Bacteriology Lecture 2024-2025 PDF

Bacteriology Department of Microbiology & Immunology Faculty of Pharmacy, Helwan University  Bacteriology Courses: I. Gram positive organisms II. Gram negative organisms III. Viruses  Bacteriology Gram positive organisms: A. Gram positive cocci...

Bacteriology Department of Microbiology & Immunology Faculty of Pharmacy, Helwan University  Bacteriology Courses: I. Gram positive organisms II. Gram negative organisms III. Viruses  Bacteriology Gram positive organisms: A. Gram positive cocci B. Gram positive rods  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 2. Streptococci  Streptococci scanning electron micrograph showing disease-causing Streptococcus bacteria, Oliver Meckesr/Photo Researchers, Inc.  Gram positive cocci 2. Streptococci Diseases : Streptococci produce a wide variety of infections, ranging from pharyngitis and cellulitis to sepsis. They also can trigger immunologic disorders such as: – rheumatic fever and – acute glomerulonephritis.  Gram positive cocci 2. Streptococci Important Properties : Streptococci are spherical cocci usually arranged in chains or pairs. All streptococci are catalase negative,  Gram positive cocci 2. Streptococci Important Properties : One of the most important criteria for identification is the type of hemolysis. (1) Alpha-hemolytic: from a green zone around their colonies as a result of incomplete lysis of red blood cells in the agar.  Gram positive cocci. 2. Streptococci Important Properties : (2) Beta-hemolytic streptococci: form a clear zone around their colonies, since complete lysis of the red cells occurs. Beta-hemolysis is due to the production of enzymes (hemolysins): streptolysin O and streptolysin S  Gram positive cocci 2. Streptococci (3) gamma-hemolytic streptococci: Some streptococci are non hemolytic.  Gram positive cocci 2. Streptococci There are 2 important antigens of beta-hemolytic streptococci: (1) C carbohydrate: determines the group of beta-hemolytic streptococci. It is located in the cell wall  Gram positive cocci 2. Streptococci There are 2 important antigens of beta-hemolytic streptococci: (2) M protein: is the most important virulence factor and determines the type of group A beta-hemolytic streptococci.  Gram positive cocci 2. Streptococci The classification of streptococci is as follows: A. Beta-hemolytic Streptococci:  Gram positive cocci 2. Streptococci A. Beta-hemolytic Streptococci: arranged into groups A-U (Lancefield groups) on the basis of antigenic differences in C carbohydrate.  Gram positive cocci 2. Streptococci A. Beta-hemolytic Streptococci: Group A streptococci (Streptococcus pyogenes) are among the most important human pathogens. They are the most frequent bacterial cause of pharyngitis.  Gram positive cocci 2. Streptococci Description – Strep throat /pharyngitis is caused by group A streptococcus bacteria. Provider – CDC/Dr. Heinz F. Eichenwald  Gram positive cocci 2. Streptococci A. Beta-hemolytic Streptococci: Group B streptococci (Streptococcus agalactiae): colonize the genital tract of some women. can cause neonatal meningitis and sepsis. They are usually Bacitracin-resistant.  Gram positive cocci 2. Streptococci Group D streptococci: includes Enterococci – (e.g., Enterococcus faecalis, formerly known as Streptococcus faecalis) Non-enterococci (e.g., Streptococcus bovis).  Gram positive cocci 2. Streptococci Group D streptococci: Enterococci: grow in 6.5% NaCl. are not killed by penicillin G. They occur as part of the normal flora in the gut  Gram positive cocci 2. Streptococci Group D streptococci: – Nonenterococci are inhibited by 6.5% NaCl and killed by penicillin G.  Gram positive cocci 2. Streptococci Group D streptococci: The hemolytic reaction of group D streptococci is variable: some are beta-hemolytic, whereas most are alpha hemolytic or Non-hemolytic.  Gram positive cocci 2. Streptococci B. Non-Beta-Hemolytic Streptococci: Some produce no hemolysis (ᵞ); others produce alpha hemolysis. The principal alpha-hemolytic organisms are: S pneumoniae and the viridans group of streptococci.  Gram positive cocci 2. Streptococci B.Non-Beta-Hemolytic Streptococci: The viridans streptococci (eg, Streptococcus mitis, S sanguis, and S mutans) are not bile-soluble and not inhibited by optochin !!!-in contrast to S pneumoniae !!!  Gram positive cocci 2. Streptococci B. Non-Beta-Hemolytic Streptococci: The viridans streptococci Viridans streptococci are part of the normal flora of the human pharynx. intermittently reach the bloodstream to cause infective endocarditis.  Gram positive cocci 2. Streptococci B. Non-Beta-Hemolytic Streptococci: The viridans streptococci: S mutans synthesizes polysaccharides (dextrans) that are found in dental plaque and lead to dental caries.  Gram positive cocci 2. Streptococci Transmission : Most streptococci are part of the normal flora of the human throat, skin, and intestines Produce disease when they gain access to tissues or blood.  Gram positive cocci 2. Streptococci Transmission : 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 female genital tract;  Gram positive cocci 2. Streptococci Pathogenesis : Group A streptococci produce the following eight important toxins and enzymes: A. Inflammation-Related Enzymes (1) Streptokinase (fibrinolysin) activates plasminogen to form plasmin, which dissolves fibrin clots, thrombi, and emboli.  Gram positive cocci 2. Streptococci Pathogenesis : A. Inflammation-Related Enzymes (2) Dnase (streptodornase) depolymerizes DNA in exudates or necrotic tissue.  Gram positive cocci 2. Streptococci Pathogenesis : A. Inflammation-Related Enzymes (3) Hyaluronidase hydrolyzes the ground substance of connective tissue, which aids the spread of streptococci.  Gram positive cocci 2. Streptococci Pathogenesis : B. Toxins and Hemolysins : (4) Erythrogenic toxin causes the rash of scarlet fever. (5) Streptolysin O is a hemolysin that is inactivated by oxidation (oxygen- labile).  Gram positive cocci 2. Streptococci Pathogenesis : B. Toxins and Hemolysins : (6) Streptolysin S is a hemolysin (oxygen-stable). It is not antigenic but is responsible for beta-hemolysis  Gram positive cocci 2. Streptococci Pathogenesis : B. Toxins and Hemolysins : (7) Pyrogenic exotoxin A is a toxin similar to staphylococcal toxic shock syndrome toxin (TSST).  Gram positive cocci 2. Streptococci Pathogenesis : B. Toxins and Hemolysins : (8) Exotoxin B is a protease that rapidly destroys tissue and is produced in large amounts by the strains of S pyogenes that cause necrotizing fasciitis.  Gram positive cocci 2. Streptococci Clinical Findings : S pyogenes causes three types of diseases: (1) pyogenic diseases such as pharyngitis and cellulitis, (2) toxigenic diseases such as scarlet fever and toxic shock syndrome, and (3) immunologic diseases such as rheumatic fever and acute glomerulonephritis.  Gram positive cocci 2. Streptococci Clinical Findings : S pyogenes (group A beta-hemolytic streptococcus) is the most common bacterial cause of sore throat. Pharyngitis is characterized by: – inflammation, exudate, – fever, – leukocytosis, – and tender cervical lymph nodes. If untreated, spontaneous recovery occurs in 10 days. Strawberry tongue  Gram positive cocci 2. Streptococci Clinical Findings : However, pharyngitis may extend to otitis, sinusitis, and meningitis. If the infecting streptococci: produce erythrogenic toxin If the host lacks antitoxin, scarlet fever may result.  Gram positive cocci 2. Streptococci Clinical Findings : S pyogenes (group A beta-hemolytic streptococcus): Rheumatic fever may occur, especially following pharyngitis S pyogenes also causes another toxin-mediated disease, streptococcal toxic shock syndrome, which has clinical findings similar to those of staphylococcal toxic shock syndrome.  Gram positive cocci 2. Streptococci Clinical Findings : Group A streptococci can enter skin defects to produce: cellulitis, necrotizing fasciitis (streptococcal gangrene), lymphangitis, or bacteremia.  Gram positive cocci 2. Streptococci Clinical Findings : Group A streptococci They can enter the uterus after delivery to produce endometritis and sepsis (puerperal fever).  Gram positive cocci 2. Streptococci Clinical Findings : Group A streptococci Streptococcal pyoderma (impetigo) is a superficial infection of abraded skin that forms pus or crusts.  Gram positive cocci 2. Streptococci Clinical Findings : Group A streptococci Glomerulonephritis may occur, especially following skin infections.  Gram positive cocci 2. Streptococci Clinical Findings : Group B streptococci cause neonatal sepsis and meningitis. Children born prior to 37 weeks’ gestation (pre- term!) have a greatly increased risk of disease.  Gram positive cocci 2. Streptococci Clinical Findings : Infective endocarditis is commonly caused by viridans streptococci that intermittently enter the bloodstream from the oropharynx (as a result of poor dentition or after dental surgery).  Post streptococcal (Nonsuppurative) Diseases A. Acute Glomerulonephritis : (AGN) typically occurs 2-3 weeks after skin infection by certain group A streptococcal types in children (M protein type!). AGN is more frequent after skin infections than after pharyngitis.  Post streptococcal (Nonsuppurative) Diseases A. Acute Glomerulonephritis : Most patients recover completely. Reinfection with streptococci rarely leads to recurrence of acute glomerulonephritis.  Post streptococcal (Nonsuppurative) Diseases A. Acute Glomerulonephritis : It can be prevented by early eradication of nephritogenic streptococci from skin colonization sites (by penicillin) but not administration of penicillin after onset of the symptoms. Don’t wait!  Post streptococcal (Nonsuppurative) Diseases B. Rheumatic Fever : May develop approximately 2 weeks after any type of group A streptococcal infection-usually pharyngitis characterized by: fever, migratory polyarthritis, and carditis, The carditis damages myocardial and endocardial tissue, especially the mitral and aortic valves. ASO titers and the ESR are elevated.  Post streptococcal (Nonsuppurative) Diseases B. Rheumatic Fever : is due to an immunolgic reaction resulting from cross-reactions between streptococcal antigens and antigens of joint and heart tissue. It is an autoimmune disease, greatly affected by recurrence of strept infections.  Gram positive cocci 2. Streptococci Laboratory Diagnosis : Microbiologic Smears are useless in pharyngitis (WHY?) Because viridans streptococci are members of the normal flora and cannot be visually distinguished from the pathogenic S. pyogenes. However, stained smears from skin lesions or wounds that reveal streptococci are diagnostic.  Gram positive cocci 2. Streptococci Laboratory Diagnosis : Cultures of swabs from the pharynx or lesion on blood agar plates show small, translucent beta- hemolytic colonies in 18-48 hours. If inhibited by Bacitracin disk, they are likely to be group A streptococci.  Gram positive cocci 2. Streptococci Laboratory Diagnosis : Serologic : ASO titers are high soon after group A streptococcal infections.  Gram positive cocci 2. Streptococci Treatment : All group A streptococcal are susceptible to penicillin G, but neither rheumatic fever nor AGN patients benefit from penicillin treatment after onset. Endocarditis caused by most viridans streptococcal is curable by prolonged penicillin treatment.  Gram positive cocci 2. Streptococci Prevention : Rheumatic fever can be prevented by prompt ttt of group A strept pharyngitis with penicillin. 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.  Gram positive cocci 2. Streptococci STREPTOCOCCUS PNEUMONIAE  STREPTOCOCCUS PNEUMONIAE Diseases : Pneumocooci cause: pneumonia, bacteremia, meningitis, and Infections of the upper respiratory tract such as otitis and sinusitis.  STREPTOCOCCUS PNEUMONIAE Important Properties : Pneumocooci are 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 alpha-hemolysis.  STREPTOCOCCUS PNEUMONIAE Important Properties : Pneumococci possess polysaccharide capsules of more than 85 antigenticlly distinct types. With type-specific antiserum, capsules swell (quellung reaction), and this can be used to identify the type. Capsules are virulence factors; i.e., they interfere with phagocytosis.  STREPTOCOCCUS PNEUMONIAE Pathogenesis : Pneumococci produce no toxins known to play a role in pathogenesis. They do produce IgA protease that may enhance the organism’s ability to colonize the mucosa of the upper respiratory tract. Pneumococci multiply in tissues and cause inflammation.  STREPTOCOCCUS PNEUMONIAE Pathogenesis : Factors that lower resistance and predispose persons to pneumococcal infection include (1) alcohol or drug intoxication (2) abnormality of the respiratory tract (eg, viral infections), (3) abnormal circulatory dynamics (eg, pulmonary congestion and heart failure); splenectomy;  STREPTOCOCCUS PNEUMONIAE 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 15-25% of cases. Spontaneous recovery may begin in 5-10 days. Accompanied by develop. of anti capsular Abs.  STREPTOCOCCUS PNEUMONIAE Clinical Findings : Pneumococci are a prominent cause of: otitis media, sinusitis, purulent bronchitis, bacterial meningitis, and sepsis, especially in immune compromised patients.  STREPTOCOCCUS PNEUMONIAE Laboratory Diagnosis : PRACTICAL! NOTES  STREPTOCOCCUS PNEUMONIAE Treatment : Most Pneumocooci are susceptible to: Penicillins erythromycin.  STREPTOCOCCUS PNEUMONIAE Prevention : They should be immunized with the polyvalent (23-type) polysaccharide vaccine. The vaccine is safe and fairly effective and provides long-lasting protection (at least 5 years).