Aspergillus niger is a common mold ubiquitously found worldwide in decaying organic matter. It is also found in food products and condiments such as pepper. The colonies are initially white and in two to three days black colored conidia are seen on the aerial hyphae. Human beings are regularly exposed to the spores of Aspergillus niger when working with decaying organic matter like soil, plants or moldy hay. In this way it gains direct entry into the lungs but can also be inoculated into wounds both in natural as well as healthcare settings. Reports of injection abscesses occurring due to molds are not uncommon in developing countries.
Diseases caused by Aspergillus niger
It is the most common fungus which causes otitis externa. The predisposing factors for otomycosis are as follows:
Superficial infections: It is the most common fungus which causes otitis externa. The predisposing factors for otomycosis are as follows:
chronic infections of the ear
use of oils, ear-drops
evidence of fungal infections elsewhere in the body like nail infections.
Wetness predisposes to the fungal infection. Treatment involves removal of the debris from the external auditory canal. Careful drying and cleaning of the external auditory canal is done by suction evacuation. Syringing should be avoided as it is likely to spread the infection further. Topical antifungal agents such as nystatin and immidazole groups of agents can be used for complete cure of otitis externa. Econazole nitrate is a broad spectrum antifungal agent which has high quality action against A.niger. Powder preparations are preferred to ear drops for treatment of otitis externa due to the fact that they coat the entire external auditory canal and also have much higher concentration in the local area of infection. Ear drops are likely to produce humidity and cause localized irritation and inflammation. The treatment must be continued for a minimum of three weeks due to the fact that fungal spores in the deeper layers of the skin take longer to be eradicated. Similarly, nail infections also need to be treated for 3 to 6 months contingent on the site of involvement.
Invasive infections: Aspergillus niger is considered to be a fungus of low virulence and, until recently, was not frequently implicated in invasive diseases. The advent of organ transplants and immunosuppressive therapy has shown that Aspergillus niger has the ability to initiate invasive disease in this group of patients. Aspergillus niger spores can be inhaled into the lungs where it can invade blood vessels resulting in invasive disease. Cavitatory lesions of the lungs with fungal balls called aspergillomas are classically seen in immunocompromised patients such as renal transplants. Some strains of A.niger produce oxalic acid as a metabolic by-product of fermentation. These acids can combine with calcium ions at physiological pH and get deposited in various tissues. This disease can present as acute renal failure with hyperoxaluria and lung lesions which eventually can be fatal.
Mycotoxicosis is caused by the ingestion of certain preformed substances produced by the molds on particular foods. Consumption of such foods contaminated with mycotoxins may lead to fatal consequences. Ochratoxins are produced by A.niger which grows on cereals, coffee-beans or bread. Ochratoxins have proven to be not only nephrotoxic but also teratogenic, carcinogenic and immunosuppressive in experimental animal studies. It produces a fatal renal disease called endemic nephropathy in the rural population of Croatia, Bosnia & Herzegovina, Yugoslavia, Bulgaria and Romania. This is also known as Balkan endemic nephropathy (BEN). Mycotoxic porcine nephropathy (MPN) is a major disease caused by Ochratoxin A in Denmark and USA. This entity has been linked to urinary tract tumors. The International Agency for Research on Cancer (IARC) has therefore classified Ochratoxin A as a compound possibly carcinogenic to humans.
Allergic disorders: Aspergillus niger has been known to cause allergic diseases in immunocompromised people. Such diseases include Farmer’s lung and Allergic Bronchopulmonary Aspergillosis (ABPA). These allergic conditions are due to sensitization of individuals upon exposure to the inhaled spores. Repeated exposure after sensitization induces asthmatic attacks and leads to severe disability.
Role of Aspergillus niger in healthcare environment:
In the age of transplants and iatrogenically induced immunocompromised status, fungi of low virulence such as A. niger have become important opportunistic pathogens. To prevent hospital acquired fungal spore infections, immunocompromised patients such as those on chemotherapy are placed in positive pressure rooms. Such rooms do not allow the outside air to contaminate the room air as the pressure inside is lower than that of the corridor. The Centers for Disease Control and Prevention has also advocated the use of High Efficiency Particulate Air Filters (HEPA) for the filtration of air in such isolation rooms or wards utilized for immunocompromised patients. These filters have a filtration capacity for particles from 0.02μm to an efficiency of 99.99%.
Environmental surveillance of such rooms must be done at regular intervals to know if the engineering controls are functioning well. Air samples must be free from any fungal growth. Growth of even a single colony forming unit (CFU) of the fungus is considered to be a failure of the air filtering unit. This necessitates attention towards the cleaning and maintenance of the HEPA filters used in these areas.
Biocides with antifungal properties
Biocides are chemical disinfectants used to kill molds.
Alcohols: 70% alcohols are effective fungicidal agents but are rendered inactive in presence of organic matter and are also highly inflammable.
Phenols: Phenols in the concentration of 0.4% to 0.5% are good fungicidal agents but have irritant and corrosive effects.
Quaternary Ammonium compounds and iodophors are also effective agents but like alcohols become inactivated in presence of organic matter.
Hypochlorite: 1% available chlorine is known to rapidly inactivate A.niger present on environmental surfaces. But the disadvantages of hypochlorite are that it is not only toxic and corrosive to the surface but also is rendered inactive in presence of organic matter.
Aldehydes: 2% Gluteraldehyde is a commonly used high level disinfectant for destruction of not only fungi but also M.tuberculosis and other viruses and bacteria. It is an excellent disinfectant but is known produce toxic fumes that irritate the mucosae and is also carcinogenic in the long run.
Hydrogen peroxide is also a high level disinfectant used in 3% or more concentration used for the destruction of fungal molds in the environment.