''Metarhizium granulomatis'' is a fungus in the family Clavicipitaceae associated with systemic mycosis in veiled

chameleon Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. The members of this family are best known for their distinct range of colors, bein ...

s. The genus '' Metarhizium'' is known to infect

arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

, and collectively are referred to green-spored asexual pathogenic fungi. This species grows near the roots of plants and has been reported as an agent of disease in captive

veiled chameleon The veiled chameleon (''Chamaeleo calyptratus'') is a species of chameleon (family Chamaeleonidae) native to the Arabian Peninsula in Yemen and Saudi Arabia. Other common names include cone-head chameleon and Yemen chameleon. They are born pas ...

s. The etymology of the species epithet, "granulomatis" refers to the ability of the fungus to cause

granuloma A granuloma is an aggregation of macrophages that forms in response to chronic inflammation. This occurs when the immune system attempts to isolate foreign substances that it is otherwise unable to eliminate. Such substances include infectious ...

tous disease in susceptible reptiles.

History and taxonomy

Originally named ''Chameleomyces granulomatis'', ''M. granulomatis'' resembles ''Paecilomyces viridis''. Because of the polyphyletic nature of the genus '' Paecilomyces'' Sigler and co-workers decided this species was better accommodated in a new genus in the family Clavicipitaceae. The first documented case of ''M. granulomatis'' was seen in the Copenhagen Zoo, showing morphology similar to ''

Metarhizium viride ''Metarhizium'' is a genus of entomopathogenic fungi in the Clavicipitaceae family. With the advent of genetic profiling, placing these fungi in proper taxa has now become possible. Most turn out to be the asexual forms (anamorphs) of fungi in ...

'' (previously called ''P. viridis''). This fungus causes fatal disseminated mycosis in veiled chameleons ('' Chamaeleo calyptratus''). Small subunit

18S rDNA 18S ribosomal RNA (abbreviated 18S rRNA) is a part of the ribosomal RNA. The S in 18S represents Svedberg units. 18S rRNA is an SSU rRNA, a component of the eukaryotic ribosomal small subunit ( 40S). 18S rRNA is the structural RNA for the small ...

(SSU), nuclear ribosomal

internal transcribed spacer Internal transcribed spacer (ITS) is the spacer DNA situated between the small-subunit ribosomal RNA (rRNA) and large-subunit rRNA genes in the chromosome or the corresponding transcribed region in the polycistronic rRNA precursor transcript. I ...

(ITS) ITS1-5.8S-ITS2, and domains D2 and D2 of the large subunit

28S rDNA 28S ribosomal RNA is the structural ribosomal RNA (rRNA) for the LSU rRNA, large subunit (LSU) of eukaryotic cytoplasmic ribosomes, and thus one of the basic components of all eukaryotic cells. It has a size of 25S in plants and 28S in mammals, ...

(LSU) were used to demarcate the fungal species ''M. granulomatis'' and differentiate it from closely related species, particularly ''M. viride''.

Growth and morphology

Colonies of ''M. granulomatis'' differ in morphology depending on the growth medium used. Colonies on

Potato dextrose agar Potato dextrose agar (BAM Media M127
from the U.S.

(PDA) after 3 days incubation at are white in colour and reach 3 mm in diameter. Cultures developed on

Sabouraud dextrose agar Sabouraud agar or Sabouraud dextrose agar (SDA) is a type of agar growth medium containing peptones. It is used to cultivate dermatophytes and other types of fungi, and can also grow filamentous bacteria such as '' Nocardia''. It has utility ...

(SDA) are similar in appearance although they grow more slowly on this medium. After 10 days, colonies on PDA reached a diameter of 27 mm and produced a diffusible brownish-grey pigment. Colonies the SDA are 12 mm in diameter and grey-ochre in colour. The hyphae of ''M. granulomatis'' are

septate In biology, a septum (Latin for ''something that encloses''; plural septa) is a wall, dividing a cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Human anatomy * Interatri ...

and bear phialides that have single apical openings (monophialides) resembling a wine bottle. The

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

produced are in short, curved, chains, appearing glassy and smooth. Conidia are spherical-to-oval and 3.3-3.8 μm in length by 1.2-1.6 μm in width. The fungus produces a yeast-like stage in vitro on PDA after 3 days incubation at 35°C.

Pathogenicity

''Metarhizium granulomatis'' is a rare fatal disease that infects veiled chameleons. Similar symptoms of disease are seen in ''M. viride''. Common clinical signs seen in the veiled chameleons for this fungal disease are anorexia, hemorrhages in the tongue, necrotic toes, and ulcerative skin lesions. When observing the organs commonly infected, including the visceral organs,

s, glossitis,

pharyngitis Pharyngitis is inflammation of the back of the throat, known as the pharynx. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, difficulty swallowing, swollen lymph nodes, and a hoarse voice ...

are seen. After death, cultures from the veiled lizard can be taken from the tongue, liver, lung, heart, kidney, small and large intestines. 1 to 3 mm spherical yeast-like yellow-to-white nodules are visible in the lung, liver and kidney.

Antifungal treatment

Treatment with nystatin and/or

terbinafine Terbinafine, sold under the brand name Lamisil among others, is an antifungal medication used to treat pityriasis versicolor, fungal nail infections, and ringworm including jock itch and athlete's foot. It is either taken by mouth or applied to ...

may prevent further spreading or infection. When isolated most isolates susceptible to terbinafine,

clotrimazole Clotrimazole, sold under the brand name Lotrimin, among others, is an antifungal medication. It is used to treat vaginal yeast infections, oral thrush, diaper rash, tinea versicolor, and types of ringworm including athlete's foot and jock itch ...

amphotericin B Amphotericin B is an antifungal medication used for serious fungal infections and leishmaniasis. The fungal infections it is used to treat include mucormycosis, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, and cryptococcosis. Fo ...

voriconazole Voriconazole, sold under the brand name Vfend among others, is an antifungal medication used to treat a number of fungal infections. This includes aspergillosis, candidiasis, coccidioidomycosis, histoplasmosis, penicilliosis, and infections by '' ...

and

posaconazole Posaconazole, sold under the brand name Noxafil among others, is a triazole antifungal medication. It was approved for medical use in the United States in September 2006, and is available as a generic medication. Medical uses Posaconazole is u ...

. Although ''M. granulomatis'' is also resistant to some of the antifungals previously mentioned such as amphotericin B, voriconazole,

fluconazole Fluconazole is an antifungal medication used for a number of fungal infections. This includes candidiasis, blastomycosis, coccidiodomycosis, cryptococcosis, histoplasmosis, dermatophytosis, and pityriasis versicolor. It is also used to prevent ...

, and itraconazole.

References

{{Taxonbar , from = Q56884458 Clavicipitaceae Fungi described in 2014