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SUMMARY This review presents the current taxonomy of the genera Proteus, Providencia, and Morganella, along with the current methods for the identification of each species within the three genera, incorporating both conventional biochemical and commercial methods. While all of these organisms are ubiquitous in the environment, individual case reports and nosocomial outbreak reports that demonstrate their ability to cause major infectious disease problems are presented. Lastly, anticipated antimicrobial susceptibility patterns are reviewed. Many of these organisms are easily controlled, but the advent of newer and more powerful antimicrobial agents has led to some problems of which laboratorians need to be aware.

Salmonellosis is a major cause of illness in the United States. To highlight recent trends, data for 1987-1997 from the National Salmonella Surveillance System were analyzed. A total of 441,863 Salmonella isolates were reported, with the highest age-specific rate among infants (159/100,000 infants at 2 months). Annual isolation rates decreased from 19 to 13/100,000 persons; however, trends varied by serotype. The isolation rate of Salmonella serotype Enteritidis increased until 1996, whereas declines were noted in Salmonella serotypes Hadar and Heidelberg. Overall, serotypes that increased in frequency were significantly more likely than those that decreased to be associated with reptiles (P=.008). Salmonella infections continue to be an important cause of illness, especially among infants. Recent declines in food-associated serotypes may reflect changes in the meat, poultry, and egg industries that preceded or anticipated the 1996 implementation of pathogen-reduction programs. Additional educational efforts are needed to control the emergence of reptile-associated salmonellosis.

Vibrio vulnificus, a recently described halophilic Vibrio species, has been isolated from the blood, wounds, and other skin lesions of patients with primary sepsis or wound infections. Because no study of risk factors for infections with V vulnificus has been reported, a case-control study was performed with the 30 patients from whom V vulnificus isolates were recently submitted to the Centers for Disease Control (Atlanta, Georgia). Patients with primary sepsis were more likely than controls to have eaten raw oysters recently (P less than .01) and to have a history of liver disease (P less than .02). Persons with liver disease should be warned that raw oysters are an important source of this life-threatening infection. Patients with wound infections were more likely than controls to have had recent exposure of the skin to salt water or shellfish (P less than .05). Physicians should therefore consider V vulnificus in the differential diagnosis of severe wound infections with these exposures.

Salmonella isolates have traditionally been classified by serotyping, the serologic identification of two surface antigens, O-polysaccharide and flagellin protein. Serotyping has been of great value in understanding the epidemiology of Salmonella and investigating disease outbreaks; however, production and quality control of the hundreds of antisera required for serotyping is difficult and time-consuming. To circumvent the problems associated with antiserum production, we began the development of a system for determination of serotype in Salmonella based on DNA markers. To identify flagellar antigen-specific sequences, we sequenced 280 alleles of the three genes that are known to encode flagellin in Salmonella, fliC, fljB, and flpA, representing 67 flagellar antigen types. Analysis of the data indicated that the sequences from fliC, fljB, and flpA clustered by the antigen(s) they encode not by locus. The sequences grouped into four clusters based on their conserved regions. Three of the four clusters included multiple flagellar antigen types and were designated the G complex, the Z4 complex, and the ␣ cluster. The fourth cluster contained a single antigen type, H:z 29 . The amino acid sequences of the conserved regions within each cluster have greater than 95% amino acid identity, whereas the conserved regions differ substantially between clusters (75 to 85% identity). Substantial sequence heterogeneity existed between alleles encoding different flagellar antigens while alleles encoding the same flagellar antigen were homologous, suggesting that flagellin genes may be useful targets for the molecular determination of flagellar antigen type.

Classification of Proteus vulgarisStrains traditionally identified as Proteus vulgaris formed three biogroups. Biogroup 1, characterized by negative reactions for indole production, salicin fermentation and aesculin hydrolysis, is now known as Proteus penneri. Biogroup 2, characterized by positive reactions for indole, salicin and aesculin, was shown by DNA hybridization (hydroxyapatite method) to be a genetic species separate from biogroup 1 and from biogroup 3 which is positive for indole production and negative for salicin and aesculin. In this study, 52 strains were examined, of which 36 strains were Proteus vulgaris biogroup 3, which included the current type strain of the species P. vulgaris (ATCC 29905 T ), and compared to seven strains of Proteus vulgaris biogroup 2 and nine type strains of other species in the genera Proteus, Providencia and Morganella. By DNA hybridization, these 36 strains were separated into four distinct groups, designated as Proteus genomospecies 3, 4, 5 and 6. DNAs within each separate Proteus genomospecies were 74-99 % related to each other in 60 SC hybridization reactions with a 45 % divergence between related sequences. Proteus genomospecies 3 contained the former P. vulgaris type strain and one other strain and was negative in reactions for salicin fermentation, aesculin hydrolysis and deoxyribonuclease, unlike the reactions associated with strains considered as typical P. vulgaris which are positive in reactions for salicin, aesculin and DNase. Genomospecies 3 can be distinguished from Proteus genomospecies 4, 5 and 6 because it is negative for Jordan's tartrate. Proteus genomospecies 4, containing five strains, was differentiated from Proteus penneri, genomospecies 3 and 6 and most, but not all, strains of genomospecies 5, by its ability to ferment L-rhamnose. Proteus genomospecies 5 and 6, containing 18 and 11 strains, respectively, could not be separated from each other by traditional biochemical tests, by carbon source utilization tests or SDS-PAGE of whole-cell proteins. In an earlier publication, a request was made to the Judicial Commission that the former type strain of P. vulgaris (ATCC 13315) be replaced by P. vulgaris biogroup 2 strain ATCC 29905 T , a strain considered more biochemically typical of P. vulgaris strains. This would have the effect of assigning the name P. vulgaris to P. vulgaris biogroup 2. Since this request has been acceded to, the name Proteus hauseri is herein proposed for Proteus vulgaris genomospecies 3. Its type strain is ATCC 700826 T . Proteus genomospecies 4, 5 and 6 will remain unnamed until better phenotypic differentiation can be accomplished. All Proteus genomospecies were similar in their antimicrobial susceptibility patterns. Nineteen strains were isolated from urine, four from faeces, two from wounds, nine from other human sources and two from animals.

Vib' ri.o . L. v. vibrio move rapidly back and forth, vibrate; M.L. masc. n. Vibrio the vibrating, darting organism. Proteobacteria / Gammaproteobacteria / “Vibrionales” / Vibrionaceae / Vibrio Small, straight, slightly curved, curved, or comma‐shaped rods , 0.5–0.8 × 1.4–2.6 µm. Involution forms often occur in old cultures and are formed under adverse growth conditions. Do not form endospores or microcysts. Gram negative. In liquid media, motile by monotrichous or multitrichous polar flagella enclosed in a sheath continuous with the outer membrane of the cell wall. On solid media, some species synthesize numerous lateral flagella with a wavelength shorter than that of the sheathed polar flagellum. Facultative anaerobes capable of both fermentative and respiratory metabolism . Molecular oxygen is a universal electron acceptor. Most do not denitrify or fix molecular nitrogen. All are chemoorganotrophs; most are able to grow in a mineral medium containing D ‐glucose as the sole carbon source and NH + as the sole nitrogen source . A few strains have organic growth factor requirements. Na 4 + stimulates growth of all species and is an absolute requirement for most ; the minimal concentration necessary for optimal growth ranges from 5 to 700 mM (0.029–4.1%). Most species grow well in media containing a seawater base. All ferment D ‐glucose producing acid but rarely gas ; several species produce acetoin and acetyl methyl carbinol ( positive Voges–Proskauer test ). Most ferment and utilize D ‐fructose, maltose, and glycerol; are oxidase positive and reduce nitrate to nitrite . Several grow at 4°C; all grow at 20°C; most grow at 30°C; many grow at 35–37°C. A few species are bioluminescent , as are a few strains of normally nonluminescent species. Primarily aquatic ; species distribution is usually dependent on Na + and nutrient content of the water as well as its temperature. Very common in marine and estuarine environments and on the surfaces and in the intestinal contents of marine animals. Species with a low Na + requirement are also found in freshwater habitats. Twelve species occur in human clinical specimens; 11 of these are apparently pathogenic for humans, causing diarrhea or extraintestinal infections. Several species cause diseases of other vertebrates and invertebrates . The mol % G + C of the DNA is : 38–51. Type species : Vibrio cholerae Pacini 1854, 411.