Lecture 9 - Skin, Eyes and Central Nervous System Diseases PDF

Microbes and human diseases: Skin, Eyes and Central Nervous System Diseases  Structure and Function of the Skin The epidermis is the thin outer portion, composed of several layers of epithelial cells. - the stratum corneum, consists of many rows of dead cells that cont...

Microbes and human diseases: Skin, Eyes and Central Nervous System Diseases  Structure and Function of the Skin The epidermis is the thin outer portion, composed of several layers of epithelial cells. - the stratum corneum, consists of many rows of dead cells that contain a waterproofing protein called keratin. The dermis is the inner, relatively thick portion of skin, composed mainly of connective tissue.  Normal Microbiota of the Skin Staphylococcus epidermidis Staphylococcus aureus Micrococcus species α-Hemolytic and nonhemolytic streptococci (eg, Streptococcus mitis) Corynebacterium species Propionibacterium species Peptostreptococcus species Acinetobacter species Small numbers of other organisms (Candida species, Pseudomonas aeruginosa, etc).  Normal Microbiota of the Skin Gram-positive rods called diphtheroids - Cutibacterium (Propionibacterium) acnes, are typically anaerobic and inhabit hair follicles. These bacteria produce propionic acid, which helps maintain the low pH of skin, generally between 3 and 5. A yeast, Malassezia furfur, is capable of growing on oily skin secretions and is associated with the scaling skin condition known as dandruff. Ketoconazole and zinc pyrithione or selenium sulfide.  Bacterial Diseases of the Skin Staphylococcal Skin Infections Coagulase-negative Staphylococcus epidermidis Coagulase-positive S. aureus – pathogenic - it can enter the body through natural openings such as the hair follicle and cause folliculitis, A more serious hair follicle infection is the furuncle, which is a type of abscess. - Antibiotics do not penetrate well into abscesses, and the infection is therefore difficult to treat.  Staphylococcal Skin Infections Impetigo - mostly affecting children 2 to 5 years of age. Spread by direct contact. Streptococcus pyogenes can also cause impetigo. - Nonbullous impetigo – most common form. The pathogen usually enters through some minor break in the skin. The lesions eventually rupture and form lightcolored crusts. - bullous impetigo - caused by a staphylococcal toxin and is a form of staphylococcal scalded skin syndrome. Staphylococcal scalded skin syndrome  Streptococcal Skin Infections S. pyogenes Group A beta hemolytic streptococci Streptolysins M Proteins  Streptococcal Skin Infections Erysipelas Can cause sepsis Necrotizing fasciitis Commonly affected limbs Streptococcal toxic shock syndrome Bacteremia, organ damage M protein + fibrinogen complex binds neutrophils Lesions of erysipelas  Classification of Acne Comedonal (mild) Acne Inflammatory (moderate) Acne Nodular cyctic (severe) Acne  Comedonal Acne Mild form - Sebum channels blocked with shed cells Treatment Azelaic acid Salicyclic acid preparations Retinoids (derivatives of vitamin A)  Inflammatory Acne Propionibacterium acnes - Gram+, anaerobic rod - Nutritional requirement for glycerol Treatment Preventing formation of sebum Topical agents are not effective for this Antibiotics Benzoyl peroxide  Nodular Cyctic Acne Severe Nodules or cysts filled with pus Leaves scars Treatment Isotretinoin, which reduces the formation of sebum  Viral Diseases of the Skin Wart Papilloma virus More than 50 types of papillomavirus cause different kinds of warts Incubation period several weeks Treatment cold liquid nitrogen (cryotherapy) dry with an electrical current (electrodesiccation) burn with acids salicylic acids are effective  Viral Diseases of the Skin Smallpox (Variola) Orthopoxvirus - variola major, with a mortality rate of 20–60% variola minor, with a mortality rate of less than 1% Transmitted by the respiratory route Smallpox rashes Eradicated in 1977 by vaccination  Viral Diseases of the Skin Chickenpox Varicellazoster virus (human herpesvirus 3) Transmitted by the respiratory route Causes pus filled vesicles Lesions on the face, lower back, chest, shoulders Prevention: Live attenuated vaccine  Herpes Simplex Human herpesvirus 1 (HSV-1) and 2 (HSV-2) Cold sores and fever blisters Herpes gladiatorum (vesicles on skin) common among wrestlers Herpes encephalitis HSV-1 can remain latent in trigeminal nerve ganglia  Measles (Rubeola) Extremely contagious viral disease Transmitted by respiratory route Macular rash and Koplik’s spot Complications – middle ear infections or pneumonia Prevented by vaccination  Rubella Rubella, or German measles Macular rash of small red spots and fever Complications are rare Transmitted by the respiratory route Congenital rubella syndrome Prevented by vaccination  Microbial Diseases of the Eye Conjunctivitis Inflammation of the conjunctiva – Red eye or pinkeye Haemophilus influenzae is the most common bacterial cause Viral conjunctivitis is usually caused by adenoviruses Swimming pool conjunctivitis - Chlamydia trachomatis Trachoma – eye infection caused by Chlamydia trachomatis  Infectious Diseases of the Eye Herpetic Keratitis - herpes simplex type 1 virus (HSV-1) Acanthamoeba Keratitis - This ameba has been found in fresh water, tap water, hot tubs, and soil. Affects a cornea, common in people who wear contact lenses. - early stages - mild inflammation - later stages - severe pain Treatment with 2% chlorhexidine and propamidine isethionate eye drops or topical neomycin. Diagnosis is confirmed by the presence of trophozoites and cysts. The drug trifluridine is often an effective treatment. Structure and Function of the Nervous System Central Nervous System (CNS) – Brain and the spinal cord - Controls the entire body Picks up sensory information from the environment Interprets the information Sends impulses that coordinate the body’s activities Peripheral nervous system (PNS) consists of all the nerves that branch off from the brain (cranial nerves) and spinal cord (spinal nerves).  Structure and Function of the Nervous System Meninges. - Dura mater – the outermost - Arachnoid mater - the middle -Subarachnoid space contains cerebrospinal fluid (CSF) - Pia mater - the innermost Blood-brain Barrier  Inflammation of Nervous System Meningitis - inflammation of the meninges Encephalitis - inflammation of the brain Meningoencephalitis - inflammation of both  Bacterial Meningitis Majority causes of Meningitis Haemophilus influenzae type B Neisseria meningitidis Streptococcus pneumoniae All three of these pathogens possess a capsule Other species that can cause meningitis: Listeria monocytogenes, group B streptococci, staphylococci, and certain gram-negative bacteria. Symptoms: fever, headache, stiff neck Nausea and vomiting often follow Treatment: Cephalosporins, vancomycin  Haemophilus influenzae Meningitis Aerobic, gram-negative bacterium, throat normal flora Occurs mostly in children under age 4 Capsule antigen type B Mortality rate - 6% The incidence is decreasing because of the vaccine  Neisseria meningitidis Meningitis (Meningococcal Meningitis) Caused by Neisseria meningitidis Aerobic, gram-negative diplococcus Virulence factor - polysaccharide capsule Transmitted by droplet aerosols or direct contact with secretions Begins with a throat infection, leading to bacteremia and eventually meningitis. Occurs in children under 2 years The meningococcus occurs in six capsular serotypes associated with invasive disease (A, B, C, W-135, X, and Y). Vaccine against some serotypes are available Treatment: penicillin and cephalosporins  Streptococcus pneumoniae Meningitis (Pneumococcal Meningitis) Streptococcus pneumoniae is a gram-positive, encapsulated diplococcus The leading cause of bacterial meningitis 70% of the general population are healthy carriers Common inhabitant of the nasopharyngeal region Occur among children between the ages of 1 month and 4 years Prevented by vaccination  Listeriosis Listeria monocytogenes is a gram-positive rod Excreted in animal feces, it is widely distributed in soil and water. Listeriosis has become the fourth most common cause of bacterial meningitis. Foodborne pathogen Cause abortion or stillbirth in pregnant woman Capable of growth at refrigerator temperatures FDA approved bacteriophage-containing spray capable of killing at least 170 L. monocytogenes strains.  Tetanus Clostridium tetani – obligately anaerobic, endospore-forming, gram-positive rod. Neurotoxin It enters the CNS via the peripheral nerves or the blood The tetanus neurotoxin blocks the relaxation pathway so that both opposing sets of muscles contract, resulting in the characteristic muscle spasms. Growth in deep wounds Prevention be vaccination Treatment: tetanus immune globulin  Botulism Caused by Clostridium botulinum Obligately anaerobic, endospore-forming gram-positive rod Found in soil and many aquatic sediments Food poisoning (anaerobic environments, such as sealed cans, the microorganism produces an exotoxin). Intoxication comes from ingesting botulinal toxin Toxin blocks release of neurotransmitter acetylcholine, causing flaccid paralysis Symptoms: blurred vision, difficulty swallowing, weakness  Viral Diseases of the Nervous System Poliomyelitis Poliovirus Transmitted by ingestion Initial symptoms: sore throat and nausea Viremia may occur; if persistent, virus can enter the CNS; destruction of motor cells and paralysis occurs in