Gram-Positive and Gram-Negative Cocci PDF

Chapter 6 Gram positive and negative cocci Dra Verónica Veses Jiménez [email protected] Chapter overview Part I: – Genus Staphylococcus S. aureus – Genus Streptococcus S. pyogenes S. agalactiae S. pneumonia – Genus Enteroco...

Chapter 6 Gram positive and negative cocci Dra Verónica Veses Jiménez [email protected] Chapter overview Part I: – Genus Staphylococcus S. aureus – Genus Streptococcus S. pyogenes S. agalactiae S. pneumonia – Genus Enterococcus fecalis and feces Part II: – Genus Neisseria N. gonorrhoeae N. meningitidis 2 Staphylococcus Only 3 species are important in human disease: – S. aureus—causes a number of diseases – S. epidermidis—present in normal flora (normally benign, except when introduced via catheters, seen in hospital-acquired infections) – S. saprophyticus—causes urinary tract infections 3 Staphylococcus aureus 4 Staphylococcus aureus on the skin normal golden color = aureus Important human pathogen, causes both minor and serious diseases Can exist on dry surfaces for a long period Heat-resistant Staphylococcus aureus in (temperature range of skin. Micrograph from 18º- 40ºC) Dennis Kunkell website© 5 Morphology and physiology 30% of people are infected (normally hospital people) Gram-positive purple cluster formation = grape grape-like clusters, but in clinical specimens, can be seen as single cocci or diplococci Facultative anaerobic both Grows in media containing up to 10% NaCl infection not grape 6 Virulence factors of S. aureus: structural components Capsule and slime layer: may not be found growing on media, but it is usually present in vivo. Mediates attachment to medical devices, inhibits chemotaxis and phagocytosis Protein A: specific affinity for Fc of IgGs, avoiding the clearing action of antibodies. Teichoic acids (phosphate containing polysaccharides), which mediate attachment to fibronectin (mucosal membranes) Peptidoglycan: inhibits phagocytosis, confers osmotic resistance 7 Virulence factors of S. aureus: secretion of enzymes Coagulase - binds to fibrinogen and makes insoluble fibrin, aggregating all the bacterial cells together Fibrinolysin (staphylokinase)—dissolve fibrin clots Hyaluronidase —degrades connective tissues (facilitates spread; is present in 90% of S. aureus strains) Lipases—required for invasion into cutaneous and subcutaneous tissues Nuclease—hydrolysis viscous DNA Penicilase (from 1941 the microorganisms have developed resistance to penicillin by producing this enzyme, that breaks the β-lactamic ring) 8  Virulence factors of S. aureus: secretion of toxins break down human c Five cytolytic (membrane-damaging by pores) toxins: – Alpha, beta, delta, gamma, leukocidin – All cause lysis of neutrophils leading to massive lysosomal enzyme not ask the details secretion. Aditionally: only 5 cytoliotic names and all target neutrophil – Alpha is also toxic for red blood cells, hepatocites and platelets – Beta is toxic for rbc, fibroblasts, and macrophages – Delta is toxic for rbc and many other cells Two exfoliative toxins, A and B, also known as exfoliatin or epidermolytic toxin, separates epidermal layer from the dermis, which causes blistering and peeling of the skin and exposes a red underlayer. The general appearance of skin is like burned skin. 9 Virulence factors of S. aureus: secretion of toxins II Toxic Shock Syndrome Toxin-1 (TSST-1): associated with the use of vaginal tampons (cellulose-based) contaminated by skin staphilococcus The mode of infection: – Ultra-absorbent tampons bind Mg2+ ions – Low [Mg2+] triggers TSST-1 production by resident vaginal Staphylococci, TSST-1 stimulates production of IL-1 by macrophages and extravasations of endothelial cells, and fever – Initial symptoms: high fever, vomiting, diarrhea, myalgia hypovolemic shock and multiorgan faillure – 10 days from onset: hand and soles of feet develop sunburn-like rash, resulting in peeling of the skin. – Shock due to hypotension – Death due to respiratory failure (in 2-5% of cases) 10 Laura Wasser lost her leg in 2012 by TSST-1 11 Virulence factors of S. aureus: secretion of toxins III Eight enterotoxins (A-E, G-I) – Resistant to hydrolysis by gastric and jejunal enzymes. – Stable to heating at 100ºC for 30 minutes. – Mechanism of toxin activity not understood; no satisfactory animal model. – Stimulate intestinal peristalsis and have effects on central nervous system accompanied by intense vomiting. 12 Epidemiology Humans are major reservoir for S. aureus It colonizes the nose and is found in about 30% of individuals Transiently found on skin, oropharynx, and feces Transmitted via hand contact and aerosols Certain occupations are more prone to colonization Dentists, doctors, nurses, hospital workers Certain classes of patients are more prone to colonization Diabetics, hemodialysis patients, drug abusers, HIV patients 13 Pathogenesis of S. aureus Localized superficial infections – Folliculitis – Furuncle – Carbuncle – Impetigo Toxigenic infections: – scalded skin syndrome – Staphylococcal food-poisoning – Toxic Shock Syndrome Systemic diseases – Bacteremia – Pneumonia – Osteomyelitis 14 Superficial Infections Localized cutaneous infections, invade skin through wounds, follicles, or glands: – Folliculitis: superficial inflammation of hair follicle; usually resolved with no complications but it can progress – Furuncle (boil): inflammation of hair follicle or sebaceous gland progresses into abscess or pustule. – Carbuncle: larger and deeper lesion created by aggregation and interconnection of a cluster of furuncles. – Impetigo: bubble-like swellings that can break and peel away, most commonly seen in newborns. 15 Toxigenic disease – Food intoxication: ingestion of heat stable enterotoxins. It causes gastroenteritis. – Staphylococcal scalded skin syndrome: toxin induces bright red flush, blisters, then desquamation of the epidermis. – Toxic shock syndrome: toxemia leading to shock and organ failure. 16 Systemic infections – Osteomyelitis: infection is established in the metaphysis, and an abscess is formed. – Bacteremia: the primary origin is bacteria arriving to the bloodstream from another infected site or medical devices. It can lead to endocarditis (inflammation of the endocardium). 17  Clinical manifestations bubble like swelling impetigo scalded skin syndrome Toxic shock syndrome 18 Clinical manifestations: summary 19 Treatment Antibiotics methicillin resistant = resistante to all of them Methicillin, oxacillin, nafcillin, and dicloxacillin (semisynthetic penicillins resistant to ß-lactam hydrolysis) Majority of patients can be treated, but many of S. aureus strains are resistant nowadays. 20 MRSA 21 What is MRSA MRSA is Methicillin Resistant Staphylococcus aureus Is a bacteria that is resistant to a synthetic penicillin- methicillin. MRSA causes a variety of disseminated, lethal infections in humans. Has the ability to easily transfer resistant genes to other species directly and indirectly 22 in 3 years = resistance 23 Source of MRSA infections Nasal carriage is the most common Own epithelial flora-self contamination Hospitals Dirty hands, towels Daycare centers need to be tested a,nd after treating to eradicate Community 24 Predisposing factors open Integument injury Burns and trauma Foreign objects A history of chronic Infections Hormonal changes and stress Immunocompromised 25 Clinical manifestations A localized, superficial abscess. Invasion of lymphatics, blood, and major organs. 26 Treatment Vancomycin: acts by interfering with the construction of cell wall. Side effects: hearing loss and nephrotoxicity Linezolid: protein synthesis inhibitor Daptomycin: causes membrane depolarization in bacteria, interrupting membrane transport Alternatives: Rifampin Third-Line agents: TMP-SMX 27 New therapies Oritavancin, a new glycopeptide, similar to vancomycin, approved by the FDA in 2014. Less secondary effects Tigecyclin: a glycylcycline, which is not affected by either specific efflux pump or ribosomal protection mechanisms of resistance. Dalbavancin- semisynthetic lipoglycopeptide, designed to improve the effect of vancomycin. Development of StaphVAX®, a polysaccharide conjugate vaccine against S. aureus infections. Not approved by the FDA yet. 28 STREPTOCOCCUS 29 Streptococcus Gram positive cocci in chains Facultative anaerobic Sensitive to penicillin Human reservoir—passed species that carry it the most from person to person Streptococci constitute a part of the commensal flora of the human mouth, skin, intestine, and upper respiratory tract Can cause a variety of human diseases (pharyngitis; meningitis; pneumonia; endocarditis; necrotizing fasciitis) 30 Clasification criteria 1. Lancefield antigens (initially A to W, now in use: A, B, C, F and G) 2. Hemolysis α – Iron in haemoglobin oxidised, greenish color β – Complete disruption of red cells, clear zone around colonies (Further characterized by Lancefield serotyping, distinguishing between strains by cell wall carbohydrates) γ - Non-hemolytic streptococci 3. Biochemical characteristics 31 Streptococci relevant in human disease 1. Alpha hemolytic: Streptococcus pneumonia yellow 2. Beta hemolytic: brown - Group A: Streptoccocus pyogenes - Group B: Streptoccocus agalactiae - Group C - Group F - Group G 3. Non hemolytic: - Group D: now Enterococci 32 Streptococcus pyogenes 33 Virulence factors of Streptococcus pyogenes Avoid phagocytosis: – Capsule – M protein – F protein – Lipoteichoic acid no LPS 34  production of pus Virulence factors of Streptococcus pyogenes II Production of toxins: – Streptolysin O (O2 labile): causes hemolysis of red blood cells, leucocytes and platelets – Streptolysin S (O2 stable). It is produced in the presence of serum. It causes hemolysis of red blood cells, leucocytes and platelets and other cells – Streptococcal pyrogenic exotoxins (A, B, C, and F). Also known as erythrogenic toxins, mediators of typical red rash in scarlet fever and shock and multiorganic failure in the streptococcal toxic shock syndrome. scarlet fever : scarlatina = complication of pharyngitis w no antibio 35 Virulence factors of Streptococcus pyogenes III Enzymes – Streptokinases (A and B). Anticlotting properties, by degrading plasminogen, fibrine and fibrinogen – DNases (A to D), depolymerize free DNA in pus abcesses, increasing the dissemination of the microorganisms – Hyaluronidase – spreading factor 36  Streptococcus pyogenes infections Acute bacterial pharyngitis/tonsillitis (about 1/3 of all sore throats are “strep throats”) angine – Sore throat, malaise, fever, headache Scarlet fever: is a complication of pharyngitis and causes rash on trunk and extremities. Mediated by the action of the pyrogenic toxin. from trunk to the extremities need to know where it started = dep on the origin change the type of infection 37 Streptococcus pyogenes suppurative infections Impetigo (pyoderma) – superficial lesions that break and form highly contagious crust; often occurs in epidemics in school children; also associated with insect bites, poor hygiene, and crowded living conditions Erysipelas: acute infection of the skin. Patients experience localized pain, inflammation, lymph node enlargment and fever, chills and leokocytosis. Cellulitis: pathogen enters through a break in the skin and eventually spreads to the dermis and subcutaneous tissues; can remain superficial or become systemic Necrotizing fasciitis: infection of deep areas of subcutaneous tissue, destroying muscle and adipose tissues 38  Streptococcal suppurative infections white = pus of the bacteria (no viral) bact and neutrophil fight tonsillitis Erysipelas tonsillitis sore throught last week green partial hemolysis red but not maculo papula (evlevation ) Scarlet fever Necrotizing fasciitis 39 Beth, in Little Women dies of scarlet fever ( 1994 and in the 2019 remake) 40 Nonsuppurative streptococcal infections Streptococcal toxic shock like syndrome (TSLS) – Initial infection may have been pharyngitis, cellulitis, peritonitis, or other wound infections – From the skin or wound infection bacteria reaches bloodstream – Death rate ~30%; over 10-fold higher than TSST (Toxic Shock Syndrome Toxin of S. aureus ) – High fatality rate because rapid development of shock and multiple organ failure, similar to staphylococcal toxic shock 41 Streptococcal toxic shock like syndrome (TSLS) Features in common with scarlet fever Occur in healthy people Both associated with high fatality rate Produce same exotoxin: streptococcal pyrogenic exotoxin (Spe) Similar in mechanism to TSST-1 Rash, fever, shock, multiple organ failure Both toxins are superantigens Same mechanisms of action 42 Nonsuppurative streptococcal infections II Rheumatic fever: nonsuppurative complication of pharyngeal infections – Fever – Inflammation of the heart, joints, blood vessels, and subcutaneous tissues – Chronic, progressive damage to the heart valves (evidence suggests cross-reactivity between Streptococcal antigens and heart tissue) 43 Nonsuppurative streptococcal infections III Acute glomerulonephritis (AGN) from either cutaneous or pharyngeal infections – More common in children than adults – Antigen-antibody complexes deposit in the glomerulus – Inflammatory response causes damage to the glomerulus and impairs the kidneys infection streptococcus ; in the heart they remember inflammation ; later might activate and recognized normal heart tissue = autoimmune disease 44 S. pyogenes treatment Generally, Streptoccoci are not routinely tested for susceptibility since penicillin is the drug of choice. If the patient is allergic to penicillin use erythromycin. TSLS is a medical emergency – Surgical debridement of wounds prevents further production of toxin – Antibiotics; penicillin (if allergy use erythromycin) – intravenous rehydration required to counteract toxic effects of TSST-1 (such as hypotension) 45 To prevent Streptococcal Sequellae Doctors should recommend prophylactic penicillin before surgical work Kill bacteria escaping into blood stream from mouth (oral bacteria are susceptible to penicillin) Reduces chance of colonization and avoid streptococcal sequellae such as rheumatic fever 46 Streptococcus agalactiae 47 Streptococcus agalactiae Colonizes the urogenital tract of pregnant women (10-30% rate), can cause complications such as premature rupture of membranes and premature delivery Causes diseases in pregnant women and in newborns The main virulence factor is an antiphagocytic capsule do not cause disease to healthy people 48 Clinical manifestations Early-onset infection – Occurs in neonates who are less than 7 days old – Vertical transmission of the microorganism from the mother (Pregnant women are screened at 35-37 weeks gestation) – Manifests in the form of pneumonia or meningitis with bacteremia – Associated with a high mortality rate 49 Streptococcus agalactiae Late-onset infection – Occurs between 1 week and 3 months after birth – Usually occurs in the meningitis form – Mortality rate is not as high as early-onset In adults – Occurs in immunosuppressed patients or those with underlying diseases – Associated with postpartum endometritis, wound infection and UTI 50 Treatment Penicillin G IV If allergy, vancomycin last resort but only possible Prophylactic antibiotic intrapartum for positive pregnant women 51 Streptococcus pneumoniae 52 Streptococcus pneumoniae General characteristics – Inhabits the nasopharyngeal areas of healthy individuals – Typical opportunist Virulence factors – Polysaccharide capsule 53 Streptococcus pneumoniae Clinical infections – Pneumonia (most common cause of bacterial pneumonia) – Meningitis – Bacteremia – Sinusitis – otitis media (most common cause of otitis media in children < 3 years) 54 Treatment Penicillin For pneumonia: fluoroquinolons or vancomycin plus ceftriaxone Available vaccine: Prevenar® 55 ENTEROCOCCUS 56 Enterococci Gram positive cocci in short chains Part of the normal bowel flora. Inhabit the GI tract, genitourinary tract and oral cavity Very common cause of nosocomial infections 57 Enterococcus and human disease Clinically Significant Isolates – E. faecalis – E. faecium Associated infections – Bacteremia – Urinary tract infections – Wound infections E. faecalis D. Kunkel© – Nosocomial Infections – Severe complications: endocarditis – Polymicrobial infections 58 Virulence factors of Enterococcus Surface adhesins Cytolysin: induces local tissue damage and inhibits Gram positive bacterial growth Pheromone: regulate inflammatory response Gelatinase: hydrolysis of gelatin, collagen and hemoglobin Multiple plasmid and antibiotic resistance GENE 59 Treatment for Enterococcus – Antibiotic resistance seen with Enterococcus – Vancomycin, linezolid, selected fluoroquinolones – High prevalence of VRE 60 GRAM NEGATIVE COCCI 61 Chapter overview Genus Neisseria – N. gonorrhoeae – N. meningitidis 62 Genus Neisseria Gram negative cocci often arranged in pairs with adjacent sides flattened (resembling coffee beans) NEED CO2 Aerobic to microaerophilic Non-pathogenic strains grow normally in nutrient agar N. gonorrhoeae is fastidious, capnophilic and susceptible to cool temperatures, drying and fatty acids – Requires complex media pre-warmed to 35-37C – Soluble starch added to neutralize fatty acid toxicity – Grow best in moist atmosphere supplemented with CO2 63 Neisseria and human disease This genus includes two species pathogenic for humans: N. gonorrhoeae (gonococci) N. meningitidis (meningococci) Other species (N. lactamica, N. sicca, N. subflava, N. flavescens) are normal inhabitants of the human upper respiratory tract (oropharyngeal area) as commensals. They are of importance only for the differential diagnosis. 64 Neisseria gonorrhoeae 65 Gonococcal virulence factors Antiphagocytic capsule-like negative surface charge Only fimbriated cells are virulent Outer membrane proteins (formerly Proteins I, II, & III) Por (porin protein) prevents phagolysosome fusion FOR ENTRY following phagocytosis and thereby promotes intracellular CHANNELS OF THINGS survival Opa (opacity protein) mediates firm attachment to epithelial cells and subsequent invasion into cells Rmp (reduction-modifiable protein) protects other surface antigens from bactericidal antibodies (Por protein, LOS) 66 Gonococcal virulence factors II Acquisition of iron: – Tbp 1 and Tbp 2 (transferrin-binding proteins) – Lbp (lactoferrin binding protein) steel iron – Hbp (hemoglobin-binding protein) Lipooligosaccharide (LOS; incomplete Lipopolysaccharide; still retains endotoxin activity) IgA1 protease Acquisition in last two decades of two types of antibiotic resistance: – Plasmid-encoded beta-lactamase production – Chromosomally-mediated changes in cellular permeability inhibit entry of penicillin, tetracycline, erythromycin, aminoglucosides 67 Epidemiology of gonorrhea Transmitted by sexual contact Asymptomatic patients are the major reservoir Lack of protective immunity and therefore reinfection, is partly due to antigenic diversity of strains Higher risk of disseminated disease in patients with late complement deficiencies spread all over the body hemorragic rash 68 Pathogenesis of N. gonorrhoeae Fimbriated cells attach to intact mucus membrane epithelium The microorganism has the capacity to invade intact mucus membranes or skin with abrasions, and then penetration and multiply before passing through mucosal epithelial cells and establish infection in the sub-epithelial layer Most common sites of inoculation: – Cervix or vagina in the female – Urethra or penis in the male 69 Clinical diseases Gonorrhoea – Men – Women Disseminated infections Ophthalmia neonatorum 70 Gonorrhea in men Urethritis; Epididymitis Most infections amongst men are acute and symptomatic with purulent discharge and dysuria (painful urination) after 2-5 day incubation period The two bacterial agents primarily responsible for urethritis amongst men are N. gonorrhoeae and Chlamydia trachomatis 71 Gonorrhea in women Cervicitis; Vaginitis; Pelvic Inflammatory Disease (PID); Disseminated Gonococcal Infection (DGI) Women are often asymptomatic or have unrecognized sympthoms); Often untreated until PID complications develops Pelvic Inflammatory Disease (PID) – May also be asymptomatic, but difficult diagnosis accounts for many false negatives – Can cause scarring of fallopian tubes leading to infertility or ectopic pregnancy 72 Disseminated Gonococcal Infection (DGI): Affects 1-3 % women as a result of gonococcal bacteremia Often presents with skin lesions – Petechiae (small, purplish, hemorrhagic spots) – Pustules on extremities Arthralgias (pain in joints) Tendosynovitis (inflammation of tendon sheath) Septic arthritis Occasional complications: hepatitis; rarely endocarditis or meningitis 73 Neisseria gonorrhoeae in urethral exudates 74 Treatment Penicillin is no longer the drug of choice due to resistance For uncomplicated infections: ceftriaxone, cefixime or fluoroquinolones Combined with doxycycline or azithromycin for dual infections with Chlamydia Opthalmia neonatorum: – Chemoprophylaxis of newborns against with 1% silver nitrate, 1% tetracycline, or 0.5% erythromycin eye ointments – Treatment: ceftriaxone QS 75 Neisseria meningitidis 76 Neisseria meningitidis virulence factors Pili-mediated, receptor-specific colonization of nonciliated cells of nasopharynx Antiphagocytic polysaccharide capsule allows systemic spread in absence of specific immunity Toxic effects mediated by hyperproduction of lipooligosaccharide 77 Epidemiology Person-to-person transmission by aerosolization of respiratory tract secretions in crowded conditions Highest incidence in children younger than 5 years and particularly those younger than 1 year of age as passive maternal antibody declines and as infants immune system matures Second most common cause (after S. pneumoniae) of community-acquired meningitis in previously healthy adults 78 Clinical diseases Meningitis Septicemia (meningococcemia) with or without meningitis Meningoencephalitis Pneumonia Arthritis Urethritis 79 N. meningitidis Cerebrospinal Fluid Skin Lesions 80 Treatment Penicillin is the drug of choice for treatment along with supportive therapy for meningeal symptoms – Increasing MIC mediated by genetic alteration of target penicillin binding proteins is being monitored – Chloramphenicol or cephalosporins as alternatives Prophylaxis of close contacts with rifampicin 81