Lecture 3 - The Cocci PDF

Lecture 3 — The Cocci Dr. Ed El Sayed NURS 342 spherical basteria Objectives What are the major features and characteristics of Gram positive cocci? What are some clinically relevant examples? What are the major features and characteristics of Gram negative cocci? What are some clinically relevant e...

Lecture 3 — The Cocci Dr. Ed El Sayed NURS 342 spherical basteria Objectives What are the major features and characteristics of Gram positive cocci? What are some clinically relevant examples? What are the major features and characteristics of Gram negative cocci? What are some clinically relevant examples? Special Gram Negative organism: Helicobacter pylori A. Gram positive cocci 1. Staphylococcus (S. aureus, S. epidermidis) 2. Streptococcus (S. pneumoniae, S. pyogenes, and the viridians group) 3. Loading… Enterococcus (E. faecalis and E. faecium) 1. Staphylococcus Gram positive cocci in clusters Common inhabitant of many host cells (some species are part of the flora, others are not i.e. cause disease) Staphylococcus epidermidis is normal part of skin flora, causes disease upon penetration injury (catheters, stabbing wounds) Staphylococcus aureus is the most serious and responsible for high morbidity, mortality and antibiotic resistant infections in the U.S (both nosocomial and community) Multiple routes of transmission for S. aureus — most common is skin-to-skin contact Systemic infection — caused when bacteria enters blood (e.g. bacteremia, toxic shock syndrome) Humans are the major reservoir (especially in nose and skin), but other animal reservoirs exist Loading… C A B Staph skin infections: A — Paronychia B — Impetigo C — Boils D — Cellulitis D Onychomycosis (L) vs Paronychia (R) Enzymes are substances produced by bacteria to overcome host defenses Some enzymes produced by staphylococcus: Coagulase — clots blood Catalase — neutralizes hydrogen peroxide Lipase — Digests fatty/oily cells in skin DNase — Breaks down DNA Penicillinase — Breaks down penicillin Toxins are substances produced by bacteria to damage host cells Some toxins produced by staphylococcus: Exotoxins — Released by bacteria while still alive, illicit a vigorous inflammatory responses at a site remote from infection. Examples: Enterotoxin — Damages gastrointestinal epithelia Hemolysin — Breaks down RBCs Exfoliative toxin — Breaks epidermal tissues Toxic shock toxin — Damages internal organs 2. Streptococcus Gram positive cocci in chains Common in humans, animals and environment Ability to form endospores to survive harsh environments Loading… Common inhabitant of many host cells (some species are part of the flora, others are not i.e. cause disease) Multiple routes of transmission — skin infections more common in summer while pharyngeal and respiratory infections more common in winter Humans are the major reservoir A. Streptococcus pyogenes: Most common pathogenic bacteria in this group. Causes: Pharyngitis (“Strep throat”) Rheumatic fever Cellulitis Glomerulonephritis Scarlet fever Toxic Shock ↳ systems immune part ofmicrobiota B. Streptococcus pneumoniae: -Not disease Normally colonizes upper respiratory tract in majority of people Elderly, toddlers, smokers and immunocompromised patients are at higher risk for disease Upper respiratory tract (sinusitis, bronchitis, pneumonia) ⑳ Meningitis (brain disease) disease NO Kidney Bacteremia and sepsis This is a vaccine preventable infection Virulence factors of Streptococcus: C-carbohydrate — a membrane bound polysaccharide that protects the bacteria from host cell lysozymes Lipoteichoic acid — another membrane bound structure that enables the bacteria to to adhere to host epithelial cells Hyaluronic acid — enables the bacteria to form an endospore and evade the immune system Streptokinase — Dissolves blood clots so that bacteria can spread Streptolysin O and S — toxins that break down RBCs, WBCs and damage internal organs resulting in organ failure and shock; also act as “superantigens” which leads to recruitment of T-cells and inflammatory cascade 3. Enterococcus Formerly classified as group D gamma-hemolytic streptococcus (GAD) Dispersed in short chains Normally present in gastrointestinal tract in healthy people Higher risk of disease in immunocompromised situations (elderly, cancer, HIV, etc) Predilection to cause disease in heart (endocarditis), urinary tract (cystitis) and colon (cancer) Drug resistance is a major concern with enterococcus species Poor hygiene is the major route of transmission (fecal-oral); contaminated medical instruments (more often in developing countries or resource-limited settings) Enterococcus faecalis endocarditis B. Gram negative cocci 1. Neisseria (N. meningitides, N. gonorrhoeae) 2. Acinetobacter species 1. Neiserria Gram negative diplococci Ability to replicate within neutrophils N. gonorrhoeae is transmitted sexually or vertically (mom-to-baby) N. meningitides is transmitted by close contact with an infected person through respiratory droplets (coughing and sneezing) causes CNS disease (meningitis) and/or septicemia (meningococcemia) Humans are the only known reservoir Increase risk of recurrent infection with Neisseria in patients with terminal complement deficiency Diplicocci Notable differences between Neisseria species N. gonorrhoeae N. meningitides Polysaccharide capsule absent Polysaccharide capsule present (protects from immune system) No vaccine available Vaccine preventable Pili present Pili absent 2. Acinetobacter Gram negative bacteria that varies in shape (cocci/bacilli) Found in soil, water, sewage Most infections are hospital acquired among patients who are on ventilators or with catheters (community acquired infection is possible but rare in U.S) Virulence factors include pili (enhances attachment to host cells) and ability to form biofilm (evades immune system) Associated with myriad of disease — pneumonia, meningitis, septicemia, cystitis, endocarditis, cellulitis and osteomyelitis Resistant to many antibiotics — limited treatment options Special Gram Negative organism: Helicobacter pylori Gram negative bacteria that is predominantly spiral in shape Microaerophilic (i.e. can survive in environments with limited oxygen) Loading… Motile by flagella Half of the world’s population is infected (up to 90% of population infected in developing countries) Oral-fecal transmission Infection causes peptic ulcer disease Not a vaccine preventable infection, but curable with antibiotics H. pylori H. pylori was discovered in 1982 by Robin Warren and Barry Marshall So they won the Nobel Prize in 2005 H. pylori virulence factors “Don’t limit your challenges. Challenge your limits.”