Enterobacter hormaechei subsp. oharae subsp. nov., E. hormaechei subsp. hormaechei comb. nov., and E. hormaechei subsp. steigerwaltii subsp. nov., Three New Subspecies of Clinical Importance

Abstract

Six species and six additional genovars are combined within the so-called Enterobacter cloacae complex, with one of them being the species Enterobacter hormaechei. In a recent population genetic study, two genetic clusters were found in close phylogenetic proximity to the genetic cluster of E. hormaechei. In order to prove the hypothesis that these three genetic clusters belong to the same species, we performed cross-hybridization experiments in microplates with DNAs of representatives of each genetic cluster. The close phylogenetic relationship among the clusters was reflected by their relatively low ⌬T m values, ranging from 0.3 to 4.8, confirming the hypothesis that the clusters are parts of the same species. These clusters can be distinguished from the other species of the E. cloacae complex, which have ⌬T m values of 5.6 to 10.3. Forty-eight E. hormaechei strains from the different genetic clusters were phenotypically characterized with 129 biochemical tests. In this way, E. hormaechei could be differentiated from the other species of the E. cloacae complex because it tests negative in the 3-hydroxy-butyrate test. The three genetic clusters of E. hormaechei could also be differentiated from each other by using phenotypic tests. Hence, we propose three new subspecies of E. hormaechei corresponding to genetic clusters VI, VII, and VIII of the E. cloacae complex. E. hormaechei subsp. hormaechei comb. The genus Enterobacter was first described by Hormaeche and Edwards (9). Since the transfer of Enterobacter agglomerans to the genus Pantoea (5), 14 species are included in the genus (1), including Enterobacter aerogenes, which is considered a homotypic synonym of Klebsiella mobilis because it has the same type strain (13). Around Enterobacter cloacae, six genetically related and phenotypically similar species have been combined within the so-called E. cloacae complex (7), i.e., E. cloacae, Enterobacter asburiae, Enterobacter dissolvens, Enterobacter hormaechei, Enterobacter kobei, and Enterobacter nimipressuralis. In addition to these species, at least six genetic clusters are phylogenetically delineated within the complex (7).Two of the most prominent clusters (clusters VI and VIII) are closely related to the species E. hormaechei, together forming the so-called E. hormaechei metacluster. They displayed 98 to 99% sequence identity in an analysis of three housekeeping genes and showed nearly identical restriction patterns of their ampC genes, which chromosomally code for a Bush class 1 beta-lactamase (7).E. hormaechei was first described on the basis of 23 isolates sent to the Centers for Disease Control and Prevention (Atlanta, Ga.) for identification. At that time, they could not be assigned to a species, since they were negative in D-sorbitol and melibiose tests and did not fit the biochemical profile of any established Enterobacter species. Later, this preselected set of isolates turned out to be genetically closely related to each other. The species E. hormaechei was proposed to be lactose, D-sorbitol, raffi...

Cultivation of Enterobacter Hormaechei from Human Atherosclerotic Tissue

“…DNA was purified and analyzed from all five initial isolates. As a result of this analysis, the sequence was assigned to the Enterobacter genus 16) , and specifically to sequence S000544285, which belongs to Enterobacter hormaechei 17) .…”

“…Enterobacteriaceae have been implicated in bloodstream infections, in addition to peritonitis, cholangitis, and other intraabdominal infections 23) . E. hormaechei is the species of E. cloacae complex most frequently recovered from clinical specimens 17) . In particular, E. hormaechei is often associated with nosocomial outbreaks and demonstrates -lactamase activity 24) .…”

Specific Distribution within the Enterobacter cloacae Complex of Strains Isolated from Infected Orthopedic Implants

“…hormaechei (cluster VII), and E. hormaechei subsp. steigerwallti (cluster VIII) (10). Species names were not attributed to clusters III, IV, and IX and to sequence crowd xiii, although at least cluster III is of significant clinical importance (8,26).…”

“…These microorganisms are saprophytic in the environment and commensal in the enteric flora since they are found in soil and sewage, as well as in the human gastrointestinal tract (17,22). The taxonomy of the Enterobacter genus has been iteratively updated (8)(9)(10)(11)(12)19). Several species are described in this taxon (Enterobacter aerogenes, E. amnigenus, E. cancerogenus, E. cowanii, E. gergoviae, E. intermedius, E. pyrinus), as is a genetic complex, referred to as the "E. cloacae complex," in which other species have been identified (E. asburiae, E. kobei, E. ludwigii, E. hormaechei, E. nimipressuralis, and E. cloacae).…”

Identificación bacteriana basada en el espectro de masas de proteínas: Una nueva mirada a la microbiología del siglo XXI

“…En el caso del género Salmonella, es posible la diferenciación de serovars de Salmonella enterica subespecie enterica especialmente serovars Enteritidis, Typhimurium, Virchow, Infantis y Hadar 36 . Se han descrito dificultades en la identificación con puntaje < 2 en Enterobacter cloacae complex 37 en Streptococcus sp 10,29,30,32,34,42 con excepción de S. pneumoniae y Streptococcus parasanguinis del grupo mitis ya que tienen perfiles proteicos muy parecidos, por lo que el fabricante recomienda una prueba fenotípica adicional para su identificación; lo que no representa un problema de error de identificación ya que el puntaje es generalmente bajo. En el género Enterococcus la diferenciación de E. faecium y E. fecalis ha mostrado una alta exactitud y representa una ayuda en la diferenciación entre E. faecium y E. gallinarum y E. flavus, que por métodos convencionales en muy inexacta 29,31,32 .…”