Chapter 21 Microbial Diseases of the Skin and Eye PDF

Microbiology an Introduction Thirteenth Edition, Global Edition Chapter 21 Microbial Diseases of the Skin and Eyes Copyright © 2021 Pearson E...

Microbiology an Introduction Thirteenth Edition, Global Edition Chapter 21 Microbial Diseases of the Skin and Eyes Copyright © 2021 Pearson Education Ltd. All Rights Reserved Structure and Function of the Skin (2 of 3) Epidermis: thin outer portion of skin; composed of layers of epithelial cells Keratin: waterproofing protein coating outer layer of epidermis Dermis: inner, thick portion of skin; composed mainly of connective tissue Copyright © 2021 Pearson Education Ltd. All Rights Reserved  Hair Oil gland Hair erector Hair shaft follicle (produces sebum) muscle Figure 21.1 The Stratum Structure of corneum Sweat pore Human Skin Epidermis Dermis Subcutaneous layer Adipose Nerve Blood Sweat gland Duct of tissue (fat) vessels (produces sweat gland perspiration) Copyright © 2021 Pearson Education Ltd. All Rights Reserved Structure and Function of the Skin (3 of 3) Perspiration provides moisture and some nutrients for microbial growth. However, it contains: - salt, which inhibits many microorganisms - the enzyme lysozyme, which is capable of breaking down the cell walls of certain bacteria - antimicrobial peptides. Sebum secreted by oil glands contains fatty acids that inhibit pathogens. Copyright © 2021 Pearson Education Ltd. All Rights Reserved Mucous Membranes (1 of 2) Line the body cavities open to the exterior Tightly packed epithelial cells attached to an extracellular matrix – Cells secrete mucus – Some cells have cilia Often acidic Membrane of eyes washed by tears containing lysozyme Often folded to maximize surface area Copyright © 2021 Pearson Education Ltd. All Rights Reserved Normal Microbiota of the Skin (2 of 3) Resistant to drying and high salt concentration Large numbers of gram-positive cocci – Staphylococci – Micrococci Areas with moisture have higher populations. – Metabolize sweat and contribute to body odor Copyright © 2021 Pearson Education Ltd. All Rights Reserved Normal Microbiota of the Skin (3 of 3) Gram-positive pleomorphic rods (diphtheroids) such as: – Cutibacterium (Propionibacterium) acnes inhabits hair follicles; anaerobic  Produce acids that maintain low skin pH – Corynebacterium xerosis occupy the skin surface; aerobic Yeast – Malassezia furfur; causes dandruff Copyright © 2021 Pearson Education Ltd. All Rights Reserved Microbial Diseases of the Skin (4 of 4) Vesicles: small, fluid-filled lesions Bullae: vesicles larger than 1 cm in diameter Macules: flat, reddened lesions Papules: raised lesions Pustules: raised lesions with pus Exanthem: skin rash arising from a disease Enanthem: rash on mucous membranes arising from a disease Copyright © 2021 Pearson Education Ltd. All Rights Reserved Macule Vesicles Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 21.2 Skin lesions. (a) Vesicles are small, fluid-filled lesions. (b) Bullae are larger fluid-filled lesions. (c) Macules are flat lesions that are often reddish. (d) Papules are raised lesions; when they contain pus, as shown here, they are called pustules. 1 cm Fluid Epidermis Dermis 1 cm Vesicle Macule 1 cm Pus Bulla Pustule (papule) Copyright © 2021 Pearson Education Ltd. All Rights Reserved Staphylococcal Skin Infections (1 of 8) Staphylococci – Spherical gram-positive bacteria; form irregular clusters – May produce coagulase  Enzyme that clots fibrin in the blood  Used to identify types of staphylococci Copyright © 2021 Pearson Education Ltd. All Rights Reserved Staphylococcal Skin Infections (2 of 8) Staphylococcus epidermidis – Ninety percent of normal skin microbiota – Healthcare-associated pathogen – Produces biofilm on catheters – Coagulase-negative Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 21.3 Coagulase-Negative Staphylococci Biofilm Surface of catheter Biofilm Catheter sur- Most of the face with adhering bacteria produc- bacteria. Biofilm, light green, is ing the slime are not visible beginning to appear. under the biofilm. Copyright © 2021 Pearson Education Ltd. All Rights Reserved Staphylococcal Skin Infections (3 of 8) Staphylococcus aureus – Carried in the nasal passages of 20% of the population – Golden-yellow colonies – Coagulase-positive – May produce damaging toxins and cause sepsis – Avoids host defenses in the skin  Secretes proteins and toxins that kill phagocytic cells – MRSA strains are antibiotic-resistant. – Vancomycin, VRSACopyright © 2021 Pearson Education Ltd. All Rights Reserved Staphylococcal Skin Infections (4 of 8) Folliculitis: infections of the hair follicles Sty: folliculitis of an eyelash Furuncle (boil): a type of abscess; localized region of pus surrounded by inflamed tissue Carbuncle: damage and inflammation of deep tissue from a spreading furuncle Impetigo: crusting (nonbullous) sores, spread by autoinoculation Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 21.4 Lesions of Impetigo Copyright © 2021 Pearson Education Ltd. All Rights Reserved Staphylococcal Skin Infections (5 of 8) Scalded skin syndrome – Bullous impetigo – Toxin B causes exfoliation. – Pemphigus neonatorum: impetigo of the newborn Toxic shock syndrome (TSS) – Fever, vomiting, shock, and organ failure caused by toxic shock syndrome toxin 1 (TSST-1) in the bloodstream Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 21.5 Lesions of Scalded Skin Syndrome Copyright © 2021 Pearson Education Ltd. All Rights Reserved Streptococcal Skin Infections (6 of 8) Streptococci are gram-positive cocci in chains Produce hemolysins that lyse red blood cells Beta-hemolytic streptococci often cause disease – Streptococci differentiated into groups A through T based on antigenic cell wall carbohydrates Copyright © 2021 Pearson Education Ltd. All Rights Reserved Streptococcal Skin Infections (7 of 8) Group A streptococci (GAS), also known as Streptococcus pyogenes – Eighty immunological types – Produce virulence factors  Streptolysins: lyse RBCs  M proteins: external to the cell wall; allow adherence and immune system avoidance  Hyaluronidase: dissolves connective tissue  Streptokinases: dissolve blood clots Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 21.6 The M protein of group A beta-hemolytic streptococci. Part of each cell shown carries M protein on Mprotein Fimbriae lacking fimbriae on fimbriae M protein Copyright © 2021 Pearson Education Ltd. All Rights Reserved Streptococcal Skin Infections (8 of 8) Erysipelas – S. pyogenes infects the dermal layer of the skin.  Causes local tissue destruction and sepsis Necrotizing fasciitis – “Flesh-eating” disease, may destroy tissue rapidly , and mortality rates from systemic toxicity can exceed 40%. – Extotoxin A produced by S. pyogenes acts as a superantigen Streptococcal toxic shock syndrome – Similar to staphylococcal TSS Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 21.7 Lesions of Erysipelas, Caused by Group A Beta-hemolytic Streptococcal Toxins Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 21.8 Necrotizing Fasciitis of a Leg Due to Group A Streptococci Copyright © 2021 Pearson Education Ltd. All Rights Reserved Infections by Pseudomonads Pseudomonas aeruginosa – Gram-negative, aerobic rod – Pyocyanin produces a blue-green pus. – Produces exo- and endotoxins; grows in biofilms – Pseudomonas dermatitis  Self-limiting rash acquired in swimming pools – Otitis externa  “Swimmer’s ear” – Opportunistic in burn patients – Resistant to many antibiotics Copyright © 2021 Pearson Education Ltd. All Rights Reserved Buruli Ulcer Caused by Mycobacterium ulcerans – Produces the toxin mycolactone Enters via a break in the skin or an insect bite Causes deep, damaging ulcers – May require amputation Primarily found in western and central Africa Copyright © 2021 Pearson Education Ltd. All Rights Reserved Acne (1 of 2) Most common skin disease in humans Normally, skin cells that are shed inside the hair follicle are able to leave, but acne develops when cells are shed in higher than normal numbers, combine with sebum, and the mixture clogs the follicle. As sebum accumulates, whiteheads (comedos) form; if the blockage protrudes through the skin, a blackhead (comedone) forms. The dark color of blackheads is due not to dirt, but to lipid oxidation and other causes. Sebum formation is affected by hormones, not diet. Comedonal (mild) acne – Easily treated with topical formations Copyright © 2021 Pearson Education Ltd. All Rights Reserved Acne (2 of 2) Inflammatory (moderate) acne – Caused by Propionibacterium acnes  P. acnes metabolizes sebum forming fatty acids, which produce an inflammatory response – Treated with antibiotics and benzoyl peroxide Nodular cystic (severe) acne – Inflamed lesions with pus deep in the skin Copyright © 2021 Pearson Education Ltd. All Rights Reserved Figure 21.9 Severe Acne Copyright © 2021 Pearson Education Ltd. All Rights Reserved Viral Diseases of the Skin Many are transmitted via respiratory routes and are systemic. Many cause problems in children and developing fetuses. Copyright © 2021 Pearson Education Ltd. All Rights Reserved Warts Papillomas: small skin growths Transmitted via contact Caused by papillomavirus – More than 100 types – Some cause skin and cervical cancers. ( HPV types16 and 18) The most common medical treatments for warts are: - To apply extremely cold liquid nitrogen (cryotherapy) - Dry them with an electrical current (electrodesiccation) - Or burn them with salicylic acid Copyright © 2021 Pearson Education Ltd. All Rights Reserved Smallpox (Variola) (1 of 2) Caused by an orthropoxvirus Two forms of the disease – Variola major has 20–60% mortality – Variola minor has