Medical Biology Lab Notes PDF

Al-Maarif University College Department of Dentistry Medical Biology Lab Stage -1- Medical biology Lec. 9 Prepared by: Assistant Lec. Zaid Ahmad Hameed,...

Al-Maarif University College Department of Dentistry Medical Biology Lab Stage -1- Medical biology Lec. 9 Prepared by: Assistant Lec. Zaid Ahmad Hameed, MSc. Cancer Bio, BSc. Biology  Bacteria Gram-Positive Gram-negative Staphylococcus Streptococcus Two of the most important human pathogens, Staphylococcus aureus and Streptococcus pyogenes.  Staphylococcus Including 1. S. aureus 2. S. epidermidis 3. S. saprophyticus ✔ Gram +Ve ✔ Non Motile ✔ Not Form Spores ✔ Cocci or spherical ✔ Catalase +Ve  Characteristics 1- Staphylococcus aureus Gram-positive cocci in clusters. Coagulase and Catalase-positive. Most isolates produce β-lactamase  Staphylococcus aureus —Gram stain. Arrows point to two “grapelike” clusters of gram-positive cocci.  β-lactamase :produced by bacteria that provide multi-resistance to beta- lactam antibiotics such as penicillins, cephalosporins. Catalase Staphylococci produce catalase degrades H 2 O 2 into O 2 and H 2 O  Coagulase test—Upper tube inoculated with Staphylococcus aureus; lower tube inoculated with Staphylococcus epidermidis. Arrow points to clotted plasma formed by coagulase produced by Sta. aureus.  Diseases ✔ Abscess of many organs, endocarditis, osteomyelitis, septic arthritis, and impetigo. ✔ Hospital-acquired pneumonia, surgical wound infections, and sepsis. ✔ exotoxin-mediated diseases such as food poisoning, toxic shock syndrome, and scalded skin syndrome. ✔ Skin infection: Folliculitis , Cellulitis ,and impetigo  Abscess on foot. Note central raised area of whitish pus surrounded by erythema. An abscess is the classic lesion caused by Staphylococcus aureus Staph.Scalded skin syndrome(SSSS). Caused by an exotoxin produced by Staphylococcus aureus Folliculitis. Note the multiple, small pustules on the chin and neck. Staphylococcus aureus is the most common cause of folliculitis. Impetigo. Note vesicular lesions covered with “honey-colored” crust erythema. Impetigo is caused by either Staphylococcus aureus or Streptococcus pyogenes  Habitat and Transmission—Main habitat is human nose; also found on human skin. Transmission is via the hands.  Laboratory Diagnosis Gram-stained smear and culture. Yellow or gold colonies on blood agar; colonies often beta hemolytic. Staphylococcus aureus is coagulase-positive; Staphylococcus epidermidis is coagulase-negative. Serologic tests not useful  Treatment Penicillin G for sensitive isolates; β-lactamase–resistant penicillins such as Nafcillin for resistant isolates; Vancomycin for isolates resistant to Nafcillin. About 85% are resistant to penicillin G.. Resistance to Nafcillin is caused by changes in binding proteins. Some isolates are tolerant to penicillin. Rare Vancomycin-resistant strains have emerged.  Prevention—Cefazolin is used to prevent surgical wound infections. No vaccine is available. Hand washing reduces spread.  2-Staphylococcus epidermidis Diseases—Endocarditis on prosthetic heart valves, prosthetic hip infection, intravascular catheter infection, CSF infection, neonatal sepsis.  Characteristics Gram-positive cocci in clusters. Coagulase Negative. Catalase-Positive.  Habitat and Transmission Normal flora of the human skin and mucous membranes. It is probably the patient’s own strains that cause infection, but transmission from person to person via hands may occur.  Laboratory Diagnosis Gram-stained smear and culture. Whitish, non-hemolytic colonies on blood agar. It is coagulase negative. S. epidermidis is sensitive to novobiocin, whereas the other coagulase-negative staphylococcus, S. saprophyticus, is resistant. Serologic tests are not useful.  Treatment—Vancomycin plus either rifampin or an aminoglycoside. It produces β-lactamases and is resistant to many antibiotics. Prevention—There is no drug or vaccine.  3-Staphylococcus Saprophyticus Gram-positive cocci in clusters. Coagulase-negative. catalase positive Resistant to Novobiocin in contrast to S.epidermidis, which is sensitive. Causes community-acquired urinary tract infections in young women (but Escherichia coli is a much more common cause).