Characterizing and Classifying Eukaryotes

Part 2

Chapter 12

Chapter 12 includes the fungal pathogens section from chapter 22 and Helminths from chapter 23

Fungi

Chemoheterotrophic

Have cell walls typically composed of chitin

Do not perform photosynthesis

Lack chlorophyll

Fungi

100,000 species divided into 2 groups:

Macroscopic fungi (mushrooms, puffballs, gill fungi)

Microscopic fungi (molds, yeasts)

Majority are unicellular or colonial; a few have cellular specialization

Substrate

Phototrophic layer

Fungal hyphae

Ascocarp of fungus

Soredium

Algal cell

Fungal hyphae

Figure 12.25

Microscopic Fungi

• Exist in two morphologies:

• Yeast – round ovoid shape, asexual reproduction

• Hyphae – long filamentous fungi or molds

• Some exist in either form – dimorphic – characteristic of some pathogenic molds

Septum

The dimorphic nature of true fungal pathogens

Figure 22.2

Spores

In environment(<30ºC)

In human(37ºC)

Buddingyeastcells

Hypha

Histoplasma capsulatum – HistoplasmosisCoccidioides immitis - Coccidioidomycosis

Fungal nutrition

• All are heterotrophic

• Majority are harmless saprobes living off dead plants and animals

• Some are parasites, living on the tissues of other organisms, but none are obligate

• Mycoses – fungal infections

• Extremely widespread distribution in many habitats

Fungal organization

• Yeast – soft, uniform texture and appearance

• Reproduce through an asexual process called budding

Figure 22.1

Fungal organization

• Filamentous fungi – mass of hyphae called mycelium; cottony, hairy, or velvety texture

•Hyphae may be divided by cross walls – septate

•Hyphae without cross walls-aseptate

•Vegetative hyphae – digest

and absorb nutrients

•Reproductive hyphae –

produce spores for

reproduction

Aseptate hyphaSeptate hypha

Figure 12.15

Fungal reproduction

Primarily through spores formed on reproductive hyphae

SporangiosporeSporangiophore Sporangium Chlamydospore

Conidiophore Conidia

Figure 12.18

Fungal reproduction

Sexual reproduction

• spores are formed by fusion of two different strains and formation of sexual structure

• Sexual spores and spore-forming structures are one basis for classification

• Zygospores, ascospores, and basidiospores

Asexual reproduction

• spores are formed through budding or mitosis

• Conidia or sporangiospores

Fungal identification

• Isolation on specific media

• Macroscopic and microscopic observation of:

• Asexual spore-forming structures and spores

• Hyphal type

• Colony texture and pigmentation

• Physiological characteristics

• Genetic makeup

Roles of fungi

• Adverse impact

• Mycoses, allergies, toxin production

• Destruction of crops and food storages

• Beneficial impact

• Decomposers of dead plants and animals

• Sources of antibiotics, alcohol, organic acids, vitamins

• Used in making foods and in genetic studies

Clinical Manifestations of Fungal Diseases (Mycoses)

Fungal infections

Most common mycoses

Caused by presence of true pathogens or opportunists

The infections can be systemic or cutaneous

Toxicoses

Acquired through ingestion

Occur when poisonous mushrooms are eaten

Allergies

Most often result from the inhalation of fungal spores

Systemic Mycoses Caused by Pathogenic Fungi

Infections spread throughout the body

Caused by four pathogenic fungi of the division Ascomycota

Blastomyces dermatidis - Blastomycosis

Coccidioides immitis - Coccidiomycosis

Histoplasma capsulatum - Histoplasmosis

Paracoccidioides brasiliensis - Paracoccidiomycosis

Acquired through inhalation

Begins as generalized pulmonary infection

Disseminates via the blood to the rest of the body

Systemic Mycoses Caused by Pathogenic Fungi

All four fungi are dimorphic

Grow as mycelia in the environment

Grow as spherical yeasts in the body

Invasive form

Individuals working with these fungi must take precautions

to avoid exposure to spores

Cutaneous blastomycosis in an American woman

Figure 22.6

Coccidioidomycosis lesions in subcutaneous tissue.

Figure 22.9

Systemic Mycoses Caused by Opportunistic Fungi

Opportunistic mycoses don't typically affect healthy humans

Infections limited to people with poor immunity

More important as the number of AIDS patients rises

Difficult to identify because their symptoms are often atypical

The Emergence of Fungal Opportunists in AIDS Patients

AIDS patients vulnerable to opportunistic fungal infections

Permanent immune dysfunction makes cure of infections unlikely

Mycoses account for most deaths associated with AIDS

Infection with various fungi partly define end-stage AIDS

Emergence of new fungal opportunists

Increase in immunocompromised individuals

Use of antifungal drugs selects for fungi resistant to the drugs

Three emerging pathogens are particularly problematic

Fusarium species

Cause respiratory distress, disseminated infections, and fungemia

Toxin accumulation can occur when fungi ingested in food

Penicillium marneffei

Produces pulmonary disease if inhaled

Trichosporon beigelii

Can cause fatal systemic disease in AIDS patients

Enters through the lungs, gastrointestinal tract, or catheters

Examples of Fungal Opportunists in AIDS Patients

Candidiasis (Example of opportunistic systemic mycosis)

Candida albicans is the most common causative agent

Common microbiota of the skin and mucous membranes

All cases of disease result from an opportunistic infection

Candida can be transmitted between individuals

Systemic disease seen mostly in immunocompromised individuals

Figure 22.12

a) Oral thrushb) Diaper rashc) Nail infection

Cutaneous Mycoses

Are the most commonly reported fungal diseases

All are opportunistic infections

Localized at sites at or near the surface of the body

Acquired by person-to-person contact or environmental exposure

Diseases are usually not life threatening

Can cause chronic or recurring infections

Algae

Photosynthetic organisms

Microscopic forms are unicellular, multi-cellular, filamentous

Macroscopic forms are colonial and multicellular

Contain chloroplasts with chlorophyll and other pigments

Cell wall

May or may not have flagella

Most are free-living in fresh and marine water – plankton

Provide basis of food web in most aquatic habitats

Produce large proportion of atmospheric O2

Dinoflagellates can cause red tides and give off toxins that cause food poisoning with neurological symptoms

Algae

http://protist.i.hosei.ac.jp/pdb/images/Chlorophyta/Spirogyra/index.html

Parasitic Helminths

Multicellular animals, organs for reproduction, digestion, movement, protection

Parasitize host tissues

Have mouthparts for attachment to or digestion of host tissues

Most have well-developed sex organs that produce eggs and sperm

Fertilized eggs go through larval period in or out of host body

http://www.neglecteddiseases.gov/

Major groups of parasitic helminths

1. Flatworms – flat, no definite body cavity; digestive tract a blind pouch; simple excretory and nervous systems

• Cestodes (tapeworms)

• Trematodes or flukes, are flattened, non-segmented worms with sucking mouthparts

2. Roundworms (nematodes) – round, a complete digestive tract, a protective surface cuticle, spines and hooks on mouth; excretory and nervous systems poorly developed

Helminth classification and identification

• Classify according to shape, size, organ development, presence of hooks, suckers, or other special structures, mode of reproduction, hosts, and appearance of eggs and larvae

• Identify by microscopic detection of worm, larvae, or eggs

Major routes by which humans acquire parasitic infections

Figure 23.1

Distribution and importance of parasitic worms

• Approximately 50 species parasitize humans

• Distributed worldwide; some restricted to certain geographic regions with higher incidence in tropics

• Acquired through ingestion of larvae or eggs in food; from soil or water; some are carried by insect vectors

• Afflict billions of humans

https://www.bcm.edu/education/schools/national-school-of-tropical-medicine/

Nematode (Roundworm) infestations

Most abundant animal groups; 50 species that affect humans

Elongated, cylindrical worms with protective cuticles, circular muscles, a complete digestive tract, and separate sexes

Divided into intestinal nematodes and tissue nematodes

Ascaris lumbricoides

Figure 23.22

Fertilized egg of A. lumbricoides in unstained wet mounts of stool, with embryos in the early stage of development.

www.cdc.gov

Adult female A. lumbricoides. Image courtesy of the Orange County Public Health Laboratory, Santa Ana, CA.

Posterior end of a male A. lumbricoides, showing the curled tail. www.cdc.gov

Ascaris lumbricoides

A large intestinal roundworm. Indigenous to humans

Most cases in the U.S. occur in the southeastern states

Ascaris spends its larval and adult stages in humans; release embryonic eggs in feces, and are spread to other humans; food, drink, or contaminated objects

Ingested eggs hatch into larvae and burrow through the intestine into circulation and travel to the lungs and pharynx and are swallowed

Adult worms complete cycle in intestines and reproduce – 200,000 eggs/day

Hookworms

• Characteristic curved ends and hooked mouths

• Necator americanus and Ancylostoma duodenale

• Humans shed eggs in feces, which hatch into filariform larvae and burrow into the skin of bare feet

CDC

• Larvae travel from blood to lungs, proceed up bronchi and throat and are swallowed

• Worms mature and reproduce in small intestine and complete the cycle

• May cause pneumonia, nausea, vomiting, cramps, and bloody diarrhea

• Blood loss is significant – anemia

Hookworms

Figure 23.23

Tissue Nematodes

• Complete their life cycle in human blood, lymphatics, or skin

• Cause chronic, deforming disease

• Wuchereria bancrofti

• Elephantiasis

Figure 23.25

A microfilaria of Wuchereria bancrofti in blood.

Figure 23.26

Trematodes or Flukes

Flatworms with ovoid leaflike bodies

Have digestive, excretory, neuromuscular, and reproductive systems

Lack circulatory and respiratory systems

Animals such as snails or fish are usually the intermediate hosts and humans are the definitive hosts

Three types: Blood flukes, liver flukes, Lung flukes

Mouth

VentralsuckerIntestines

Eggs incoileduterus Testes

Figure 23.19

Blood Flukes: Schistosomes

• Schistosomiasis – prominent parasitic disease

• Schistosoma mansoni, S. japonicum, S. haematobium

• Adult flukes live in humans who release eggs into water; early larva (miracidium) develops in freshwater snail into a 2nd larva (cercaria)

• Cercaria penetrates human skin and moves into the liver to mature; adults migrate to intestine or bladder and shed eggs, giving rise to chronic organ enlargement

An egg of Schistosoma mansoni, from a stool sample.

Figure 23.21 Adults of S. mansoni. The thin female resides in the gynecophoral canal of the thicker male. Note the tuberculate exterior of the male. www.cdc.gov

Cestode (Tapeworm) Infestations

• Flatworms

• Long, very thin, ribbonlike bodies composed of sacs (proglottids) and a scolex that grips the intestine

• Each proglottid is an independent unit adapted to absorbing food and making and releasing eggs

• Taenia saginata

• Taenia solium

Taenia solium tapeworm scolex displaying foursuckers and two rows of hooks. www.cdc.gov

VectorsArthropod vectors are animals that carry pathogens

Disease vectors belong to two classes of arthropod

Arachnida

Insecta

Ticks are the most important arachnid vectors

Hard ticks are most prominent tick vectors

A few mite species transmit Rickettsial diseases

Insect vectors

Fleas

Lice

Flies

Mosquitoes (Most important arthropod vectors of disease)

Kissing bugs