This is an evaluation of dermatophyte microorganisms, which have particular relevance in podiatry.
The basic cell structure of fungi is common to all types. They consist of the nucleus and chromosomes contained in the nuclear membrane, ribosomes and mitochondria, the whole surrounded by the cell membrane and wall. The cells have no flagella and are thus non motile. Unlike bacteria and protozoa, fungi are plant cells, however they do not photosynthesise. Fungal cells have the ability to produce extra cellular enzymes, these break down lipids, proteins and polysaccharides causing skin damage. Dermatophytes generally are able to produce keratinase to metabolise keratin as a food source, as in onychomycosis. The cell wall does not contain peptidoglycan, so although it will react to Gram stain this will give no information about the structure. The structure of the cell membrane is basically the same as a bacterium or a human cell, so causing difficulties in the development of treatments. However the sterol lipids in fungal cells and human cells differ and it is this difference that is used in many anti fungal treatments. Another possible target is the cell wall, as human cells do not have one.
Reproduction is of two main types; yeasts reproduce by budding a new cell from an existing cell. Moulds produce hairlike chains of cells called hyphae, these mat together to form the mycelium. They have the ability to form a new mycelium from a single piece of hyphae, so fragments shed with skin easily cause new infections. Additionally, moulds and some yeasts can produce fungal spores. These are more resistant than hyphae, especially to dry conditions. Asexual spores produced from one parent are present in larger numbers in the atmosphere, more so than sexual spores which require genetic input from two parents.
Infection spreads horizontally, where one person infects many contemporaries in the same population. Fit, healthy skin with normal levels of natural flora and normal ph is much more resistant to infection, and will require a much higher level of exposure to the infecting organism. Human skin is normally too dry for fungi to flourish, so it is important to prevent excess sweating. It should be noted that antibiotics can affect levels of skin flora causing an increased susceptibility.
Symptoms of fungal infections of the skin include intense itching of the infected area, maceration of skin tissue and cracking of the epidermis with associated pain. In later stages there may be vesiculation and desquamation of the epidermal cells leaving the area very sore and tender.
Fungal nail infections (onychomycosis) are able to proliferate in the nail bed and nail plate. An infected nail plate becomes thickened and brittle, it has a yellowish brown appearance and a distinctive odour As the infection progresses the nail becomes onycholytic as debris builds up underneath, white marks may also appear indicating Assuring of the nail. Treatment with systemic antifungals should continue until the new nail plate has formed which may take many months.
A suspected fungal infection can be confirmed by microscopy, when spores or hyphae can be identified in skin or nail samples. It is important that no fibres are introduced whilst collecting the sample (cotton wool strands duplicate fungal hyphae under microscopic examination), as this will make the hyphae more difficult to determine. There are also commercially available culture trays, which will give results in 24 hours, for yeasts and 2 to 5 days for dermatophytes.
Treatment is usually by topical anti fungal creams like Clotrimazole (Canesten) or Terbinafine (Lamasil), which work well on skin, many of these can be bought over the counter. These preparations belong to the Imidazole group and are fungicidal, rupturing the cell membrane and killing the cell; they are not generally well absorbed as a systemic treatment. The choice of product is not by anti fungal activity but, rather infection site, solubility, toxicology etc., so it is important to know the medication properties before use. Anti fungal dusting powders are of limited use in treatment, but may be useful in helping to prevent re-infection. Deep infections especially nail infections will require systemic treatments such as Grisovin (Griseofluvin) or Nizoral (Ketoconazole), which target the nail bed and act on the membranes of fungal cells to prevent active growth. The active ingredient of Nizoral is Ketoconazole which is an imidazole that is better absorbed than others, however it has been associated with liver damage. Griseofulvin, the active ingredient if Grisovin is generally well tolerated and can be used for children. These are prescription only medicines and cannot be supplied by the podiatrist, so the patient should be referred to their GP.
Each case should be judged individually and treated accordingly, a good treatment plan should effect a fairly rapid recovery. Patient compliance is important as the treatment needs to be consistent, so the podiatrist must be sure the patient (or carer) fully understands the regime. In addition to the medicaments already mentioned, there are other steps which will expedite recovery and, or prevent reinfection and cross-infection. A good standard of hygiene, regular washing of the feet and hosiery is essential. Good skin quality is of importance, the skin needs to be kept dry and wearing sandals without socks where possible is beneficial. Shoe sprays should be used to kill the infection in footwear, and suitable footwear such as Flip Flops should be worn in public areas to prevent cross-infection. It should also be stressed that the patient should never wear another person's shoes and vice versa.
It is important to continue with the treatment even after the symptoms have disappeared, as re-infection is likely. Fungal organisms are destroyed at relatively low temperatures, typically 60 degrees centigrade. A normal wash cycle would therefore eliminate these in hosiery, however fungal spores may survive several washes before being completely eliminated.
The podiatrist should always be aware of the possible presence of fungal infections and employ aseptic techniques at all times. Although fungi are classified as non motile their construction gives them the ability to travel on air currents and thus land anywhere. This should be considered when such infections are being treated, especially with regard to the post treatment cleaning process.
With this information on fungi, the diagnosis and treatment of fungal infections, and prevention of re-infection, and cross infection, the podiatrist should be more aware of the organisms involved and be able to develop a good standard operating procedure as well as effective treatments.
Malcolm Holmes MInstchp BSC (Pod Med) DCHM LCh
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|Title Annotation:||TECHNICAL ARTICLE|
|Date:||Mar 1, 2014|
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