The Proteus and Providencia genera belong to the Proteeae of the Enterobacteriaceae family. The members of both these genera are gram negative, motile bacilli, aerobic and facultative anaerobic and can grow in basic media.A characteristic feature that distinguishes tribe Proteeae from other members of Enterobacteriaceae is the presence of the enzyme phenylalanine- deaminase, which converts phenylalanine to phenylpyruvic acid( PPA reaction). It also produces a powerful urease enzyme that quickly hydrolyses urea into ammonia.
Characteristics of Proteeae
They are gram- negative bacilli, 1- 3 μm long and 0.6 μm broad. They are unencapsulated and actively motile by peritrichous flagella. The name ‘ Proteus‘ refers to its pleomorphism, after the Greek god Proteus who could take any form.Four species are recognized: Proteus mirabilis, Proteus vulgaris, Proteus penneri and Proteus myxofaciens. Proteus mirabilis, Proteus vulgaris are widely recognized as human pathogens.
Cultural characteristics of Proteus species
These can grow in ordinary media, such as nutrient agar with a characteristic fishy or seminal smell.On MacConkey and Teepol lactose agar, lactose non fermenting pale colonies are formed about 2- 3 mm in size.Solid media, such as blood and nutrient agar Proteus mirabilis and Proteus vulgaris, show characteristic swarming growth in the form of a uniform film that spreads over the entire surface of the plate.In young swarming cultures, many bacteria are long, curved and filamentous, sometimes up to 80 μm in length.When two different strains of swarming proteus mirabilis encounter each other on an agar plate, swarming stops and a visible line of demarcation forms.This is called the Dienes phenomenon.
Proteus swarming can be prevented by the following methods
- Increase agar concentration from 1- 2 percent to 6 percent.
- Incorporation of sodium azide, boric acid or chlorine hydrate.
- Introduction of growth inhibitors such as sulphonamides.
- On Teepol Lactose agar by Teepol( active surface agent)
- On MacConkey agar or DCA by bile salts.
- On CLED agar by the absence of electrolytes.
- In liquid medium( peptone water, nutrient broth), Proteus produces uniform turbidity with a slight powdery deposit and an ammonia odour.
Biochemical reactions of Proteus species
Like all other members of the Enterobacteriaceae family, all species of the genus Proteus are catalase positive, oxidase negative, reduce nitrates to nitrites and show fermentative reactions to the media of Hugh Leifson.All members of the tribe Proteeae are PPA- positive and hydrolysis urea to ammonia that differentiates them from other Enterobacteriaceae.
|Biochemical Reactions||Proteus mirabilis||Proteus vulgaris||Providencia stuartii||Providencia rettgeri||Providencia alcalifaciens|
|Gas from glucose||+||+||–||–||+|
Antigenic structures of Proteus species
The bacilli have a thermostable O’ antigen( somatic) and a thermolabile’ H’ antigen( flagellar). Weil and Felix observed that certain non- motile strains of P vulgaris, known as ‘X’ strains, were agglutinated by sera from patients with typhus fever.This heterophilic agglutination, due to the sharing of carbohydrate antigen by certain strains of Proteus and Rickettsia, forms the basis of the Weil Felix reaction and is used to diagnose rickettsial infections.
Proteus typing methods
- Phage typing
- Dienes typing
- Bacteriocin(proticin) typing
Dienes phenomenon: This method forms the basis for the typing of Proteus swarming strains for local epidemiological studies.Different cultures are inoculated as discrete spots on the same plate and are allowed to swarm to each other. A line of complete or partially inhibited growth is formed where cultures of different strains meet; there is no line between cultures of the same strain.
Pathogenicity of proteus species
Proteus species are saprophytic and widely distributed in nature. They also occur in the intestine as commensals. They are opportunistic pathogens and can cause many types of infections, such as:
- Urinary tract infections( UTI) with upper UTI predilection. It produces urease that releases ammonia from urea. The alkaline conditions lead to phosphate precipitation and calculus formation in the urinary tract.
- Pyogenic lesions
- Bed sores
- Wound infections
- Otitis media
Proteus species laboratory diagnosis
The types of specimens :
- UTI- midstream urine
- Wound/ abscesses, osteomyelitis, otitis media: pus
- Meningitis: CSF
- Septicaemia – blood culture
Culture media: Clinical specimens should be cultivated on MacConkey agar / Teepol lactose agar, 6 percent blood agar and CLED urine( cysteine lactose electrolyte deficient agar).Cultural media are incubated for 18- 24 hours at 37oC.Pale colored Non- Lactose Fermentation( NLF) colonies are seen on MacConkey agar.Identification is carried out by standard biochemical reactions mentioned above.
Antibiotic susceptibility: Proteus are resistant to many of the common antibiotics, except P mirabilis which is sensitive to ampicillin and cephalosporins but nitrofurantoin is not effective.
An overview of the Genus Providencia
Like Proteus, Providencia strains are non- lactose fermentation( NLF), methyl red and PPA positive bacilli, which are motile by peritrichous flagella.However, they don’t swarm on solid media.They can often be recognized by their ” fruity” smell.Three major pathogenic species include Providencia alcalifaciens, Providencia rettgeri, and Prov stuartii.It has been suggested that Providencia alcalifaciens causes diarrhea, Providencia rettgeri and Providencia stuartii are associated with hospital- acquired urinary tract, wound and other infections.Providencia is very resistant to antibiotics, especially Providencia stuartii, which is also resistant to disinfectants, making it a major pathogen in burn units.