Infections Caused by Fungi

Chapter 9 This chapter discusses the relationship between humans and microorganisms, focusing on the role of microorganisms in causing infections. It explores different types of infections caused by bacteria, viruses, fungi, and parasites, as well as the challenges of antibiotic resistance. The chapter highlights the importance of vaccines and immunotherapy in protecting against infections. Fungal Morphology Fungi can exist in mold or yeast forms, and some are dimorphic Infections Caused by Fungi Infections caused by fungi are called mycoses Mycoses can be superficial, deep, or opportunistic Superficial mycoses occur on or near the skin or mucous membranes Dermatophytes are fungi that invade the skin, hair, or nails, causing tineas (ringworm) Fungal diseases are controlled by phagocytes and T lymphocytes, and low white blood cell counts can promote fungal infection Common Pathogenic Fungi Common pathogenic fungi include Malassezia furfur, dermatophytes like Trichophyton and Candida albicans Superficial fungal diseases include tinea versicolor, seborrheic dermatitis, and dandruff Cutaneous fungal diseases include athlete's foot (tinea pedis) and jock itch (tinea cruris) Fungal Infections: Tinea corporis caused by Microsporum (ringworm) Cutaneous candidiasis caused by Candida albicans Sporotrichosis caused by Sporothrix schenckii Black mold disease caused by Stachybotrys chartarum Coccidioidomycosis (Valley fever) caused by Coccidioides immitis Histoplasmosis caused by Histoplasma capsulatum Blastomycosis caused by Blastomyces dermatitidis Aspergillosis caused by Aspergillus fumigatus, Aspergillus flavus Pneumocystis pneumonia (PCP) caused by Pneumocystis jiroveci Cryptococcosis caused by Cryptococcus neoformans Systemic candidiasis caused by Candida albicans Effects and toxins: Fungal infections damage tissue directly by enzyme secretion and indirectly by the inflammatory response Mycotoxins produced by molds on nuts, beans, and grains can affect muscle coordination, cause tremors, and may be fatal Some fungal toxins, like aflatoxins from Aspergillus species, can cause cancer Candida albicans: Most common cause of fungal infections in humans An opportunistic yeast that resides in the skin, gastrointestinal tract, mouth, and vagina In healthy individuals, it is controlled by local defense mechanisms and the bacterial microbiome In immunocompromised individuals, disseminated infection may occur Parasitic Infections: Parasites range from unicellular protozoan to large worms Helminths include intestinal and tissue nematodes, flukes, and tapeworms Pathogenic protozoa include malaria (Plasmodium), amebae (Entamoeba histolytica), and flagellates (Giardia lamblia, Trypanosoma) Common parasitic infections in the US include Toxoplasma gondii (causes blindness, miscarriage, and CNS issues) Important parasites of humans Protozoa Entamoeba histolytica - Amebiasis (Dysentery, liver abscess) Giardia lamblia - Giardiasis (Diarrhea) Trichomonas vaginalis - Trichomoniasis (Inflammation of reproductive organs) Trypanosoma cruzi - Chagas disease: Generalized, progressing to cardiac and central nervous system symptoms Trypanosoma brucei - African sleeping sickness Balantidium coli - Balantidiasis (Small intestines, invasion of colon, diarrhea) Cryptosporidium parvum - Cryptosporidiosis (Intestine, diarrhea) Cryptosporidium hominis Plasmodium spp. - Malaria (Blood, liver) Toxoplasma gondii - Toxoplasmosis (Intestine, eyes, blood, heart, liver) Helminths Fasciola hepatica - Fasciolosis (Liver destruction) Schistosoma mansoni - Schistosomiasis (Blood, diarrhea, bladder, generalized symptoms) Taenia solium - Pork tapeworm (Encysts in muscle, brain, liver) Ascaris lumbricoides - Ascariasis (Intestinal obstruction, bile duct obstruction) Necator americanus - Hookworm disease (Intestinal parasite) Trichinella spiralis - Trichinosis (Intestine, diarrhea, muscle, CNS, death) Wuchereria bancrofti - Filariasis, Lymphatics elephantiasis Enterobius vermicularis - Pinworm infection (Intestines) Onchocerca volvulus - Onchocerciasis (Blindness, dermatitis) Transmission of protozoa Many protozoan parasites are transmitted through vectors or ingested Vectors include the tsetse fly (Trypanosoma cruzi, Trypanosoma brucei) and sand fleas (leishmaniasis) Water and food can be contaminated with protozoal parasites (e.g., E. histolytica, G. lamblia) Transmission of Plasmodium is through the bite of an infected female Anopheles mosquito Mechanisms of action of antibiotics Inhibition of the function or production of the cell wall/membrane Prevention of protein synthesis Blockage of DNA Antibiotic resistance Antibiotic-resistant microorganisms observed after widespread antibiotic use Develops in over 2 million individuals annually, resulting in over 23,000 deaths Rapid progression of resistance from single antibiotics to multiple-antibiotic resistance Urgent antibiotic-resistant pathogens C. difficile Carbapenem-resistant Enterobacteriaceae species (Klebsiella and E. coli) Drug-resistant N. gonorrhoeae Other antibiotic-resistant infections Methicillin-resistant Staphylococcus aureus (MRSA) Resistant Streptococcus pneumoniae causing pneumonia, meningitis, and acute otitis media Increases in resistant Salmonella typhi, Shigella, Acinetobacter, Campylobacter, Enterococcus, Pseudomonas aeruginosa, and M. tuberculosis Antibiotic-resistant fungi and malarial parasites Mechanisms of antibiotic resistance Resistance genes spread within bacterial community through horizontal gene transfer Antibiotics degraded by microbe-released enzymes Antibiotics altered by enzymes within the microbe Efflux pumps in cell membrane eject antibiotics from inside the microbe Cell wall modified to prevent antibiotic binding or uptake