6 FINAL

• Integument


  Skin, together with the hair, nails, and sweat and oil glands
• Skin


  • Total surface area of 1.5 to 2 square meters
  • Thickness varies from 1.5 millimeters at places such as the eyelids to 4 millimeters on the soles of the feet
• Parts of the skin

  • Epidermis
  • Dermis

  
• Epidermis


  • Outermost portion of the skin
  • Can be further subdivided into four or five distinct layers

  
• Stratum corneum


  • Found on top of the epidermis
  • Thick layer of epithelial cells
  • About 25 cells thick
  • Cells in this layer are dead and have migrated from the deeper layers during the normal course of cell division
  • Packed with a protein called keratin, which the cells produce in very large quantities

  
• Dermis


  • Found underneath the epidermis
  • Composed of connective tissue instead of epithelium
  • Rich matrix of fibroblast cells and fibers such as collagen
  • Contains macrophages and mast cells
  • Harbors a dense network of nerves, blood vessels, and lymphatic vessels

  
• Millions of cells from the stratum corneum slough off every day, and attached microorganisms slough off with them
• The skin is also brimming with antimicrobial substances
• Antimicrobial peptides


  Small molecules identified in epithelial cells that act by disrupting the negatively charged membranes of bacteria
• Sebum


  • Secretion of sebaceous glands
  • Has a low pH, which makes the skin inhospitable to many microorganisms
  • Oily due to its high concentration of lipids that can serve as nutrients for normal microbiota, but breakdown of the fatty acids contained in lipids leads to toxic by-products that inhibit the growth of microorganisms not adapted to the skin environment
• Sweat


  • Inhibitory to microorganisms, because of both its low pH and its high salt concentration
  • Lysozyme is an enzyme found in sweat (and tears and saliva) that specifically breaks down peptidoglycan, a unique component of bacterial cell walls
• Normal Biota of the Skin

  • Streptococcus
  • Staphylococcus
  • Corynebacterium
  • Propionibacterium
  • Pseudomonas
  • Lactobacillus
  • Yeasts such as Candida

  
• Normal Biota of the Skin


  • Microbes are relatively sparsely distributed over dry, flat areas of the body, such as on the back, but they can grow into dense populations in moist areas and skin folds, such as the underarm and groin areas
  • The normal microbiota also live in the protected environment of the hair follicles and glandular ducts
  • According to the Human Genome Project (HMP) hundreds of species of microbes, including some well-known pathogens, inhabit our epidermis, dermis, and subcutaneous skin layers
  • It is also common for different species to favor different areas of our bodies, and for different people to have different species
  • It is common for an individual's microbiota to remain relatively constant over time

  
• Skin Defenses


  • Keratinized surface
  • Sloughing
  • Low pH
  • High salt
  • Lysozyme
  • Antimicrobial peptides

  
• MRSA


  • Methicillin-resistant Staphylococcus aureus
  • Common cause of skin lesions in non-hospitalized people
  • Usually resistant to multiple antibiotics

  
• Staphylococcus aureus


  • Gram-positive coccus
  • Grows in clusters
  • Nonmotile
  • Destructiveness is due to its array of superantigens
  • Can be highly virulent, but it also appears as "normal" biota in the skin
  • Strains that are methicillin-resistant are also found on healthy people
  • Considered the sturdiest of all non-endospore-forming pathogens

  
• MRSA Infections of the Skin


  • Tend to be raised, red, tender, localized lesions, often featuring pus and feeling hot to the touch
  • Occur easily in breaks in the skin caused by injury, shaving, or even just abrading
  • May localized around a hair follicle
  • Fever is a common feature

  
• Transmission and Epidemiology of MRSA


  • MRSA is a common contaminant of all kinds of surfaces you touch daily especially if the surfaces are not routinely sanitized
  • Gym equipment, airplane tray tables, electronic devices, razors, and so on, are all sources of indirect contact infection
  • Persons with active MRSA skin infections should keep them covered in order to avoid direct contact transmission to others

  
• Enzymes expressed by S. aureus


  • Coagulase
  • Hyaluronidase
  • Staphylokinase
  • Nuclease
  • Lipases
• Because 97% of all human isolates of S. aureus produce coagulase, its presence is considered the most diagnostic species characteristic

  
• Culture and/or Diagnosis of MRSA


  • Polymerase chain reaction (PCR)
  • Inoculation on blood agar
  • Selective media such as mannitol salt agar
  • Catalase test
  • Coagulase test

  
• Catalase test


  Production of catalase, an enzyme that breaks down hydrogen peroxide accumulated during oxidative metabolism, can be used to differentiate the staphylococci, which produce it, from the streptococci, which do not

  
• Coagulase test


  Used for separating S. aureus from other species of Staphylococcus; any isolate that coagulates plasma is S. aureus; all others are coagulase-negative

  
• Prevention and Treatment of MRSA


  • Prevention is only possible with good hygiene
  • Treatment starts with incision of the lesion and drainage of the pus
  • Antimicrobial treatment should include more than one antibiotic, such as clindamycin, TMP/SMZ, or doxycycline
• Maculopapular rash


  Flat to slightly raised colored bumps

  
• Measles


  • Also called as rubeola
  • Children may develop laryngitis, bronchopneumonia, and bacterial secondary infections such as ear and sinus infections
  • Occasionally, measles progresses to pneumonia or encephalitis, resulting in various central nervous system (CNS) changes ranging from disorientation to coma that can result to permanent damage or epilepsy
  • A large number of measles patients experience secondary bacterial infections

  
• Subacute Sclerosing Panencephalitis (SSPE)


  • Most serious complication caused by measles
  • A progressive neurological degeneration of the cerebral cortex, white matter, and brain stems
  • One case in a million measles infections
  • Afflicts primarily male children and adolescents
  • Pathogenicity involves a defective virus that lost its ability to form a capsid and released from an infected cell, instead spreading unchecked through the brain by cell fusion, gradually destroying neurons and accessory cells and breaking down myelin
  • The disease causes profound intellectual and neurological impairment
  • The course of the disease invariably leads to coma and death in a matter of months or years

  
• Transmission and Epidemiology of Measles


  • One of the most contagious infectious diseases
  • Transmitted principally by respiratory droplets
  • No reservoir other than humans
  • A person is infectious during the periods of incubation, prodrome phase, and the skin rash but usually not during convalescence

  
• Diagnosis of Measles


  • Can be diagnosed on clinical presentation alone
  • Further identification is required, an ELISA test is available that tests for patient IgM to measles antigen, indicating a current infection

  
• Prevention of Measles


  • The MMR vaccine (for measles, mumps, and rubella) contains live attenuated measles virus, which confers protection for up to 20 years
  • Measles immunization is recommended for all healthy children at the age of 12 to 15 months, with a booster before the child enters school

  
• Treatment of Measles


  • Relies on reducing fever, suppressing cough, and replacing lost fluid
  • Complications require additional remedies to relieve neurological and respiratory symptoms and to sustain nutrient, electrolyte, and fluid levels
  • Vitamin A supplements are recommended by some physicians; they have been found effective in reducing the symptoms and decreasing the rate of complications
• Rubella


  • Also known as German measles and 3-day measles
  • Rubella is derived from the Latin for "little red," causes a relatively minor rash disease with few complications, except when a fetus is exposed to the virus while in its mother's womb (in utero)
• Clinical Forms of Rubella


  • Postnatal Rubella
  • Congenital Rubella
• Postnatal Rubella


  • Develops in children or adults
  • Rash of pink macules and papules first appear on the face and progresses down the trunk and toward the extremities, advancing and resolving in about 3 days
  • Rash is milder looking than the measles rash
  • Adult rubella often characterized by joint inflammation and pain rather than a rash

  
• Congenital Rubella


  • Infection of the fetus, expressed in the newborn as various types of birth defects
  • A strongly teratogenic virus
  • Transmission of the rubella virus to a fetus in utero can result in a serious complication called congenital rubella
  • The mother is able to transmit the virus even if she is asymptomatic
  • Infection in the first trimester is most likely to induce miscarriage or multiple permanent defects in the newborn
  • Most common defects: deafness, cardiac abnormalities, ocular lesions, deafness, and mental and physical retardation in varying combinations; Less drastic sequelae that usually resolve in time are anemia, hepatitis, pneumonia, carditis, and bone infection

  
• Rubella Virus


  • A Rubivirus, in the family Togaviridae
  • Has the ability to stop mitosis, which is an important process in a rapidly developing embryo and fetus
  • Also induces apoptosis (programmed cell death) of normal tissue cells which can do irreversible harm to organs it affects
  • Damages vascular endothelium, leading to poor development of many organs

  
• Transmission and Epidemiology of Rubella


  • A disease with worldwide distribution
  • Infection is initiated through contact with respiratory secretions and occasionally urine
  • Virus is shed during the prodromal phase and up to a week after the rash appears
  • Congenitally infected infants are contagious for a much longer period of time
  • Because the virus is only moderately communicable, close living conditions are required for its spread
  • Most cases are reported among adolescents and young adults in military training camps, colleges, and summer camps

  
• Diagnosis of Rubella


  • Relies on the same twin techniques discussed earlier for measles
  • Rubella should not be diagnosed on clinical grounds alone
  • IgM antibody to rubella virus can be detected early using an ELISA technique or a latex-agglutination card
  • Women in developed countries routinely undergo antibody testing at the beginning of pregnancy to determine their immune status

  
• Prevention and Treatment of Rubella


  • Attenuated rubella virus vaccine is usually given to children in the combined form (MMR Vaccination) at 12 to 15 months and a booster at 4 or 6 years of age
  • Vaccine for rubella can be administered on its own, without the measles and mumps components
• Congenitally infected infants are contagious for a much longer period of time