water and clinical samples: suggestive evidence of water-to-human transmission

A total of 227 isolates of Aeromonas obtained from different geographical locations in the United States and different parts of the world, including 28 reference strains, were analyzed to determine the presence of various virulence factors. These isolates were also fingerprinted using biochemical identification and pulse-field gel electrophoresis (PFGE). Of these 227 isolates, 199 that were collected from water and clinical samples belonged to three major groups or complexes, namely, the A. hydrophila group, the A. caviae-A. media group, and the A. veronii-A. sobria group, based on biochemical profiles, and they had various pulsotypes. When virulence factor activities were examined, Aeromonas isolates obtained from clinical sources had higher cytotoxic activities than isolates obtained from water sources for all three Aeromonas species groups. Likewise, the production of quorum-sensing signaling molecules, such as N-acyl homoserine lactone, was greater in clinical isolates than in isolates from water for the A. caviae-A. media and A. hydrophila groups. Based on colony blot DNA hybridization, the heat-labile cytotonic enterotoxin gene and the DNA adenosine methyltransferase gene were more prevalent in clinical isolates than in water isolates for all three Aeromonas groups. Using colony blot DNA hybridization and PFGE, we obtained three sets of water and clinical isolates that had the same virulence signature and had indistinguishable PFGE patterns. In addition, all of these isolates belonged to the A. caviae-A. media group. The findings of the present study provide the first suggestive evidence of successful colonization and infection by particular strains of certain Aeromonas species after transmission from water to humans.

Microbiological quality of sushi from sushi bars and retailers

Sushi is a traditional Japanese food, mostly consisting of rice and raw fish. Fish is considered a healthy food, but as with other animal products, consumption of raw muscle incurs potential health risks such as ingestion of pathogenic bacteria or parasites. In this study, 250 sushi samples were analyzed for their microbiological status and the prevalence of pathogenic bacteria. A comparison was made between frozen sushi from supermarkets and fresh sushi from sushi bars. Aerobic mesophilic bacteria counts differed for sushi from these two sources, with means of 2.7 log CFU/g for frozen sushi and 6.3 log CFU/g for fresh sushi. The prevalence of Escherichia coli and Staphylococcus aureus was higher in the fresh samples. Salmonella was found in four (1.6%) of the sushi samples, and Listeria monocytogenes was found in three (1.2%) of the samples. These results indicate that the microbiological quality of industrially processed sushi is higher than that of freshly prepared sushi. The quality of freshly prepared sushi strongly depends on the skills and habits of the preparation cooks, which may vary.

Aeromonas spp. isolated from oysters (Crassostrea rhizophorea) from a natural oyster bed, Ceará, Brazil

Between April and October 2002, thirty fortnightly collections of oysters (Crassostrea rhizophorea) from a natural oyster bed at the Cocó River estuary in the Sabiaguaba region (Fortaleza, Ceará, Brazil) were carried out, aiming to isolate Aeromonas spp. strains. Oyster samples were submitted to the direct plating (DP) and the presence/absence (P/A) methods. Aeromonas were identified in 15 (50%) samples analyzed by the DP method and in 13 (43%) analyzed by the P/A method. A. caviae, A. eucrenophila, A. media, A. sobria, A. trota, A. veronii bv. sobria, A. veronii bv. veronii and Aeromonas sp. were isolated. The predominant species was A. veronii (both biovars), which was identified in 13 (43%) samples, followed by A. media in 11 (37%) and A. caviae in seven (23%). From the 59 strains identified, 28 (48%) presented resistance to at least one of the eight antibiotics tested.

Occurrence of foodborne pathogenic bacteria in retail prepackaged portions of marine fish in Spain

AIMS

To survey the presence of indigenous and nonindigenous foodborne bacterial pathogens in displayed prepacked portions of fresh marine fish.

METHODS AND RESULTS

A survey of 50 different samples of fresh marine fish (conger, swordfish, sole, grouper and whiting) was conducted over a period of 5 months. Trays of fillets and steaks were obtained at retail level and tested for foodborne bacterial pathogens. Vibrio cholerae and Salmonella were not detected. Two samples (4%) yielded Vibrio strains carrying a DNA fragment specific for Vibrio parahaemolyticus, but resulted negative to PCR amplification of the virulence-related tdh gene. Levels of motile Aeromonas ranging from 2.29 to 7.20 log CFU g(-1) were found in 31 (62%) samples. All fish portions were positive for the Aeromonas hlyA gene and 38 for both aerA and hlyA genes, which may contribute to diarrhoea-related virulence. The incidence of Listeria monocytogenes was 10%. Levels of Staphylococcus aureus lower than 2 log CFU g(-1) were found in 15 (30%) samples. Numbers of presumptive Clostridium perfringens ranging from 1.82 +/- 0.22 to 4.26 +/- 1.25 log CFU g(-1) were detected in 42 (84%) samples. Edwardsiella tarda was detected in two samples of grouper fillets.

CONCLUSIONS

Displayed portions of raw fish carried bacteria that can cause foodborne disease. The risk posed by fresh fish when properly cooked is low, but high when destined to be consumed raw, undercooked or very lightly processed.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study revealed that raw fish sold in Spain could be a source of foodborne bacterial pathogens. Improvements in handling and processing are needed to minimize the prevalence of pathogenic bacteria.

Growth of Aeromonas hydrophila in the whey cheeses Myzithra, Anthotyros, and Manouri during storage at 4 and 12 degrees C

The fresh whey cheeses Myzithra, Anthotyros, and Manouri were inoculated with Aeromonas hydrophila strain NTCC 8049 (type strain) or with an A. hydrophila strain isolated from food (food isolate) at levels of 3.0 to 5.0 x 10(2) CFU/g of cheese and stored at 4 or 12 degrees C. Duplicate samples of cheeses were tested for levels of A. hydrophila and pH after up to 29 days of storage. At 4 degrees C, A. hydrophila grew in Myzithra and Anthotyros with a generation time of ca. 19 h, but no growth was observed in Manouri. In Myzithra, average maximum populations of 8.87 log CFU/g (type strain) and 8.79 log CFU/g (food isolate) were recorded after 20 and 22 days of storage at 4 degrees C, respectively. The average maximum populations observed in Anthotyros stored at 4 degrees C were 6.72 log CFU/g (food isolate) and 6.13 log CFU/g (type strain) and were observed after 15 and 16 days of storage, respectively. A. hydrophila grew rapidly and reached high numbers in cheeses stored at 12 degrees C. The average generation times were 3.7 and 3.9 h (Myzithra), 4.1 and 6.1 h (Anthotyros), and 8.0 and 9.2 h (Manouri) for the type strain and the food isolate, respectively. Among the different whey cheese trials, the highest A. hydrophila population recorded (10.13 log CFU/g) was in Myzithra that had been inoculated with the food isolate after 8 days of storage at 12 degrees C. To prevent A. hydrophila growth in whey cheeses, efforts must be focused on preventing postprocessing contamination and temperature abuse during transportation and storage.

Isolation and Characterization of Potentially Human Pathogenic, Cytotoxin-producing Aeromonas Strains from Retailed Seafood in Berlin, Germany

The presence of potentially human pathogenic strains of Aeromonas was investigated in 84 samples of seafood which were purchased from retail traders in Berlin, Germany in spring 2000. A total of 134 Aeromonas strains were isolated on selective [GSP agar and Aeromonas (Ryan) agar] and unselective (standard count agar and enterohaemolysin agar) media from 27 (32.1%) of the samples and were classified as Aeromonas hydrophila (67.9%), A. caviae (26.1%) and A. sobria (6.0%) by biotyping. Thirteen (48.1%) of the 27 positive samples contained more than one species of Aeromonas. Production of haemolysins on enterohaemolysin agar was found with 132 (98.5%) of the strains at 28 degrees C and with 130 strains (97.0%) at 37 degrees C growth temperature. Vero cytotoxins were produced by 99 (73.9%) of the strains when grown at 28 degrees C but only by 24 of the strains (17.9%) at 37 degrees C. The latter strains were identified as A. hydrophila (n = 22) and A. sobria (n = 2) which came from 17 (20.2%) samples of raw seafood and from ready-to-eat salted herring 'Matjes' products. Cytotoxin-encoding genes for aerolysin (aer) and haemolysin A (hlyA) were investigated by PCR. Aer and hlyA genes were detected in both, strains which produced toxins only at 28 degrees C and strains which produced toxins at 37 degrees C. Our data indicate that raw seafood and ready-to-eat fish products can harbour potential human pathogenic, cytotoxin producing Aeromonas strains.

Aeromonas hydrophila Cytotoxic Enterotoxin Activates Mitogen-activated Protein Kinases and Induces Apoptosis in Murine Macrophages and Human Intestinal Epithelial Cells

A cytotoxic enterotoxin (Act) of Aeromonas hydrophila possesses several biological activities, induces an inflammatory response in the host, and causes apoptosis of murine macrophages. In this study, we utilized five target cell types (a murine macrophage cell line (RAW 264.7), bone marrow-derived transformed macrophages, murine peritoneal macrophages, and two human intestinal epithelial cell lines (T84 and HT-29)) to investigate the effect of Act on mitogen-activated protein kinase (MAPK) pathways and mechanisms leading to apoptosis. As demonstrated by immunoprecipitation/kinase assays or Western blot analysis, Act activated stress-associated p38, c-Jun NH(2)-terminal kinase (JNK), and extracellular signal-regulated kinase 1/2 (ERK1/2) in these cells. Act also induced phosphorylation of upstream MAPK factors (MAPK kinase 3/6 (MKK3/6), MKK4, and MAP/ERK kinase 1 (MEK1)) and downstream effectors (MAPK-activated protein kinase-2, activating transcription factor-2, and c-Jun). Act evoked cell membrane blebbing, caspase 3-cleavage, and activation of caspases 8 and 9 in these cells. In macrophages that do not express functional tumor necrosis factor receptors, apoptosis and caspase activities were significantly decreased. Immunoblotting of host whole cell lysates revealed Act-induced up-regulation of apoptosis-related proteins, including the mitochondrial proteins cytochrome c and apoptosis-inducing factor. However, mitochondrial membrane depolarization was not detected in response to Act. Taken together, the data demonstrated for the first time Act-induced activation of MAPK signaling and classical caspase-associated apoptosis in macrophages and intestinal epithelial cells. Given the importance of MAPK pathways and apoptosis in inflammation-associated diseases, this study provided new insights into the mechanism of action of Act on host cells.

Infections related to the ingestion of seafood Part I: viral and bacterial infections

Foodborne diseases cause an estimated 76 million illnesses in the USA each year. Seafood is implicated in 10-19% of these illnesses. A causative agent can be traced in about 44% of seafood-related outbreaks, viruses accounting for around half of these illnesses. Although viruses are the most common cause of seafood-related infections, most hospitalisations and deaths are due to bacterial agents. A wide variety of viruses, bacteria, and parasites have been implicated in seafood-related outbreaks, which are reported worldwide. The factor most commonly associated with infection is consumption of raw or undercooked seafood. People with underlying disorders, particularly liver disease, are more susceptible to infection. The first part of this two-part review summarises the general incidence of seafood-related infections and discusses the common viral and bacterial causes of these infections. For each agent, the microbiology, epidemiology, mode of transmission, and treatment are discussed. In the May issue of the journal we will discuss parasites associated with seafood consumption, the safety of seafood, and the measures put in place in the USA to increase its safety.

Characterisation of Aeromonas spp. isolated from frozen fish intended for human consumption in Mexico

A total of 82 strains of presumptive Aeromonas spp. were identified biochemically and genetically (16S rDNA-RFLP). The strains were isolated from 250 samples of frozen fish (Tilapia, Oreochromis niloticus niloticus) purchased in local markets in Mexico City. In the present study, we detected the presence of several genes encoding for putative virulence factors and phenotypic activities that may play an important role in bacterial infection. In addition, we studied the antimicrobial patterns of those strains. Molecular identification demonstrated that the prevalent species in frozen fish were Aeromonas salmonicida (67.5%) and Aeromonas bestiarum (20.9%), accounting for 88.3% of the isolates, while the other strains belonged to the species Aeromonas veronii (5.2%), Aeromonas encheleia (3.9%) and Aeromonas hydrophila (2.6%). Detection by polymerase chain reaction (PCR) of genes encoding putative virulence factors common in Aeromonas, such as aerolysin/hemolysin, lipases including the glycerophospholipid-cholesterol acyltransferase (GCAT), serine protease and DNases, revealed that they were all common in these strains. Our results showed that first generation quinolones and second and third generation cephalosporins were the drugs with the best antimicrobial effect against Aeromonas spp. In Mexico, there have been few studies on Aeromonas and its putative virulence factors. The present work therefore highlights an important incidence of Aeromonas spp., with virulence potential and antimicrobial resistance, isolated from frozen fish intended for human consumption in Mexico City.

Distribution of Aeromonas spp. as identified by 16S rDNA restriction fragment length polymorphism analysis in a trout farm

AIMS

This study used restriction fragment length polymorphism (RFLP) with Aeromonas-specific primers to identify species of Aeromonas and to investigate their distribution in a trout farm and stream.

METHODS AND RESULTS

In January, May, August and November 2000, presumptive Aeromonas species were recovered from a farm and a sedimentation pond in a fish farm and stream, and identified by PCR-RFLP analysis with Aeromonas-specific primers. The specificity of Aeromonas-specific primers and the suitability of PCR-RFLP analysis for identifying Aeromonas spp. were confirmed with fatty acid methyl esters (FAMEs) and 16S rDNA sequencing analyses, respectively. Levels of Aeromonas spp. sampled in May and August were higher than in January and November at all sampling sites. Aeromonas salmonicida was the dominant species in January and November, and the proportion of pathogenic species (Aer. hydrophila, Aer. caviae and Aer. veronii) increased in May and August.

CONCLUSIONS

PCR-RFLP analysis with Aeromonas-specific primers is a rapid and reliable method for identifying widely distributed Aeromonas spp. from environmental samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

To minimize human health risk, monitoring the levels and species composition of Aeromonas in fish farm is advisable.

PCR detection of potentially pathogenic aeromonads in raw and cold-smoked freshwater fish

AIMS

Development of a PCR assay for detection of aeromonads carrying the hlyA and/or aerA genes in fish.

METHODS AND RESULTS

The protocol involves an overnight selective enrichment step in tryptic soy broth yeast extract containing 10 microg ml(-1) of ampicillin followed by extraction of DNA and PCR amplification of two haemolysin genes that contribute to the virulence of Aer. hydrophila. This procedure can detect initial populations of 1-10 cfu g(-1) within 24 h in artificially contaminated samples. In naturally contaminated fish, both genes were detected in 13 out of 14 fresh fish lots (aeromonads levels between < 1 and 5.42 log cfu g(-1)) and in 4 out of 16 lots of vacuum-packed cold-smoked fish (aeromonads levels between < 1 and 3.37 log cfu g(-1)). Before enrichment, dominant species were Aer. hydrophila HG1 (aerA+hlyA+), Aer. bestiarum HG2 (aerA+hlyA+) and Aer. caviae HG4 (aerA-hlyA-). After enrichment, Aer. hydrophila HG1 (aerA+hlyA+) was dominant.

CONCLUSIONS

Fresh fish and even smoked fish carry hlyA+ and/or aerA+ aeromonads that can be detected by PCR within 24 h.

SIGNIFICANCE AND IMPACT OF THE STUDY

The PCR assay described offers considerable potential as a rapid method with specificity, sensitivity and simplicity.

Biochemical identification and numerical taxonomy of Aeromonas spp. isolated from environmental and clinical samples in Spain

AIMS

To study the phenotypic characteristics of Aeromonas spp. from environmental and clinical samples in Spain and to cluster these strains by numerical taxonomy.

METHODS AND RESULTS

A collection of 202 Aeromonas strains isolated from bivalve molluscs, water and clinical samples was tested for 64 phenotypic properties; 91% of these isolates were identified at species level. Aeromonas caviae was predominant in bivalve molluscs and Aerom. bestiarum in freshwater samples. Cluster analyses revealed eight different phena: three containing more than one DNA-DNA hybridization group but including strains that belong to the same phenospecies complex (Aerom. hydrophila, Aerom. sobria and Aerom. caviae), Aerom. encheleia, Aerom. trota and three containing unidentified Aeromonas strains isolated from bivalve molluscs.

CONCLUSIONS

Aeromonas spp. are widely distributed in environmental and clinical sources. A selection of 16 of the phenotypical tests chosen allowed the identification of most isolates (91%), although some strains remain unidentified, mainly isolates from bivalve molluscs, suggesting the presence of new Aeromonas species. Numerical taxonomy was not in total concordance with the identification of the studied strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

Numerical taxonomy of Aeromonas strains isolated from different sources revealed the presence of potentially pathogenic Aeromonas spp., especially in bivalve molluscs, and phena with unidentified strains that suggest new Aeromonas species.

Foodborne pathogenic bacteria in prepackaged fresh retail portions of farmed rainbow trout and salmon stored at 3 degrees C

Twelve lots of fresh unskinned fillets of rainbow trout (Oncorhynchus mykiss) and 10 lots of fresh sliced salmon (Salmo salar) prepacked in trays wrapped with an oxygen-permeable film were obtained immediately after packing from two supermarkets having in-plant facilities for packaging wet fish. During storage at 3 degrees C, Listeria innocua was detected in eight lots of trout fillets after 4 days storage. L. monocytogenes was recovered from a single lot also contaminated with L. innocua. Initial numbers of aeromonads were significantly (p < 0.05) lower in trout fillets (3.35 +/- 0.62 log cfu g(-1)) than in salmon slices (4.20 +/- 0.89 log cfu g(-1)). In both fish products, these bacteria significantly (p < 0.05) increased up until spoilage. Most Aeromonas spp. isolates from trout fillets were assigned to A. veronii biovar sobria HG8 (hybridisation group 8), A. caviae HG4, A. eucrenophila HG6, A. hydrophila HG1 and A. veronii biovar veronii HG10. Strains of HG12 (A. schubertii), HG4 and HG8 formed the majority of aeromonads recovered from salmon slices.

Role of various enterotoxins in Aeromonas hydrophila-induced gastroenteritis: generation of enterotoxin gene-deficient mutants and evaluation of their enterotoxic activity

Three enterotoxins from the Aeromonas hydrophila diarrheal isolate SSU have been molecularly characterized in our laboratory. One of these enterotoxins is cytotoxic in nature, whereas the other two are cytotonic enterotoxins, one of them heat labile and the other heat stable. Earlier, by developing an isogenic mutant, we demonstrated the role of a cytotoxic enterotoxin in causing systemic infection in mice. In the present study, we evaluated the role of these three enterotoxins in evoking diarrhea in a murine model by developing various combinations of enterotoxin gene-deficient mutants by marker-exchange mutagenesis. A total of six isogenic mutants were prepared in a cytotoxic enterotoxin gene (act)-positive or -negative background strain of A. hydrophila. We developed two single knockouts with truncation in either the heat-labile (alt) or the heat-stable (ast) cytotonic enterotoxin gene; three double knockouts with truncations of genes encoding (i) alt and ast, (ii) act and alt, and (iii) act and ast genes; and a triple-knockout mutant with truncation in all three genes, act, alt, and ast. The identity of these isogenic mutants developed by double-crossover homologous recombination was confirmed by Southern blot analysis. Northern and Western blot analyses revealed that the expression of different enterotoxin genes in the mutants was correspondingly abrogated. We tested the biological activity of these mutants in a diet-restricted and antibiotic-treated mouse model with a ligated ileal loop assay. Our data indicated that all of these mutants had significantly reduced capacity to evoke fluid secretion compared to that of wild-type A. hydrophila; the triple-knockout mutant failed to induce any detectable level of fluid secretion. The biological activity of selected A. hydrophila mutants was restored after complementation. Taken together, we have established a role for three enterotoxins in A. hydrophila-induced gastroenteritis in a mouse model with the greatest contribution from the cytotoxic enterotoxin Act, followed by the Alt and Ast cytotonic enterotoxins.

Aeromonas species in foods

Aeromonas species have been recognized as potential or emerging foodborne pathogens for more than 20 years. Aeromonads are estuarine bacteria and are ubiquitous in fresh water, fish and shellfish, meats, and fresh vegetables. Actual sourced foodborne outbreaks are few, but epidemiological evidence suggests that the bacterium can cause self-limiting diarrhea, with children being the most susceptible population. Most aeromonads are psychrotrophic and can grow in foods during cold storage. Aeromonads are not resistant to food processing regimes and are readily killed by heat treatment. A host of virulence factors are present, but the exact role of each in human disease has not been fully elucidated.

Growth and survival of clinical vs. environmental species of Aeromonas in tap water

The ability of four species of Aeromonas (two of clinical and two of environmental origin) to survive and/or grow in tap water microcosms supplemented with sodium thiosulphate was tested. After bottling, the autochthonous microflora reached 6 x 10(5) cfu ml(-1) after a 5-day incubation period in tap water unfiltered and which was non-autoclaved. In filtered tap water, "ultramicrocells" were detected and final populations of ca. 10(6) cfu ml(-1) after 7 days were obtained. Aeromonas was inoculated at an initial cell concentration of ca. 10(4) cfu ml(-1). All strains were able to grow in tap water samples, which were filtered and autoclaved, and a final concentration of 10(5)-10(6) cfu ml(-1) was observed. Any inherent capability of Aeromonas to grow in tap water was eliminated by the presence of autochthonous microflora and "ultramicrocells" bacteria. Survival rates were strain- and microcosm-dependent. In unfiltered-non-autoclaved water, viable counts declined to below the detection limit (i.e. 1 log cfu ml(-1)) in 1.5 to 20 days. The declines in viable counts were even more pronounced in the filtered microcosm. Although inoculation ratios (100/1 in unfiltered-non-autoclaved and 1,000/1 in filtered microcosms) were favourable for aeromonads, at least for I to 3 days, the organisms disappeared in these microcosms. Thus, competition for nutrients was an unlikely cause of the limitation of aeromonads. The bacteriolytic effect of enzymes released by membrane vesicles from the autochthonous microflora and of "tail phage-like particles" bacteriocins were suggested as an in situ control of aeromonad populations. The present study showed that environmental strains of Aeromonas had no ecological advantage over clinical isolates. Thus, waterborne infections and contaminations of foods by pathogenic Aeromonas species could not be discounted.

The occurrence of aerolysin-positive Aeromonas spp. and their cytotoxicity in Norwegian water sources

AIMS

The aim of the study was to investigate the occurrence of Aeromonas spp. and their aerolysin status in Norwegian natural water sources.

METHODS AND RESULTS

Seventy-one samples from 33 Norwegian water sources were examined for the presence of Aeromonas spp. From most of the sample sites, the strains were isolated on blood-ampicillin-agar and Difco Aeromonas agar simultaneously. The majority of the samples (73/77) contained Aeromonas spp., with an average of 35-100 cfu 100 ml(-1). The highest counts were found in faecally-contaminated water. Using PCR, 445 isolates were screened for the presence of aerolysin, and 79% of them were found to be carriers of the aerolysin gene. A selection of the isolated strains was tested on Vero cell cultures and 83% of them showed cytotoxicity.

CONCLUSION

There is widespread occurrence of aerolysin-positive cytotoxic Aeromonas spp. in many different Norwegian natural waters, including drinking water sources.

SIGNIFICANCE AND IMPACT OF THE STUDY

The widespread occurrence of potentially-pathogenic Aeromonas spp. in the environment demands that these bacteria should not be ignored in drinking water supplies and in the food industry.