The Genus Hafnia
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The Genus Hafnia MEGAN E. MCBEE AND DAVID B. SCHAUER
Introduction
Habitat
The genus Hafnia was recognized by Møller (1954) while studying amino acid decarboxylase patterns among Enterobacteriaceae. Members of this taxon are Gram-negative, facultatively anaerobic rods that are typically methyl red and Voges-Proskauer positive, positive for lysine and ornithine decarboxylase, and negative for arginine dihydrolase. The taxonomic position of these organisms has been the subject of some controversy, and over the years they have been referred to as Bacillus asiaticus (cited by Ewing and Fife, 1968), Bacterium cadaveria (Gale and Epps, 1943), Aerobacter species biotype 32011 (Stuart et al., 1943b), Enterobacter alvei (Sakazaki, 1961), Enterobacter aerogenes subsp. hafniae (Ewing, 1963), and Enterobacter hafniae (Ewing and Fife, 1968). However, DNA hybridization studies have shown that these organisms are distinct from Enterobacter (Steigerwalt et al., 1976), and Hafnia alvei (the only recognized species of the genus) is a legitimate taxon. Barbe described two H. alvei biotypes, which can be distinguished by hydrolysis of arbutin and esculin and fermentation of salicin and Darabinose (cited in Introduction to the Family Enterobacteriaceae in the second edition). Janda et al. (2002) subsequently identified isolates that fell into two additional biogroups (Table 1). These authors reported that isolates belonging to biogroup 2 were less common than isolates belonging to biogroup 1 and that isolates belonging to biogroups 3 and 4 were rare (Janda et al., 2002). Both DNA relatedness (Steigerwalt et al., 1976) and 16S ribosomal RNA gene sequencing (Janda et al., 2002) indicate that there are at least two distinct genomospecies of H. alvei. Because the genomospecies cannot be clearly distinguished by phenotypic characteristics, they remain classified as a single heterogeneous species. It has been suggested that genomospecies 1, which includes the majority of isolates as well as the type strain (ATCC 13337), should be considered H. alvei sensu stricto (Janda et al., 2002).
Hafnia alvei can be isolated from feces in apparently healthy individuals, as well as from mammals, birds, reptiles and fish. It can also be isolated from a range of environmental sources, including soil, water and sewage, as well as from food. Early studies incriminated biotype 32011 of paracolon bacteria, now classified as H. alvei, as a cause of diarrhea (cited in The Genus Hafnia in the second edition). Diarrhea-associated isolates, more recently identified as H. alvei and shown to possess a locus of enterocyte effacement (LEE) pathogenicity island and to produce attaching and effacing lesions (Albert et al., 1991; Albert et al., 1992), were subsequently found to be distinct from true H. alvei (Ridell et al., 1995; Ismaili et al., 1996; Janda et al., 1999). These strains are now classified as Escherichia albertii (Abbott et al., 2003; Huys et al., 2003). Thus, the role of H. alvei as a primary cause of gastroenteritis and di
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