Prevalence, virulence and antimicrobial resistance patterns of Aeromonas spp. isolated from children with diarrhea

Aeromonas characteristics in Iran, Southwest Asia; a systematic review and meta-analysis on epidemiology, reservoirs and antibiotic resistance profile from aquatic environments to human society during 2000-2023

BACKGROUND

As recent evidence shows the prevalence and transmission of Aeromonas species in Southwest Asia, and there is no updated information on the characteristics of Aeromonas in Iran, we conducted this review. We systematically searched biomedical databases (PubMed, Web of Sciences, Scopus, SID, ISC, and Google Scholar) to identify relevant studies investigating the prevalence, antibiotic resistance, and main reservoirs of Aeromonas in aquatic animals and human clinical specimens during 2000-2023 in Iran. Cochrane's Q test and I^2 statistical test was used to assess heterogeneity, and publication bias was assessed using funnel plots and random effects tests.

RESULTS

In Iran, among 8347 human clinical samples and 1802 animal and food samples, only 87 (1.04%) and 388 (21.53%) samples were positive for Aeromonas spp. respectively, and the most isolated species was A. hydrophila. The main reservoir for Aeromonas spp. were twenty-four genera of aquatic animals besides minced meat, pigeon stool and chicken meat. In Iran, Aeromonas spp. isolates showed maximum resistance to ampicillin, tetracycline, nalidixic acid and vancomycin. The heterogeneity test for prevalence of Aeromonas species on human samples and animals or food products was significant (88.1256, (5), P-value < 0.0001) and the heterogeneity rate was 97.34% with a confidence interval of 0.2-4.3 and (194.02, (10), P-value < 0.0001) and the heterogeneity rate was 94.85% with a confidence interval of 15,124 - 33,335 respectively.

CONCLUSIONS

According to these results, it is essential for exclusive attention to the prevalence and antibiotic resistance of Aeromonas in different provinces of Iran. Furthermore, special planning should be done for prevention, outbreak control and proper treatment of infections in the aquaculture industry and human societies.

Infection Status, Etiological Analysis of Aeromonas Spp. in Foodborne Diarrhea Patients from 2019 to 2023 in Wenzhou

The infection status and etiological analysis of Aeromonas spp. from foodborne diarrhea patients in Wenzhou were carried out to provide the etiological basis for healthy diet and clinical treatment. Aeromonas isolates (n = 41) collected from foodborne diarrhea patients were identified using the automatic bacteriologic analyzer and mass spectrometer. Species identification, multilocus sequence typing, prediction of virulence genes, and antimicrobial resistance genes were analyzed by the data of whole genome sequencing. The antibiotic resistance of these isolates was determined using miniaturization of the broth dilution susceptibility test. A total of 1829 stool samples of diarrhea patients were collected, and the detection rate of Aeromonas spp. was 2.24% (41/1829). Moreover, Aeromonas spp. are more easily detected in warmer months (from June to August), which were identified as follows: A. veronii (53.66%, 22/41), A. caviae (21.95%, 9/41), A. hydrophila (9.76%, 4/41), A. dhakensis (4.88%, 2/41), A. rivipollensis (4.88%, 2/41), A. enteropelogenes (2.44%, 1/41), and A. media (2.44%, 1/41). All strains can be divided into 38 sequence types, 31 of which were novel, suggesting that Aeromonas spp. had high genetic diversity, multiple clones, and various sources in diarrhea patients. High number of genetic diversity and resistance were found in the Aeromonas isolates. In addition, the category distribution of the virulence genes was significantly different among the seven species of Aeromonas. Aeromonas spp. had different degrees of resistance to antibiotics, and tetracycline was the most serious, with a resistance rate of 27%. What's more, for some antimicrobial classes in silico antimicrobial resistance gene detection was highly correlated with phenotypic antimicrobial resistance patterns with an overall sensitivity of 93.3% and a specificity of 66.7%. The findings from this research highlighted the importance for development of prevention and control strategies to reduce the risk of foodborne diarrhea caused by Aeromonas spp.

A Systematic Review and Meta-Analysis of Aeromonas-Associated Diarrhea Among Children in Asia

Background: Diarrheal illness is a prominent public health worry in developing countries, resulting in high mortality among children. Sociodemographic characteristics and geographic settings are the main effective factors for the increased incidence of childhood diarrhea. Aeromonas is a neglected organism capable of causing dysentery and diarrhea. The aim of this systematic review and meta-analysis was to determine the prevalence of Aeromonas as an agent in the causation of diarrhea in Asian children. Methods: We conducted a systematic review using Web of Science, PubMed, Wiley Online Library, Science Direct, and Google Scholar for peer-reviewed articles published between January 2000 and February 2023. We considered studies that found Aeromonas in diarrheal stool. A random-effects model was used to determine the pooled prevalence of Aeromonas. Results: Our search returned 2,057 articles, with 17 articles from seven Asian nations being included in the systematic review. The pooled prevalence of Aeromonas was 4.5% (95% confidence interval [CI]: 2.9%-6.8%), with heterogeneity (I2 = 96.85; p < 0.001). There was a greater prevalence in areas with high population living in poverty (12.2%; 95% CI: 5.8%-24%) and lower-middle-income countries (5.0%; 95% CI: 2.7%-9.0%). In addition, the prevalence of Aeromonas was greater in South Asia (10.0%; 95% CI: 5.6%-17.2%), in India (12.9%; 95% CI: 6.8%-23%), and in countries with open defecation rate of 5%-25% (11.3%; 95% CI: 6.3%-19.2%). Conclusion: The prevalence of Aeromonas-associated diarrhea in children in Asia estimated in the present study highlighted the high burden of Aeromonas in some parts of Asia.

Evaluation of the prevalence of Aeromonas spp., Campylobacter spp., and Clostridioides difficile in immunocompromised children with diarrhea

AIM

Diarrhea is a common disease in immunocompromised patients and can be associated with greater morbidity and even mortality. Therefore, the present study was designed to determine the prevalence of Aeromonas spp., Campylobacter spp., and C. difficile among immunocompromised children.

METHODS

This study was conducted on 130 stool samples from patients with diarrhea who had defects in the immune system and were referred to Hazrat Masoumeh Children's Hospital in Qom. Demographic information, clinical symptoms, immune status, and duration of chemotherapy were also recorded for each child. DNAs were extracted from the stool, and then direct PCR assays were done by specific primers for the detection of Aeromonas spp., Campylobacter spp., and toxigenic C. difficile, including tcdA/B and cdtA/B genes. Co-infection in patients was also evaluated.

RESULTS

60.8% and 39.2% were male and female, respectively, with a m ± SD age of 56.72 ± 40.49 months. Most cases of immunocompromised states were related to Acute Lymphocytic Leukemia (77.7%) and Non-Hodgkin Lymphoma (14.6%). 93.1% of patients were undergoing chemotherapy during the study. Among patients, most clinical symptoms were related to bloody diarrhea (98.5%) and fever (92.3%). Based on PCR, 14.6, 9.2, and 1.5% were positive for Aeromonas spp., C. difficile, and C. jejuni, respectively. Among the C. difficile-positive cases, the tcdA gene was only detected in one patient. In total, three co-infections were identified, which included Aeromonas spp./C. difficile (tcdA+), C. jejuni/C. difficile, and C. jejuni/Aeromonas spp.

CONCLUSIONS

This is the first study in Iran to investigate the simultaneous prevalence of some pathogens in immunocompromised children with diarrhea. Because Aeromonas spp., Campylobacter spp., and C. difficile are not routinely detected in some laboratories, infections caused by them are underappreciated in the clinic. Our results showed that these pathogens are present in our region and can cause gastroenteritis in children, especially those with underlying diseases. Therefore, increasing the level of hygiene in some areas and controlling bacterial diarrheal diseases should be given more attention by health officials.

Watery Diarrhea Is Not Always Clostridioides difficile: A Case Report of Aeromonas hydrophila Gastroenteritis

Aeromonas species can cause acute gastroenteritis but are much less commonly observed in the hospital setting than other bacteria. Most cases of Aeromonas hydrophila gastroenteritis reported in the literature have occurred in pediatric, elderly, and/or immunocompromised patients. We present a case of subacute watery diarrhea due to A. hydrophila infection in an otherwise healthy 48-year-old female patient with prior abdominal surgeries and recent hospitalization for a catheter-associated urinary tract infection (CAUTI) for which she received antibiotics. The patient presented with 10 days of increasingly frequent non-bloody, watery, foul-smelling diarrhea as well as decreased oral intake, cramping bilateral upper abdominal pain, chills, and malaise. Initial diagnoses considered included Clostridioides difficile in the setting of CAUTI and antibiotic use, small intestinal bacterial overgrowth, dumping syndrome related to bariatric surgery, and malabsorption. A computed tomography scan of her abdomen/pelvis, admission labs, and flexible sigmoidoscopy showed no relevant findings. Stool cultures eventually returned positive for A. hydrophila. The case is an uncommon presentation of Aeromonas infection that could be easily missed while other diagnoses are pursued. Early treatment of Aeromonas infection can be crucial in preventing advanced forms of disease such as septicemia and necrotizing fasciitis.

Virulence genes of Aeromonas spp. isolates from stool in Spain

INTRODUCTION

The role of Aeromonas species in gastrointestinal disease is controversial. The aim was to analyze not only the virulence genes between different species of Aeromonas isolated from feces, but the distribution of these virulence genes between enterotoxigenic strains and co-pathogen strains.

METHODS

Retrospective study of isolates of Aeromonas spp. in feces (2016-2021). The protocol included coproculture, identification by MALDI-TOF and confirmation by multiplex PCR. SPSS Statistics program was used.

RESULTS

A total of 288 strains were studied for the virulence genes between different species of Aeromonas. To compare virulence genes between Aeromonas as co-pathogen and those isolated alone, 218 strains of the global set were used; 52 as co-pathogens compared with 166 Aeromonas without associated pathogen as controls.

CONCLUSIONS

We found no significant differences in the distribution of virulence genes versus co-existence of co-pathogens or not. A. hydrophila is the potentially most virulent species of our set.

An estimation of global Aeromonas infection prevalence in children with diarrhoea: a systematic review and meta-analysis

OBJECTIVES

Diarrhoea is the most commonly related disease caused by Aeromonas. To improve knowledge on prevalence, this systematic review and meta-analysis was performed to evaluate the global prevalence of Aeromonas in children with diarrhoea worldwide.

METHODS

We systematically searched PubMed, Google scholar, Wiley Online Library, ScienceDirect, and Web of sciences to identify all cross-sectional published papers between 2000 and 10 July 2022. After initial scrutinizing, 31 papers reporting the prevalence of Aeromonas in children with diarrhoea were found to be adequate for meta-analysis. The statistical study was accompanied by using random effects models.

RESULTS

A total of 5660 identified papers, 31 cross-sectional studies encompassing 38,663 participants were included in the meta-analysis. The pooled prevalence of Aeromonas in children with diarrhoea worldwide was 4.2% (95% CI 3.1-5.6%). In the subgroup analysis, the highest prevalence was seen among children in Upper middle-income countries with pooled prevalence of 5.1% (95% CI 2.8-9.2%). The prevalence of Aeromonas in children with diarrhoea was higher in countries with populations of over 100 million people (9.4%; 95% CI 5.6-15.3%), and water and sanitation quality score of less than 25% (8.8%; 95% CI 5.2-14.4%). Additionally, Cumulative Forest Plot showed a decreasing trend in the prevalence of Aeromonas infection in children with diarrhoea over time (P = 0.0001).

CONCLUSION

The results of this study showed a better comprehension of Aeromonas prevalence in children with diarrhoea on a global scale. As well as our findings showed that much work is still required to decline the burden of bacterial diarrhoea in countries with high populations, low-level income, and unsanitary water.

Multidrug-resistant Aeromonas bacteria prevalence in Nile tilapia broodstock

BACKGROUND

Aeromonas hydrophila is an opportunistic pathogen. Thus, it has received significant attention mainly in the fish sectors with high production scales. Nile tilapia broodstock confined in the environment of fish hatcheries can be stressed. Hence, they are vulnerable to A. hydrophila.

RESULTS

Sequencing of the gyr B gene revealed the presence of 18 different A. hydrophila strains (kdy 10,620-10,637), which were deposited in the NCBI under accession numbers ON745861-ON745878. The median lethal doses of the isolates ranged from 2.62 × 10⁴ to 3.02 × 10⁶ CFU/mL. Antibiotic resistant genes, sulfonamide (sul1) and tetracycline (tetA) were found in the eighteen isolates. Approximately 83.3% of A. hydrophila strains were sensitive to ciprofloxacin and florfenicol. Further, eight A. hydrophila strains had high MDR indices at 0.27-0.45. All isolates presented with hemolysin activity. However, only 72.22% of them had proteolytic activity, and only 61.11% could form biofilms. Bacterial isolates harbored different pattern virulence genes, the heat-stable cytotonic enterotoxin (ast), cytotoxic enterotoxin (act), and hemolysin (hly) genes were the most prevalent. Also, a trial to inhibit bacterial growth was conducted using titanium dioxide nanoparticles (TiO₂ NPs) with three sizes (13, 32, and 123 nm). If A. hydrophila strains with a high MDR index were tested against TiO₂ NPs (20 µg/mL) for 1, 12, and 24 h, those with a small size had a greater bactericidal action than large ones. Bacterial strains were inhibited at different percentages in response to TiO₂ NP treatment.

CONCLUSIONS

Nile tilapia broodstock, mortality is associated with different A. hydrophila strains, which harbored virulent and MDR genes. Furthermore, TiO₂ NPs had bactericidal activity, thereby resulting in a considerable reduction in bacterial load.

Prevalence of Aeromonas spp. Infection in Pediatric Patients Hospitalized with Gastroenteritis in Latvia between 2020 and 2021

Purpose: Aeromonas species are emerging human enteric pathogens. However, there is no systematic analysis of Aeromonas infection in the pediatric population in Latvia. The aim of the study was to describe potential sources, prevalence of infection, associated virulence factors and antimicrobial resistance of Aeromonas spp. isolated from fecal samples. Methods: Stool samples (n = 1360) were obtained from the Children’s Clinical University Hospital between 2020 and 2021. The target population was pediatric patients, 0 to 18 years of age, with a preliminary diagnosis of gastroenteritis. Identification was performed by Maldi-TOF, antimicrobial resistance by Vitek2 and 9 virulence factors by polymerase chain reaction (PCR). Results: Aeromonas spp. were isolated in 50 stool samples; positive findings made up 3.6% of all study cases and included four species: A. hydrophila, A. caviae, A. veronii, and A. eucrenophila. In 42% of the samples, Aeromonas spp. appeared alongside the other significant pathogens: Campylobacter jejuni, Salmonella Enteritidis, Salmonella Typhimurium, Yersinia enterocolitica, norovirus, adenovirus, and rotavirus. The study population positive for Aeromonas spp. infection contained 28 male (56%) and 22 female (44%) patients; median age was 4.56 years. The most common symptoms were: diarrhea, blood in stool, vomiting, abdominal pain, and fever. Aside from expected natural resistance, no significant antibacterial resistance was detected. The presence of multiple virulence genes was noticed in all isolates. No statistically significant correlation was found between the virulence patterns, bacterial species, and the intensity of clinical symptoms. Discussion: According to the clinical data and the results of this study Aeromonas spp. has an important role in pediatric practice and requires appropriate attention and monitoring.

Aeromonas and Human Health Disorders: Clinical Approaches

The genus Aeromonas comprises more than 30 Gram-negative bacterial species and naturally inhabitants from aquatic environments. These microorganisms, commonly regarded as pathogens of fish and several other animals, have been gaining prominence on medical trial due to its ability to colonize and infect human beings. Besides water, Aeromonas are widely spreaded on most varied sources like soil, vegetables, and food; Although its opportunistic nature, they are able to cause infections on immunocompromised or immunocompetent patients. Aeromonas species regarded as potential human pathogens are usually A. hydrophila, A. caviae, and A. veronii biovar sobria. The main clinical manifestations are gastrointestinal tract disorders, wound, and soft tissue infections, as well as septicemia. Regarding to antibiotic responses, the bacteria present a diversified susceptibility profile and show inherence resistance to ampicillin. Aeromonas, as an ascending genus in microbiology, has been carefully studied aiming comprehension and development of methods for detection and medical intervention of infectious processes, not fully elucidated in medicine. This review focuses on current clinical knowledge related to human health disorders caused by Aeromonas to contribute on development of efficient approaches able to recognize and impair the pathological processes.

Isolation, Identification and Characteristics of Aeromonas caviae from Diseased Largemouth Bass (Micropterus salmoides)

The largemouth bass (Micropterus salmoides) is one of the most economically valuable fish species in China. In this study, a bacterial pathogen was isolated from the internal organs of diseased M. salmoides, and the strain was named WH21406. This isolate was identified as Aeromonas caviae on the basis of its morphology, biochemical features and 16S rDNA phylogenetic analysis. Four virulence genes related to pathogenicity, namely, flagella (fla), elastase (ela), haemolysin (hly) and aerolysin (aer), were detected in this isolate. The median lethal dosage (LD50) of A. caviae WH21406 for M. salmoides was calculated to be 3.46 × 105 CFU mL−1. The histopathological analysis showed obvious tissue damage in the gill, liver, kidney, spleen and gut of the diseased fish. The antibiotic susceptibility test demonstrated that strain WH21406 was highly sensitive to enrofloxacin, norfloxacin, streptomycin and amikacin. The results of this study provide a foundation for the diagnosis, prevention and treatment of A. caviae infection in M. salmoides.

Bacteriophages in the Control of Aeromonas sp. in Aquaculture Systems: An Integrative View

Aeromonas species often cause disease in farmed fish and are responsible for causing significant economic losses worldwide. Although vaccination is the ideal method to prevent infectious diseases, there are still very few vaccines commercially available in the aquaculture field. Currently, aquaculture production relies heavily on antibiotics, contributing to the global issue of the emergence of antimicrobial-resistant bacteria and resistance genes. Therefore, it is essential to develop effective alternatives to antibiotics to reduce their use in aquaculture systems. Bacteriophage (or phage) therapy is a promising approach to control pathogenic bacteria in farmed fish that requires a heavy understanding of certain factors such as the selection of phages, the multiplicity of infection that produces the best bacterial inactivation, bacterial resistance, safety, the host’s immune response, administration route, phage stability and influence. This review focuses on the need to advance phage therapy research in aquaculture, its efficiency as an antimicrobial strategy and the critical aspects to successfully apply this therapy to control Aeromonas infection in fish.

Comparative genomics analysis of strains from diverse sources reveals the evolutionary relationship of Aeromonas veronii

Aeromonas veronii (A. veronii, AV) strains are emerging zoonotic and aquatic pathogens, yet we know very little about their genomics. This study aims to utilize comparative genomics to investigate the intraspecific genetic diversity, differences in virulence factors and evolutionary mechanisms of A. veronii strains from diverse sources and to fundamentally demonstrate their pathogenic mechanisms. We conducted comparative genomics analysis of 39 A. veronii strains from different sources and found that 1993 core genes are shared by these strains and that these shared core genes may be necessary to maintain the basic characteristics of A. veronii. Additionally, phylogenetic relationship analysis based on these shared genes revealed that a distant relationship between the AMC34 strain and the other 38 strains but that, the genetic relationship among the 38 strains is relatively close, indicating that AMC34 may not belong to A. veronii. Furthermore, analysis of shared core genes and average nucleotide identity (ANI) values showed no obvious correlation with the location of A. veronii isolation and genetic relationship. Our research indicates the evolutionary mechanism of A. veronii from different sources and provides new insights for a deeper understanding of its pathogenic mechanism.

Functional analysis of fis in Aeromonas veronii TH0426 reveals a key role in the regulation of virulence

Aeromonas veronii is a comorbid pathogen that can infect humans, and animals including various aquatic organisms. In recent years, an increasing number of cases of A. veronii infection has been reported, indicating serious risks. This bacterium not only threatens public health and safety but also causes considerable economic loss in the aquaculture industry. Currently, some understanding of the pathogenic mechanism of A. veronii has been obtained. In this study, we first constructed the A. veronii TH0426 fis gene deletion strain Δfis and the complementation strain C-fis through homologous recombination technology. The results showed that the adhesion and invasion ability of the Δfis strain towards Epithelioma papulosum cyprini (EPC) cells and the cytotoxicity were 3.8-fold and 1.38-fold lower, respectively, than those of the wild-type strain. In the zebrafish infection model, the lethality of the deleted strain is 3-fold that of the wild strain. In addition, the bacterial load of the deletion strain Δfis in crucian carp was significantly lower than the wild-type strain, and the load decreased with time. In summary, deletion of the fis gene led to a decrease in the virulence of A. veronii. Our research results showed that the deletion of the fis gene significantly reduces the virulence and adhesion ability of A. veronii TH0426. Therefore, the fis gene plays a vital role in the pathogenesis of A. veronii TH0426. This preliminary study of the function of the fis gene in A. veronii will help researchers further understand the pathogenic mechanism of A. veronii.

Comparison of the Multiple Platforms to Identify Various Aeromonas Species

We compared several identification methods for Aeromonas genus members, including traditional biochemical testing, multiplex-PCR amplification, mass spectrometry identification, whole-genome sequencing, multilocus phylogenetic analysis (MLPA), and rpoD, gyrA, and rpoD-gyrA gene sequencing. Isolates (n = 62) belonging to the Aeromonas genus, which were came from the bacterial bank in the laboratory, were used to assess the identification accuracy of the different methods. Whole-genome sequencing showed that the Aeromonas spp. isolates comprised A. caviae (n = 21), A. veronii (n = 18), A. dhakensis (n = 8), A. hydrophila (n = 7), A. jandaei (n = 5), A. enteropelogenes (n = 2), and A. media (n = 1). Using the whole-genome sequencing results as the standard, the consistency of the other methods was compared with them. The results were 46.77% (29/62) for biochemical identification, 83.87% (52/62) for mass spectrometric identification, 67.74% (42/62) for multiplex-PCR, 100% (62/62) for MLPA typing, 72.58% for gyrA, and 59.68% for rpoD and gyrA-rpoD. MLPA was the most consistent, followed by mass spectrometry. Therefore, in the public health laboratory, both MLPA and whole-genome sequencing methods can be used to identify various Aeromonas species. However, rapid and relatively accurate mass spectrometry is recommended for clinical lab.

Isolation and molecular identification of Aeromonas species from the tank water of ornamental fishes

Aeromonads are recognised as important pathogens of fishes. In this study, ten water samples were randomly collected from pet shops' fish tanks and home aquaria inhabited by several fish species (silver arowana, koi, goldfish, catfish, pictus fish, silver shark and silver dollar fish). Altogether 298 colonies were isolated using Aeromonas selective agar. A total of 154 isolates were then confirmed as belonging to the genus Aeromonas using the GCAT gene. Using ERIC-PCR, a total of 40 duplicate isolates were excluded from the study and 114 isolates were subjected to PCR-RFLP targeting the RNA polymerase sigma factor (rpoD) gene using lab-on-chip. A total of 13 different Aeromonas species were identified. The most prevalent species were A. veronii (27%, 31/114), followed by A. dhakensis (17%, 19/114), A. finlandiensis (9%, 10/114), A. caviae (8%, 9/114), A. hydrophila (4%, 4/114), A. jandaei (4%, 4/114), A. rivuli (3%, 3/114), A. enteropelogens (2%, 2/114), A. tecta (2%, 2/114), A. allosaccharophila (1%, 1/114), A. eucrenophila (1%, 1/114), A. media (1%, 1/114) and A. diversa (1%, 1/114). Twenty-six isolates (23%) were unidentifiable at species level. The present study demonstrates that Aeromonas species are highly diverse in freshwater fish tanks, and suggests the potential risks posed by the isolated bacteria to the health of ornamental fish species.

The LysR-Type Transcriptional Regulator YeeY Plays Important Roles in the Regulatory of Furazolidone Resistance in Aeromonas hydrophila

Aeromonas hydrophila is an aquatic pathogen of freshwater fish. The emergence of widespread antimicrobial-resistance strains of this pathogen has caused increasing rates of fish infections. Our previous research reported that A. hydrophila yeeY, a LysR-type transcriptional regulator (LTTR), negatively regulated furazolidone (FZ) resistance. Although, it’s intrinsic regulatory mechanism is still unclear. In this study, a data-independent acquisition (DIA) quantitative proteomics method was used to compare the differentially expressed proteins (DEPs) between the ΔyeeY and wild-type strain under FZ treatment. When compared to the control, a total of 594 DEPs were identified in ΔyeeY. Among which, 293 and 301 proteins were substantially increased and decreased in abundance, respectively. Bioinformatics analysis showed that several biological pathways such as the secretion system and protein transport were mainly involved in FZ resistance. Subsequently, the antibiotics susceptibility assays of several gene deletion strains identified from the proteomics results showed that YeeY may regulate some important genes such as cysD, AHA_2766, AHA_3195, and AHA_4275, which affects the FZ resistance in A. hydrophila. Furthermore, 34 antimicrobial resistance genes (ARGs) from the bacterial drug resistance gene database (CARD) were found to be directly or indirectly regulated by YeeY. A subsequent assay of several ARGs mutants showed that ΔAHA_3222 increased the susceptibility of A. hydrophila to FZ, while ΔcysN and ΔAHA_3753 decreased the susceptibility rate. Finally, the chromatin immunoprecipitation (ChIP) PCR and an electrophoretic mobility shift assay (EMSA) have revealed that the genes such as AHA_3222 and AHA_4275 were directly and transcriptionally regulated by YeeY. Taken together, our findings demonstrated that YeeY may participate in antimicrobial resistance of A. hydrophila to FZ, which provides a new target for the development of novel antimicrobial agents in the future.

Molecular characterization and evaluation of virulence traits of Aeromonas spp. isolated from the tambaqui fish (Colossoma macropomum)

The present study was developed to characterize, at the species level, 34 strains of Aeromonas spp., previously isolated from stressed tambaqui fish (Colossoma macropomum), to elucidate virulence factors, as well as their antibiotic resistance profile. Amplification of the gyrB gene identified the strains as A. hydrophila, A. dhakensis, A. caviae, A. veronii and A. jandaei. Bacterial virulence was evaluated by enzymatic assays for phenotypical production of hemolysins, proteases and lipases followed by the search for genes codifying the enzymes β-hemolysin, serine protease and lipase. Phenotypical production of virulence factors was diversified and proteolytic activity demonstrated to be a common expression among the strains. On the other hand, the lip gene encoding extracellular lipase was the most expressed. Furthermore, A. hydrophila was the most prevalent species isolated from tambaqui in our work.

[Epidemiological data description of pediatric patients with diarrhea by Aeromonas spp. and the antibiotic susceptibility of this agent]

The aim of our study was to describe the epidemiological features of pediatric patients with diarrhea caused by Aeromonas spp. and to study the antibiotic susceptibility of this agent during a seven-year period. Aeromonas caviae was identified in 93 stool samples from 52.2% males and 85.6% patients younger than 36 months. The season with the lowest number of isolates was winter (14.4%). Co-infection with other diarrheagenic microorganisms was observed in 31.1% of the cases. The largest number of isolates was obtained from Emergency Department samples (45.6%); 43.3% of the patients presented with fever, 87.8% with diarrhea (43% of these cases were associated with pathological products) and 67.8% with vomiting, while 73.3% of the patients did not require hospital admission. Susceptibility higher than 87% was observed to trimethoprim-sulfamethoxazole, ciprofloxacin, cefotaxime and cefepime. All the patients overcame the infectious process and 63.3% of them did not receive any antibiotic treatment during the process. A. caviae was the isolated species associated with intestinal infection. Antibiotic treatment would be specifically indicated in cases selected for their clinical severity.

Distinct Antimicrobial Resistance Profiling Of Clinically Important Aeromonas Spp. In Southwest China: A Seven-Year Surveillance Study

Background

Co-evolution of host and aeromonads has diversified their spectrums of diseases and antibiograms, while a paucity of data was concerning about this diversity in China. To fill this gap, this study was aimed to investigate and compare antimicrobial resistance (AMR) patterns of clinically important Aeromonas spp. from various clinical sources.

Methods

A multicenter retrospective surveillance study was conducted in Chongqing from 2011 to 2017. Data of strains were retrieved from the database of China Antimicrobial Resistance Surveillance System (CARSS). Whonet 5.6 and Graphpad Prism 6 Software were adopted to determine and compare distribution and AMR patterns.

Results

Among 1135 Aeromonas strains, Aeromonas hydrophila complex (65.6%, 745/1135) was the most predominant species, followed by Aeromonas veronii complex (16.7%, 190/1135) and Aeromonas caviae complex (15.3%, 174/1135). Sputum was the most frequent source of strains (27.7%), followed by wound (20.8%), bloodstream (10.8%) and urine (8.8%). Urinary strains demonstrated the highest resistance rates to ceftriaxone (65.6%), ceftazidime (52.1%), cefepime (38.3%), ciprofloxacin (47.7%) and trimethoprim-sulfamethoxazole (56.6%). Similar AMR pattern was observed in intestinal strains, with corresponding resistance rates of 29.4%, 28.9%, 22.2%, 27.3% and 45%, respectively. However, respiratory, bloodstream and skin strains exhibited resistance rates of less than 20% to most of the antimicrobials tested. In terms of species, approximately 30% of Aeromonas hydrophila complex and Aeromonas caviae complex strains were resistant to ceftriaxone and trimethoprim-sulfamethoxazole, while Aeromonas veronii complex strains harbored resistance rates of less than 20% to all tested antimicrobials. Although antibiograms of these species were distinct, they remained constant from 2011 to 2017.

Conclusions

Distinct AMR patterns between species and sources highlighted the predominance of Aeromonas hydrophila complex and high resistance of strains in urine and intestine to extended-spectrum cephalosporins, ciprofloxacin and trimethoprim-sulfamethoxazole in Southwest China. Temporally constant AMR patterns should not relax the vigilance of antimicrobial resistance in clinically important Aeromonas species.

Diversity in gene arrangement in a DNA region lacking aerA in clinical and environmental Aeromonas hydrophila isolates

Aquatic pathogen Aeromonas hydrophila produces an array of virulence factors, many of which are excreted proteins that causes infectious disease in fish, reptiles, and humans. Aerolysin, a haemolytic toxin, is the most well-known of the A. hydrophila virulence factors and is encoded by aerA. Although used as a virulence gene marker in several studies, recent whole-genome sequencing data suggest there may be some variation in aerolysin genes, as well as in the genetic environment of these genes, among A. hydrophila strains. Here, we used PCR-based assays to examine gene arrangement in the traditional aerA region of 42 aerA-minus clinical and environmental A. hydrophila isolates. PCR primers were designed based on known genes from within the target regions of reference strains carrying non-aerA aerolysin genes. Analyses revealed four different gene arrangement patterns among the isolates, indicating considerable genetic diversity in the target region. While 19 of the 21 environmental isolates showed the same gene pattern, all four patterns were represented among the clinical isolates, implying that the gene pattern is highly conserved in the target region among environmental isolates. Further analysis of the gene regions showed that the predominant pattern among environmental isolates, which did not contain an aerolysin gene, appeared to be the progenitor of the other three patterns, which likely arose as a result of gene acquisition, deletion, and rearrangement events during the evolution of A. hydrophila, and may be linked to the acquisition of aerolysin genes. These findings shed light on the evolution of virulence in A. hydrophila.

Virulence determinants in genetically heterogeneous populations of Aeromonads recovered from an urban lagoon

The diversity and distribution of Aeromonas spp. associated with virulence profiles from the Rodrigo de Freitas Lagoon were investigated using phylogenetic analysis of gyrB/rpoB gene sequences for speciation. The concatenated gyrB/rpoB gene sequences clustered into five species: Aeromonas punctata/caviae (n = 37), A. hydrophila (n = 10), A. dhakensis (n = 16), A. jandaei (n = 1) and A. enteropelogenes/trota (n = 3). The virulence genes (atc/aerA/hlyA/asp/amp) resulted in 19 virulence profiles, distributed heterogeneously among the five Aeromonas species. Out of the 67 isolates, 16% presented five distinct profiles carrying four virulence genes and 7% showed all genes investigated. The hemolytic genes were detected as follows: act 54% (37/67), aerA 36% (24/67), hlyA 26% (18/67) and proteolytic genes such as asp 36% (24/57) and amp in 85% (57/67) were widely distributed in lagoon sampling stations. Meanwhile, 88% (59/67) and 92% (62/67) of the isolates showed hemolytic and proteolytic activity, respectively. Our results demonstrated that concatenated sequences of the gyrB and rpoB genes showed to be an adequate approach for the Aeromonas speciation and prevalence. The high heterogeneity of virulence genes among the species resulted in several virulence profiles, as well as high percentages of hemolytic and proteolytic activity, demonstrating the necessity of further epidemiological surveys of Aeromonas species pathogenicity in an aquatic recreational lagoon.

Phagolysosomal activity of macrophages in Nile tilapia (Oreochromis niloticus) infected in vitro by Aeromonas hydrophila: Infection and immunotherapy

The biochemical mechanisms involved in phagocytosis and the intracellular survival of Aeromonas hydrophila (Ah) in host macrophages (MΦs) are complex processes that affect infection success or failure. Thus, in the present study, we described the in vitro infection of Nile tilapia MΦs by a homologous bacterium and tested the effects of anti-A. hydrophila immunoglobulin Y (IgY) on the phagolysosomal activity and intracellular survival of the pathogen. The anti-Ah IgY modulated lysosomal acid phosphatase (LAP) activity as well as the production of reactive oxygen intermediates (ROIs) and nitric oxide (NO), thereby potentiating phagocytosis and the elimination of Ah. Thus, we assume that the specific IgY had a beneficial effect on infection control and postulated the use of the Nile tilapia MΦs as an important in vitro experimental model for the functional and therapeutic study of Ah infection.

The genus Aeromonas: A general approach

The genus Aeromonas comprises more than thirty Gram-negative bacterial species which mostly act as opportunistic microorganisms. These bacteria are distributed naturally in diverse aquatic ecosystems, where they are easily isolated from animals such as fish and crustaceans. A capacity for adaptation also makes Aeromonas able to colonize terrestrial environments and their inhabitants, so these microorganisms can be identified from different sources, such as soils, plants, fruits, vegetables, birds, reptiles, amphibians, among others. Infectious processes usually develop in immunocompromised humans; in fish and other marine animals this process occurs under conditions of stress. Such events are most often associated with incorrect practices in aquaculture. Aeromonas has element diverse ranges, denominated virulence factors, which promote adhesion, colonization and invasion into host cells. These virulence factors, such as membrane components, enzymes and toxins, for example, are differentially expressed among species, making some strains more virulent than others. Due to their diversity, no single virulence factor was considered determinant in the infectious process generated by these microorganisms. Unlike other genera, Aeromonas species are erroneously differentiated by conventional biochemical tests. Therefore, molecular assays are necessary for this purpose. Nevertheless, new means of identification have been considered in order to generate methods that, like molecular tests, can correctly identify these microorganisms. The main objectives of this review are to explain environmental and structural characteristics of the Aeromonas genus and to discuss virulence mechanisms that these bacteria use to infect aquatic organisms and humans, which are important aspects for aquaculture and public health, respectively. In addition, this review aims to clarify new tests for the precise identification of the species of Aeromonas, contributing to the exact and specific diagnosis of infections by these microorganisms and consequently the treatment.

Taxonomy, virulence genes and antimicrobial resistance of Aeromonas isolated from extra-intestinal and intestinal infections

BACKGROUND

Clinical characteristics (taxonomy, virulence genes and antimicrobial resistance ) of Aeromonas in isolated from extra-intestinal and intestinal infections were investigated to describe epidemiology, associated virulence factors and optimal therapy options.

METHODS

Clinical samples (n = 115) of Aeromonas were collected from a general hospital in Beijing between the period 2015 and 2017. Taxonomy was investigate by Multilocus phylogenetic analysis (MLPA), 10 putative virulence factors by use of polymerase chain reaction (PCR) and antimicrobial resistance to 15 antibiotics by use of the microbroth dilution method.

RESULTS

The most common species of Aeromonas detected in samples of intestinal tract included; A. caviae (43.9%), A. veronii (35.7%), and A. dhakensis (12.2%). Prevalent species of Aeromonas collected from extra-intestinal infections included; A. hydrophila (29.4%), A. caviae (29.4%), and A. dhakensis (23.5%). A. hydrophila were detected in 1% of stool samples and 29.4% (5/17) of extra-intestinal infections. A. hydrophila strains in extra-intestinal infections were related to malignancy. The most common medical conditions among patients with Aeromonas infections included malignancy and liver-transplant related cholecystitis. Multiple drug resistance (MDR) was prevalent in extra-intestinal isolates (82.3%, 14/17) and was greater than the prevalence in intestinal isolates (30.6%, 30/98) (P < 0.05). Resistant rates of extra-intestinal isolates were 70.6, 35.3, 23.5 and 5.9% for ceftriaxone, ciprofloxacin, gentamicin and imipenem, respectively, and were higher than found in previous studies. Despite differences in the number and type of virulence genes among samples of Aeromonas, no significant correlation was found between invasion and virulent genes in intestinal or extra-intestinal infections.

CONCLUSIONS

Overall results of this study support a role for Aeromonas spp. as a potential causative infectious agent of gastroenteritis, and malignancy, liver cirrhosis, post liver transplantation in immunocompromised patients. A. hydrophila was more prevalent in samples of extra-intestinal infections when compared to samples of intestinal infections, and was especially prominent in samples of patients presenting with malignancy. Aeromonas isolates from extra-intestinal samples had high rates of drug resistance but 3rd generation cephalosporins, fluoroquinolones and aminoglycosides remain as options to treat severe diarrhea. However, increasing MDR of extra-intestinal infection samples warrants monitoring.

Diagnostic methods for identifying different Aeromonas species and examining their pathogenicity factors, their correlation to cytotoxicity and adherence to fish mucus

Aeromonas spp. are ubiquitous in the aquatic environment, acting as facultative or obligate pathogens for fish. Identifying Aeromonas spp. is important for pathogenesis and prognosis in diagnostic cases but can be difficult because of their close relationship. Forty-four already characterized isolates of Aeromonas spp. were analysed by 16S rRNA gene sequencing, by gyrase B sequencing, by analysing their fatty acid profiles, by biochemical reactions and by MALDI-TOF MS. To determine their pathogenicity, cytotoxicity, adhesion to mucus and the expression of 12 virulence factors were tested. The susceptibility of the isolates towards 13 different antibiotics was determined. MALDI-TOF MS was found to be an acceptable identification method for Aeromonas spp. Although the method does not detect all species correctly, it is time-effective and entails relatively low costs and no other methods achieved better results. A high prevalence of virulence-related gene fragments was detected in almost all examined Aeromonas spp., especially in A. hydrophila and A. salmonicida, and most isolates exhibited a cytotoxic effect. Single isolates of A. hydrophila and A. salmonicida showed multiple resistance to antibiotics. These results might indicate the potentially pathogenic capacity of Aeromonas spp., suggesting a risk for aquatic animals and even humans, given their ubiquitous nature.

Isolation and identification of pathogenic Aeromonas veronii from a dead Yangtze finless porpoise

Diseases caused by Aeromonas veronii in freshwater fish have been widely reported, but other species such as aquatic mammals have probably been overlooked. Here, we identified one isolate of A. veronii from a Yangtze finless porpoise Neophocaena asiaeorientalis asiaeorientalis exhibiting disease and mortality, and subsequently confirmed its virulence in artificial infection of BALB/c mice. The bacterial isolate was identified as A. veronii based on physiological, biochemical, and phenotypic features, and homology of the 16S rRNA, cpn60, rpoB, dnaJ and gyrB genes. Our results expand the known host spectrum of A. veronii, which is of great importance for the etiology of porpoise, dolphin, and other cetacean diseases.

A fatal diarrhoea outbreak in farm-raised Deinagkistrodon acutus in China is newly linked to potentially zoonotic Aeromonas hydrophila

Deinagkistrodon acutus is a venomous pit viper commonly used in traditional Chinese medicine; farming these snakes has become a major industry. In 2017, an outbreak of fatal diarrhoea among farm-raised D. acutus in Hunan Province caused the deaths of 5,600 snakes within 3 weeks. We isolated a brand-new sequence type of Aeromonas hydrophila (ST516) from lesions and confirmed that this bacterium was the causal agent of the outbreak. Snakes infected with the bacterium in the laboratory showed similar clinical symptoms to those of snakes in the original outbreak. We also tested bacterial virulence in Kunming mice to examine the likelihood of zoonosis. Isolates were pathogenic to mice, causing diarrhoea within 4 hr post-challenge, which indicates that the bacterium can potentially infect mammals. Environmental analysis showed that polluted spring water likely caused the diarrhoea in snakes. This study is the first to report on a large-scale outbreak of fatal diarrhoea in farm-raised snakes, originating in a pathogen that can infect mammals. These results should raise awareness regarding potential anthropozoonosis among poikilotherms, mammals, and humans; appropriate prevention or control methods should be developed.

Enhancing the stability of a carboxylesterase by entrapment in chitosan coated alginate beads

A carboxylesterase isolated from Aeromonas caviae MTCC 7725 was immobilized by entrapping it in chitosan coated calcium alginate beads. This was characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR). The activity of the native and immobilized enzyme was measured at various temperatures, pH levels, and organic solvents. The optimum temperature for activity of the native enzyme was found to be 40 °C and this increased to 50 °C on immobilization. The immobilized enzyme showed enhanced stability and high residual activity in various organic solvents as compared to the free enzyme. An environmentally benign approach was used for the synthesis of ethyl salicylate using the immobilized enzyme. The product obtained was confirmed by GC-MS. The kinetic parameters, such as K m and Vmax, were also determined for the native and immobilized enzyme. The immobilized enzyme retained 50% of its activity after vfie cycles. The immobilized enzyme retained 80% and 40% of its activity at 4 °C and at 37 °C, respectively, at the end of 40 days. The results obtained from our study show that the immobilized enzyme can serve as a robust catalyst for industrial applications.

Occurrence and Variety of β-Lactamase Genes among Aeromonas spp. Isolated from Urban Wastewater Treatment Plant

Members of the genus Aeromonas that commonly occur in various aquatic ecosystems are taken into account as vectors spreading antibiotic resistance genes (ARGs) in the environment. In our study strains of Aeromonas spp. (n = 104) not susceptible to ampicillin were isolated from municipal sewage of different levels of purification - raw sewage, activated sludge and treated wastewater. The crucial step of the study was the identification of β-lactamase resistance genes. The identified genes encode β-lactamases from 14 families - bla_TEM, bla_OXA, bla_SHV, bla_CTX-M, bla_MOX, bla_ACC, bla_FOX, bla_GES, bla_PER, bla_{V EB}, bla_KPC, cphA, imiH, and cepH. There were no significant differences in number of identified ARGs between isolation points. Bla_OXA, bla_FOX variants and, characteristic for Aeromonas genus, metallo-β-lactamase cphA-related genes were the most commonly identified types of β-lactam resistance determinants. Moreover, we found four extended-spectrum β-lactamases (bla_{SHV -11}, bla_CTX-M-27, bla_CTX-M-98, and bla_PER-4) - and seven AmpC (bla_ACC, bla_FOX-2-like, bla_FOX-3, bla_FOX-4-like, bla_FOX-9, bla_FOX-10-like, and bla_FOX-13-like) types and variants of genes that had never been found among Aeromonas spp. before. Five of the β-lactamases families (bla_TEM, bla_OXA, bla_FOX, bla_{V EB}, and cphA) were identified in all three isolation sites, which supports the hypothesis that wastewater treatment plants (WWTPs) are hot spots of ARGs dissemination. The obtained ARGs sequences share high identity with previously described β-lactamases, but new variants of those genes have to be considered as well. Characterization of antibiotic susceptibility was performed using disk the diffusion method with 12 different antibiotics according to CLSI guidelines. Over 60% of the strains are unsusceptible to cefepime and chloramphenicol and the majority of the strains have a multidrug resistance phenotype (68%). Finally, analysis of plasmid profiles among the resistant strains showed that 62% of the isolates from all three points of the WWTP carry plasmids of different sizes. Among some of the isolated plasmids bla_FOX-4-like and bla_GES genes have been found. To sum up, the results strongly suggest that Aeromonas spp. can be considered as agents of antibiotic resistance dissemination from wastewater to the natural environment.

An Outbreak of Aeromonas hydrophila Food Poisoning in Deptsang Village, Samdrup Jongkhar, Bhutan, 2016

BACKGROUND

An outbreak investigation was carried out to determine the cause and confirm the source of food poisoning in Deptsang village for implementing prevention and control measures.

METHODS

We conducted a retrospective cohort study for the outbreak investigation. Stool specimens were collected from cases to perform culture and antibiogram. The team also inspected the environment and hygiene practices in both the construction site and the entire community. The association between the exposure to carcass meat and their outcome of acute gastroenteritis was assessed by risk ratio. P<0.05 was considered statistically significant.

RESULTS

Fifty-five villagers consumed the carcass meat during lunch and dinner resulting in 33 cases. Multi-drug resistant Aeromonas hydrophila was isolated from stool specimens of cases, which were susceptible to chloramphenicol only. A risk ratio of 2.1 was found between those people who consumed the carcass meat and those who did not consume the carcass meat (P<0.001).

CONCLUSIONS

The current outbreak of food poisoning was caused by the consumption of carcass meat contaminated with A. hydrophila. Provision of health education with emphasis on food hygiene is needed in remote areas to prevent such outbreaks in the future.