A re-evaluation of the taxonomic position of five strains, one assigned to Cronobacter sakazakii (strain 1330^T, isolated from spiced meat purchased in Slovakia), two previously assigned to Cronobacter genomospecies 1 (strains NCTC 9529^T and 731, isolated from water and a leg infection, respectively) and two previously assigned to Cronobacter turicensis (strains 96 and 1435, isolated from onion powder and rye flour, respectively) was carried out. The analysis included phenotypic characterization, 16S rRNA gene sequencing and multilocus sequence analysis (MLSA) of seven housekeeping genes (atpD, fusA, glnS, gltB, gyrB, infB, ppsA; 3036 bp). 16S rRNA gene sequence analysis and MLSA showed that strain 1330^T formed an independent phylogenetic lineage in the MLSA, with Cronobacter dublinensis LMG 23823^T as the closest neighbour. DNA–DNA reassociation and phenotypic analysis revealed that strain 1330^T represented a novel species, for which the name Cronobacter condimenti sp. nov. is proposed (type strain 1330^T = CECT 7863^T = LMG 26250^T). Strains NCTC 9529^T, 731, 96 and 1435 clustered together within an independent phylogenetic lineage, with C. turicensis LMG 23827^T as the closest neighbour in the MLSA. DNA–DNA reassociation and phenotypic analysis confirmed that these strains represent a novel species, for which the name Cronobacter universalis sp. nov. is proposed (type strain NCTC 9529^T = CECT 7864^T = LMG 26249^T).

Arcobacter species are highly abundant in sewage where they often comprise approximately 5-11% of the bacterial community. Oligotyping of sequences amplified from the V4V5 region of the 16S rRNA gene revealed Arcobacter populations from different cities were similar and dominated by one to three members, with extremely high microdiversity in the minor members. Overall, nine subgroups within the Arcobacter genus accounted for >80% of the total Arcobacter sequences in all samples analyzed. The distribution of oligotypes varied by both sample site and temperature, with samples from the same site generally being more similar to each other than other sites. Seven oligotypes matched with 100% identity to characterized Arcobacter species, but the remaining 19 abundant oligotypes appear to be unknown species. Sequences representing the two most abundant oligotypes matched exactly to the type strains for A. cryaerophilus group 1B (CCUG 17802) and group 1A (CCUG17801), respectively. Oligotype 1 showed generally lower relative abundance in colder samples and higher relative abundance in warmer samples; the converse was true for Oligotype 2. Ten other oligotypes had significant positive or negative correlations between temperature and proportion in samples as well. The oligotype that corresponded to A. butzleri, the Arcobacter species most commonly isolated by culturing in sewage studies, was only the eleventh most abundant oligotype. This work suggests that Arcobacter populations occupy unique niches in sewer infrastructure and are modulated by temperature. Furthermore, current culturing methods used for identification of Arcobacter fail to identify some abundant members of the community and may underestimate the presence of species with affinities for growth at lower temperatures. Understanding the ecological factors that affect the survival and growth of Arcobacter spp. in sewer infrastructure may better inform the risks associated with these emerging pathogens.

The genus Arcobacter is composed of 17 species which have been isolated from various sources. Of particular interest are A. butzleri , A. cryaerophilus , and A. skirrowii , as these have been associated with human cases of diarrhea, the probable transmission routes being through the ingestion of contaminated drinking water and food. To date, only limited studies of virulence traits in this genus have been undertaken. The present study used 60 Arcobacter strains isolated from different sources, representing 16 of the 17 species of the genus, to investigate their ability to adhere to and invade the human intestinal cell line Caco-2. In addition, the presence of five putative virulence genes ( ciaB , cadF , cj1349 , hecA , and irgA ) was screened for in these strains by PCR. All Arcobacter species except A. bivalviorum and Arcobacter sp. strain W63 adhered to Caco-2 cells, and most species (10/16) were invasive. The most invasive species were A. skirrowii , A. cryaerophilus , A. butzleri , and A. defluvii . All invasive strains were positive for ciaB (encoding a putative invasion protein). Other putative virulence genes were present in other species, i.e., A. butzleri ( cadF , cj1349 , irgA , and hecA ), A. trophiarum ( cj1349 ), A. ellisii ( cj1349 ), and A. defluvii ( irgA ). No virulence genes were detected in strains which showed little or no invasion of Caco-2 cells. These results indicate that many Arcobacter species are potential pathogens of humans and animals.

Although rarely, Arcobacter spp. have been associated with diarrhoea and bacteraemia. We report a persistent case in a healthy 26‐year‐old Spanish male of bloody diarrhoea, which was attributed to Campylobacter but in fact was caused by Arcobacter cryaerophilus, as determined by sequencing of the rpoB gene. The isolate was re‐identified by matrix‐assisted laser desorption ionization time of flight (MALDI‐TOF) and genotyped for five putative virulence genes and for seven genes included in the Arcobacter multilocus sequence typing database. The low score obtained by MALDI‐TOF indicates the need to complement the database with more isolates. Only the ciaB gene, which encodes for an invasin, was detected. Despite the isolate belonging to a new sequence type, three of the alleles (glnA, pgm and tkt) had been found previously in isolates from faeces of patients with diarrhoea. This study, together with the reviewed literature, indicates that Arcobacter can produce bacteraemia and that the isolation from patients with diarrhoea range from 0.11% to 1.25%. This study also demonstrates that Arcobacter species are confused with Campylobacter spp., as previously suggested. This is one of the factors that leads to underestimation of their incidence together with the use of inappropriate detection and identification methods.

A study employing a polyphasic taxonomic approach was undertaken to clarify the position of 12 isolates recovered from sewage samples. These isolates were recognized as a potential novel species because a new and specific pattern was produced with the 16S rRNA-RFLP Arcobacter identification method. The sequences of the 16S rRNA gene not only supported the classification of these novel strains as members of the genus Arcobacter, but also showed that they formed a separate phylogenetic line. Strain SW28-11^T, chosen as the representative of these strains, showed 16S rRNA gene sequence similarity of 95.6 % with the closest related species Arcobacter nitrofigilis. The phylogenetic position of the novel strains was further confirmed by analysis of the housekeeping genes hsp60, rpoB and, for the first time, gyrB. The latter proved to be an excellent additional gene for establishing the phylogeny of this genus. These data, together with phenotypic characterization, revealed that this group of isolates represent a novel species of the genus Arcobacter. The name Arcobacter defluvii sp. nov., is proposed, with the type strain SW28-11^T ( = CECT 7697^T = LMG 25694^T).