| Spezies | Risiko- gruppe | Bemer- kungen | Status |
| Uliginosibacterium | |||
| Uliginosibacterium gangwonense | 1 | ||
| Uliginosibacterium paludis | 1 | neu | |
| Ulvibacter | |||
| Ulvibacter antarcticus | 1 | ||
| Ulvibacter litoralis | 1 | ||
| Ulvibacter marinus | 1 | ||
| Umboniibacter | |||
| Umboniibacter caenipelagi | 1 | neu | |
| Umboniibacter marinipuniceus | 1 | ||
| Umboniibacter roseus | 1 | neu | |
| Umezawaea | |||
| Umezawaea endophytica | 1 | neu | |
| Umezawaea tangerina (Saccharothrix tangerinus) | 1 | ||
| Undibacterium | |||
| Undibacterium amnicola | 1 | neu | |
| Undibacterium aquatile | 1 | neu | |
| Undibacterium arcticum | 1 | neu | |
| Undibacterium danionis | 1 | neu | |
| Undibacterium jejuense | 1 | ||
| Undibacterium macrobrachii | 1 | ||
| Undibacterium oligocarboniphilum | 1 | ||
| Undibacterium parvum | 1 | ||
| Undibacterium pigrum | 1 | ||
| Undibacterium seohonense | 1 | ||
| Undibacterium squillarum | 1 | neu | |
| Undibacterium terreum | 1 | ||
| Ureaplasma | |||
| Ureaplasma canigenitalium | 1 | neu | |
| Ureaplasma cati | 1 | ||
| Ureaplasma diversum | 2 | t | |
| Ureaplasma felinum | 1 | ||
| Ureaplasma gallorale | 2 | t | |
| Ureaplasma parvum | 2 | ||
| Ureaplasma urealyticum | 2 | ht | |
| Ureibacillus | |||
| Ureibacillus composti | 1 | ||
| Ureibacillus defluvii | 1 | ||
| Ureibacillus suwonensis | 1 | ||
| Ureibacillus terrenus | 1 | ||
| Ureibacillus thermophilus | 1 | ||
| Ureibacillus thermosphaericus (Bacillus thermosphaericus) | 1 | ||
| Uruburuella | |||
| Uruburuella suis | 2 | t | |
| Uruburuella testudinis | 2 | t | neu |