Shewanella putrefaciens (syn. Pseudomonas putrefaciens): Culture; Molecular diagnosis (PCR)

Shewanella putrefaciens (formerly known as Pseudomona putrefaciens) is a pleomorphic, gram-negative, facultative anaerobic bacterium of the genus Shewanella, family Shewanellaceae. At present, the genus Shewanella has a great diversity of species, S. putrefaciens and S. algae being the most clinically and pathologically relevant for people. S. algae is responsible for 80% of human infections attributable to Shewanella and the most virulent.

S. putrefaciens is widely distributed in numerous geographic areas of temperate climates. Since its identification in 1931 in dairy products, this bacterium has been isolated mainly in marine environments, although it can be found in all types of aquatic ecosystems, in natural energy reserves, in the soil, as well as in food products of animal origin (fish, meat, poultry and dairy). This microorganism is one of the main bacteria of food decomposition, which in turn can affect human health creating a problem for the food industry. It also has an even greater problem for the food industry due to its ability to form film on food processing equipment that is made mainly of steel. In processing equipment, S. putrefaciens may be the major source of bacterial contamination, as well as causing corrosion of the equipment itself.

In meat products, this bacterium acts in a similar way to the Pseudomonas in the aerobic alteration of the meat. S. putrefaciens is very sensitive to pH and appears mainly in meats such as DFD (Dark, firm and dry), with pH values ​​of 6.0 or higher but not detected in meat products with values of pH 5.5 or lower. When the pH conditions and the low availability of oxygen occur, the growth of S. putrefaciens is favored, which produces a large amount of hydrogen sulfide that reacts with muscle myoglobin, forming sulfomyoglobin that produces a greenish color of the meat. Likewise, this bacterium, along with some species of Pseudomonas, is one of the main responsible for the appearance of anomalous odors.

Although it is rare that this microorganism acts as a human pathogen, there have been cases of infections and bacteremia caused by S. putrefaciens in people. Because the species of Shewanella are usually isolated as part of a mixed bacterial flora, their clinical pathology can be masked by the rest of the microorganisms. However, infections caused by S. putrefaciens occur mainly in soft tissues, such as the skin, intra-abdominal areas, or in the blood. Specifically, this bacterium can produce various types of syndromes and infections, being found in patients with infectious endocarditis, blood infection (bacteremia, sepsis), skin and soft tissue infections (abscesses in the lower extremities, necrotizing fasciitis, cellulitis, foot paddle ), ear infections (otitis), heart infection (endocarditis, purulent pericarditis), central nervous system infection (meningitis, brain abscess), lung infection (pneumonia, pneumonia associated with the use of mechanical ventilation, empyema, cavitated tumor), ocular infections (keratitis, conjunctivitis), infections in the peritoneum (abscess, peritonitis), in the liver (abscess, cholangitis) and in the bone (arthritis, osteomyelitis, espindilodiscitis).

There is current evidence that most reports of human infections attributed to S. putrefaciens have been caused by S. algae. Conventional tests are based on the differences between the two species, in this way S. algae uses carbohydrates, grows at 42°C or in 6.5% NaCl and produces hemolysin, while S. putrefaciens grows at 4°C and produces acid from L-arabinose and maltose, which is not done by S. algae. Another differential aspect is that S. algae has an acid production from ribose, and sometimes from glucose and fructose, whereas S. putrefaciens produces acid from maltose and glucose, sucrose and, occasionally, arabinose. In addition, S. algae, unlike S. putrefaciens, shows ability to produce mucoid-like colonies and reduce nitrites.

Tests carried out in IVAMI:

  • Culture for bacteria.
  • Molecular diagnosis (PCR: Polymerase Chain Reaction), to detect Shewanella putrefaciens DNA.

Recommended sample:

  • Sample from people: Total blood extracted with EDTA (1 to 2 mL), urine (10 mL), feces, skin lesion biopsy.
  • Sample from Food Industry: food product (minimum 25 grams, in suitable protected packaging).

Conservation and shipment of the sample:

  • Refrigerated (preferred) for less than 2 days (essential for microscopic examination).
  • Frozen: more than 2 days (only for molecular diagnostic tests).

Delivery of results:

  • Cultivation for isolation: 4 business days.
  • Molecular diagnosis (PCR): 24 to 48 hours.

Cost of the test:

  • Diagnosis and molecular identification of species (PCR and sequencing): Consult