Acute gastroenteritis caused by Hafnia alvei in children

Microbiology of Hafnia alvei

Hafnia alvei is a Gram-negative facultatively anaerobic bacillus that constitutes part of the human gut flora. Until recently, H. alvei strains could be mistakenly identified by conventional methods, miniaturisation or automatic systems as members of the Serratia, Escherichia, Citrobacter, Yokenella, Obesumbacterium or Salmonella genera. Consequently, molecular techniques were required for their definitive identification in the clinical laboratory. In addition, a new Hafnia species, H. paralvei, has recently appeared, which undoubtedly includes many of the strains reported in the literature as H. alvei. Alrhough H. alvei isolation from human clinical specimens remains uncommon, the development of drug resistance due to this species is emerging and it is likely that this organism will gain increasing importance in the future. Moreover, although H. alvei shares some virulence mechanisms with other Gram-negative enteropathogens, little is known about the factors that contribute to its pathogenesis in humans. The present article reviews the current identification methods, antimicrobial resistance and virulence factors of this bacterium.

Defining causality in emerging agents of acute bacterial diarrheas: a step beyond the Koch’s postulates

Diarrheal illnesses account for significant morbidity and mortality worldwide. Most cases of diarrhea are caused by bacteria, viruses or parasites. Advances in molecular biology and epidemiology have allowed the identification of emerging pathogens that may cause or, at least, may be associated with diarrhea. However, the same advances have also revealed the complexity of the gut microbiome, suggesting that a potential agent of diarrhea may also been found in healthy individuals. In addition, most of the newly identified emerging agents of diarrhea are ubiquitous and have not yet fulfilled Koch’s postulates. Research investigations should address appropriate matched controls and integrate findings from medical microbiology, epidemiology and molecular biology. This integrative approach should provide insights to our knowledge regarding exposition to common source or risk factors. Here, we aim to review some of these emerging bacterial agents of diarrheas and propose guidelines or prescriptions that may help in defining causality.

Invasion and intracellular survival of Hafnia alvei strains in human epithelial cells

AIMS

The aim of this study was to investigate the invasion and intracellular survival of different Hafnia alvei strains in HeLa cells.

METHODS AND RESULTS

We performed different experiments on the bacterial invasion of different strains of H. alvei into the HeLa cell line using gentamicin protection assays and immunofluorescence. We also report the time course of cell internalization and the effects of inhibitors on the invasion of H. alvei. Levels of invasion varied depending on the conditions (strain, time and inoculum size) used.

CONCLUSIONS

This study revealed that H. alvei strains were able to enter and persist in a human epithelial cell line.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our in vitro findings highlight the possibility that some H. alvei strains may exploit nonprofessional phagocytes or nonphagocytic cells to spread in vivo, which may be important for the persistence and establishment of an asymptomatic carrier state.

Role of RNA polymerase sigma-factor (RpoS) in induction of glutamate-dependent acid-resistance of Escherichia albertii under anaerobic conditions

Escherichia albertii is a potential enteric food-borne pathogen with poorly defined genetic and biochemical properties. Acid resistance is perceived to be an important property of enteric pathogens, enabling them to survive passage through stomach acidity so that they may colonize the mammalian gastrointestinal tract. We analyzed glutamate-dependent acid-resistance pathway (GDAR) in five E. albertii strains that have been identified so far. We observed that the strains were unable to induce GDAR under aerobic growth conditions. Mobilization of the rpoS gene restored aerobic induction of this acid-resistance pathway, indicating that all five strains may have a dysfunctional sigma-factor. On the other hand, under anaerobic growth conditions where GDAR is induced in an RpoS-independent manner (i.e. in Shigella spp. and Escherichia coli O157:H7 strains), only three out of five E. albertii strains successfully induced GDAR. The remainder of the two strains exhibited dependence on functional RpoS even under anaerobic conditions to express GDAR, a regulatory function previously considered to be redundant. The data indicate that certain E. albertii strains may have an alternate RpoS-dependent pathway for acid-resistance under anaerobic growth conditions.

Structure and serological analysis of the Hafnia alvei 481-L O-specific polysaccharide containing phosphate in the backbone chain

The lipopolysaccharide was extracted from cells of Hafnia alvei 481-L bacterial strain and, after mild acid hydrolysis, the O-specific polysaccharide was isolated and characterised. On the basis of chemical analyses and NMR spectroscopic studies of the polysaccharide and oligosaccharides obtained after Smith degradation, or hydrogen fluoride treatment, it was found that the repeating unit of the O-specific polysaccharide is a phosphorylated hexasaccharide: [see text]. The biological repeating unit of the H. alvei 481-L O-antigen has galactose phosphate at the nonreducing terminus. Serological tests indicate that this strain represents an individual serotype in the H. alvei genus.

The genus Hafnia: from soup to nuts

The genus Hafnia, a member of the family Enterobacteriaceae, consists of gram-negative bacteria that are occasionally implicated in both intestinal and extraintestinal infections in humans. Despite the fact that the genus currently contains only a single species (H. alvei), more extensive phylogenetic depth (two or more species) is apparent based upon DNA relatedness and 16S rRNA gene sequencing studies. Hafnia causes a variety of systemic infections, including septicemia and pneumonia; however, its role as a gastrointestinal pathogen is controversial. Many of the data supporting a role for hafniae as enteric pathogens were incorrectly attributed to this genus rather than to the actual pathogen, Escherichia albertii. There are numerous gaps in our understanding of this genus, including ecologic habitats and population genetics, disease-producing role in animals, phenetic and genetic methods useful in distinguishing genomospecies within the H. alvei complex, and bona fide pathogenicity factors.

Abdominal abscess and Hafnia alvei septicemia occurring during the aplastic phase after autologous stem-cell transplantation in a patient with diffuse large B-cell lymphoma

Hafnia alvei is a motile gram-negative bacterium that is rarely isolated from human specimens, but that sometimes can be found as part of the gastrointestinal flora. Here we report a rare case of Hafnia alvei septicemia with an abdominal abscess in a 60-year-old woman with diffuse large B-cell lymphoma involving the spleen, liver, and then lymph nodes. She initially received a splenectomy, and, over a 2-year period, four courses of chemotherapy. After achieving complete remission status, she underwent autologous peripheral blood stem-cell transplantation (PBSCT). During the aplastic phase following transplantation, the patient developed fever, diarrhea, and abdominal pain, with blood cultures positive for Hafnia alvei and an abscess in the splenic recess. Considering the high surgical risk, the infection was treated, successfully, with antibiotics (imipenem/cilastatin), without surgery or computed tomography (CT)-guided percutaneous drainage. Infections due to Hafnia alvei are rare, and this is the first reported case of Hafnia alvei septicemia in an adult hematologic patient undergoing a stem-cell transplantation procedure.

Virulence factors and pathogenicity of Hafnia alvei for gilthead seabream, Sparus aurata L

Virulence factors (eae gene, haemolytic capacity, fimbriae, resistance to the bactericidal effect of serum, siderophore production) and pathogenicity for gilthead seabream, Sparus aurata L., were analysed for 23 Hafnia alvei strains. None of the strains used in LD50 studies were lethal for seabream at doses as high as >10(8) cfu mL(-1). In chronic challenge studies differences in severity of the inflammatory response were observed between strains. On the basis of correlation of the inflammatory response to different strains of H. alvei in seabream with those virulence factors studied, it was only possible to establish a positive correlation between pathogenicity and resistance to the bactericidal effect of fish serum. Gilthead seabream is thus a species with considerable resistance to experimental infection with H. alvei. The bacterium does, however, have the capacity to remain viable in seabream for up to 3 months, without any clinical signs. Hafnia alvei is a well-recognized human and animal pathogen. Thus, as the pathogen can coexist with aquaculture operations, cultured gilthead seabream could represent a risk to human health as a carrier in some circumstances.

Natural antimicrobial susceptibility patterns and biochemical identification of Escherichia albertii and Hafnia alvei strains

Bangladeshi diarrheagenic Hafnia alvei-like strains have been described recently as the new species Escherichia albertii (Int J Syst Evolut Microbiol. 2003;53:807-810). The natural susceptibility of 21 E. albertii and 76 H. alvei strains to 69 antimicrobial agents was examined, applying a microdilution procedure in IsoSensitest broth (for all the strains) and cation-adjusted Mueller-Hinton broth (for some strains). Examining the phenotypic features of both taxa with commercial identification systems and conventional tests, a database for an accurate biochemical separation of E. albertii from H. alvei was also established. Both taxa were naturally sensitive or sensitive and of intermediate susceptibility to aminoglycosides, acylureidopenicillins, ticarcillin, several cephalosporins, carbapenems, aztreonam, quinolones, folate pathway inhibitors, and nitrofurantoin. They were naturally resistant to tetracycline, penicillin G, oxacillin, all macrolides except for azithromycin, lincosamides, streptogramins, glycopeptides, rifampicin, and fusidic acid. Taxon-related differences in natural susceptibility affecting clinical assessment criteria were seen with doxycycline, minocycline, aminopenicillins, some cephalosporins, azithromycin, and fosfomycin. E. albertii was more susceptible than H. alvei to these agents and was naturally sensitive to all beta-lactams (except for penicillin G and oxacillin), azithromycin, and fosfomycin. H. alvei was naturally resistant or of intermediate susceptibility to all tetracyclines, amoxicillin, amoxicillin-clavulanate, ampicillin-sulbactam, narrow-spectrum cephalosporins, azithromycin, and fosfomycin. Motile malonate-negative Hafnia strains (indicating genospecies 2 of the H. alvei complex) were less susceptible to some cephalosporins than nonmotile, malonate-positive hafniae (indicating genospecies 1). Proline deaminase, hydroxyproline amidase, tripeptidase, chitinase, Voges-Proskauer reaction, and assimilation of histidine as well as acid production from glycerol, rhamnose, and xylose were suitable tests to separate strains of E. albertii from those of the H. alvei complex. Although out of the scope of this study, it should be noted that several strains of E. albertii showed acquired resistances to some penicillins and antifolates.

Sepsis nosocomial por Hafnia alvei en una unidad de cuidados intensivos neonatales

Hafnia alvei is a member of the Enterobacteriaceae family, which is rarely associated with infection in pediatric patients and exceptionally in the neonatal period. Infections caused by this organism are usually opportunistic. H. alvei bacteremias are mostly associated with abdominal disease or immunosuppression. We report four cases of nosocomial sepsis in preterm infants with positive blood cultures to H. alvei that were treated in our institution within a short period of time.

Identification of Hafnia alvei with the MicroScan WalkAway system

Hafnia alvei is a gram-negative facultatively anaerobic bacillus that belongs to the family Enterobacteriaceae. This organism is a causative agent of intestinal disorders and is found in different environments. H. alvei has received increased clinical attention as a cause of different infections in humans. This study was performed to compare the MicroScan WalkAway automated identification system in conjunction with the new MicroScan Combo Negative type 1S panels with conventional biochemical methods for identification of 21 H. alvei strains. The MicroScan WalkAway system was found capable of correctly identifying 20 of the 21 strains tested.

Prototypal diarrheagenic strains of Hafnia alvei are actually members of the genus Escherichia

We analyzed five bacterial strains, designated 19982, 9194, 10457, 10790, and 12502, that were isolated from stool specimens of individuals with diarrheal illness by the International Centre for Diarrhoeal Disease Research in Dhaka, Bangladesh (M. J. Albert, S. M. Faruque, M. Ansaruzzaman, M. M. Islam, K. Haider, K. Alam, I. Kabir, and R. Robins-Browne, J. Med. Microbiol. 37:310-314, 1992). The strains were initially identified as Hafnia alvei with a commercial identification system and were reported to contain the eae gene of enteropathogenic Escherichia coli. Results of conventional biochemical analyses, testing of susceptibility to cephalothin, lysis by a Hafnia-specific phage, and amplification of the outer membrane protein gene phoE with species-specific primers support the identification of these strains as members of the genus Escherichia rather than Hafnia alvei. These strains varied from typical E. coli strains by their inability to produce acid from lactose or D-sorbitol and failure to elaborate the enzyme beta-D-glucuronidase. PCR analysis confirmed previous findings that the strains were positive for the eae gene and negative for other virulence markers present among recognized categories of diarrheagenic E. coli. Our findings support the hypothesis that these strains are a new category of diarrheagenic isolates belonging to the genus Escherichia and illustrate the importance of using multiple methodologies when identifying new bacterial agents of diarrheal disease.

The sensitivity of Hafnia alvei strains to the bactericidal effect of serum

Most Hafnia alvei strains are sensitive to the bactericidal action of normal bovine serum (NBS) as well as to a serum in which the alternative pathway of complement activation has been thermally blocked. Introduction of polysaccharides (PS) to NBS lowers the bactericidal effect. In a serum in which the alternative pathway of complement activation is blocked, PS completely cancels the bacterial effect.

Characterization of Hafnia alvei by biochemical tests, random amplified polymorphic DNA PCR, and partial sequencing of 16S rRNA gene

Hafnia alvei strains which possess the attachment-effacement gene (eaeA) may have clinical importance as new diarrhea-causing pathogens and should therefore be differentiated from other H. alvei strains. We characterized diarrheal H. alvei strains, which were positive in the PCR test for the eaeA gene, using biochemical tests not routinely used for identification of members of the family Enterobacteriaceae, and compared them with eaeA-negative strains isolated from different clinical and nonclinical sources to find characteristics useful for identification. Random amplified polymorphic DNA (RAPD)-PCR and partial sequencing of the 16S rRNA gene were utilized to study the genetic diversity of the isolates. The eaeA-positive strains were found to have many characteristic biochemical properties. Negative reactions in the 2-ketogluconate and histidine assimilation tests and a positive reaction in the 3-hydroxybenzoate assimilation test may be useful in routine diagnostics. Nearly identical RAPD-PCR profiles and identical 353-bp fragments of the 16S rRNA genes indicated little genetic diversity among the eaeA-positive strains. The low level of homology (92%) in the partial 16S rRNA genes of eaeA-positive and -negative H. alvei strains raises questions about the taxonomic positioning of eaeA-positive H. alvei.

Hafnia alvei in stool specimens from patients with diarrhea and healthy controls

We found an epidemiological association of Hafnia alvei with diarrhea, because the organism was isolated from 12 of 77 (16%) adult Finnish tourists to Morocco who developed diarrhea and from 0 of 321 tourists without diarrhea (P < 0.001). From another group of 112 adult Finnish diarrheal patients, only 2 (2%) yielded H. alvei. In contrast to some Bangladeshi strains of H. alvei, the Finnish strains were negative for the attachment-effacement lesion by an in vitro fluorescent acting staining test and also did not show homology to the Escherichia coli attachment-effacement gene (eaeA) by PCR. These results suggest that a mechanism or mechanisms other than the attachment-effacement lesion may also be involved in the association of H. alvei with diarrhea.