CORYNEBACTERIUM PSEUDOTUBERCULOSIS: CHARACTERISTICS, MORPHOLOGY - BIOLOGY - 2025

Corynebacterium pseudotuberculosis is a bacterium of the order Actinomycetales. It is a bacillus that, in cultures, has the shape of a mallet or club, does not present a capsule or flagellum. It ferments maltose and galactose but not lactose.

C. pseudotuberculosis is a facultative intracellular bacterium, which multiplies within the macrophages of its host. It can cause a number of diseases, including caseous lymphadenitis (CLA) and ulcerative lymphangitis in animals such as goats, deer, horses, cattle, or camels. It can also affect humans.

Caseous lymphadenitis in sheep. Source: commons.wikimedia.org

General characteristics

The bacterium Corynebacterium pseudotuberculosis is an intracellular pathogen, Gram positive, facultative anaerobic, does not form spores. It reaches its optimum development at 37 ºC in media with neutral pH (between 7.0 and 7.2).

It produces catalase, phospholipase D and urease. It ferments maltose, mannose, glucose and galactose. It does not ferment lactose. It is oxidase negative.

It does not present proteolytic activity, nor does it hydrolyze gelatin. It also does not digest casein. It has a pyogenic lipid layer, but not an immunogenic one. This layer makes it difficult for the bacteria to be phagocytosed, thus increasing their virulence and their ability to survive within macrophages.

Morphology

Organisms of this species are pleomorphic (that is, they occur in various distinct forms). They can be coconut-shaped to filamentous rod-shaped.

They are generally elongated, measuring 0.5-0.6 µm in width and 1.0-3.0 µm in length. They do not have capsules or flagella, but they do have fimbriae and generally contain metachromatic granules.

Its cell wall has meso-diaminopimelic, arabinogalactan and chorinomycolic acids. They also have arabinose and galactose (sugars) and short chains of mycolic acid.

Taxonomy

The species C. pseudotuberculosis was first described in 1888 by Edmound Nocard, a French veterinarian. The description was based on material isolated from cattle with lymphangitis.

In 1891, the Hungarian bacteriologist Hugo von Preisz isolated a similar bacterium affecting sheep. Due to both findings, the bacterium was baptized with the bacillus name "Preisz-Nocard".

The genus Corynebacterium is taxonomically located in the suborder Corynebacterineae (Actinobacteria: Actinobacteridae: Actinomycetales). This suborder includes the families Corynebacteriaceae, Mycobacteriaceae, and Nocardiaceae, which are commonly referred to as the CMN group.

The bacteria of the CMN group have a cell wall composed mainly of peptidoglycans, arabinogalactan and mycolic acids. Another characteristic of the members of this group is that they present a proportion of guanine and cytosine that can exceed 70% of the total number of nitrogenous bases.

The CMN group includes many species of medical and veterinary importance, including C. pseudotuberculosis, responsible for pseudotuberculosis or caseous lymphadenitis (CLA) in goats and sheep and nosocomial infections in humans.

Culture

Corynebacterium pseudotuberculosis grows well in enriched media such as blood agar, Brain Heart Infusion (BHI) medium, and in animal serum-enriched media.

Cultures in BHI media enriched with yeast extract, tryptose or lactalbumin improve the growth of the bacteria. Polysorbate 80 has also been used to enrich the culture media.

In a solid culture medium, the initial growth is poor, then it increases and the bacteria organize in groups. The colonies are dry, opaque and concentric.

Growth in liquid media occurs as a biofilm on the surface of the medium. This biofilm is due to the presence and quantity of lipids in the cell membrane.

There is better bacterial growth in the presence of CO2 in the atmosphere, at a concentration of 5%. Cultures have recently been carried out in media composed of dibasic phosphate, vitamins and amino acids.

Pathogeny

Corynebacterium pseudotuberculosis is capable of producing several virulence factors, however, chorynomycolic acids and phospholipase D toxin are primarily responsible for its disease-causing potential.

These two factors contribute to the inflammatory process, the appearance of edema, and the spread during the development of abscesses.

Caseous lymphadenitis in sheep. Source: commons.wikimedia.org

The bacillus multiplies within the macrophages of the hosts. The outer lipid layer of the cell wall allows it to survive the action of phagolysosomal enzymes.

The bacteria generally enter the host through the oral, nasal, or ocular mucosa, or through skin wounds. Once inside the host, the bacillus spreads freely or within macrophages.

The main route of spread is the afferent lymphatic system. From there, it spreads to local lymph nodes and internal organs.

The infectious process of the bacterium depends on its ability to infect host macrophages, resist its phagolysosomes, and kill cells and release new bacteria. Experimental infections in mice have shown that, three minutes after intraperitoneal inoculation in mice, phagocytic vacuoles appear.

In the case of experimental infections in goats, 60-80% of their macrophages contain bacteria one hour after inoculation. Two hours later, acid phosphatase is present in the vesicles containing the bacteria.

In sheep, microabscesses develop in the drainage of the lymph nodes one day after an experimental skin infection. Three to 10 days after infection, pyogranulomas form.

Effect of exotoxins

The exotoxins of the bacterium hydrolyze the lecithin and sphingomyelin present in the endothelial cell membranes of the host's blood and lymphatic vessels.

This hydrolysis causes the rupture of the cell membrane, increases vascular permeability, the appearance of edema and facilitates the colonization of the host.

One of these exotoxins, phospholipase D, also inhibits the responsiveness of neutrophils to chemical stimuli. Phospholipase D also inhibits the ability of phagocytic cells to release antimicrobial cytotoxic molecules. This favors bacterial survival and multiplication in the host.

Zoonotic potential of

Corynebacterium pseudotuberculosis causes disease mainly in sheep and goats. However, it can cause infections in a wide spectrum of hosts, including humans. Due to this, C. pseudotuberculosis is considered an emerging problem in public health.

This bacterium can produce diphtheria toxin, it can also infect humans and cause suppurative lymphadenopathy. Infections are traditionally due to contact with contaminated farm animals and milk products.

However, there are documented cases of people who have acquired diseases caused by C. pseudotuberculosis in which there has been no previous contact with contaminated animals or food.

References

1. AFC Nassar, GT Daniel, R. Ruiz, S. Miyashiro, EM Scannapieco, JS Neto, L. Gregory (2015). Diagnostic comparison of Corynebacterium pseudotuberculosis through microbiological culture and PCR in sheep samples. Archives of the Biological Institute, São Paulo.
2. AD Hawari (2008). Corynebacterium pseudotuberculosis infection (caseous lymphadenitis) in camels (Camelus dromedarius) in Jordan. American Journal of Animal and Veterinary Sciences.
3. LGC Pacheco, RR Pena, TLP Castro, FA Dorella, RC Bahia, R. Carminati, MNL Frota, SC Oliveira, R. Meyer, FSF Alves, A. Miyoshi, V. Azevedo (2007). Multiplex PCR assay for identification of Corynebacterium pseudotuberculosis from pure cultures and for rapid detection of this pathogen in clinical samples. Journal of Medical Microbiology.
4. FA Dorella, LGC Pacheco, SC Oliveira, A. Miyoshi, V. Azevedo (2006). Corynebacterium pseudotuberculosis: microbiology, biochemical properties, pathogenesis and molecular studies of virulence. Veterinary Research.
5. A. Ribeiro, FA Dorella, LGC Pacheco, N. Seyffert, TLP Castro, RWD Portela, R. Meyer, A. Miyoshi, MCR Luvizotto, V. Azevedo (2013). Subclinical diagnosis of caseous lymphadenitis based on ELISA in sheep from Brazil. Journal of Bacteriology and Parasitology.
6. AS Guimarães, FB Carmo, RB Pauletti, N. Seyffert, D. Ribeiro, AP Lage, MB Heinemann, A. Miyoshi, V. Azevedo, AM Guimarães Gouveia (2011) Caseous lymphadenitis: epidemiology, diagnosis, and control. The IIOAB Journal.