Fundamental Medical Mycology

Errol Reiss, H. Jean Shadomy, G. Marshall Lyon

• Publisher: Wiley-Blackwell
• Year: 2011
• ISBN:
  9781118101766
• Edition: 1
• Topic: Ciencias biológicas
• Subtopic: Microbiología

Medical mycology deals with those infections in humans, and animals resulting from pathogenic fungi. As a separate discipline, the concepts, methods, diagnosis, and treatment of fungal diseases of humans are specific. Incorporating the very latest information concerning this area of vital interest to research and clinical microbiologists, Fundamental Medical Mycology balances clinical and laboratory knowledge to provide clinical laboratory scientists, medical students, interns, residents, and fellows with in-depth coverage of each fungal disease and its etiologic agents from both the laboratory and clinical perspective. Richly illustrated throughout, the book includes numerous case presentations.

Part I

Introduction to Fundamental Medical Mycology, Laboratory Diagnostic Methods, and Antifungal Therapy

Chapter 1

Introduction to Fundamental Medical Mycology

1.1 Topics not Covered, or Receiving Secondary Emphasis

The Table of Contents is explicit but it is well to advise readers that some topics are either outside the scope of Fundamental Medical Mycology or receive secondary emphasis. Although caused by, or associated with, fungi it is not within the scope of this work to discuss mushroom poisoning (ingestion of toxins present in mushrooms), mycotoxicosis (ingestion of a fungal toxin), or allergies, except when encountered as a complication of one of the fungal diseases discussed.

• More information on mushroom poisoning (mycetismus) can be found in Benjamin (1995).
• Allergies caused by fungi are discussed in Kurup and Fink (1993) and Breitenbach et al. (2002). The health effects of exposure to molds, apart from infection, may be found in Storey et al. (2005) and U.S. Environmental Protection Agency publication 402K-01-001 (2001).
• Environmental mycology is discussed as it relates to the ecologic niche of the causative agents of mycoses.
• Veterinary medical mycology is covered in a concise section, “Veterinary Forms,” in each disease-specific chapter.

1.2 Biosafety Considerations: Before You Begin Work with Pathogenic Fungi...

Safety in the laboratory is of prime importance. Clinical laboratory supervisors and principal investigators have the serious responsibility to train all technologists and students in the safe manipulation of clinical specimens and pathogenic fungi. Before working with pathogenic microbes, including fungi, microbiologists should participate in their organization's safety training program, be certified to work with pathogens, and, when questions about biosafety arise, consult the supervisor and the CDC/NIH biosafety manual: Biosafety in Microbiological and Biomedical Laboratories, 5th edition (BMBL). The manual is available online at the URL http://www.cdc.gov/biosafety/publications/bmbl5/index.htm. This will ensure a safe work environment where the workers will not be afraid to work with fungi but instead will have confidence that they are observing prudent precautions.

Molds growing on Petri plates can produce far more infectious propagules (conidia or spores) than an environmental exposure! Therefore, mold cultures should be transferred to screw cap- or cotton-stoppered agar slants. Mold cultures on Petri plates should never be opened on the open laboratory bench. All cultures of unknown molds should be handled inside a biological safety cabinet (BSC). Petri plates should be sealed with shrink seals, which are colorless transparent cellulose bands. “Occupational Hazards from Deep Mycoses” is a useful and cautionary article summarizing laboratory infections (Schwarz and Kauffman, 1977; Padhye et al., 1998).

The BMBL should also be consulted for further information about selection of BSCs, and biosafety considerations of work with pathogenic fungi. If further questions arise on matters of fungal biosafety, please contact the State Department of Health in the United States of America or the CDC Mycotic Diseases Branch, which is the World Health Organization Center for Mycoses.

1.2.1 Biological Safety Cabinets (BSC)

What are the characteristics of Class II Biological Safety Cabinets? The Class II BSC is designed with inward airflow velocity (75–100 linear feet/min) and is fitted with high efficiency particulate air (HEPA) filters. This design ensures that the workspace in the cabinet receives filtered, downward, vertical laminar airflow. These characteristics protect personnel and the microbiologic work conducted in the BSC.

HEPA-filtered-exhaust air ensures protection of the laboratory and the outside environment. All Class II cabinets are designed for work involving microorganisms assigned to biosafety levels 1, 2, and 3.1. Fungi pathogenic for humans are classed in biosafety level 2 and work with them should be conducted in the BSC, and not on the open bench. Certain manipulations of fungal pathogens or environmental samples require biosafety level 3 (please see below).

Class II BSCs provide a microbe-free work environment. Class II BSCs are classified into two types (A and B) based on construction, airflow, and exhaust systems. Type A cabinets are suitable for microbiologic work in the absence of volatile or toxic chemicals and radionuclides, since air is recirculated within the cabinet. Type A cabinets may be exhausted into the laboratory or to the outdoors via a special connection to the building exhaust system. Type B cabinets are hard-ducted to the building exhaust system and contain negative pressure plenums to allow work to be done with toxic chemicals or radionuclides. A list of products that meet the standards for Class II BSCs are available from the National Sanitation Foundation International, Ann Arbor, Michigan. It is mission-critical that BSCs be tested and certified in situ at the time of installation, at any time the BSC is moved, and at least annually after that.

1.2.2 Precautions to Take in Handling Etiologic Agents that Cause Systemic Mycoses

The major known reasons for laboratory exposures to pathogenic fungi are dropped cultures, preparing soil suspensions and inoculating animals, opening Petri plates, and aerosols from needles and syringes (Padhye et al., 1998). The portals of entry for the fungi, resulting from the above exposures, are minor skin wounds or the inhalation of fungal conidia.

Pathologists and veterinarians should be mindful that autopsies and necropsies have caused accidental hand wounds, which have become infected. These infections are localized to the wound and have not disseminated. Needle stick injuries have also been the source of laboratory infections, and they too have remained localized. Localized infections require systemic antifungal therapy.

Laboratory exposures to aerosolized conidia (spores) have led to pulmonary infections and, in the case of Coccidioides species, to serious or even fatal infections. Some cases of coccidioidomycosis have occurred in laboratories beyond the endemic area and resulted when the laboratory did not suspect the mold they had isolated was Coccidioides.

Biosafety level 2 (BSL 2) practices, containment equipment, and facilities are recommended for handling and processing clinical specimens, identifying isolates, and processing animal tissues suspected of containing pathogenic fungi. BSL 2 is also sufficient for mold cultures identified as Blastomyces dermatitidis, Cryptococcus neoformans, dermatophytes, Penicillium marneffei, and Sporothrix schenckii. In addition to these agents, certain melanized molds have caused serious infection in immunocompetent hosts following inhalation or accidental penetrating injuries: Bipolaris species, Cladophialophora bantiana, Wangiella (Exophiala) dermatitidis, Exserohilum species, Fonsecaea pedrosoi, Ochroconis gallopava, Ramichloridium mackenziei, and Scedosporium prolificans.

All manipulations of clinical specimens and culture work are performed inside an annually inspected and certified, well-functioning, laminar flow biological safety cabinet (BSC), equipped with HEPA filtered exhaust. Workers should wear personal protective equipment (PPE).

• Clothing: laboratory coats with fronts fastened and shoes with closed fronts.
• Eye protection: safety glasses, goggles, as recommended by the supervisor.
• Gloves: latex or plastic.
• Respiratory protection: goggles, mask, face shield, or other splatter guards are used when the cultures must be handled outside the BSC. Surgical masks are not respirators and do not provide protection against aerosolized infectious agents. The N95 disposable respirator provides a level of protection. Supervisors should consult the National Institute of Occupational Safety and Health (NIOSH) Publication No. 99–143: TB Respiratory Protection Program in Health Car...