Proteus penneri is a Gram-negative, facultatively anaerobic, rod-shaped bacterium. It is an invasive pathogen and a cause of nosocomial infections of the urinary tract or open wounds. Pathogens have been isolated mainly from the urine of patients with abnormalities in the urinary tract, and from stool. P. penneri strains are naturally resistant to numerous antibiotics, including penicillin G, amoxicillin, cephalosporins, oxacillin, and most macrolides, but are naturally sensitive to aminoglycosides, carbapenems, aztreonam, quinolones, sulphamethoxazole, and co-trimoxazole. Isolates of P. penneri have been found to be multiple drug-resistant (MDR) with resistance to six to eight drugs. β-lactamase production has also been identified in some isolates. History The Proteus penneri group of bacteria was named in 1982. It reclassified a group of strains formerly known as Proteus vulgaris biogroup 1. In 1978, Brenner et al. showed through DNA hybridization studies that P. vulgaris was a heterogenous species. In 1981, Hickman et al conducted experiments on 20 indole-negative strains previously grouped with P.vulgaris and demonstrated the existence of three P. vulgaris biogroups. P. vulgaris biogroup 1, or indole-negative P. vulgaris, was distinguished as a new species within the genus Proteus in 1982. The new species was named Proteus penneri in honor of John Penner, a Canadian microbiologist. Lab identification and differentiation Extended biochemical tests have characterized P. penneri as being uniformly salicin negative. The inability to produce ornithine decarboxylase differentiates P. penneri from another indole-negative Proteus species, P.mirabilis. P. penneri isolates are not fermenters of salicin and not users of citrate, but acidify sucrose and maltose. Other chief characteristics of this species that enable its differentiation from other Proteus species include failure to acidify esculin, failure to produce hydrogen sulfide on triple sugar iron agar, and resistance to chloramphenicol. The resistance of P. penneri to cefuroxime and the marked inhibitory activity of cefoxitin against this species also distinguishes P. penneri from the other Proteus. Similar to other Proteus species, P. penneri has a cell-bound hemolytic factor, which has been shown to facilitate penetration of the organism into cultured Vero cells without any cytotoxic effects. It also has a filterable cytotoxic alpha-hemolysin rarely found in other Proteus species. A highly active urease produced by P. penneri may also have a role in the establishment of an infectious process. The application of molecular techniques such as the polymerase chain reaction to produce DNA fingerprints and other 16S ribosomal RNA gene (ribotyping) methods of strain analysis