Aeromonas aquariorum septicemia and enterocolitis in a cirrhotic patient

Complexation of a Polypeptide-Polyelectrolytes Bioparticle as a Biomaterial of Antibacterial Activity

The development of biomaterials to enable application of antimicrobial peptides represents a strategy of high and current interest. In this study, a bioparticle was produced by the complexation between an antimicrobial polypeptide and the biocompatible and biodegradable polysaccharides chitosan-N-arginine and alginate, giving rise to a colloidal polyelectrolytic complex of pH-responsive properties. The inclusion of the polypeptide in the bioparticle structure largely increases the binding sites of complexation during the bioparticles production, leading to its effective incorporation. After lyophilization, detailed evaluation of colloidal structure of redispersed bioparticles evidenced nano or microparticles with size, polydispersity and zeta potential dependent on pH and ionic strength, and the dependence was not withdrawn with the polypeptide inclusion. Significant increase of pore edge tension in giant vesicles evidenced effective interaction of the polypeptide-bioparticle with lipid model membrane. Antibacterial activity against Aeromonas dhakensis was effective at 0.1% and equal for the isolated polypeptide and the same complexed in bioparticle, which opens perspectives to the composite material as an applicable antibacterial system.

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.

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.

Aeromonas dhakensis, an Increasingly Recognized Human Pathogen

Aeromonas dhakensis was first isolated from children with diarrhea in Dhaka, Bangladesh and described in 2002. In the past decade, increasing evidence indicate this species is widely distributed in the environment and can cause a variety of infections both in human and animals, especially in coastal areas. A. dhakensis is often misidentified as A. hydrophila, A. veronii, or A. caviae by commercial phenotypic tests in the clinical laboratory. Correct identification relies on molecular methods. Increasingly used matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) may be able to identify Aeromonas specie rapidly and accurately. A. dhakensis has shown its potent virulence in different animal models and clinical infections. Although several virulence factors had been reported, no single mechanism is conclusive. Characteristically A. dhakensis is the principal species causing soft tissue infection and bacteremia, especially among patients with liver cirrhosis or malignancy. Of note, A. dhakensis bacteremia is more lethal than bacteremia due to other Aeromonas species. The role of this species in gastroenteritis remains controversial. Third generation cephalosporins and carbapenems should be used cautiously in the treatment of severe A. dhakensis infection due to the presence of AmpC ββ-lactamase and metallo-β-lactamase genes, and optimal regimens may be cefepime or fluoroquinolones. Studies of bacterial virulence factors and associated host responses may provide the chance to understand the heterogeneous virulence between species. The hypothesis A. dhakensis with varied geographic prevalence and enhanced virulence that compared to other Aeromonas species warrants more investigations.

Bacterial infections in cirrhosis: A critical review and practical guidance

Bacterial infection is common and accounts for major morbidity and mortality in cirrhosis. Patients with cirrhosis are immunocompromised and increased susceptibility to develop spontaneous bacterial infections, hospital-acquired infections, and a variety of infections from uncommon pathogens. Once infection develops, the excessive response of pro-inflammatory cytokines on a pre-existing hemodynamic dysfunction in cirrhosis further predispose the development of serious complications such as shock, acute-on-chronic liver failure, renal failure, and death. Spontaneous bacterial peritonitis and bacteremia are common in patients with advanced cirrhosis, and are important prognostic landmarks in the natural history of cirrhosis. Notably, the incidence of infections from resistant bacteria has increased significantly in healthcare-associated settings. Serum biomarkers such as procalcitonin may help to improve the diagnosis of bacterial infection. Preventive measures (e.g., avoidance, antibiotic prophylaxis, and vaccination), early recognition, and proper management are required in order to minimize morbidity and mortality of infections in cirrhosis.

Aeromonas dhakensis pneumonia and sepsis in a neonate Risso's dolphin Grampus griseus from the Mediterranean Sea

A neonate Risso's dolphin Grampus griseus was found stranded alive on a beach in Catalonia, Spain. Rehabilitation attempts were unsuccessful and it died 2 d later, showing pneumonia and sepsis. A pure bacterial culture was obtained from all tissues and blood and identified as Aeromonas hydrophila using the API 20NE. However, sequencing the rpoD gene showed that the strain in fact belongs to A. dhakensis, making this the first report of fatal haemorrhagic-necrotizing pneumonia and sepsis due to this species in a marine mammal. The A. dhakensis strain GMV-704 produced β-haemolysis, possessed several virulence genes and showed sensitivity to several antimicrobials. This study provides a new potential host for A. dhakensis, and its potential virulence in dolphins and its presence in the marine environment may warrant considering this species a potential threat to marine mammals.

Practical Guidance for Clinical Microbiology Laboratories: Diagnosis of Bacterial Gastroenteritis

Bacterial gastroenteritis is a disease that is pervasive in both the developing and developed worlds. While for the most part bacterial gastroenteritis is self-limiting, identification of an etiological agent by bacterial stool culture is required for the management of patients with severe or prolonged diarrhea, symptoms consistent with invasive disease, or a history that may predict a complicated course of disease. Importantly, characterization of bacterial enteropathogens from stool cultures in clinical laboratories is one of the primary means by which public health officials identify and track outbreaks of bacterial gastroenteritis. This article provides guidance for clinical microbiology laboratories that perform stool cultures. The general characteristics, epidemiology, and clinical manifestations of key bacterial enteropathogens are summarized. Information regarding optimal specimen collection, transport, and processing and current diagnostic tests and testing algorithms is provided. This article is an update of Cumitech 12A (P. H. Gilligan, J. M. Janda, M. A. Karmali, and J. M. Miller, Cumitech 12A, Laboratory diagnosis of bacterial diarrhea, 1992).

Clinical implications of species identification in monomicrobial Aeromonas bacteremia

BACKGROUND

Advances in Aeromonas taxonomy have led to the reclassification of aeromonads. Hereon, we aimed to re-evaluate the characteristics of Aeromonas bacteremia, including those of a novel species, Aeromonas dhakensis.

METHODOLOGY/PRINCIPAL FINDINGS

A retrospective study of monomicrobial Aeromonas bacteremia at a medical center in southern Taiwan from 2004-2011 was conducted. Species identification was based on rpoB sequencing. Of bacteremia of 153 eligible patients, A. veronii (50 isolates, 32.7%), A. dhakensis (48, 31.4%), A. caviae (43, 28.1%), and A. hydrophila (10, 6.5%) were the principal causative species. A. dhakensis and A. veronii bacteremia were mainly community-acquired and presented as primary bacteremia, spontaneous bacterial peritonitis, or skin and soft-tissue infection, whereas A. caviae was associated with hospital-onset bacteremia. The distribution of the AmpC β-lactamase and metallo-β-lactamase genes was species-specific: bla(AQU-1), bla(MOX), or bla(CepH) was present in A. dhakensis, A. caviae, or A. hydrophila, respectively, and bla(CphA) was present in A. veronii, A. dhakensis, and A. hydrophila. The cefotaxime resistance rates of the A. caviae, A. dhakensis, and A. hydrophila isolates were higher than that of A. veronii (39.5%%, 25.0%, and 30% vs. 2%, respectively). A. dhakensis bacteremia was linked to the highest 14-day sepsis-related mortality rate, followed by A. hydrophila, A. veronii, and A. caviae bacteremia (25.5%, 22.2%, 14.0%, and 4.7%, respectively; P = 0.048). Multivariate analysis revealed that A. dhakensis bacteremia, active malignancies, and a Pitt bacteremia score ≥ 4 was an independent mortality risk factor.

CONCLUSIONS/SIGNIFICANCE

Characteristics of Aeromonas bacteremia vary between species. A. dhakensis prevalence and its associated poor outcomes suggest it an important human pathogen.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Monomicrobial Aeromonas and Vibrio bacteremia in cirrhotic adults in southern Taiwan: Similarities and differences

BACKGROUND/PURPOSE

Aeromonas and Vibrio are important water-borne pathogens causing substantial morbidity and mortality in cirrhotic patients in Taiwan, but the differences in clinical manifestations of Aeromonas and Vibrio bacteremia have not been reported in detail.

METHODS

From January 2003 to September 2013, cirrhotic patients with monomicrobial Aeromonas or Vibrio bacteremia at a medical center in Taiwan were included in this study.

RESULTS

The study population consisted of 77 cirrhotic patients with Aeromonas bacteremia and 48 patients with Vibrio bacteremia. Both pathogens clustered during the summer season; Vibrio bacteremia was more correlated with higher temperatures (Vibrio: r(2) = 0.95, p < 0.0001; Aeromonas: r(2) = 0.74, p = 0.006) and was associated with ingestion of undercooked seafood (p = 0.03) or cutaneous exposure (p < 0.001). Vibrio bacteremia mainly occurred in mildly or moderately decompensated cirrhosis (Child-Pugh class A and B: 45.8% vs. 20.8%, p = 0.003), and caused more soft-tissue infections (31.3% vs. 5.2%; p < 0.001) and renal dysfunction (1.6 ± 1.2 mg/dL vs. 1.3 ± 0.8 mg/dL, p = 0.006). Sepsis-related mortality was similar in the cases of Vibrio and Aeromonas bacteremia (14.6% vs. 14.3%, p = 0.96), but those with Vibrio bacteremia underwent a fulminant course, as evidenced by a shorter time from bacteremia onset to death (3.1 days vs. 8.2 days, p = 0.04).

CONCLUSION

In cirrhotic patients, bacteremia caused by Aeromonas and Vibrio species clustered in summer months and caused similar mortality, but Vibrio bacteremia led to a more severe and fulminant sepsis.

Peritonitis caused by Aeromonas species at a hospital in southern Taiwan

OBJECTIVE

This study was conducted to investigate the clinical characteristics of patients with Aeromonas peritonitis, particularly secondary peritonitis.

METHODS

Patients with Aeromonas peritonitis treated between July 2004 and December 2011 were identified from the computerized database of a regional hospital in southern Taiwan. The medical records of these patients were retrospectively reviewed.

RESULTS

A total of 50 patients with Aeromonas peritonitis were identified. Nine cases were classified as spontaneous bacterial peritonitis, and 41 cases were classified as secondary peritonitis. The most common etiology of secondary peritonitis was acute appendicitis (n=26), followed by small bowel perforation (n=7) and colon perforation (n=6). The patients with spontaneous bacterial peritonitis were more likely to be immunocompromised (p=0.0013) and more frequently had an initial presentation of shock (p=0.0129), an abnormal liver function (p<0.05) and concomitant bacteremia (p=0.0024) than the patients with secondary peritonitis. Although the patients with secondary peritonitis had higher levels of inflammatory parameters, including leukocytes and C-reactive protein, and more frequent polymicrobial infections, their survival outcome rates, such as in-hospital mortality, were significantly lower (p=0.0007). The overall in-hospital mortality rate was 20%, and initial shock was the only independent prognostic factor for mortality (p=0.012).

CONCLUSION

The clinical characteristics, including outcomes, of patients with spontaneous and secondary Aeromonas peritonitis differ. In-hospital mortality is significantly associated with the initial presentation of shock.