Enteric Aeromonas Infection: a Common Enteric Bacterial Infection with a Novel Infection Pattern Detected in an Australian Population with Gastroenteritis

Human macrophage response to the emerging enteric pathogen Aeromonas veronii: Inflammation, apoptosis, and downregulation of histones

This study investigated the pathogenic mechanisms of Aeromonas veronii in macrophages. THP-1 derived macrophages were used as a human macrophage model and were treated with A. veronii strain AS1 isolated from intestinal biopsies of an IBD patient, or Escherichia coli strain K-12. RNA was extracted and subjected to RNA sequencing and comparative transcriptomic analyses. Protein levels of IL-8, IL-1β, IL-18, and TNFα were measured using ELISA, and apoptosis was assessed using caspase 3/7 assays. Both A. veronii AS1 and E. coli K-12 significantly upregulated the expression of many genes involving inflammation. At the protein level, A. veronii AS1 induced significantly higher levels of IL-8, TNFα, mature IL-18 and IL-1β than E. coli K-12, and led to greater elevation of caspase 3/7 activities. Both A. veronii AS1 and E. coli K-12 upregulated the expression of CASP5, but not other caspase genes. A. veronii AS1 significantly downregulated the expression of 20 genes encoding histone proteins that E. coli K-12 did not. The more profound pathogenic effects of A. veronii in inducing inflammation and apoptosis in macrophages than E. coli K-12 are consistent with its role as a human enteric pathogen. The upregulated expression of CASP5 and increased release of IL-1β and IL-18 support the role of CASP5 in activation of non-canonical inflammasome. The downregulation of histone genes by A. veronii suggests a unique impact on host cell gene expression, which may represent a novel virulence strategy. These findings advance the understanding of pathogenic mechanisms of the emerging human enteric pathogen A. veronii.

Age-Dependent Variations in the Distribution of Aeromonas Species in Human Enteric Infections

Aeromonas species are enteropathogens that cause gastroenteritis with a unique three-peak infection pattern related to patient age. The contributions of individual Aeromonas species to age-related infections remain unknown. Multi-locus sequence typing (MLST) was performed to determine the species of Aeromonas strains from Australian patients with gastroenteritis. Public database searches were conducted to collect strains of enteric Aeromonas species, identified by either MLST or whole genome sequencing with known patient age. Violin plot analysis was performed to assess Aeromonas infection distribution across patients of different ages. Generalized additive model (GAM) analysis was employed to investigate the relationship between Aeromonas species and patient age. A total of 266 strains of seven Aeromonas species met the selection criteria, which were used for analyses. The violin plots revealed distinct patterns among individual Aeromonas species in relation to patient age. The GAM analyses identified a significant association between Aeromonas species and patient age (p = 0.009). Aeromonas veronii (153 strains) showed the highest probability of infection in most ages, particularly among young adults. Aeromonas caviae (59 strains) is more common in young children and adults over 60 years of age. The probability of infection for Aeromonas hydrophila (34 strains) and Aeromonas dhakensis (9 strains) was generally low, there was a slight increase in individuals aged 50-60 for A. hydrophila and over 60 years for A. dhakensis. These findings provide novel evidence of the varied contributions of different Aeromonas species to human enteric infections related to patient age, offering valuable insights for epidemiology and clinical management.

Epidemiology and clinical characteristics of Aeromonas-associated gastroenteritis in Northern Israel: Insights and implications for public health

The role of Aeromonas spp. in gastroenteritis is controversial due to varied clinical presentations and variable prevalence in asymptomatic. This study, conducted in Northern Israel, aimed to compare positivity rate and demographic characteristics of patients with Aeromonas-associated gastroenteritis (AAG) to asymptomatic, and examine the role of Aeromonas in AAG by comparing clinical and epidemiological characteristics between AAG and Campylobacter-associated gastroenteritis (CAG) patients. Results showed that 4.24%-4.81% of AAG patients had Aeromonas spp. in stools as a sole pathogen in 2020-2022, compared to 4.9% of asymptomatic. Analysis of 243 CAG patients versus 70 AAG patients revealed significantly less diarrhea, fever, abdominal pain, and muscle pain in AAG patients. Multivariate analysis identified higher Ct values, recent restaurant dining, and prolonged diarrhea as predictive factors for AAG versus CAG. In conclusion, similar positivity rates of Aeromonas spp. in symptomatic and asymptomatic making the distinction between true pathogen versus commensal bacteria difficult, unlike CAG.

Analysis of global Aeromonas caviae genomes revealed that strains carrying T6SS are more common in human gastroenteritis than in environmental sources and are often phylogenetically related

Aeromonas caviae is an emerging human enteric pathogen. However, the genomic features and virulence genes of A. caviae strains from human gastroenteritis and other sources have not been fully elucidated. Here, we conducted a genomic analysis of 565 global A. caviae strains isolated from different sources, including 261 strains isolated from faecal samples of gastroenteritis patients, of which 18 genomes were sequenced in this study. The presence of bacterial virulence genes and secretion systems in A. caviae strains from different sources was compared, and the phylogenetic relationship of A. caviae strains was assessed based on the core genome. The complete genome of A. caviae strain A20-9 isolated from a gastroenteritis patient was obtained in this study, from which 300 putative virulence factors and a T4SS-encoding plasmid, pAC, were identified. Genes encoding T4SS were also identified in a novel genomic island, ACI-1, from other T4SS-positive strains. The prevalence of T4SS was significantly lower in A. caviae strains from gastroenteritis patients than in environmental strains (3 %, P<0.0001 vs 14 %, P<0.01). Conversely, the prevalence of T6SS was significantly higher in A. caviae strains isolated from gastroenteritis patients than in environmental strains (25 %, P<0.05 vs 13  %, P<0.01). Four phylogenetic clusters were formed based on the core genome of 565 A. caviae strains, and strains carrying T6SS often showed close phylogenetic relationships. T3SS, aerolysin and thermostable cytotonic enterotoxin were absent in all 565 A. caviae strains. Our findings provide novel information on the genomic features of A. caviae and suggest that T6SS may play a role in A. caviae-induced human gastroenteritis.

Genomic analysis of clinical Aeromonas isolates reveals genetic diversity but little evidence of genetic determinants for diarrhoeal disease

Aeromonas spp. are associated with a number of infectious syndromes in humans including gastroenteritis and dysentery. Our understanding of the genetic diversity, population structure, virulence determinants and antimicrobial resistance of the genus has been limited by a lack of sequenced genomes linked to metadata. We performed a comprehensive analysis of the whole genome sequences of 447 Aeromonas isolates from children in Karachi, Pakistan, with moderate-to-severe diarrhoea (MSD) and from matched controls without diarrhoea that were collected as part of the Global Enteric Multicenter Study (GEMS). Human-associated Aeromonas isolates exhibited high species diversity and extensive antimicrobial and virulence gene content. Aeromonas caviae, A. dhankensis, A. veronii and A. enteropelogenes were all significantly associated with MSD in at least one cohort group. The maf2 and lafT genes that encode components of polar and lateral flagella, respectively, exhibited a weak association with isolates originating from cases of gastroenteritis.

The effect of changing diagnostic method from culture to PCR on the number of episodes of human campylobacteriosis in Denmark: a retrospective study (2015-2022)

IMPORTANCE

This study is important because it shows the potential epidemiological silence associated with the use of culture as the primary diagnostic method for the laboratory identification of human campylobacteriosis. Also, we show how polymerase chain reaction methods are associated with a systematic increase in the number of human campylobacteriosis episodes as reported by routine disease surveillance. These findings are operationally relevant and have public health implications because they tell how crucial it is to consider changes in diagnostic methods, e.g., in the epidemiological analysis of historical data and in the interpretation of future data in light of the past. We also believe that this study highlights how the synergy between microbiology and epidemiology is essential for disease surveillance.