Genome sequence of the emerging pathogen Aeromonas caviae.

Aeromonas caviae is a Gram-negative, motile and rod-shaped facultative anaerobe that is increasingly being recognized as a cause of diarrhea in children. Here we present the first genome sequence of an A. caviae strain that was isolated as the sole pathogen from a child with profuse diarrhea.

High frequency of hemolytic and cytotoxic activity in Aeromonas spp. isolated from clinical, food and environmental in Rio de Janeiro, Brazil.

Molecular study of aerolysin and cytotonic enterotoxin genes by PCR and colony blot hybridization was performed in 117 strains of Aeromonas spp. isolated from different sources. Homogeneous distribution of these genes in A. hydrophila complex strains was observed. For A. caviae and A. sobria complex strains, aerolysin genes were more frequent than cytotonic enterotoxins genes. Of 64 A. caviae complex strains, only one (1.5%) amplified the 451 bp product for the aer gene, however, the same primers detected a 400 bp product in 50 (78%) strains. This product was sequenced and had two short regions with homology to several hemolysin genes. The genotype aer (+)/aerA(+)/hly (+)/ast (+)/alt (+) was detected in six A. hydrophila strains from food and environmental source. The most common genotype found in A. hydrophila strains was hly (+) (85%) and aerA(+) (78.7%), while in A. caviae complex strains was aerA(+) (32.8%). All A. veronii complex sobria strains were aer (+)/aerA(+). All A. caviae and A. hydrophila were positive when tested with aer probe using the colony blot test. Thirty-seven percent of A. hydrophila and 53% of A. caviae tested were positive for ast probe. Eighty-nine percent of samples were cytotoxic in Vero cells. Our data demonstrated that Aeromonas spp. can harbor and express virulence genes and reinforce the potential of Aeromonas as a human pathogen.

Lectin-binding properties of Aeromonas caviae strains / Propriedades lectínicas de amostras de Aeromonas caviae

The cell surface carbohydrates of four strains of Aeromonas caviae were analyzed by agglutination and lectin-binding assays employing twenty highly purified lectins encompassing all sugar specificities. With the exception of L-fucose and sialic acid, the sugar residues were detected in A. caviae strains. A marked difference, however, in the pattern of cell surface carbohydrates in different A. caviae isolates was observed. Specific receptors for Tritricum vulgaris (WGA), Lycopersicon esculentum (LEL) and Solanum tuberosum (STA) (D-GlcNAc-binding lectins) were found only in ATCC 15468 strain, whereas Euonymus europaeus (EEL, D-Gal-binding lectin) sites were present exclusively in AeQ32 strain, those for Helix pomatia (HPA, D-GalNAc-binding lectin) in AeC398 and AeV11 strains, and for Canavalia ensiformes (Con A, D-Man-binding lectin) in ATCC 15468, AeC398, AeQ32 and AeV11 strains, after bacterial growing at 37ºC. On the other hand, specific receptors for WGA and EEL were completely abrogated growing the bacteria at 22ºC. Binding studies with 125I- labeled lectins from WGA, EEL and Con A were performed. These assays essentially confirmed the selectivity, demonstrated in the agglutination assays of these lectins for the A. caviae strains.

Os carboidratos de superfície celular de quatro amostras de Aeromonas caviae foram analisados por aglutinação e ensaios de ligação de lectinas empregando vinte lectinas altamente purificadas com especificidade para açúcares. Com exceção da L-fucose e do ácido siálico, os resíduos de açúcar foram detectados em amostras de A. caviae. Entretanto, foi observada uma diferença marcante no padrão de carboidratos de superfície celular em diferentes amostras de A. caviae. Receptores específicos para Tritricum vulgaris (WGA), Lycopersicon esculentum (LEL) e Solanum tuberosum (STA), lectinas de ligação a D-GlcNAc, foram encontrados apenas na amostra ATCC 15468, enquanto sítios de Euonymus europaes (EEL), lectina de ligação a D-Gal, estavam presentes exclusivamente na amostra AeQ32, sítios de Helix pomatia (HPA), lectina de ligação a D-GalNac, nas amostras AeC398 e AeV11 e de Canavalia ensiformis (Com A), lectina de ligação a D-Man, nas amostras ATCC 15468, AeC398, AeQ32 e AeV11, após crescimento bacteriano a 37ºC. Por outro lado, receptores específicos para WGA e EEL foram completamente abolidos após o crescimento das bactérias a 22ºC. Estudos de ligação com lectinas WGA, EEL e Con A marcadas com 125I também foram realizados. Esses ensaios confirmaram a seletividade, demonstrada em ensaios de aglutinação dessas lectinas para as amostras de A. caviae.

Lectin-binding properties of Aeromonas caviae strains.

The cell surface carbohydrates of four strains of Aeromonas caviae were analyzed by agglutination and lectin-binding assays employing twenty highly purified lectins encompassing all sugar specificities. With the exception of L-fucose and sialic acid, the sugar residues were detected in A. caviae strains. A marked difference, however, in the pattern of cell surface carbohydrates in different A. caviae isolates was observed. Specific receptors for Tritricum vulgaris (WGA), Lycopersicon esculentum (LEL) and Solanum tuberosum (STA) (D-GlcNAc-binding lectins) were found only in ATCC 15468 strain, whereas Euonymus europaeus (EEL, D-Gal-binding lectin) sites were present exclusively in AeQ32 strain, those for Helix pomatia (HPA, D-GalNAc-binding lectin) in AeC398 and AeV11 strains, and for Canavalia ensiformes (Con A, D-Man-binding lectin) in ATCC 15468, AeC398, AeQ32 and AeV11 strains, after bacterial growing at 37°C. On the other hand, specific receptors for WGA and EEL were completely abrogated growing the bacteria at 22°C. Binding studies with (125)I- labeled lectins from WGA, EEL and Con A were performed. These assays essentially confirmed the selectivity, demonstrated in the agglutination assays of these lectins for the A. caviae strains.

Influence of polarisation and differentiation on interaction of 43-kDa outer-membrane protein of Aeromonas caviae with human enterocyte-like Caco-2 cell line.

It has been recognised that adherence and invasion to host cells are important steps in the pathogenesis of entero-pathogenic bacteria, including Aeromonas caviae. However, the virulence factors of A. caviae remain, for the most part, poorly known. This study examined the interaction of A. caviae isolates to Caco-2 cells in different polarisation and differentiation conditions. The adherence of A. caviae may be related to accessibility of host cell basolateral receptors. Aggregative A. caviae isolates, grown at 22 degrees C, were more adherent in both non-polarised and undifferentiated Caco-2 cells and EGTA-treated polarised and differentiated Caco-2 cells. Furthermore, monolayers pre-incubated with 43-kDa outer-membrane protein (OMP) or A. caviae strains pre-incubated with rabbit IgG anti-43-kDa OMP decreased adherence of some A. caviae strains to EGTA-treated polarised and differentiated Caco-2 cells, suggesting an interaction of 43-kDa OMP with basolateral cell receptors. Bacterial cells were observed adhering to microvilli and to plasma membrane on both the apical and basal surfaces of the monolayer. Pedestal-like formation with cytoskeletal rearrangement was also observed. The bacteria entered the Caco-2 cells and were observed enclosed in single and multiple membrane-bound vacuoles within the host cell cytoplasm. Furthermore, A. caviae were observed free in the cytosol of Caco-2 cells, suggesting escape form cytoplasmatic vacuoles.

Aeromonas hydrophila vacuolating activity in the Caco-2 human enterocyte cell line as a putative virulence factor.

A non-enterotoxigenic strain of Aeromonas hydrophila isolated from diarrheic stools of an 8-month-old child was found to cause vacuolation in Caco-2 cells. The vacuoles became prominent 60 min after addition of the bacterial culture to the cell monolayers and, after 120 min, a complete disruption of the monolayers was observed. Cell vacuolation was not detected when Caco-2 monolayers were tested with sterile filtrates of overnight cultures of the A. hydrophila vacuolating strain AH14846. This strain produced a diffuse adherence pattern in Caco-2 cell monolayers, but did not produce detectable cytotonic enterotoxin in the suckling mouse test and only produced small quantities of aerolysin. By demonstrating the ability to induce vacuolation in mammalian cells of enterocytic lineage, the current study raises the possibility that such activity might contribute to gastrointestinal symptoms in infections involving Aeromonas strains which do not express well-established enterotoxins.