BC_MedMic. Aerobic Gram-Positive Bacteria.pdf

Introduction to Gram-Positive Bacteria Agenda (A) Aerobic Gram-Positive Cocci (B) Aerobic Gram-Positive Rods Staphylococcus aureus Interesting Facts about Aerobic β-Hemolytic Streptococci Gram-Positive Rods Streptococcus pneumoniae Bacillus anthracis Virid...

Introduction to Gram-Positive Bacteria Agenda (A) Aerobic Gram-Positive Cocci (B) Aerobic Gram-Positive Rods Staphylococcus aureus Interesting Facts about Aerobic β-Hemolytic Streptococci Gram-Positive Rods Streptococcus pneumoniae Bacillus anthracis Viridans Streptococci Bacillus cereus Enterococcus Listeria monocytogenes Corynebacterium diphtheriae  (A) AEROBIC GRAM-POSITIVE COCCI This category includes notable genera such as Staphylococcus and Streptococcus, which are significant in both clinical and environmental contexts. These bacteria can cause a range of infections in humans, including skin infections, pneumonia, and endocarditis. (A1) Staphylococcus aureus Characteristics Pathogenicity Clinical Significance Staphylococcus aureus is a This bacterium is known for Staphylococcus aureus is a major spherical, Gram-positive causing a range of infections, from cause of hospital-acquired bacterium found in clusters. It is mild skin infections to severe infections (HAI) and is often facultatively anaerobic and can conditions like pneumonia and resistant to antibiotics, grow in high salt concentrations, sepsis. It produces toxins and particularly methicillin-resistant making it adaptable to various enzymes that contribute to its Staphylococcus aureus (MRSA), environments. virulence. complicating treatment options. Important Staphylococcus species Clinical Diseases of Staphylococcus S. aureus Toxin-Mediated Diseases Food Poisoning: Rapid onset of vomiting, diarrhea, and cramps from preformed enterotoxins in contaminated food; resolves in 24 hours. Scalded Skin Syndrome: Toxin-induced blistering and peeling of the skin, mostly in young children. Toxic Shock Syndrome: Toxin affects multiple organs, starting with fever, hypotension, and rash; high mortality without prompt treatment. Clinical Diseases of Staphylococcus S. aureus Pyogenic Diseases Impetigo: Localized skin infection with pus-filled vesicles, mostly on the face and limbs of children. Folliculitis: Impetigo affecting hair follicles, like the beard area. Furuncles/Carbuncles: Large, pus-filled nodules that can spread to deeper skin layers and other body areas. Wound Infections: Erythema and pus at trauma or surgery sites; harder to treat with foreign bodies; often MRSA; recurrent infections common. Pneumonia: Lung abscesses, mainly in young and old, often following viral respiratory infections. Endocarditis: Infection of the heart lining with rapid progression and high mortality. Osteomyelitis: Bone destruction, especially in long bones of children. Septic Arthritis: Joint infection causing swelling, redness, and pus; most common in children. Differential Media: Blood Agar Used as an enrichment medium for fastidious microbes as well as differential media Hemolysins: enzymes that lyse (break down) red blood cells to release iron-rich hemoglobin Beta-hemolysis: complete lysis of red blood cells Alpha-hemolysis: incomplete lysis of red blood cells Gamma-hemolysis: no hemolysis Lisa Burgess/McGraw Hill 8 (A2) β-Hemolytic Streptococci β-Hemolytic Streptococci are classified into groups based on Lancefield Classification classification, primarily groups A and B. Group A Streptococcus (S. pyogenes) is known for causing pharyngitis, scarlet Pathogenicity fever, and rheumatic fever, while Group B Streptococcus (S. agalactiae) is a significant cause of neonatal infections. Diagnosis and Diagnosis is typically via culture or rapid antigen tests; treatment often Treatment involves penicillin or other β-lactam antibiotics. Beta-Hemolytic Streptococci Virulence factors of Streptococcus 1. Capsule: Outer hyaluronic acid capsule (single serotype) protects S. pyogenes from phagocytosis (non-immunogenic). 2. Cell Wall Proteins: M proteins, M-like proteins, and C5a peptidase block complement-mediated phagocytosis. 3. Adherence and Invasion: M proteins and F protein aid in adherence to and invasion of epithelial cells. 4. Hydrolytic Enzymes: Streptolysin S and O: Lyse erythrocytes, leukocytes, platelets, and cultured cells. Streptokinase: Lysates blood clots and fibrin deposits, promoting rapid spread. DNases: Break down free DNA in abscesses, aiding spread. 5. Toxins: Four distinct heat-labile streptococcal pyrogenic exotoxins enhance release of pro-inflammatory cytokines, contributing to severe streptococcal disease symptoms. (A3) S. pneumoniae versus S. agalactiae 01 02 03 04 Streptococcus pneumoniae is Streptococcus agalactiae, S. pneumoniae is S. agalactiae is characterized a Gram-positive, also a Gram-positive optochin-sensitive and by its ability to hydrolyze lancet-shaped bacterium, bacterium, appears in chains bile-soluble, aiding in its sodium hippurate and its often found in pairs, and is a leading cause of identification in the lab. CAMP test positivity. responsible for pneumonia neonatal infections. and meningitis.  (A4) Viridans Streptococci Viridans Streptococci are a group of alpha-hemolytic streptococci that 1 1 primarily inhabit the oral cavity and upper respiratory tract. These bacteria are known to contribute to dental caries and can form 2 2 biofilms on heart valves, leading to endocarditis. 3 Generally considered opportunistic pathogens, they can cause infections 3 in immunocompromised individuals, particularly in cases of bacteremia. Viridans Streptococci Although relatively avirulent, individual species have a predilection of producing disease in specific anatomic sites (abscess formation, endocarditis, meningitis)  (A5) Enterococcus Enterococcus species are normal intestinal flora but can Clinical cause serious infections, especially in Significance immunocompromised patients, leading to urinary tract infections and endocarditis. Enterococcus is notable for its intrinsic resistance to many Antibiotic antibiotics, including penicillin, and its ability to acquire Resistance resistance to vancomycin, making infections difficult to treat. In healthcare settings, Enterococcus can lead to outbreaks, Infection Control emphasizing the need for stringent infection control measures and appropriate antibiotic stewardship.  (B) AEROBIC GRAM-POSITIVE RODS Aerobic Gram-Positive Rods are a significant group of bacteria characterized by their ability to thrive in the presence of oxygen and their thick peptidoglycan cell wall, which retains the crystal violet stain used in Gram staining. This category includes important genera such as Bacillus and Listeria, which are notable for their roles in both health and disease. Bacillus anthracis, the causative agent of anthrax, and Listeria monocytogenes, associated with foodborne illness, exemplify the pathogenic potential of these organisms. Interesting Facts about Aerobic Gram-Positive Rods 1 2 3 4 Aerobic Gram-Positive Some species, like Bacillus These bacteria can Certain aerobic Rods are crucial in subtilis, are used as produce enzymes that are Gram-positive rods, such as various industries, probiotics and in beneficial in Listeria monocytogenes, including food fermentation processes. bioremediation, aiding in are significant pathogens, production and the breakdown of causing serious foodborne biotechnology. pollutants. illnesses. Bacillus anthracis and Bacillus cereus Similarities between Bacillus anthracis and Bacillus cereus Differences and Clinical Implications Both are rod-shaped, spore-forming bacteria Bacillus anthracis is the causative agent of anthrax, belonging to the Bacillus genus. a serious infectious disease. They are aerobic or facultatively anaerobic and can Bacillus cereus is primarily associated with food thrive in various environments. poisoning, causing gastrointestinal symptoms. Both can cause foodborne illnesses and possess Anthrax can be lethal, requiring immediate medical virulence factors. intervention, while B. cereus infections are usually self-limiting. (B1) Bacillus anthracis (B1) Bacillus anthracis Cutaneous anthrax (most common in humans): ○ painless papule progresses to ulceration with surrounding vesicles and then to eschar formation; painful lymphadenopathy, edema, and systemic signs may develop Gastrointestinal Anthrax (most common herbivores): ○ ulcers format site of invasion(e.g., mouth, esophagus, intestine) leading to regional lymphadenopathy, edema, and sepsis Inhalation Anthrax(bioterrorism): ○ Initial non specific signs followed by the rapid onset of sepsis with fever, edema, and lymphadenopathy (mediastinal lymph nodes); meningeal symptoms in half of the patients, and most patients will die unless treatment is initiated immediately (B2) Bacillus cereus  (B2) Bacillus cereus Gastroenteritis: ○ Emetic form: Rapid onset (few hours) of vomiting and abdominal pain, short duration (