Peptoniphilus asaccharolyticus is a commonly isolated Gram-positive anaerobic coccus (GPAC) (7). However, the type strain, ATCC 14963, is not representative of the species. Huss et al. (4) described the DNA-DNA homology between the type strain and clinical isolates as being <25%.
Because of this finding, new species were described (6), among them Peptoniphilus harei. P. harei has the same biochemical features as P. asaccharolyticus and can be differentiated from P. asaccharolyticus only by its irregular colony and cell morphologies (5). The clinical relevance of P. harei was unknown. However, in studies using molecular techniques to identify clinical isolates, a remarkable number of P. harei organisms were found. Song et al. (9) identified 25.3% of all GPAC as P. harei. In another study (10), 17.0% were identified as P. harei by fluorescent in situ hybridization. P. asaccharolyticus was not encountered in either study. To substantiate the genotypic identity of P. asaccharolyticus, reference strains were needed. To this end, a number of type strains were reidentified by using 16S rRNA gene sequencing. These were P. asaccharolyticus strains from the Culture Collection of the University of Göteburg (Sweden): CCUG42643, CCUG43862, CCUG44165, CCUG47015, and CCUG48151. DNA was isolated and amplified as described previously (1, 2). Sequences were aligned, and a filter was set at Escherichia coli positions 257 and 1436. Sequence similarities with closest relatives and P. asaccharolyticus were calculated using the DNA distance matrix in BioEdit (http://www.mbio.ncsu.edu/BioEdit/bioedit.html).
For each strain, the closest relative was P. harei, with sequence similarities between 99.0 and 99.4% (Table 1). The sequence similarity with P. asaccharolyticus was between 89.2 and 89.6%. The original identification of these strains was based on their biochemical features. Since P. harei and P. asaccharolyticus share the same biochemical features, it is clear that these strains were misidentified in the past.
Table 1.
Sequence similarities between the 16S rRNA genes of the type strains of P. harei and P. asaccharolyticus and several strains originally identified as P. asaccharolyticus
| Strain (GenBank accession no.) | % similarity |
|
|---|---|---|
| P. harei ATCC BAA-601T | P. asaccharolyticus ATCC 14963T | |
| ATCC 29743 (DQ986463) | 99.4 | 89.5 |
| CCUG 42643 (HQ326629) | 99.1 | 89.2 |
| CCUG 43862 (HQ326630) | 99.0 | 89.4 |
| CCUG 44165 (HQ326631) | 99.3 | 89.4 |
| CCUG 47015 (HQ326632) | 99.2 | 89.3 |
| CCUG 48151 (HQ326633) | 99.3 | 89.3 |
| P. harei ATCC BAA-601T | 100 | 89.6 |
Song et al. (8) developed a flow chart for the phenotypical identification of GPAC. It is mentioned that the alkaline phosphatase test might be useful to differentiate the species. The sequence similarity of P. asaccharolyticus strain ATCC 29743 with P. harei was 99.6% (Table 1), indicating that it is not P. asaccharolyticus. However, in the study of Song et al. (8), this strain was assumed to be P. asaccharolyticus. This confirms that P. harei and P. asaccharolyticus cannot be differentiated from each other phenotypically. Holdeman-Moore et al. (3) commented in 1986 that one should be cautious in reporting on isolation and incidence of P. asaccharolyticus. In our opinion, this caution still stands. The fact that the type strain of P. asaccharolyticus, ATCC 14963, is atypical of clinical isolates might be due to the true identity of the clinical isolates used for comparison. This can explain the low DNA-DNA homology (4) between the type strain and clinical isolates.
We are convinced that the incidence of P. asaccharolyticus in clinical material is highly overestimated. The clinical importance of P. harei in the pathogenesis of anaerobic infections still has to be defined.
Nucleotide sequence accession numbers.
The 16S rRNA gene sequences of strains CCUG 42643, CCUG 43862, CCUG 44165, CCUG 47015, and CCUG 48151 have been deposited in GenBank under accession numbers HQ 326629, HQ 326630, HQ 326631, HQ 326632, and HQ 326633, respectively.
Footnotes
Published ahead of print on 19 January 2011.
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