Introduction to Microbiology

1. Introduction to Microbiology Anas Abu-Humaidan M.D. Ph.D. Lecture 22

2. Fungi overview • Fungi are eukaryotes with a higher level of biologic complexity than bacteria. • most are freeliving in nature where they function as decomposers in the energy cycle. Of the more than 90 000 known species, fewer than 200 have been reported to produce disease in humans. • They are spore bearing; reproducing both sexually and asexually • We all have regular contact with fungi. They are so widely distributed in our environment that thousands of fungal spores are inhaled or ingested every day. Some species are so well adapted to humans that they are common members of the microbiota. Despite this ubiquity, clinically apparent systemic fungal infections are uncommon.

3. FUNGI • Fungi exist in either yeast or mold forms. • The smallest of yeasts are similar in size to bacteria, but most are larger (2–12 μm) and multiply by budding. • Molds form tubular extensions called hyphae, which, when linked together in a branched network, form the fuzzy structure seen on neglected bread slices.

5. Fungal cell wall The cell wall, as the most external cellular component, plays a crucial role in the interaction with host cells mediating processes such as adhesion or phagocytosis that are essential during infection. Adherence is mediated by fungal adhesins and host cell receptors. Mannoprotein is an adhesin, and fibronectin a receptor on human cells it also carries important antigenic determinants (PAMPs) in healthy persons there is a high level of innate immunity to most fungal infections (through PRR).

6. Fungal immunity In healthy persons there is a high level of innate immunity to most fungal infections (through PRR), and Most fungi are readily killed by neutrophils. Some fungal pathogens can escape innate immunity, (e.g. Candida albicans is able to bind complement components in a way that interferes with phagocytosis.) T-cell–mediated responses of primary importance and progressive fungal diseases occur in the immunocompromised Systemic disease associated with deficiencies in neutrophils and T-cell–mediated immunity

7. Fungi pathogenesis • Fungal infections are acquired from the environment or may be endogenous in the few instances where they are members of the resident flora • Fungal pathogenesis is similar to bacteria. Most fungi are opportunists. • Disease caused by fungi is called mycosis have unique clinical and microbiologic features and are increasing in immunocompromised patients

8. Fungal diseases • Diseases caused by fungi are often described by the site they infect • Superficial & Cutaneous infections : • Infections involve the skin, mucous membrane, nail or hair with or without tissue destruction & immunological reaction • Systemic mycoses • Are primarily pulmonary lesion that may disseminate to any organ.

9. Superficial fungal infections • Dermatophytoses are superficial infections of the skin and its appendages, common diseases are nail infections, ringworm, vaginal candidiasis. • Dermatophytes are highly adapted to the nonliving, keratinized tissues of nails, hair, and the stratum corneum of the skin. • The source of infection may be humans, animals, or the soil. • Other than a weakened immune system, People who use public showers or locker rooms, athletes (particularly those who are involved in contact sports such as wrestling), people who wear tight shoes and have excessive sweating, and people who have close contact with animals may also be more likely to come in contact with the fungi that cause ringworm.

12. Fungal Nail Infections • Fungal nail infections (called onychomycosis) are common infections of the fingernails or toenails that can cause the nail to become discolored, thick, and more likely to crack and break. • Predisposing factors include A nail injury or nail surgery, Diabetes, A weakened immune system, Blood circulation problems, and Athlete’s foot. • Topical antifungal agents can be used but are often ineffective. • Surgical debridement or removal of the affected nail is also a consideration for cases that are resistant to antifungals

13. Ringworm القوباء الحلقية • Ringworm is a common skin infection that is caused by a fungus. It’s called “ringworm” because it can cause a circular rash (shaped like a ring) that is usually red and itchy. It can affect several areas of the body: • Feet (tinea pedis or “athlete’s foot”): The symptoms of ringworm on the feet include red, swollen, peeling, itchy skin between the toes (especially between the pinky toe and the one next to it). The sole and heel of the foot may also be affected. In severe cases, the skin on the feet can blister.

14. Ringworm • Scalp (tinea capitis): Ringworm on the scalp usually looks like a scaly, itchy, red, circular bald spot. The bald spot can grow in size and multiple spots might develop if the infection spreads. Ringworm on the scalp is more common in children than it is in adults. • Groin (tinea cruris or “jock itch”): Ringworm on the groin looks like scaly, itchy, red spots, usually on the inner sides of the skin folds of the thigh. • Beard (tinea barbae): Symptoms of ringworm on the beard include scaly, itchy, red spots on the cheeks, chin, and upper neck. The spots might become crusted over or filled with pus, and the affected hair might fall out.

15. Fungal disease diagnosis • Microscopy is often an important part of fungal diagnosis, and the sample is commonly taken directly from the lesion and treated with a Potassium hydroxide (KOH) stain to look for fungal elements (hyphe and yeast) • Culture: Fungal culture on Sabouraud’s medium or dermatophyte test medium (DTM) can be used to identify the infecting organism

16. Fungal disease treatment The drugs used to treat bacterial diseases have no effect on fungal infection. it usually depends on presence of ergosterol in fungal cell membranes Amphotercin B and nystatin are polynes (Fungicidal) & various azoles (fungistatic) are commonly used for treatment of fungal infection.

17. Candida infections of the mouth, throat, and esophagus • Candidiasis is an infection caused by a yeast called Candida. Candida normally lives inside the body (in places such as the mouth, throat, gut, and vagina) and on skin without causing any problems • Candidiasis in the mouth and throat is also called “thrush” or oropharyngeal candidiasis. Candidiasis in the esophagus is called esophageal candidiasis and is common in immune compromised patients, especially AIDS patients. • White patches on the inner cheeks, tongue, roof of the mouth, and throat (photo showing candidiasis in the mouth), Redness or soreness, Cotton-like feeling in the mouth, Loss of taste, Pain while eating or swallowing, Cracking and redness at the corners of the mouth.

18. Vulvovaginal candidiasis • Candidiasis is an infection caused by Candida albicans, which is an opportunistic pathogenic yeast that is a common member of the human gut flora. • Candida spp. may be found in the lower genital tract of 10– 20% of asymptomatic women. • 29– 49% of premenopausal women reporting at least one episode of candidiasis. • Candidal infection is uncommon in prepubertal women

19. Vulvovaginal candidiasis / signs and symptoms • C. albicans is the cause of 80– 92% of cases • Recurrent infection— defined as ≥4 episodes a year and seen in 5– 8% of women. susceptibility seems to be largely determined genetically.

20. Vulvovaginal candidiasis / diagnosis and treatment • wet mount of the discharge with 10% KOH may allow recognition of yeast and hyphae, but microscopy is negative in around 50%. • Perform culture in patients with persistent discharge or recurrent symptoms unresponsive to azole treatment • 90% of cases represent uncomplicated infections (healthy, non- pregnant women with mild/ moderate symptoms, infrequent episodes and infection with C. albicans). • Oral and topical treatments are similarly effective, with topical therapy relieving symptoms more rapidly, but oral being preferred by women, e.g. PO fluconazole.

21. Further reading: • Sherris Medical Microbiology, sixth edition • Chapter 23: Antibacterial agents and resistance