Gram-Positive Cocci - Staph., Strept., & Pneumo. PDF

Gram-Positive Prepared & Presented by ❖ Introduction : ✓ There are two medically important genera of gram-positive cocci: Staphylococcus and Streptococcus. ✓ Staphylococci and streptococci are nonmotile and do not form spores. ✓ Both staphylococci and streptococci are gram- positive cocci...

Gram-Positive Prepared & Presented by ❖ Introduction : ✓ There are two medically important genera of gram-positive cocci: Staphylococcus and Streptococcus. ✓ Staphylococci and streptococci are nonmotile and do not form spores. ✓ Both staphylococci and streptococci are gram- positive cocci, but they are distinguished by two main criteria: 1) Microscopically, staphylococci appear in grapelike clusters, whereas streptococci are in chains. 2) Biochemically, staphylococci produce catalase (i.e., they degrade hydrogen peroxide), whereas streptococci do not. 2 Dr. Omar Aldossary ❖ Staphylococci : ❑ Important Properties : Staphylococci are spherical gram-positive cocci arranged in irregular grapelike clusters. All staphylococci produce catalase (degrades H2O2 into O2 and H2O). Catalase is an important virulence factor. Three species of staphylococci are important human pathogens: S. aureus, S. epidermidis, and S. saprophyticus. 3 Dr. Omar Aldossary  ❖ Staphylococci : Staphylococcus aureus causes abscesses, Abscess on foot various pyogenic infections (e.g., endocarditis, septic arthritis, and osteomyelitis), food poisoning, scalded skin syndrome, and toxic shock syndrome. It is one of the most common causes of hospital- acquired pneumonia, septicemia, and surgical- wound infections. Folliculitis It is an important cause of skin and soft tissue infections, such as folliculitis, cellulitis, and impetigo. It is the most common cause of bacterial conjunctivitis. Impetigo 4 Dr. Omar Aldossary ❖ Staphylococci : Staphylococcus epidermidis causes prosthetic valve endocarditis and prosthetic joint infections. It is the most common cause of central nervous system shunt infections and an important cause of sepsis in newborns. Staphylococcus saprophyticus causes urinary tract infections, especially cystitis. 5 Dr. Omar Aldossary ❖ Staphylococci : ❑ Transmission : ✓ Human’s bodies are the reservoir for staphylococci. ✓ The nose is the main site of colonization of S. aureus, and approximately 30% of people are colonized at any one time. People who are chronic carriers of S. aureus in their nose have an increased risk of skin infections caused by S. aureus. ✓ The skin, especially of hospital personnel and patients, is also a common site of S. aureus colonization. Hand contact is an important mode of transmission, and handwashing decreases transmission. ✓ S. epidermidis is found primarily on the human skin and can enter the bloodstream at the site of intravenous catheters that penetrate through the skin. ✓ S. saprophyticus is found primarily on the mucosa of the genital tract, and cause Urinary tract infection. 6 Dr. Omar Aldossary ❖ Staphylococci : ❑ Pathogenesis : Osteomyelitis, Arthritis 7 Dr. Omar Aldossary  ❖ Staphylococci : ❑ Clinical Findings : The important clinical manifestations caused by S. aureus can be divided into two groups: pyogenic (pus-producing) and toxin-mediated. ▪ These include: abscess, impetigo, furuncles, cellulitis, folliculitis, conjunctivitis, and eyelid infections. ▪ Septicemia (sepsis) can originate from any localized lesion, especially wound infections. ▪ Endocarditis may occur on normal or prosthetic heart valves, especially right-sided endocarditis. ▪ Osteomyelitis and septic arthritis. ▪ Pneumonia can occur in postoperative patients or following viral respiratory infection, especially influenza. 8 Dr. Omar Aldossary ❖ Staphylococci : ❑ Clinical Findings : The important clinical manifestations caused by S. aureus can be divided into two groups: pyogenic (pus-producing) and toxin-mediated. ▪ Food poisoning (gastroenteritis) is caused by ingestion of enterotoxin, which is preformed in foods and has a short incubation period (1–8 hours). Vomiting is typically more prominent than diarrhea. ▪ Toxic shock syndrome is characterized by fever; hypotension; a diffuse, macular, sunburn-like rash. Involve: liver, kidney, gastrointestinal tract, CNS, muscle, or blood. ▪ Scalded-skin syndrome is characterized by fever, large bullae, and an erythematous macular rash. 9 Dr. Omar Aldossary  ❖ Staphylococci : ❑ Treatment : ✓ 90% or more of S. aureus strains are resistant to penicillin G. Most of these strains produce β-lactamase. Such organisms can be treated with β-lactamase–resistant penicillins (e.g., nafcillin or cloxacillin), some cephalosporins, or vancomycin. Treatment with a combination of a β-lactamase–sensitive penicillin (e.g., amoxicillin) and a β-lactamase inhibitor (e.g., clavulanic acid) is also useful. ✓ Approximately 20% of S. aureus strains are methicillin resistant or nafcillin-resistant (MRSA or NRSA). The drug of choice is vancomycin, to which gentamicin is sometimes added. 10 Dr. Omar Aldossary  ❖ Staphylococci : ❑ Treatment : ✓ Some strains with intermediate resistance to vancomycin (VISA strains) and others with complete resistance to vancomycin (VRSA strains). Daptomycin (Cubicin) can be used to treat infections by these organisms. Quinupristin-dalfopristin (Synercid) is another useful choice. ✓ The treatment of toxic shock syndrome involves correction of the shock by using fluids, pressor drugs, and inotropic drugs; Pooled serum globulins, which contain antibodies are useful. 11 Dr. Omar Aldossary ❖ Staphylococci : ❑ Prevention : 12 Dr. Omar Aldossary ❖ Streptococci : ❑ Important Properties : Streptococci are a family of G +ve, nonmotile, nonsporeforming, catalase-negative cocci. The Streptococcus genus are the most common facultative anaerobic cocci. They are divided into three groups based on their ability to induce hemolysis on blood agar: α-hemolytic Streptococcus (also known as Strept. viridans, incomplete, green hemolysis) form a green zone around their colonies as a result of incomplete lysis of red blood cells in the agar, β-hemolytic Streptococcus (clear, complete lysis of red cells) because complete lysis of the red cells occurs, γ-hemolytic Streptococcus (also known as nonhemolytic Streptococci). 13 Dr. Omar Aldossary  ❖ Streptococci : Pharyngitis ❑ Diseases : ✓ Streptococci cause a wide variety of infections. ✓ Streptococcus pyogenes (group A streptococcus) is the leading bacterial cause of pharyngitis, cellulitis, an impetigo, necrotizing fasciitis, and streptococcal Cellulitis toxic shock syndrome. It is also the inciting factor of two important immunologic diseases, rheumatic fever and acute glomerulonephritis (AGN). ✓ Streptococcus agalactiae (group B streptococcus) is the leading cause of neonatal sepsis and meningitis. ✓ Viridans group streptococci are the most common cause of endocarditis, in patients undergo to surgical procedures in oral cavity. 14 Dr. Omar Aldossary Endocarditis ❖ Streptococci : ❑ Transmission : ✓ Most streptococci are part of the normal flora of the human throat, skin, and intestines but produce disease when they gain access to tissues or blood; ✓ Viridans streptococci and S. pneumoniae are found chiefly in the oropharynx; ✓ S. pyogenes is found on the skin and in the oropharynx in small numbers; ✓ S. agalactiae occurs in the vagina and colon; and both the enterococci and anaerobic streptococci are located in the colon. 15 Dr. Omar Aldossary ❖ Streptococci : ❑ Pathogenesis : 16 Dr. Omar Aldossary  ❖ Streptococci : ❑ Clinical Findings : Streptococcus pyogenes causes three types of diseases: 1) Pyogenic diseases such as pharyngitis and cellulitis, Pharyngitis (sore throat) characterized by throat pain and fever. On examination, an inflamed throat and tonsils, often with A yellowish exudate, are found, accompanied by tender cervical lymph nodes. Untreated pharyngitis may extend to the middle ear (otitis media), the sinuses (sinusitis), the mastoids (mastoiditis), or the meninges (meningitis). 2) Toxigenic diseases such as scarlet fever and toxic shock syndrome, 17 Dr. Omar Aldossary ❖ Streptococci : ❑ Clinical Findings : 3) Immunologic diseases such as rheumatic fever and acute glomerulonephritis (AGN) (Poststreptococcal - Nonsuppurative). AGN is more frequent after skin infections than after pharyngitis. The most striking clinical features are hypertension, edema of the face (especially periorbital edema) and ankles. 4) Viridans streptococci (e.g., S. mutans, S. sanguinis, S. salivarius, and S. mitis) are the most common cause of infective endocarditis. They enter the bloodstream (bacteremia) from the oropharynx, typically after dental surgery. Signs of endocarditis are fever, heart murmur, anemia, and embolic events such as splinter hemorrhages, subconjunctival petechial hemorrhages, and Janeway lesions. 18 Dr. Omar Aldossary  ❖ Streptococci : ❑ Treatment : Group A streptococcal infections can be treated with either Penicillin G or Amoxicillin, but neither rheumatic fever nor AGN patients benefit from penicillin treatment after the onset of the two diseases. In mild group A streptococcal infections, oral Penicillin V can be used. In penicillin allergic patients, Erythromycin or one of its long-acting derivatives (e.g., Azithromycin) can be used. Clindamycin can also be used in penicillin-allergic patients. Streptococcal pyogenes is not resistant to penicillins. Endocarditis caused by most viridans streptococci is curable by prolonged Penicillin treatment. However, enterococcal endocarditis can be eradicated only by a Penicillin or Vancomycin combined with an Aminoglycoside. 19 Dr. Omar Aldossary  ❖ Streptococci : ❑ Prevention : ✓ Rheumatic fever can be prevented by prompt treatment of group A streptococcal pharyngitis with Penicillin G or Oral Penicillin V. ✓ Prevention of streptococcal infections (usually with Benzathine Penicillin once each month for several years) in persons who have had rheumatic fever is important to prevent recurrence of the disease. ✓ There is no evidence that patients who have had AGN require similar Penicillin Prophylaxis. 20 Dr. Omar Aldossary  ❖ Streptococci : ❑ Prevention : ✓ To avoid unnecessary use of antibiotics, it is recommended to give Amoxicillin Prophylaxis only to those patients who have the highest risk of severe consequences from endocarditis (e.g., those with prosthetic heart valves or with previous infective endocarditis) and who are undergoing high-risk dental procedures. ✓ There are no vaccines available against any of the streptococci except Streptococci pneumoniae. 21 Dr. Omar Aldossary  ❖ Pneumococci : ❑ Diseases : ✓ Strept. pneumoniae is also known as the pneumococcus (plural, Pneumococci). ✓ Strept. pneumoniae causes pneumonia, bacteremia, meningitis, and infections of the upper respiratory tract such as otitis media, mastoiditis, and sinusitis. Pneumococci are the most common cause of community-acquired pneumonia, meningitis, sepsis in splenectomized individuals, otitis media, and sinusitis. ✓ They are a common cause of conjunctivitis, especially in children. 22 Dr. Omar Aldossary ❖ Pneumococci : ❑ Important Properties : Pneumococci are gram-positive lancet-shaped cocci arranged in pairs (diplococci) or short chains. The term lancet-shaped means that the diplococci are oval with somewhat pointed ends rather than being round. On blood agar, they produce α-hemolysis. 23 Dr. Omar Aldossary ❖ Pneumococci : ❑ Important Properties : Pneumococci possess polysaccharide capsules of more than 85 antigenically distinct types. With type-specific antiserum, capsules swell (quellung reaction), and this can be used to identify the type. Capsules are virulence factors. Another important surface component of S. pneumoniae is a teichoic acid in the cell wall called C-substance (also known as C-polysaccharide). It is medically important not for itself, but because it reacts with a normal serum protein made by the liver called C-reactive protein (CRP). 24 Dr. Omar Aldossary ❖ Pneumococci : ❑ Transmission : ✓ Humans are the natural hosts for pneumococci; there is no animal reservoir.; ✓ Because a proportion (5%–50%) of the healthy population harbors virulent organisms in the oropharynx, pneumococcal infections are not considered to be communicable; ✓ Resistance is high in healthy young people, and disease results most often when predisposing factors are present. 25 Dr. Omar Aldossary ❖ Pneumococci : ❑ Pathogenesis : The most important virulence factor is the capsular polysaccharide, and anti-capsular antibody is protective. Lipoteichoic acid, which activates complement and induces inflammatory cytokine production, contributes to the inflammatory response. Pneumolysin, the hemolysin that causes α-hemolysis, may also contribute to pathogenesis. 26 Dr. Omar Aldossary ❖ Pneumococci : ❑ Pathogenesis : Pneumococci produce IgA protease that enhances the organism’s ability to colonize the mucosa of the upper respiratory tract by cleaving IgA. Pneumococci multiply in tissues and cause inflammation. When they reach alveoli, there is outpouring of fluid and red and white blood cells, resulting in consolidation of the lung. Trauma to the head that causes leakage of spinal fluid through the nose predisposes to pneumococcal meningitis. 27 Dr. Omar Aldossary  ❖ Pneumococci : ❑ Clinical Findings : Pneumonia often begins with a sudden chill, fever, cough, and pleuritic pain. Sputum is a red or brown “rusty” color. Bacteremia occurs in 15% to 25% of cases. Spontaneous recovery may begin in 5 to 10 days. Pneumococci are a prominent cause of otitis media, sinusitis, mastoiditis, conjunctivitis, purulent bronchitis, pericarditis, bacterial meningitis, and sepsis. Pneumococci are the leading cause of sepsis in patients without a functional spleen. 28 Dr. Omar Aldossary ❖ Pneumococci : ❑ Treatment : Most pneumococci are susceptible to Penicillins and Erythromycin. ▪ In penicillin-allergic patients, Erythromycin or one of its long- acting derivatives (e.g., Azithromycin) can be used. In severe pneumococcal infections, penicillin G is the drug of choice, whereas in mild pneumococcal infections, oral penicillin V can be used. Vancomycin is the drug of choice for the penicillin-resistant pneumococci, especially for severely ill patients. Ceftriaxone or levofloxacin can be used for less severely ill patients. 29 Dr. Omar Aldossary  ❖ Pneumococci : ❑ Prevention : ✓ Despite the efficacy of antimicrobial drug treatment, the mortality rate of pneumococcal infections is high in immuno-compromised (especially splenectomized) patients and children under the age of 5 years. ▪ Such persons should be immunized with the 13-valent pneumococcal conjugate vaccine. ✓ The immunogen in this vaccine is the pneumococcal polysaccharide of the 13 most prevalent serotypes conjugated (coupled) to a carrier protein (diphtheria toxoid). ✓ The unconjugated 23-valent pneumococcal vaccine (Pneumovax 23) should be given to healthy individuals age 50 years or older. 30 Dr. Omar Aldossary  ❖ Pneumococci : ❑ Prevention : ✓ These vaccines are safe and effective and provide long-lasting (at least 5 years) protection. ✓ A booster dose is recommended for: 1) People older than 65 years who received the vaccine more than 5 years ago and who were younger than 65 years when they received the vaccine, 2) People between the ages of 2 and 64 years who are asplenic, infected with human immunodeficiency virus (HIV), receiving cancer chemotherapy, or receiving immunosuppressive drugs to prevent transplant rejection. 31 Dr. Omar Aldossary