Bacteriology Lecture 2 2024-2025 PDF

BACTERIOLOGY Lecture 2  I. Gram-positive organisms A. Gram-positive Cocci There are 2 medically important genera: Staphylococcus and Streptococcus. They are non-motile and do not form spores. I. Gram-positive organisms A. Gram-positive Cocci STAPHYLOCOCCUS  Gram...

BACTERIOLOGY Lecture 2  I. Gram-positive organisms A. Gram-positive Cocci There are 2 medically important genera: Staphylococcus and Streptococcus. They are non-motile and do not form spores. I. Gram-positive organisms A. Gram-positive Cocci STAPHYLOCOCCUS  Gram positive cocci Staphylococcus Diseases : Staphylococcus aureus causes: abscesses, various pyogenic infections (e.g., endocarditis and osteomyelitis), food poisoning, and toxic shock syndrome.  Gram positive cocci Staphylococcus Diseases : Staphylococcus epidermidis can cause endocarditis Staphylococcus saprophyticus causes: urinary tract infections.  Gram positive cocci Staphylococcus Important Properties : PRACTICAL COURSE ! spherical cocci arranged in irregular grape like clusters. All staphylococci produce catalase, (streptococci do not!!!) catalase degrades H2O2 into O2 and H2O.  Gram positive cocci Staphylococcus Important Properties : S. aureus is by far the most important, S. aureus is distinguished from the others primarily by: coagulase production (coagulate clots citrated plasma). it usually ferments mannitol and hemolyzes blood, whereas the other do not.  Gram positive cocci Staphylococcus Important Properties : S. aureus has several important cell wall components and antigens. (1) Protein A (2) Teichoic acids mediate adherence of the staphylococci to mucosal cells.  Gram positive cocci Staphylococcus Transmission : Staphylococci are found primarily in the normal human flora. S. epidermidis is regularly present on normal skin and mucous membranes. S. aureus is often found in the nose and sometimes on the skin, especially in hospital staff and patients.  Gram positive cocci Staphylococcus Transmission : Additional sources of staphylococcal infection are shedding from human lesions and vomits contaminated by these lesions. Disease production is favored by: a heavily contaminated environment (e.g., family members with boils) and a compromised immune system.  Gram positive cocci Staphylococcus Pathogenesis: Staphylococci cause disease both by: producing toxins and by multiplying in tissue and causing inflammation. The typical lesion of S aureus infection is an abscess. Abscesses undergo central necrosis and usually drain to the outside (e.g., furuncles and boils), but organisms may disseminate via the bloodstream as well.  Gram positive cocci Staphylococcus Pathogenesis: Several important toxins and enzymes are produced by S. aureus. (1) Enterotoxin is a protein that causes vomiting and watery, non bloody diarrhea. It is fairly heat-resistant and so it is usually not inactivated by brief cooking. There are 6 immunological types of enterotoxin, types A-F.  Gram positive cocci Staphylococcus Pathogenesis: Several important toxins and enzymes are produced by S. aureus. (2) Toxic shock syndrome toxin (TSST) toxic shock in tampon-using menstruating women or in individuals with wound infections. It is indistinguishable from enterotoxin F. Toxic shock syndrome  Gram positive cocci Staphylococcus Pathogenesis: Several important toxins and enzymes are produced by S. aureus. (3) Exfoliatin which causes : scalded skin” syndrome in young children. (4) Several toxins can cause death of leukocytes (leukocidins) and necrosis of tissues in vivo. the most important is alpha toxin, which causes marked necrosis of the skin and hemolysis.  Gram positive cocci Staphylococcus Pathogenesis: Several important toxins and enzymes are produced by S. aureus. (5) Enzymes include: Catalase coagulase, fibrinolysin, hyaluronidase, proteases, nucleases, and lipases.  Gram positive cocci Staphylococcus Clinical Findings : The important clinical manifestations caused by S aureus can be divided into 2 groups: inflammatory and toxin-mediated.  Gram positive cocci Staphylococcus Clinical Findings : A. Inflammatory : (1) skin infections, including impetigo, furuncles, carbuncles, cellulitis, surgical wound infections, eyelid infections , and postpartum breast infections; (2) Bacteremia from any localized lesion especially wound infection, or as a result of intravenous drug abuse (bacteremia may lead to endocarditis);  Gram positive cocci Staphylococcus Clinical Findings : A. Inflammatory : (3) endocarditis on normal or prosthetic heart valves (prosthetic valve endocarditis is often caused by S epidermidis); (4) osteomyelitis and arthritis, either hematogenous or traumatic; it is a very common cause of osteomyelitis and arthritis, especially in children;  Gram positive cocci Staphylococcus Clinical Findings : A. Inflammatory : (5) pneumonia in postoperative patients of following viral respiratory infection, especially influenza (staphylococcal pneumonia) (6) abscesses (metastatic) in any organ, after bacteremia;  Gram positive cocci Staphylococcus Clinical Findings : B. Toxin – Mediated (7) food poisoning (characterized by vomiting being more prominent than diarrhea) due to ingestion of enterotoxin, which is preformed in foods and hence has a short incubation periods (1-8 hours);  Gram positive cocci Staphylococcus Clinical Findings : B. Toxin – Mediated (8) toxic shock syndrome, which includes fever, hypotension, a rash that goes on to desquamate, and multisystem involvement;  Gram positive cocci Staphylococcus Clinical Findings : B. Toxin – Mediated (9) scalded skin syndrome, in which the superficial layers of the epidermis slough in response to the presence of exfoliatin.  Gram positive cocci Staphylococcus Clinical Findings : There are 2 coagulase-negative staphylococci of medical importance: S epidermidis and S saprophyticus.  Gram positive cocci Staphylococcus Clinical Findings : S epidermidis is part of the normal human flora on the skin and mucous membranes but can cause infections of intravenous catheters and prosthetic implants, eg, heart valves. S epidermidis is also a major cause of sepsis in neonates.  Gram positive cocci Staphylococcus Clinical Findings : S saprophyticus causes urinary tract infections, particularly in sexually active young women. It is second to E. coli as a cause of community-acquired urinary tract infections in this population.  Gram positive cocci Staphylococcus Laboratory Diagnosis : Gram Staining Culture Biochemical tests  Gram positive cocci Staphylococcus Treatment : More than 80% of S aureus strains are resistant to penicillin g. most of them produce -lactamase Such organisms can be treated with - lactamase-resistant penicillin’s, e.g. cloxacillin, some cephalosporins, vancomycin. The drug of choice for these staphylococci is vancomycin.  Gram positive cocci Staphylococcus Treatment : Drainage (spontaneous or surgical) is the corner stone of abscess treatment. S epidermidis is highly antibiotic resistant. The drug of choice is Vancomycin..  Gram positive cocci Staphylococcus Prevention : There is no effective immunization with toxoid or bacterial vaccines. Cleanliness, frequent hand washing, and aseptic management of lesions help to control spread