Draft of Lichtheimia corymbifera (Cohn) Vuill. for 2010/2011 EOL University Species Pages Initiative by Katie Ransohoff
Description status: Approved
(Latest review: 2010-12-18 05:36:24 NZDT (+1300) by Anne Pringle)
Lichtheimia corymbifera (which was called Absidia corymbifera until 2009, and are also known as Myocladus coryimbifer) is a saprobic zygomycete fungus, meaning it is largely a decomposer. The fact that it is a decomposer contributes to its ability to survive all around the globe in many types of habitats. L. corymbifera is mostly found in soil, underground, or in the air, and can also survive in humans and other mammals, making it one of the only infectious members of the phylum Zygomycota.
Identification of the fungus in nature is difficult. It is microscopic, but observational studies can demonstrate some of the interesting morphological feature of this interesting fungus. Hyphae, which are branched structures for fungi, contain stalks called sporangiophores, at the end of which are spore-containing structures. The spores of L. corymbifera are black in color and held inside a pear-shaped structure called a pyriform sporangia. Spores, which distribute genetic material for a new organism to grow, are distributed when this pyfirom sporangia bursts. When the spores are released, a remaining “collarette,” like a hat, may remain on the stalk that they were sitting on.
If L. corymbifera is found in nature it can be taken to the laboratory to grow in culture on agar. The cultures grow best at temperatures of 35-37 degrees Celsius.
The optimal growth temperature for L. corymbifera is in the range of 35-37 degrees Celsius, which is close to human body temperature, 37 degrees Celsius. In agar culture, L. corymbifera forms white (initially) or gray (as time passes) colonies. Colonies grow to around 3-9cm in around 7. Once mature, cultures are gray-white on top, due to the spores, and whitish underneath. Furthermore, this fungus can be grown on bread cultures. One issue with using culture for diagnostic purposes is that L. corymbifera is a common lab contaminant, which means that growth in culture is not necessarily indicative of presence in the sample.
The last place that L. coryimbifera can be found is in mammals, where it causes infections of a variety of organ systems. Since L. corymbifera grows in soil, decaying grass, or hay it is a common infectious agent in farm animals such as cows and horses, where it can cause death rather quickly if untreated. L. corymbifera can also infect people; however, most people with normal immune systems will not be infected with this fungus simply by being near it or playing in the soil. Rather, it is an “opportunistic pathogen” meaning that it can only infect (and harm) someone with a weakened immune system, from diseases such as Human Immunodeficiency Virus (HIV)/Acquired Immune Deficiency Syndrome(AIDS), diabetes, certain types of blood cancers such as leukemia or large open skin wounds such as those caused by burns. When humans are infected, treatment can be difficult. Antifungal drugs such as amphotericin B are effective, but side effects can be negative.
L. corymbifera have a very high optimal growth temperature, and are somewhat heat tolerant (can grow up to 50 degrees C) relative to other related taxa, form apophysate sporangia, and are aseptate except for a single septa formed beneath the sporangium. Rhizoids are able to form, but the occurrence is rare. Sporangia are 20-120 microns, sporangiophores are 3-4.5 microns. The sporangia themselves are small, pyriform (pear-shaped) and supported by an apopyhsis, which is funnel-shaped. Spores are darkly colored. Mucor and Rhizomucor appear similar, but can be distinguished as based off of sporangiophore location (nodal versus internodal) and aphophysis presence.
A 1999 study by Voight et al. which sequenced ribosomal DNA for all clinically significant zygomycetes reported that L corymbifera is a sister group of Rhizomucor miehei-Rhizomucor pusillus.
L. corymbifera was described in the very early 1900s in France. The fungus has been isolated worldwide, including Europe, the Middle East, North and South America, Africa, and India. It is nearly ubiquitous, in both rural and urban settings, and can thrive and survive in a variety of areas and habitats, leading to its global distribution. It has been found domestically; for example, Davies et al. found the isolate in dust in homes in Britain in 1960. In 1994, it was reported by Haselwandter and colleagues that the Ice Man, a prehistoric human discovered in the Alps, contained a sample of L. corymbifera on his shoe, suggesting an age of over 5,300.
The natural habitat for these fungi is in soil and decaying grasses, and the optimum pH is 3.0 to 8.0. One study conducted in India found that the optimum soil depth was 35-40 cm. The fungus grows very well in humid or moist environments, such as grasslands, swamps, sewage, and dung. L. corymbifera has been found globally in soil and in decaying debris, as well as in moldy breads and vegetables in domestic settings. It has been found in hay in farms, which is a contribution to its animal pathogenicity. Furthermore, the fungus has been found on cotton, grains, and straw. The fungus can even survive indoors, and was reported to have been surviving in a supply cabinet in a hospital, which led to infection of an entire Burns unit, as reported by Christiaens et al. in 2005.
The key feature that distinguishes L. corymbifera from Mucor and Rhizomucor is the presence of the apophysis, which is a funnel-like object that supports the sporangia. Additionally, L. corymbifera contain a pyriform sporangium, while Mucor, Rhizomucor, and Rhizopus do not. Mucor and Rhizopus sporangia are larger and more round/globose in shape, compared to the pear-shaped pyriform sporangia of the L. corymbifera. Furthermore, Rhizopus from sporangia at the nodes (opposite the rhizoids) while L. corymbiferaform sporangiophores at the internode between rhizoids. In culture, L. corymbifera (and all Lichtheimia) can be distinguished from Apophysomyces due to the abundant sporulation of the former. In distinguishing Lichtheimia from Apophysomyces in non-culture settings, care must be taken; While Lichtheimia form a septum below the sporangium and Apophysomyces do not, Apophysomyces have a dark band underneath the sporangium that can be mistaken for a septum.
L. corymbifera is one of the most difficult to treat human pathogens, and infection can often be fatal (mortality rate is near 100% in patients with AIDS). It is the cause of about 2-3% of human mucormycoses, which are themselves very rare, present in about 0.7% of hospital admissions. In patients with leukemia, the rate is around 1%. In general, fungal infections due to zygomycota are called zygomycoses, and these are among the most difficult to treat clinically, with significant associated morbidity and mortality. These opportunistic human fungal infections almost only occur in patients with compromised immune systems—such as those with leukemia, diabetes, HIV, or in patients with open wounds, such as those from burns or surgery. These patients are susceptible to a wide range of infections, both bacterial and fungal; L. corymbifera is particularly fatal and difficult to treat. Infections are also more likely to occur in neonates.
Before delving into human infections, it is of note that infections are also seen in other animals. In particular, farm livestock; there have been documented cases, such as one published by Piancastelli et al. in 2009, of bovine abortion in which the aborted fetus was infected with the fungus. In this case, blood samples from the mother and fetus were tested. Doing PCR with fungal specific primers, the infection source was confirmed. Furthermore, the appearance on hyphae without septa and sporangia confirmed the fungal identity.
When infection occurs, the fungus invades the walls of blood vessels, which leads to death of nearby tissues and/or formation of large emboli (blood clots). Symptoms appear in a variety of organ systems. The sinus/craniofacial area can be affected, beginning with facial pain, impairment of muscles or nerves in the eye area, and often progressing to clots in arteries that feed brain tissue. If the lungs are infected, fever and cough can appear, but diagnosis is more difficult, since x-ray can be inconclusive in distinguishing from other infections. When the abdomen is infected, the appearance can be identical with the presentation of an abscess, so diagnosis is often made only at death.
When the fungus enters the skin at the site of a burn or wound, tissue death can be severe as the fungus invades deeper layers of skin. One of the only treatment options is complete sterilization of the wound along with antifungal drug administration, which can often lead to more opportunistic infections and is painful. Diagnosis can be made from a histological sample of the infected tissue; there is often not enough time to wait for growth in culture to confirm diagnosis, since early treatment is key.
The only present treatment is an antifungal drug called amphotericin B deoxycholate (Fungizone is the drug name). This drug binds to ergosterol (but also to other sterols) in the membrane of the fungal cells, which causes leakage of ions and sugars, and then death. It is not a targeted agent, rather it is a potent generic antifungal. Amphotericin can cause side effects ranging from relatively mild, such as chills and myalgia (muscle pain) to more severe forms of nephrotoxicity. Posaconazole, Itraconazole and Voriconazole are also effective, though azoles are generally less effective than amphotericin B, and require higher dosages for therapeutic efficacy, as demonstrated by Almyroudis et al. in 2007.
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Description author: Katie Ransohoff (Request Authorship Credit)
Created: 2010-11-27 10:41:23 NZDT (+1300) by Katie Ransohoff (kjransohoff)
Last modified: 2010-12-01 07:19:04 NZDT (+1300) by Katie Ransohoff (kjransohoff)
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