ERYSIPELOTHRIX RHUSIOPATHIAE: CHARACTERISTICS, MORPHOLOGY - BIOLOGY - 2025

Erysipelothrix rhusiopathiae is a bacterium that causes a zoonotic disease called erysipelas of animals. It especially affects turkeys and pigs, as well as birds, cattle, horses, sheep, fish, shellfish, dogs, mice, and reptiles.

In pigs the disease is known by various names, among which are porcine erysipelas, bad red, or diamond skin disease, while in birds it is called avian erysipelas.

Symptoms of Erysipelothrix rhusiopathiae infection

Although rare, it can also attack humans, causing a pathology known as eripeloid or Rosenbach's erysipeloid, especially in people with jobs related to animals, their products or waste.

The disease in humans is considered occupational, since it generally occurs in handlers of raw meat, poultry, fish or crustaceans, or in veterinarians.

This bacterium is widely distributed in nature worldwide. It has been isolated from soil, food and water, presumably contaminated with infected animals.

The domestic pig is the natural reservoir of this microorganism, isolating itself from the gastrointestinal tract of healthy pigs. The bacteria lodges in these animals specifically at the level of the tonsils and the ileocecal valve.

characteristics

Biochemistry

Erysipelothrix rhusiopathiae is a facultative or microaerophilic aerobic microorganism that grows best at 30-35 ° C with 5-10% CO ₂.

It is immobile and is characterized by being the only aerobic Gram-positive, catalase-negative bacillus that produces hydrogen sulfide (H ₂ S) in Kliger medium (KIA) or triple sugar iron agar (TSI).

They grow on blood agar supplemented with glucose. They are characterized by irregularly fermenting carbohydrates and not hydrolyzing esculin.

In gelatin agar plugs and seeded by puncture, it grows with a characteristic brush pattern.

Survival

The bacterium is able to survive in the soil for long periods outside the animal organism. Nor does it die from the salty, smoked or pickled used to preserve different types of meat.

Virulence factors

Erysipelothrix rhusiopathiae is known to produce hyaluronidase and neuraminidase, but their role in the pathogenesis of the disease is unknown.

This microorganism has the peculiarity of multiplying intracellularly within macrophages and polymorphonuclear leukocytes. This is considered a virulence factor, as it is capable of resisting the action of peroxidases and phospholipases generated in these cells due to the production of antioxidant enzymes.

Due to this last characteristic, the sample to be cultured must be a biopsy fragment of the affected tissue.

This microorganism also has a capsule that is heat labile, which is also an important virulence factor.

Taxonomy

Domain: Bacteria

Phylum: Firmicutes

Class: Erysipelotrichia

Order: Erysipelotrichales

Family: Erysipelotrichaceae

Genus: Erysipelotrix

Species: rhusiopathiae

Morphology

The morphology can be coccobacillary or Gram positive diphtheroid. In the primary culture on blood agar, two types of colonies can be observed, resembling a polymicrobial infection.

The colonies that appear are smooth and others rough. In their smooth form, the colonies are tiny (0.5 to 1mm in diameter), convex, circular and translucent.

At Gram, there are short thin rods (0.2-0.4 µm by 1.0 to 2.5 µm), straight or slightly curved, not forming Gram-positive spores distributed in small chains.

In its rough form the colonies are larger, with a matte surface with scalloped edges. At the Gram, they are observed as thin Gram-positive rods similar to long filaments of 4-15 µm in length, with a tendency to over-discoloration.

Over discoloration causes some bacilli to appear Gram negative.

After a prolonged incubation, the bacteria may develop a greenish area around the colonies on the blood agar (slight alpha hemolysis) if the blood is horse. But in other blood types it does not produce hemolysis.

Transmission

Contamination can occur through contact with the endogenous cycle, which is represented by the feces and saliva of healthy animals that carry the bacteria and in a larger number of sick animals.

Also through contamination with the exogenous cycle represented by the soils that constantly receive fecal matter with the microorganism.

Man is accidentally infected through skin abrasions, scratches, or punctures in direct contact with contaminated fish, shellfish, meat, or poultry or contaminated soil.

The contagion between animals occurs through oral, nasal or venereal secretion and even percutaneously, but also indirectly through the ingestion of contaminated water and food.

Pathology

Erysipeloid disease in humans is generally limited to the skin. The type of injury is cellulite that occurs on the hands or fingers.

There is pain, edema, and purplish erythema with sharp edges extending to the periphery, with a clear center. There is usually no fever.

Relapses may occur and the extension of lesions to distant areas is common.

In extremely rare cases the lesion becomes invasive and complications such as septicemia with arthritis and endocarditis can occur.

Diagnosis

The diagnosis is based on the isolation of the organism in skin biopsy cultures. For this, the area must be well disinfected with alcohol and povidone iodine before taking the biopsy.

The sample should be taken covering the entire thickness of the infected skin taken from the edge of the lesion in progress.

The sample is incubated in brain heart infusion broth supplemented with 1% glucose for 24 hours at 35 ° C in microaerophilicity and then it must be reseeded on blood agar.

In the event of suspected septicemia or endocarditis, blood samples will be taken for blood culture.

Special considerations

Because this disease is rare in humans, it is often misdiagnosed. It can be confused with erysipelas, but it is caused by Streptococcus pyogenes.

That is why the patient's medical history guides a lot in the diagnosis, because if the patient indicates that he works with pigs or is a fishmonger, butcher or veterinarian, it is possible to quickly associate the type of injury with this microorganism.

In addition to a history of hand injuries that may have served as a gateway for the microorganism.

Prevention

The disease does not generate permanent immunity. In animals it can be prevented through safe rearing with sanitation of the herd.

Treatment

The treatment of choice is penicillin G, other beta-lactams are also effective, such as ampicillin, methicillin, nafcillin and cephalothin, piperacillin, cefotaxime and imipenem.

Other antimicrobials that have been helpful include ciprofloxacin, pefloxacin, and clindamycin.

They are generally resistant to vancomycin, teicoplanin, trimethoprim-sulfamethoxazole, and various aminoglycosides. While they present variable sensitivity to erythromycin, chloramphenicol and tetracycline.

These data are especially important because septicemia and endocarditis are most often approached empirically initially with vancomycin alone or associated with an aminoglycoside while the culture and antibiogram results arrive.

In this case, this treatment is not effective, so once again the medical history plays a very important role in order to suspect the presence of this bacterium.

References

1. Schell C, De Luca M. Erysipelothrix rhusiopathiae An underdiagnosed occupational pathogen in Argentina? Chair of Microbiology and Parasitology of Medical Sciences UNLP, 2014; 1-8. Available at: ResearchGate
2. Finegold S, Baron E. (1986). Bailey Scott Microbiological Diagnosis. (7 ^ma ed) Argentina Editorial Panamericana.
3. Jawetz E, Melnick J, Adelberg E. (1992). Medical Microbiology. (14th Edition) Mexico, Editorial El Manual Moderno.
4. Koneman E, Allen S, Janda W, Schreckenberger P, Winn W. (2004). Microbiological Diagnosis. (5th ed.). Argentina, Editorial Panamericana SA
5. Wang Q, Chang BJ, Riley TV. Erysipelothrix rhusiopathiae. Vet Microbiol. 2010; 140 (3-4): 405-417. Available in: Pub Med.
6. Principe L, Bracco S, Mauri C, Tonolo S, Pini B, Luzzaro F. Erysipelothrix rhusiopathiae bacteremia without endocarditis: Rapid identification from positive blood culture by MALDI-TOF mass spectrometry. A case report and literature review. Infect Dis Rep. 2016; 21 8 (1): 6368.