Potential virulence and antimicrobial susceptibility of Aeromonas popoffii recovered from freshwater and seawater

Characterization of atypical pathogenic Aeromonas salmonicida isolated from a diseased Siberian sturgeon (Acipenser baerii)

Acipenser baerii (Siberian sturgeon) is native to Kazakhstan and is currently endangered and is listed within the first class of protected animals. Sturgeon aquaculture is becoming an important tool for the recovery of this endangered species. Nonetheless, diseases involving typical symptoms of skin ulceration and systemic bacterial hemorrhagic septicemia have occurred in cultured A. baerii on a fish farm located in Western Kazakhstan. In this study, an infectious strain of bacteria isolated from an ulcer of diseased A. baerii was identified as Aeromonas salmonicida (strain AB001). This identification involved analyses of 16S rRNA, gyrB, rpoD, and flaA genes' sequences. Even though strain AB001 belongs to A. salmonicida, it exhibited noticeable mobility and growth at temperatures of ≥37 °C. Profiling of virulence genes uncovered the presence of seven such genes related to pathogenicity. Antibiotic sensitivity testing showed that the strain is sensitive to aminoglycosides, amphenicols, nitrofurans, quinolones, and tetracyclines. Half-lethal doses (LD₅₀) of strain AB001 for Oreochromis mossambicus and A. baerii were determined: respectively 1.7 × 10⁸ and 7.2 × 10⁷ colony-forming units per mL. The experimentally induced infection revealed that strain AB001 causes considerable histological lesions in O. mossambicus, including tissue degeneration, necrosis, and hemorrhages of varied severity.

A Novel Aeromonas popoffii Phage AerP_220 Proposed to Be a Member of a New Tolavirus Genus in the Autographiviridae Family

Aeromonas popoffii is one of the environmental Aeromonas species. A number of factors of virulence have been described for this species and it has been reported as a causative agent of urinary tract infection. The first A. popoffii bacteriophage AerP_220 along with its host strain A. popoffii CEMTC 4062 were isolated from river water. The phage has a podovirus morphotype, shows a narrow host range and is lytic against the host strain. The AerP_220 genome comprises 45,207 bp and does not contain genes responsible for antibiotic resistance and toxin production. Fifty-nine co-directional putative ORFs were found in the AerP_220 genome. Thirty-three ORFs encoded proteins with predicted functions; the products of 26 ORFs were hypothetical proteins. AerP_220 genome analysis revealed that this phage can be considered a novel species within the Autographiviridae family. Comparative genomic and proteomic analysis revealed that AerP_220 along with the Aeromonas phage vB_AspA_Tola (OM913599) are members of a new putative Tolavirus genus in the family Autographiviridae. The Gajwadongvirus and proposed Tolavirus genera along with Pantoea phage Nufs112 and phage Reminis could form a new Tolavirinae subfamily within the Autographiviridae family.

First Record of the Rare Species Aeromonas lusitana from Rainbow Trout (Oncorhynchus mykiss, Walbaum): Comparative Analysis with the Existing Strains

The species Aeromonas lusitana was first described in 2016 with five strains recovered from untreated water and vegetables from Portugal. Since then, no further records exist of this species. During a surveillance study on the presence of Aeromonas in fish farms in Mexico, a new strain (ESV-351) of the mentioned species isolated from a rainbow trout was recovered. It was identified because it clustered phylogenetically with the type strain of A. lusitana based on the analysis of the rpoD gene sequences. In the present study, phenotypic characteristics, antimicrobial resistance profiles, and the presence of putative virulence genes of this novel strain (ESV-351) were determined in parallel to the five isolates from the original species description. Phenotypic differential characteristics exhibited by A. lusitana ESV-351 depicted an evident similarity to the characteristics exhibited by the other evaluated strains. However, the novel strain was positive for the production of indole using conventional methods, while the rest of the strains, including the type strain, were negative for its production. Furthermore, intermediate resistance to ampicillin, amoxicillin-clavulanic acid and cephalothin was detected in both the novel and the type strain. Five different virulence-related genes were detected in the novel strain and in the previously described strains, with the type strain exhibiting the highest number of virulence-related genes. In addition to this, the genome of the novel strain (ESV-351) was sequenced and compared with the genomes from the type strain (A. lusitana CECT 7828T) and other Aeromonas spp. The genomic analysis defined Aeromonas tecta as the closest species to A. lusitana with a highly similar number of predicted proteins. The genomic size, the number of protein-encoding genes and the number of different tRNAs, among other characteristics, make it possible to propose that the ESV-351 strain could potentially have the capacity to adapt to different environments. Genome comparison of the ESV-351 strain with the type strain revealed that both possess a similar sequence of the citrate synthase gene. In addition to this finding, the chromosomal region containing the citrate synthase locus of the novel strain exhibits some similarity to the chromosomal region in the genome of the A. hydrophila type strain and other known human pathogens, such as Vibrio cholerae. This could suggest a possible virulence role for the citrate synthase gene in A. lusitana (ESV-351).

Prevalence, virulence-gene profiles, antimicrobial resistance, and genetic diversity of human pathogenic Aeromonas spp. from shellfish and aquatic environments

Aeromonas are found in various habitats, particularly in aquatic environments. This study examined the presence of the most common human pathogenic Aeromonas species (Aeromonas caviae, A. hydrophila, and A. veronii) in surface water, sea water, and shellfish. The detection rates in fishing harbour seawater, shellfish farming seawater, and a river basin were 33.3%, 26.4%, and 29.4%, respectively, and high prevalence was observed in summer. The detection rates in shellfish procured from a fish market and shellfish farm were 34.9% and 13.3%, respectively. The most abundant species of human pathogenic Aeromonas detected via water sampling was A. caviae, whereas that obtained via shellfish sampling was A. veronii. The prevalence of human pathogenic Aeromonas in river water was lower in fishing harbours and in the estuary shellfish farming area. Here, 25 isolates of human pathogenic Aeromonas species were isolated from 257 samples and divided among 16 virulence profiles. The high virulence gene-carrying isolates (more than six genes) belonged to A. hydrophila. The shellfish-sourced isolates had the highest detection rates of act, aerA, and fla genes than of other virulence genes, and vice versa for seawater-sourced isolates. The Aeromonas isolates showed high levels of resistance to ampicillin-sulbactam; however, none were resistant to cefepime, ciprofloxacin, or gentamicin. The incidence of multiple drug resistance (MDR) in Aeromonas isolates was 20%. In this study, phylogenetic analysis with 16S rRNA sequencing, biochemical tests and enterobacterial repetitive intergenic consensus-polymerase chain reaction fingerprinting facilitated the distinct categorisation of three species of human pathogenic Aeromonas isolates. In addition, A. veronii isolates from the same geographical area were also concentrated in the same cluster. This study provides information on the risk of infection by Aeromonas with MDR and multiple virulence genes isolated from shellfish and aquatic environments.

Coming from the Wild: Multidrug Resistant Opportunistic Pathogens Presenting a Primary, Not Human-Linked, Environmental Habitat

The use and misuse of antibiotics have made antibiotic-resistant bacteria widespread nowadays, constituting one of the most relevant challenges for human health at present. Among these bacteria, opportunistic pathogens with an environmental, non-clinical, primary habitat stand as an increasing matter of concern at hospitals. These organisms usually present low susceptibility to antibiotics currently used for therapy. They are also proficient in acquiring increased resistance levels, a situation that limits the therapeutic options for treating the infections they cause. In this article, we analyse the most predominant opportunistic pathogens with an environmental origin, focusing on the mechanisms of antibiotic resistance they present. Further, we discuss the functions, beyond antibiotic resistance, that these determinants may have in the natural ecosystems that these bacteria usually colonize. Given the capacity of these organisms for colonizing different habitats, from clinical settings to natural environments, and for infecting different hosts, from plants to humans, deciphering their population structure, their mechanisms of resistance and the role that these mechanisms may play in natural ecosystems is of relevance for understanding the dissemination of antibiotic resistance under a One-Health point of view.

Draft Genome Sequence of Aeromonas popoffii ID682, Isolated from a Natural Water Source in Idaho

A draft genome sequence of Aeromonas popoffii ID682, isolated from a natural water source in Idaho, is presented here. A. popoffii is a relatively understudied species within a diverse, expanding freshwater genus of bacteria. Here, we describe only the second genome published for this species to date.

Pathogenicity and seasonal variation of Aeromonas hydrophila isolated from seafood and ready-to-eat sushi in South Korea

Aeromonas hydrophila is an emerging foodborne pathogen capable of causing human gastroenteritis, and the main reservoir is the aquatic environment. In this study, the prevalence and virulence of A. hydrophila in seafoods and ready-to-eat (RTE) sushi distributed in various conditions (refrigerated, dried, or frozen) or seasons was investigated. Strains were isolated from seafood (refrigerated or frozen oysters, sashimi, and processed fish; n = 333) and RTE sushi (n = 88) samples collected in South Korea and then genetically analyzed for gastroenteritis-related virulence genes (aer, ast, and alt). Raw oysters showed the highest prevalence of A. hydrophila (57.1%; 47/91) among all seafoods. Among the sashimi samples, flatfish sashimi (54.8%; 34/62) and salmon sushi (51.4%; 18/35) were the most prevalent. A. hydrophila was not detected in the oysters or anchovies distributed as either frozen or dried products. Seasonal investigations of sashimi and sushi showed that the summer prevalence of A. hydrophila with putative virulence genes was significantly lower in sashimi but highest in sushi. These results indicated that sushi could have been contaminated from several sources during the manufacturing or distribution processes. Significant correlations among the prevalence of putative virulence genes were confirmed, although no combination of genes presented a Phi correlation coefficient above 0.5 (0.26-0.43). To our knowledge, this is the first study to investigate the prevalence of A. hydrophila in various types of retail seafoods and RTE sushi in the East Asia region and then relate the prevalence to the distribution conditions of the samples. This study provides background information on the level of potential risk posed by A. hydrophila in retail seafoods and RTE sushi.

Pathogenic profile and cytotoxic activity of Aeromonas spp. isolated from Pectinatella magnifica and surrounding water in the South Bohemian aquaculture region

Pectinatella magnifica is an invasive freshwater bryozoan that has expanded in many localities worldwide, including fishing areas. It contains microbial communities, predominantly consisting of Aeromonas bacteria that are frequently associated with fish infections. The objective of this study was to investigate the potential pathogenicity of Aeromonas spp. associated with P. magnifica and evaluate the health risks for fish. Aeromonas strains were isolated from P. magnifica (101 strains) and from surrounding water (29 strains) in the South Bohemian region and investigated for the presence of 14 virulence-associated genes using PCR. We demonstrated high prevalence of phospholipase GCAT, polar flagellin, enolase, DNAse, aerolysin/cytotoxic enterotoxin, serine protease and heat-stable cytotonic enterotoxin-coding genes. Further, all twelve isolates that were analysed for cytotoxicity against intestinal epithelial cells were found to be cytotoxic. Six of the isolates were also tested as co-cultures composed of pairs. Enhanced cytotoxicity was observed when the pair was composed of strains from different species. In conclusion, P. magnifica is colonized by Aeromonas strains that have a relatively high prevalence of virulence-associated genes and the ability to provoke disease. Results also suggest a possibly increased risk arising from mixed infections.

Microbiological Quality Assessment of Water and Fish from Karst Rivers of the Southeast Black Sea Basin (Croatia), and Antimicrobial Susceptibility of Aeromonas Isolates

Karst rivers are of great interest for commercial fishing and aquaculture, yet they are quite vulnerable aquatic environments because the permeable karst rocks do not effectively filter out contaminants. To understand the current state of karst rivers water quality, we analysed the physico-chemical and microbiological parameters, focusing on antibiotic pollution and the emergence of antibiotic-resistant microbes of three such rivers in Croatia. Water quality varied between classes I and II across sampling sites, and the numbers of total coliforms, enterococci and heterotrophic bacteria varied substantially among sites. Swabs from fish gills, spleen, liver and kidneys were cultured and 94 isolates identified by MALDI-TOF mass spectrometry. The predominant genus was Aeromonas (42.5% of all identified isolates), known for its adaptability to polluted environments and its frequent association with antibiotic resistance. Of the selected Aeromonas isolates known as most pathogenic, half were resistant to at least three antibiotic categories. The Enterobacteriaceae family was represented by the greatest number of genera, most of which are pathogenic for humans and animals and are spoilage bacteria for fish. The results of this study highlight the extent of antibiotic contamination in aquatic environments and the increasing threat of pathogenic and spoilage bacteria in traditionally high-quality karst rivers.

Isolation, Identification and Characteristics of Aeromonas veronii From Diseased Crucian Carp (Carassius auratus gibelio)

Aeromonas species often cause disease in farmed fish. In the present study, dominant bacteria were isolated from diseased crucian carp (Carassius auratus gibelio). Based on this, a bacterial isolate was tentatively named CFJY-623. This isolate was identified as Aeromonas veronii based on analysis of its morphological, physiological, and biochemical features, as well as 16S rRNA and gyrB gene sequences. Six virulence genes related to pathogenicity including aerolysin, cytotonic enterotoxins, elastase, glycerophospholipid: cholesterol acyltransferase, lipase, and serine protease were identified in this A. veronii isolate. The median lethal dosage (LD50) of the CFJY-623 isolate for crucian carp was determined as 1.31 × 107 CFU/mL. Artificial experimental infection showed that the CFJY-623 isolate caused considerable histological lesions in the fish, including tissue cell degeneration, necrosis, and inflammatory cell infiltrating. Drug sensitivity testing showed that the isolate was susceptible to aminoglycosides, carbapenemes, and nitrofurans. Exploring its growing features showed that this isolate exhibited a high level of environmental adaptability. These results provided a scientific basis for the identification of A. veronii and treatment for fish infected by this pathogen.

Molecular Identification and Virulence Potential of the Genus Aeromonas Isolated from Wild Rainbow Trout (Oncorhynchus mykiss) in Mexico

The members of the Aeromonas genus are important foodborne pathogens, with a worldwide distribution. Wild rainbow trout, from the national protected area Santuario del Agua State Park, Corral de Piedra, were analyzed. Species of Aeromonas were isolated from the trout, and their pathogenic potential was analyzed based on different pathogenicity and virulence factors. The isolates were identified as A. allosaccharophila (n = 15), A. sobria (n = 8), A. veronii (n = 3), A. rivipollensis (n = 2), A. piscicola (n = 2), and A. popoffii (n = 1), by RNA polymerase sigma factor (rpoD) gene sequencing. Sequence similarity with the type strain was 92.2 to 99.6% for A. sobria isolates, 97.8 to 98.0% for A. allosaccharophila isolates, 99.2% for the A. popoffii isolate, 99.2 to 100% for A. piscicola isolates, and 98.2 to 99.2% for A. veronii isolates. Notably, isolates A30T2-gills and A30T2-spleen showed sequence similarity of 98.0% with strain A. media CECT 4232T and 99.0% with strain A. rivipollensis P2G1T. Virulence genes were detected by PCR at the following frequencies: fla and serine protease, 96.77%; aerA, 93.54%; aexT, 87.09%; lipases, 74.19%; ascV and ahyB, 67.74%; exu, 61.29%; act, 41.93%; ascF-G, 38.70%; lafA, 32.26%; alt, 6.46%; aopP, 9.67%; and ast, 3.23%. These results indicate that several Aeromonas species had the potential pathogenicity to infect wild rainbow trout in the waterway created by the Corral de Piedra dam, suggesting they could be an emerging zoonotic pathogen.

Distribution of antibiotic resistance and virulence factors among the bacteria isolated from diseased Etroplus suratensis

Considering the emerging concern with the antimicrobial resistance (AMR) evolution, the study has been designed to identify the antibiotic resistance and virulence properties of culturable bacteria isolated from the diseased fish Etroplus suratensis. This has resulted in the purification of 18 morphologically distinct bacterial isolates which were identified by both biochemical and molecular methods. Antibiotic resistance analysis showed the resistance of these isolates to multiple antibiotics and remarkable evolution of AMR. Further screening for virulence factors confirmed five isolates to be positive for haemolytic activity, eight with caseinase, four with DNase, one with gelatinase and three with biofilm-forming properties. In addition to these, the isolates were subjected to PCR-based screening to detect the presence of genes coding for aerolysin and haemolysin. Results showed the presence aerolysin gene in the isolates ESS3.2, ESS3.8, ESI3.3 and ESS3.6, while haemolysin gene was observed to be present in ESG3.1 and ESI3.2. The observed results hence indicate the need for frequent monitoring of these properties among bacterial isolates from diverse environment especially those associated with edible fish.

Genome-driven evaluation and redesign of PCR tools for improving the detection of virulence-associated genes in aeromonads

Many virulence factors have been described for opportunistic pathogens within the genus Aeromonas. Polymerase Chain Reactions (PCRs) are commonly used in population studies of aeromonads to detect virulence-associated genes in order to better understand the epidemiology and emergence of Aeromonas from the environment to host, but their performances have never been thoroughly evaluated. We aimed to determine diagnostic sensitivity and specificity of PCR assays for the detection of virulence-associated genes in a collection of Aeromonas isolates representative for the genetic diversity in the genus. Thirty-nine Aeromonas strains belonging to 27 recognized species were screened by published PCR assays for virulence-associated genes (act, aerA, aexT, alt, ascFG, ascV, ast, lafA, lip, ser, stx1, stx2A). In parallel, homologues of the 12 putative virulence genes were searched from the genomes of the 39 strains. Of the 12 published PCR assays for virulence factors, the comparison of PCR results and genome analysis estimated diagnostic sensitivities ranging from 34% to 100% and diagnostic specificities ranged from 71% to 100% depending upon the gene. To improve the detection of virulence-associated genes in aeromonads, we have designed new primer pairs for aerA/act, ser, lafA, ascFG and ascV, which showed excellent diagnostic sensitivity and specificity. Altogether, the analysis of high quality genomic data, which are more and more easy to obtain, provides significant improvements in the genetic detection of virulence factors in bacterial strains.

Chlorinated and ultraviolet radiation -treated reclaimed irrigation water is the source of Aeromonas found in vegetables used for human consumption

Wastewater is increasingly being recognized as a key water resource, and reclaimed water (or treated wastewater) is used for irrigating vegetables destined for human consumption. The aim of the present study was to determine the diversity and prevalence of Aeromonas spp. both in reclaimed water used for irrigation and in the three types of vegetables irrigated with that water. Seven of the 11 (63.6%) samples of reclaimed water and all samples of vegetables were positive for the presence of Aeromonas. A total of 216 Aeromonas isolates were genotyped and corresponded to 132 different strains that after identification by sequencing the rpoD gene belonged to 10 different species. The prevalence of the species varied depending on the type of sample. In the secondary treated reclaimed water A. caviae and A. media dominated (91.4%) while A. salmonicida, A. media, A. allosaccharophila and A. popoffii represented 74.0% of the strains in the irrigation water. In vegetables, A. caviae (75.0%) was the most common species, among which a strain isolated from lettuce had the same genotype (ERIC pattern) as a strain recovered from the irrigation water. Furthermore, the same genotype of the species A. sanarellii was recovered from parsley and tomatoes demonstrating that irrigation water was the source of contamination and confirming the risk for public health.

Antibiogram characterization and putative virulence genes in Aeromonas species isolated from pig fecal samples

Aeromonas species are broadly distributed in nature and agricultural environments and have been isolated from feces, bedding, and drinking water of healthy pigs. We assessed the incidence, virulence properties, and antimicrobial resistance profile of Aeromonas spp., isolated from pig feces. Antibiogram was done using the disc diffusion methods, and polymerase chain reaction was used for the detection of putative virulence genes. Identification of isolates revealed three phenotypic species with percentage distribution as follows: Aeromonas hydrophila 23 (45.1 %), Aeromonas caviae 16 (31.4 %), and Aeromonas sobria 12 (23.5 %). All Aeromonas isolates in the study were absolutely susceptible to cefotaxime and resistant to penicillin. A. cavaie and A. sobria demonstrated absolute susceptibility against ciprofloxacin and streptomycin. Aeromonas species showed varied susceptibility to cephalothin as follows: A. hydrophila 78.3 %, A. cavaie 93.7 %, and A. sobria 91.7 %. The percentage distribution of virulence genes among Aeromonas isolates were as follows: Aerolysin (aer) 74.5 %, flagellin gene (fla) 68.6 %, cytotoxin (hly A) 43.1 %, lipase (lip) 39.2 %, enterotoxic activities (ast) 31.3 %, and cytotonic gene (alt) 13.7 %. Reports from this study shows that Aeromonas species isolated from pig fecal samples are multi-drug resistant and possess virulence potential which may result to possible risk of human or animal infection and likely contamination of food and water from this sources.

Potential pathogenicity ofAeromonas hydrophilacomplex strains isolated from clinical, food, and environmental sources

Aeromonas are autochthonous inhabitants of aquatic environments, including chlorinated and polluted waters, although they can also be isolated from a wide variety of environmental and clinical sources. They cause infections in vertebrates and invertebrates and are considered to be an emerging pathogen in humans, producing intestinal and extra-intestinal diseases. Most of the clinical isolates correspond to A. hydrophila, A. caviae, and A. veronii bv. Sobria, which are described as the causative agents of wound infections, septicaemia, and meningitis in immunocompromised people, and diarrhoea and dysenteric infections in the elderly and children. The pathogenic factors associated with Aeromonas are multifactorial and involve structural components, siderophores, quorum-sensing mechanisms, secretion systems, extracellular enzymes, and exotoxins. In this study, we analysed a representative number of clinical and environmental strains belonging to the A. hydrophila species complex to evaluate their potential pathogenicity. We thereby detected their enzymatic activities and antibiotic susceptibility pattern and the presence of virulence genes (aer, alt, ast, and ascV). The notably high prevalence of these virulence factors, even in environmental strains, indicated a potential pathogenic capacity. Additionally, we determined the adhesion capacity and cytopathic effects of this group of strains in Caco-2 cells. Most of the strains exhibited adherence and caused complete lysis.

A Culture Independent Method for the Detection of Aeromonas sp. from Water Samples

The genus Aeromonas is present in a wide variety of water environments and is recognised as potentially pathogenic to humans and animals. Members of this genus are often confused with Vibrio when using automated, commercial identification systems that are culture-dependent. This study describes a polymerase chain reaction (PCR) detection method for Aeromonas that is culture-independent and that targets the glycerophospholopid-cholesterol acyltransferase (gcat) gene, which is specific for this genus. The GCAT-PCR was 100% specific in artificially inoculated water samples, with a detection limit that ranged from 2.5 to 25 cfu/mL. The success at detecting this pathogen in 86 water samples using the GCAT-PCR method was identical to the conventional culturing method when a pre-enrichment step was carried out, yielding 83.7% positive samples. On the other hand, without a pre-enrichment step, only 77.9% of the samples were positive by culturing and only 15.1% with the GCAT-PCR. However, 83.7% positive samples were obtained for the GCAT-PCR when the water volume for the DNA extraction was increased from 400 µL to 4 mL. The proposed molecular method is much faster (5 or 29 h) than the culturing method (24 or 48 h) whether performed directly or after a pre-enrichment step and it will enable the fast detection of Aeromonas in water samples helping to prevent a possible transmission to humans.

Antimicrobial resistance and virulence signatures of Listeria and Aeromonas species recovered from treated wastewater effluent and receiving surface water in Durban, South Africa

BACKGROUND

Treated wastewater effluent has been found to contain high levels of contaminants, including disease-causing bacteria such as Listeria and Aeromonas species. The aim of this study was to evaluate the antimicrobial resistance and virulence signatures of Listeria and Aeromonas spp. recovered from treated effluents of two wastewater treatment plants and receiving rivers in Durban, South Africa.

METHODS

A total of 100 Aeromonas spp. and 78 Listeria spp. were positively identified based on biochemical tests and PCR detection of DNA region conserved in these genera. The antimicrobial resistance profiles of the isolates were determined using Kirby Bauer disc diffusion assay. The presence of important virulence genes were detected via PCR, while other virulence determinants; protease, gelatinase and haemolysin were detected using standard assays.

RESULTS

Highest resistance was observed against penicillin, erythromycin and nalidixic acid, with all 78 (100%) tested Listeria spp displaying resistance, followed by ampicillin (83.33%), trimethoprim (67.95%), nitrofurantoin (64.10%) and cephalosporin (60.26%). Among Aeromonas spp., the highest resistance (100%) was observed against ampicillin, penicillin, vancomycin, clindamycin and fusidic acid, followed by cephalosporin (82%), and erythromycin (58%), with 56% of the isolates found to be resistant to naladixic acid and trimethoprim. Among Listeria spp., 26.92% were found to contain virulence genes, with 14.10, 5.12 and 21% harbouring the actA, plcA and iap genes, respectively. Of the 100 tested Aeromonas spp., 52% harboured the aerolysin (aer) virulence associated gene, while lipase (lip) virulence associated gene was also detected in 68% of the tested Aeromonas spp.

CONCLUSIONS

The presence of these organisms in effluents samples following conventional wastewater treatment is worrisome as this could lead to major environmental and human health problems. This emphasizes the need for constant evaluation of the wastewater treatment effluents to ensure compliance to set guidelines.

Detection and Characterization of Antimicrobial Resistance and Putative Virulence Genes in Aeromonas veronii Biovar Sobria Isolated from Gilthead Sea Bream (Sparus aurata L.)

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.

Re-identification of Aeromonas isolates from rainbow trout and incidence of class 1 integron and β-lactamase genes

Forty-eight Aeromonas isolates from rainbow trout previously identified by the 16S rDNA-RFLP technique were re-identified using 2 housekeeping genes (gyrB and rpoD). After sequencing the prevalences of the species were A. veronii (29.2%), A. bestiarum (20.8%), A. hydrophila (16.7%), A. sobria (10.4%), A. media (8.3%), A. popoffii (6.2%), A. allosaccharophila (2.1%), A. caviae (2.1%), A. salmonicida (2.1%) and one isolate (2.1%) belongs to a candidate new species "Aeromonas lusitana". Coincident identification results to the 16S rDNA-RFLP technique were only obtained for 68.8% of the isolates. PCR amplification of the enterobacterial repetitive intergenic consensus (ERIC-PCR) indicated that the 48 isolates belonged to 33 different ERIC genotypes. Several genotypes were isolated from different farms and organs in the same fish, indicating a systemic dissemination of the bacteria. The presence of genes (blaIMP, blaCphA/IMIS, blaTEM, blaSHV and intI1) that encode extended-spectrum beta-lactamases (ESBLs), metallo-beta-lactamases (MBLs) and class 1 integrons were studied by PCR. Only 39.6% (19/48) of the strains showed the presence of one or more resistance genes. The gene blaCphA/IMIS was detected in 29.2% of the isolates, followed by the intI1 (6.2%) and blaSHV (4.2%) genes. The variable region of class 1 integrons of the 3 positive isolates was sequenced revealing the presence of the gene cassette aadA1 (aminoglycoside transferase) that plays a role in streptomycin/spectinomycin resistance.

Characterization and antimicrobial susceptibility of motile aeromonads isolated from freshwater ornamental fish showing signs of septicaemia

A total of 74 phenotypically identified presumptive motile Aeromonas isolates recovered from septicaemic freshwater ornamental fish in Sri Lanka were genetically characterized by sequencing of rpoD and gyrB genes. rpoD/gyrB phylogeny confirmed only 53 isolates as Aeromonas, among which A. veronii was the predominant species (79.2%), followed by A. hydrophila (7.5%), A. caviae (5.7%), A. jandaei (1.9%), A. dhakensis (3.8%) and A. entero pelogenes (1.9%). The aeromonads confirmed by sequencing were further subjected to 16S rDNA PCR-RFLP which substantiated sequencing results for 83% of isolates. Fingerprinting of A. enteropelogenes (n = 42) using ERIC-PCR revealed no dominant clones, and the majority were genetically distinct. All isolates were screened by PCR for 7 virulence determinant genes (aer, act, ast, alt, fla, ser, exu) and 2 integrase encoding genes (intI1, intI2). Each isolate contained ≥3 of the virulence genes tested for, with a heterogeneous distribution. Of the isolates, 77% harboured the intI1 gene, while none had intI2. In vitro antimicrobial susceptibility testing showed highest resistances towards tetracycline (58.5%) and erythromycin (54.7%). Our results indicate the diverse range of aeromonads that could potentially be associated with motile aeromonad septicaemia in ornamental fish. This is the first isolation of A. dhakensis from a septicaemic ornamental fish since its original description from the same host.

Development of duplex-PCR for identification of Aeromonas species

INTRODUCTION

The number of reports of intestinal infections caused by Aeromonas spp. has increased significantly in recent years. In most clinical laboratories, identification of these bacteria is carried out by general phenotypic tests that sometimes do not accurately differentiate Aeromonas and Vibrio.

METHODS

A duplex-polymerase chain reaction (PCR) was developed directed to 2 targets identifying Aeromonas spp. pathogenic to humans.

RESULTS

The duplex-PCR results were reproducible and specific for Aeromonas spp. pathogenic to humans.

CONCLUSIONS

This method will allow differentiation between Vibrio and Aeromonas spp. in patients with in cholera-like symptoms and can also be used in water quality monitoring.

The occurrence of Aeromonas in drinking water, tap water and the porsuk river

The occurrence of Aeromonas spp. in the Porsuk River, public drinking water and tap water in the City of Eskisehir (Turkey) was monitored. Fresh water samples were collected from several sampling sites during a period of one year. Total 102 typical colonies of Aeromonas spp. were submitted to biochemical tests for species differentiation and of 60 isolates were confirmed by biochemical tests. Further identifications of isolates were carried out first with the VITEK system (BioMe˜rieux) and then selected isolates from different phenotypes (VITEK types) were identified using the DuPont Qualicon RiboPrinter® system. Aeromonas spp. was detected only in the samples from the Porsuk River. According to the results obtained with the VITEK system, our isolates were 13% Aeromonas hydrophila, 37% Aeromonas caviae, 35% Pseudomonas putida, and 15% Pseudomonas acidovorans. In addition Pseudomonas sp., Pseudomonas maltophila, Aeromonas salmonicida, Aeromonas hydrophila, and Aeromonas media species were determined using the RiboPrinter® system. The samples taken from the Porsuk River were found to contain very diverse Aeromonas populations that can pose a risk for the residents of the city. On the other hand, drinking water and tap water of the City are free from Aeromonas pathogens and seem to be reliable water sources for the community.

Molecular characterization of Aeromonas spp. and Vibrio cholerae O1 isolated during a diarrhea outbreak

This work aimed to assess pathogenic potential and clonal relatedness of Aeromonas sp. and Vibrio cholerae isolates recovered during a diarrhea outbreak in Brazil. Clinical and environmental isolates were investigated for the presence of known pathogenic genes and clonal relatedness was assessed by intergenic spacer region (ISR) 16S-23S amplification. Four Aeromonas genes (lip, exu, gcat, flaA/B) were found at high overall frequency in both clinical and environmental isolates although the lip gene was specifically absent from selected species. A fifth gene, aerA, was rarely found in A. caviae, the most abundant species. The ISR profile revealed high heterogeneity among the Aeromonas isolates and no correlation with species identification. In contrast, in all the V. cholerae isolates the four genes investigated (ctxA, tcpA, zot and ace) were amplified and revealed homogeneous ISR and RAPD profiles. Although Aeromonas isolates were the major enteric pathogen recovered, their ISR profiles are not compatible with a unique cause for the diarrhea events, while the clonal relationship clearly implicates V. cholerae in those cases from which it was isolated. These results reinforce the need for a better definition of the role of aeromonads in diarrhea and whether they benefit from co-infection with V. cholerae.

Adhesion to brown trout skin mucus, antagonism against cyst adhesion and pathogenicity to rainbow trout of some inhibitory bacteria against Saprolegnia parasitica

Biological control of saprolegniosis with bacteria might be an alternative to the use of chemical compounds. Among criteria for the selection of such bacteria are their absence of pathogenicity to fish and their ability to prevent adhesion of the pathogen to the skin mucus. The pathogenicity to rainbow trout of 21 bacterial isolates with in vitro inhibitory activity against Saprolegnia parasitica was studied. Fifteen of the isolates, identified as Aeromonas sobria, Pantoea agglomerans, Pseudomonas fluorescens, Serratia fonticola, Xanthomonas retroflexus and Yersinia kristensenii, were non-pathogenic when injected into rainbow trout. Their capacity to adhere to the skin mucus of male and female brown trout and to reduce the adhesion of S. parasitica cysts under exclusion, competition and displacement conditions was tested. The 15 bacterial isolates showed a low adhesion rate, ranging between 1.7% (for an A. sobria isolate) and 15.3% (a P. fluorescens isolate). This adhesion was greater in the case of mucus from male brown trout than from females. Similarities in the adhesion to male mucus and other substrates and correlation to that observed to polystyrene suggest that adhesion to skin mucus does not depend on the substrate. A high percentage (88.9%) of the S. parasitica cysts adhered to the skin mucus of male brown trout. Almost all of the bacteria reduced this adhesion ratio significantly under exclusion and competition conditions. However, only half of the isolates displaced cysts from skin mucus, and more bacterial cells were necessary for this effect. A novel method to study the adhesion of S. parasitica cysts to skin mucus of trout and their interactions with inhibitory bacteria is described.

Virulence factors of Aeromonas salmonicida subsp. salmonicida strains associated with infections in turbot Psetta maxima

Virulence factors for Aeromonas salmonicida subsp. salmonicida (ASS) strains isolated from cultured turbot Psetta maxima L. are unknown with regard to this host. The presence of virulence genes associated with different stages of ASS infection in salmonids (vapA, tapA, fla, ascV, ascC, aexT, satA and aspA) was analysed using a polymerase chain reaction (PCR) technique in ASS strains isolated from turbot. Other ASS strains isolated from salmonids and environmental A. salmonicida (AS) strains were included for comparison. The presence of the genes was evaluated with respect to ASS virulence in turbot based on intraperitoneal and bath challenges. The genetic profile, including all of the genes studied, that was linked to virulent behaviour after intraperitoneal challenge was significantly more frequent in strains isolated from turbot than in those from salmonids or the environment. The data prove that it is not possible to predict the virulence of ASS in turbot based only on the presence of all genes tested. Moreover, the combined PCR results of vapA, aexT, ascV and ascC were useful for separating most of the ASS from environmental A. salmonicida strains. An association between virulence or genetic profile and the geographical or facility origin of the strains was not found.

Virulence potential and genetic diversity ofAeromonas caviae,Aeromonas veronii, andAeromonas hydrophilaclinical isolates from Mexico and Spain: a comparative study

A comparative study of 109 Aeromonas clinical isolates belonging to the 3 species most frequently isolated from patients with diarrhea in Mexico and Spain was performed to investigate the distribution of 3 prominent toxin genes and the gene encoding flagellin of lateral flagella; 4 well-established virulence factors in the genus Aeromonas. The aerolysin–hemolysin toxin genes were the most prevalent, being present in 89% of the total isolates. The ast toxin gene was conspicuously absent from the Aeromonas caviae and Aeromonas veronii groups but was present in 91% of the Aeromonas hydrophila isolates. Both the alt toxin gene and the lafA flagellin gene also had a low incidence in A. caviae and A. veronii. Differences in the prevalence of alt and lafA were observed between isolates from Mexico and Spain, confirming genus heterogeneity according to geographic location. Carriage of multiple toxin genes was primarily restricted to A. hydrophila isolates, suggesting that A. caviae and A. veronii isolates circulating in Mexico and Spain possess a limited array of virulence genes. Enterobacterial repetitive intergenetic consensus – polymerase chain reaction showed that the Aeromonas populations sampled lack dominant clones and were genetically heterogeneous, with A. caviae being the most diverse species. Further surveys of virulence determinants in genetically heterogeneous populations of Aeromonas isolates circulating worldwide are required to enhance the understanding of their capacity to cause disease.

Importance of flagella and enterotoxins for Aeromonas virulence in a mouse model

A genetic characterization of eight virulence factor genes, elastase, lipase, polar flagella (flaA/flaB, flaG), lateral flagella (lafA), and the enterotoxins alt, act, and ast, was performed using polymerase chain reaction with 55 drinking water and nine clinical isolates. When 16 Aeromonas hydrophila strains, seven Aeromonas veronii strains, and seven Aeromonas caviae strains exhibiting different combinations of virulence factor genes were tested in immunocompromised mice by intraperitoneal injection, only those strains that had one or more of the enterotoxins flaA, flaB, and either flaG or lafA showed signs of being virulent. The correlation was seen in 97% (29/30) of the strains, which included strains from drinking water. Thus, Aeromonas water isolates have the potential to be pathogenic in immunocompromised hosts.

Updated phylogeny of the genus Aeromonas

Recent phylogenetic studies of the genus Aeromonas based on gyrB and rpoD gene sequences have improved the phylogeny based on 16S rRNA gene sequences first published in 1992, particularly in the ability to split closely related species. These studies did not include the recently described species Aeromonas simiae and Aeromonas molluscorum and only a single strain of Aeromonas culicicola was available for analysis at that time. In the present work, these Aeromonas species and newly isolated strains of A. culicicola were examined. Sequence analysis indicates that A. simiae and A. molluscorum belong to non-described phylogenetic lines of descent within this genus, which supports the original description of both species. The most closely related species are Aeromonas schubertii and Aeromonas encheleia, respectively, which is consistent with 16S rRNA gene sequencing results. However, while the five strains of A. molluscorum showed nucleotide differences in their gyrB and rpoD gene sequences, the only two known A. simiae strains exhibited identical gene sequences, suggesting that they are isolates of the same strain. On the basis of the rpoD gene sequence phylogeny, A. culicicola strains from the original description and new isolates from drinking water and ornamental fish clustered within the species Aeromonas veronii, suggesting inconsistencies with previous results. Other strains with previously controversial taxonomy and new isolates from other studies were included in this study in order to clarify their phylogenetic affiliation at the species level.

Determination of the viability of Aeromonas hydrophila in different types of water by flow cytometry, and comparison with classical methods

The presence of Aeromonas spp. in water can represent a risk for human health. Therefore, it is important to know the physiological status of these bacteria and their survival in the environment. We studied the behavior of a strain of Aeromonas hydrophila in river water, spring water, brackish water, mineral water, and chlorinated drinking water, which had different physical and chemical characteristics. The bacterial content was evaluated by spectrophotometric and plate count techniques. Flow cytometric determination of viability was carried out using a dual-staining technique that enabled us to distinguish viable bacteria from damaged and membrane-compromised bacteria. The traditional methods showed that the bacterial content was variable and dependent on the type of water. The results obtained from the plate count analysis correlated with the absorbance data. In contrast, the flow cytometric analysis results did not correlate with the results obtained by traditional methods; in fact, this technique showed that there were viable cells even when the optical density was low or no longer detectable and there was no plate count value. According to our results, flow cytometry is a suitable method for assessing the viability of bacteria in water samples. Furthermore, it permits fast detection of bacteria that are in a viable but nonculturable state, which are not detectable by conventional methods.

Aeromonas popoffii urinary tract infection

Aeromonas popoffii is a recently described species isolated mainly from freshwater. An isolate of Aeromonas popoffii was found to be responsible for a urinary tract infection in a 13-year-old boy suffering from spina bifida with enterocystoplasty. This is the first reported case of human infection attributed to this species.

Aeromonas hydrophilaclinical and environmental ecotypes as revealed by genetic diversity and virulence genes

Aeromonas hydrophila strains recovered from clinical samples and ambient sources were phenotypically and genetically identified. In addition, the distribution of putative virulence factors was assayed. To determine the genetic diversity of these strains, random amplification of polymorphic DNA (RAPD) and enterobacterial repetitive intergenic consensus (ERIC)-PCR markers were used. The discriminatory ability of the techniques, using Simpson's index, was 0.96 for both methods. The most consistent dendrogram was obtained when RAPD and ERIC data were combined. The genetic diversity revealed a high intra-specific genetic diversity (h=0.364+/-0.024 and I=0.538+/-0.030). The strains showed a tendency to cluster according to their origin of isolation (best-cut test 0.80 and bootstrap values >50%). The present study demonstrates and quantifies the high intra-specific diversity within this species and reveals a clear differentiation of strains according to their ecological origin. The distribution of virulence-related genes confirm that A. hydrophila is a genetically heterogeneous species that harbour ecotypes which have different pathogenic potential to human and other animals.

Tolerance and starvation induced cross-protection against different stresses in Aeromonas hydrophila

Aeromonas hydrophila is sometimes considered as a controversial human pathogen and reported to be susceptible to food processing procedures and environmental stresses. In this study, we have shown that early stationary phase cells of A. hydrophila were readily killed during up shifts in temperature (in the range 50-70 degrees C), the course of drying (at relative humidity, temperature and brightness of the laboratory) and after 5 min exposure to 20%, 30% and 40% v/v ethanol. However, this bacterium was found moderately susceptible to down shift to 4 degrees C in nutrient poor water, sodium chloride stresses (1.5 and 2 M) and to 12% and 15% v/v ethanol stresses. Tolerance against 1 M NaCl and 10% v/v ethanol was observed. At ambient temperature (24.5 degrees C), this microorganism exhibited a starvation survival state, which was largely independent of the initial cell concentrations (8.82, 7.71 and 6.76 log units). The cross-protection experiments showed that cells starved for short (1 day) or prolonged (50 days) periods developed increased resistance to down shift at 4 degrees C and ethanol stress. This may be of concern to the food-processing industry from the public health perspective.

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.

A family history of deoxyribonuclease II: surprises from Trichinella spiralis and Burkholderia pseudomallei

Deoxyribonuclease IIalpha (DNase IIalpha) is an acidic endonuclease found in lysosomes and nuclei, and it is also secreted. Though its Caenorhabditis elegans homolog, NUC-1, is required for digesting DNA of apoptotic cell corpses and dietary DNA, it is not required for viability. However, DNase IIalpha is required in mice for correct development and viability, because undigested cell corpses lead to lesions throughout the body. Recently, we showed that, in contrast to previous reports, active DNase IIalpha consists of one contiguous polypeptide. To better analyze DNase II protein structure and determine residues important for activity, extensive database searches were conducted to find distantly related family members. We report 29 new partial or complete homologs from 21 species. Four homologs with differences at the purported active site histidine residue were detected in the parasitic nematodes Trichinella spiralis and Trichinella pseudospiralis. When these mutations were reconstructed in human DNase IIalpha, the expressed proteins were inactive. DNase II homologs were also identified in non-metazoan species. In particular, the slime-mold Dictyostelium, the protozoan Trichomonas vaginalis, and the bacterium Burkholderia pseudomallei all contain sequences with significant similarity and identity to previously cloned DNase II family members. We report an analysis of their sequences and implications for DNase II protein structure and evolution.