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Medical Microbiology Part I: Infections of Skin, Respiratory & Gastrointenstinal tracts Lecture #15 Bio3124 Characterizing Microbial Diseases • Identification of pathogen is important – Determines method of treatment • Clues to rapid identification – Signs and Symptoms – Testing of specimens – Knowing patient histories • • • • Environment Occupation and social activities Nutrition Previous medical history Human infectious diseases Source and origin of pathogens • Airborne infections • Arthropod-borne diseases • Direct contact diseases • Food-borne and water-borne infections • Zoonotic infections Human infectious diseases By the site of infection, • Skin and soft tissue infections • Respiratory system infections • Gastrointenstinal tract infections • Genitourinary tract infections • Central nervous system infections • Cardiovascular system infections • Systemic infections Human skin infections • Staphylococcal infections – Boils and scalded skin syndrome • Streptococcal infections – Necrotizing faciitis • Clostridial infections – Gas Gangrene • Viral skin infections – Measles, Chickenpox , Smallpox Staphylococcal infections • members of genus of Staphylococcus – gram-positive cocci, grape-like clusters – facultative anaerobes and usually catalase positive – normal inhabitants of upper respiratory tract, skin, intestines, and vagina – S. aureus – coagulase positive, pathogenic – S. epidermidis – coagulase negative, less pathogenic – many pathogenic strains are slime producers Slime • viscous extracellular glycoconjugate that allows bacteria to adhere to smooth surfaces and form biofilms • inhibits neutrophil chemotaxis, phagocytosis, and antimicrobial agents slime Staphylococcal Skin infections • localized abscess and boils – – – – S. aureus established in a hair follicle, tissue necrosis coagulase forms fibrin wall limiting spread Liquefaction, abscess spreads may be a furuncle (boil) or carbuncle Furuncle Carbuncle Toxic shock syndrome (TSS) • caused by S. aureus strains that release toxic shock syndrome toxin (TSST-1) • disease results from body’s response to staphylococcal superantigens • Resulting in massive cytokine production leading to circulatory collapse , shock and multi-organ failure • clinical manifestations – low blood pressure, fever, diarrhea, extensive skin rash, and shedding of the skin Staphylococcal scalded skin syndrome (SSSS) • S. aureus that carry a plasmid-borne gene for exfoliative toxin (exfoliatin) • A protease, weakens skin • epidermis peels off • Diagnosis – isolation/identification of staphylococcus involved /use of commercial kits – isolation and identification based on catalase test, coagulase test, serology, DNA fingerprinting, and phage typing • Treatment, prevention, and control – antibiotic therapy: Vancomycin, cephalosporins, rifampin • many drug-resistant strains – personal hygiene and aseptic management of lesions Invasive Streptococcus A Infections • Streptococcus pyogenes: important pathogen in the group • causes invasive infections • virulence is due to: – Pyrogenic exotoxin A (SpeA), a superantigen • nonspecific T cell activation and large amount of cytokine production, damaging endothelial cells -> multiorgan failure – rapid fluid loss from tissues – A cystein protease (exotoxin B) breaks down host proteins, cause further tissue damage Necrotizing Fasciitis • clinical manifestations – necrotizing fasciitis • destruction of sheath covering skeletal muscle – myositis • inflammation and destruction of skeletal muscle and fat tissue – toxic shock-like syndrome (TSLS) • precipitous drop of blood pressure, failure of multiple organs, and high fever • Treatment: • Surgical removal of affected tissues, amputation • Penicillin G therapy Gas Gangrene or Clostridial Myonecrosis • Agent: Clostridium perfringens – gram-positive, spore-forming rod – Cause gas gangrene, a necrotizing infection of skeletal muscle or clostridial myonecrosis, produces H2 – secretes α-toxin, a lecithinase cause membrane damage and cellular death – tissue damaging enzymes eg. Collagenase → invasion • transmitted by spores from soil, bowel microbiota or infected tissues Gas gangrene… • clinical manifestations – severe pain, edema, drainage, and muscle necrosis • diagnosis – recovery of appropriate clostridial species and characteristic disease symptoms • treatment, prevention, and control – surgical debridement, administration of antitoxin, antibiotic therapy, and hyperbaric oxygen therapy – prompt treatment of all wound infections and amputation of limbs Chickenpox (Varicella) and Shingles (Herpes Zoster) • • • • Highly contagious skin disease varicella-zoster virus (VZV), Herpesviridae, dsDNA enveloped virus, icosahedral symmetry infects children 2-7 years old humans serve as reservoir • droplets carrying virus enter respiratory system • Incubation (10-23 days) • Day 0: infection of mucosa of URS, viral replication in lymph nodes • Day 6: enters blood stream (primary viremia) replication in liver and spleen • followed by secondary viremia • Day 10: moves to skin (vesicular rash) • vesicles erupt on face and upper trunk • filled with pus, rupture, covered by scabs • Diagnosis: by symptoms • Lab tests: not required, if so ELISA for IgM or PCR • Prevention: attenuated varicella vaccine • Treatment: acyclovir (Zovirax) inhibits viral DNA polymerase Chickenpox (Varicella) and Shingles (Herpes Zoster) Shingles (Herpes zoster) recovery→natural immunity virus enters a latent stage, nucleus of cranial nerves & dorsal ganglia ~ 500,000 cases per year in US virus reactivated, weaker immune system, (Herpes zoster virus) migrates down nerve axon, replicates and damages sensory nerves painful vesicles called shingles along dorsal trunk syndrome is called post-herpetic neuralgia Therapy: not required; if necessary acyclovir or other antivirals such as Famvir can be prescribed Smallpox (Variola) • caused by variola virus – large, brick-shaped virus – linear dsDNA virus of Poxviridae • transmitted by aerosol or contact – humans are only natural host • • • • • Enters to regional lymph node Incubation period 12-14 days Multiplies in macrophage and monocytes Enters blood (viremia) Prodromal stage: is the symptomatic imminent attack of disease characterized by – Virus moves to epithelial cells in mouth and throat – Severe head and body aches, high fever (40C), malaise and vomiting – Infects the capillary epithelia of skin – Vesicles filled with pus form and later rupture to leave a skin lesion Eradication of Smallpox • Protection achieved by vaccination – Vaccina virus in a live virus vaccine • use of vaccine is controversial because of its unknown efficacy • Food and Drug Administration has not approved any treatment for smallpox • 1977 – last case from a natural infection occurred in Somalia • Why eradication was possible – disease has obvious clinical features – humans are only hosts and reservoirs – there are no asymptomatic carriers – short infectivity period (3-4 weeks) Human respiratory tract infections • Infection of upper/lower respiratory tract, mostly viral • Seldom spread to other tissues • Streptococcal infections of lungs – Bacterial pneumonia • Mycobacterial infections – Tuberculosis • Viral infections of respiratory tract – Influenza – Respiratory syncytial virus infection (RSV) Streptococcal pneumonia • Opportunistic pathogen Streptococcus pneumoniae – normal microbiota in upper R.tract – polysaccharide capsule and a toxin – rapidly multiplies in alveolar spaces • Capsule prevents phagocytosis • rapid growth in alveoli • Bloody sputum • 13000-66000 death in US/year • occasionally results in otitis media • major opportunistic infection among AIDS patients Streptococcal pneumonia… • diagnosis – chest X-ray, gram stain, culture, and tests for metabolic products • clinical manifestations – abrupt onset of chills, hard labored breathing, chest pain, and rust colored sputum • treatment, prevention, and control – antibiotic therapy with penicillin G • resistant strains have appeared – Vaccine: Pneumovax vaccine pooled collection of 23 different S.pneumonia capsular polysaccharides Tuberculosis (TB) • Mycobacterium tuberculosis • At the time of identification by Robert Koch responsible for 1/7 of deaths in Europe, and 1/3 of young adults • ~ 1/3 of world’s population infected • resistance to phagocytic killing – Mycolic acids in cell wall form hydrophobic barrier – toxic to cells – Inhibit phagosome-lysosome fusion • Transmission – person to person – also transmitted from infected animals and their products TB - Course of Disease • M. tuberculosis not killed in lung phagocytes • tubercles form in alveolar lymphatic node – composed of bacteria, macrophages, T cells and human proteins – subsequent changes in tubercle may occur • caseous lesion – cheese-like consistency • Ghon complexes – calcified caseous lesion • show up prominently in chest X-rays • miliary tuberculosis: Tubercles liquefy and bacteria spread • also called reactivation tuberculosis because bacteria reactivated at initial infection site TB tubercle Persons Infected With TB • develop cell-mediated immunity (sensitized T cells) – basis for tuberculin skin test • incubation period – 4-12 weeks • symptoms – fever, fatigue, weight loss – cough • characteristic of pulmonary involvement • may result in expectoration of bloody sputum Tuberculosis… • diagnosis – observation of acid-fast bacteria, chest X-ray, DNAbased tests, Mantoux or tuberculin skin test • antimicrobial therapy – Isoniazid, rifampin, pyrazinamide and ethambutol • multi-drug-resistant strains of tuberculosis (MDR-TB) have developed • prevention and control – rapid, specific therapy to interrupt spread, retreatment of patients with MDR-TB, immunization, improved sanitation and housing, and reduction in homelessness and drug abuse Influenza (Flu) • caused by influenza virus • classified into subtypes based on hemagglutinin (HA) and neuraminidase (NA) – HA and NA function in viral attachment and virulence – 16 HA and 9 NA antigenic forms are known; they recombine to produce HA/NA influenza subtypes Influenza (Flu) • clinical manifestations – chills, fever, headache, malaise, and general muscle aches and painful joints – recovery usually within 3 to 7 days – often leads to secondary infections by bacteria • treatment, prevention, and control – rapid immunologic tests for diagnosis of subtype – symptomatic/supportive therapy – Tamiflu, neuraminidase inhibitor shortens the course of illness • Prevention: inactivated virus vaccine Gastrointestinal tract infections • Bacterial diarrhea – Enterohemorrhagic E.coli • Peptic ulcer and gasteritis – Helicobacter pylori • Viral gastroenteritis Enterohemorrhagic E.coli infection Reservoir: cattle, fecal contamination of water or food since 1982; “Jack-in-the Box” 1993 hamburger outbreak in US Walkerton, Canada (2000) Agent: EHEC strain O157:H7 Shiga toxin -> cleaves host 28S rRNA Signs and symptoms: diarrhea, fever, abdominal cramps endothelial damage in different tissues Platelet-fibrin micro-clots form leading to o Kidney failure (Hemolytic Uremic Syndrome) o Skin hemorrhage (Purpura) o Brain hemorrhage, neurological disorder, coma, & death Diagnosis: positive test for EHEC in food stock or in patient, or testing positive for toxin Treatment: cidal antibiotics not recommended due to toxin, statics in sever cases, supportive treatment for electrolytes Gastritis and Peptic Ulcer • caused by Helicobacter pylori, a spiral microaerophilic G- bacterium • Discovered in 1982 and initially named Campylobacter pylori – colonizes gastric mucus-secreting cells – produces urease, elevates pH – releases toxins that damage epithelial mucosal cells H. pylori attached to gastric cells H. pylori … • transmission probably from person to person – common source has not been ruled out • diagnosis – culture of gastric biopsy specimens, examination of stained biopsies, serological testing, urea breath test, tests for ammonia in urine, and detection of urease activity in biopsies • treatment, prevention, and control – a combination of drugs to decrease stomach acid and antibiotics to kill the bacteria Viral Gastroenteritis • acute viral gastroenteritis – inflammation of stomach or intestines – important disease of infants and children – leading cause of childhood death in developing countries (5-10 million a year) – usually spread by fecal-oral route • caused by six major groups of viruses – – – – – – Rotaviruses Adenoviruses Caliciviruses Asteroviruses Norwalk virus Noroviruses Viral Gastroenteritis • Clinical manifestations: – – – – – Asymptomatic to mild diarrhea Headache and fever Or sever diarrhea with abdominal cramps Vomiting Death is due to loss of electrolytes • Treatment: – usually self-limiting disease – Electrolytic replacement with isotonic solutions – symptomatic/supportive therapy