Lecture 1_Bacteriology 2024-2025 PDF

‫بسم هللا الرحمن الرحيم‬ Medical Microbiology Department of Microbiology & Immunology Faculty of Pharmacy, Helwan University Bacteriology  Host Parasite Relationships  ECOLOGY:  Microorganisms survive and grow in a wide variety of environments  found in virtually ever...

‫بسم هللا الرحمن الرحيم‬ Medical Microbiology Department of Microbiology & Immunology Faculty of Pharmacy, Helwan University Bacteriology  Host Parasite Relationships  ECOLOGY:  Microorganisms survive and grow in a wide variety of environments  found in virtually every ecological niche.  provide an important food source  and facilitate the degradation of organic matter Bacteriology  Host Parasite Relationships  ECOLOGY:  Microorganisms that live on inanimate organic material are described as saprophytes.  Microorganisms that grow in or on a living host, obtaining nutrients from the host are referred to as parasites … Medical microbiology  Host Parasite Relationships  ECOLOGY:  Parasites: may be beneficial to the host  symbiosis, e.g. in the stomach of ruminants  they aid in the degradation of cellulose- a vital step in the nutrition of such animals. INTRODUCTION  Host Parasite Relationships: ECOLOGY:  NORMAL FLORA:  Parasitic microorganisms associated with mammals are often referred to as normal flora or commensal.  important in preventing infection;  Reduction in the normal flora (e.g. by antibiotic therapy) may result in overgrowth of potential pathogen. INTRODUCTION  Host Parasite Relationships: ECOLOGY:  Commensal are well adapted to their environment, e.g. the dry, acidic condition found on the skin,  multiply without causing host damage. INTRODUCTION  Host Parasite Relationships: ECOLOGY:  However, commensal bacteria can cause infection, normally when host defense is compromised; for example:  Staphylococcus epidermidis, a skin commensal, is the cause of intravascular catheter infections.  Viridans streptococci (oral commensal bacteria), may cause bacterial endocarditis. INTRODUCTION  Host Parasite Relationships:  PATHOGEN:  An organism which can invade the body and cause disease.  A broader definition is:  any microorganisms, cell culture or toxin capable of entering the body and causing harm. INTRODUCTION  Host Parasite Relationships:  PATHOGENIC MICROORGANISMS:  1. Opportunistic pathogens will not cause disease except in immuno- compromised patients under condition that favors the growth of the organism  (e.g. Staphylococcus epidermidis) INTRODUCTION  PATHOGENIC MICROORGANISMS:  2. Strict pathogens are always associated with disease (e.g. Mycobacterium tuberculosis). INTRODUCTION  PATHOGENIC MICROORGANISMS:  3. Facultative pathogens may be present in the host without resulting in infection  Neisseria meningitidis, an important cause of meningitis, is a commensal of the pharynx of about 5% of adults; INTRODUCTION  3. Facultative pathogens (continue)  Streptococcus pneumoniae, the most frequent cause of bacterial pneumonia, is a pharyngial commensal in many individuals;  S. aureus, an important cause of skin infection and deep abscesses, is a nasal commensal of about one-third of individuals. INTRODUCTION INFECTION:  It is a disease caused by a pathogen.  Infection describes the clinical manifestation that occurs when a microorganism invade a host.  When the manifestation is minor or imperceptible, infections are often termed subclinical. INTRODUCTION INFECTION:  Latent infection result when pathogens persist in the body without evoking a clinical response;  periodically, infection occur following a change in patient's immune state INTRODUCTION INFECTION:  Chronic or persistent infections occur when pathogen are not eradicated completely and continue to evoke a clinical response  e.g. leprosy,  helminth infections. INTRODUCTION COMMUNICABLE DISEASE:  An infection which is capable of spreading from person to person.  Not all infections are communicable diseases.  may be transmitted by many routes:  direct person to person transfer;  respiratory transmission;  parentral inoculation;  sexual or mucosal contact;  and by insect vectors. INTRODUCTION  PATHOGENICITY:  It is the ability to cause disease.  VIRULENCE:  It is the pathogen's power to cause disease.  Pathogenicity and virulence are not necessary related. INTRODUCTION  INFECTIOUSNESS:  The ease with which a pathogen can spread in a population.  EPIDEMIOLOGY:  The study of the distribution and determinant of a disease in a population.  The distribution described in terms of:  time (day, month, year, or year of onset of symptoms),  person (age, sex, occupation)  or place (region or country). INTRODUCTION MICROBIAL STRATEGIES:  Microorganisms have developed a variety of mechanisms (virulence factor) to combat host defenses and promote transmission to new hosts. INTRODUCTION  TRANSMISSION:  Ability to survive outside the host is an important factor in transmission of organism.  Upper respiratory tract viruses (e.g. Rhinoviruses) survive poorly outside the host and successful transmission relies on the production of large quantity of infectious particles.  Other organisms can survive outside the host, Mycobacterium tuberculosis, and do not require large numbers of infectious particles for efficient transmission. INTRODUCTION  TOXIGENICITY:  Organisms can produce a variety of toxins  there are two main types:  Exotoxins & Endotoxins INTRODUCTION  TOXIGENICITY:  Endotoxins  Lipopolysaccharides-part of gram negative cell wall  Heat-stable  Liberated when Gram-negative bacteria lyse  Often posses non specific mechanism of action  E.g. Gram negative septic shock (endotoxic shock). INTRODUCTION TOXIGENICITY:  Exotoxins  Mainly produced by gram positive bacteria  Heat labile protein  High potency  Strong antigenicity  Neutralize by antitoxin  Often posses specific mechanism of action  Medical microbiology Courses: I. Gram positive organisms II. Gram negative organisms III. Viruses  Medical microbiology OVERVIEW OF THE MAJOR PATHOGENS  OVERVIEW OF THE MAJOR PATHOGENS Gram-positive cocci, Gram-positive rods, Gram-negative cocci, and Gram-negative rods.  OVERVIEW OF THE MAJOR PATHOGENS Since there are so many kinds of gram-negative rods, they have been divided into 3 groups : 1) organisms associated with the enteric tract, 2) organisms ass. with the respiratory tract, 3) organisms from animal sources (zoonotic bacteria)  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 :  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:  is the major protein in the cell wall.  Gram positive cocci Staphylococcus Important Properties : S. aureus has several important cell wall components and antigens.  (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  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 acts by stimulating the release of large amounts of Interleukin-1 and Interleukin-2.  It is fairly heat-resistant and so it is usually not inactivated by brief cooking.  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.  TSST is a super antigen and causes toxic shock by stimulating the release of large amounts of IL-1 and IL-2.  Gram positive cocci Staphylococcus Pathogenesis:  Several important toxins and enzymes are produced by S. aureus.  (3) Exfoliatin is a protein produced by staphylococci of phage group II, which causes : scalded skin” syndrome in young children.  Gram positive cocci Staphylococcus  Pathogenesis:  Several important toxins and enzymes are produced by S. aureus.  (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:  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 :  PRACTICAL COURSE!  Morphology  Biochemical tests  Gram positive cocci Staphylococcus  Treatment :  Can be treated with -lactamase-resistant penicillin’s, e.g. cloxacillin, some cephalosporins, 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