Lecture 4: Gram-Positive Bacteria & Staphylococcus (PDF)

Gene, Cell and Tissue IV Microbiology Lecture 4 ⮚Gram-positive bacteria. Streptococci part 2 ⮚Staphylococcus  Streptococcus viridans Although their virulence is very low, viridans strains can cause disease when they are protected from host defenses. ⮚ example -subacute bacterial...

Gene, Cell and Tissue IV Microbiology Lecture 4 ⮚Gram-positive bacteria. Streptococci part 2 ⮚Staphylococcus  Streptococcus viridans Although their virulence is very low, viridans strains can cause disease when they are protected from host defenses. ⮚ example -subacute bacterial endocarditis -In this disease, viridans streptococci reach previously damaged heart valves as a result of transient bacteremia associated with manipulations, such as tooth extraction, which disturb their usual habitat. Enterococcus ⮚Facultative anaerobic, catalase-negative Gram- positive cocci ⮚Arranged individually, in pairs, or short chains. ⮚Enterococci possess the group D antigen ⮚They are normal inhabitants of the intestinal tract, female genital tract, and (less commonly) oral cavity. Intestinal inhabitants resist action of bile salts. ⮚There are at least 47 species of enterococci, but associated with disease in humans are Enterococcus faecalis and Enterococcus faecium. E. faecalis is the most frequent species isolated from human intestine samples (80-90%), E. faecium accounts for 5-10% of isolates  ⮚ Person-to-person transmission of Enterococcus faecalis and E. faecium (especially E. faecium) by health care providers between patients in the hospital setting ✔ Major mode for hospital spread of vancomycin-resistant enterococci ⮚ Urinary tract infection most common usually associated with urologic abnormalities ⮚ Intra-abdominal and pelvic infection generally polymicrobial with controversial etiological role for Enterococcus Enterococci are opportunistic pathogens which affect elderly patients with underlying disease and other immunocompromised patients who have been hospitalized for long periods, treated with invasive devices, or received broad-spectrum antibiotics ⮚A major problem with the enterococci is that they can be very resistant to antibiotics. ⮚E faecium is usually much more antibiotic-resistant than E faecalis. Important Features of Pathogenesis by Streptococci Staphylococcus spp Staphylococcus spp Staphylococcus aureus causes abscesses, various pyogenic infections (e.g., endocarditis, septic arthritis, and osteomyelitis), food poisoning, scalded skin syndrome and toxic shock syndrome. It is one of the most common causes of hospital-acquired pneumonia, septicemia, and surgical- wound infections. It is an important cause of skin infections, such as folliculitis, cellulitis, and impetigo. It is the most common cause of bacterial conjunctivitis Staphylococcus spp Morphology and identification Clinically important Staphylococci are gram-positive spherical cells, usually species: arranged in grapelike irregular clusters Staphylococci are nonmotile and do not form spores Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus Colonization of pre-defined sites on the human body by staphylococci Staphylococcus spp Growth Characteristics Staphylococci grow readily on most bacteriologic media under aerobic or microaerophilic conditions. They grow most rapidly at 37°C but form pigment best at room temperature (20–25°C). Colonies on solid media are round, smooth, raised, and glistening. S aureus usually forms gray to deep golden yellow colonies. S epidermidis colonies usually are gray to white on primary isolation; many colonies develop pigment only upon prolonged incubation. Antigenic Structure (1) Protein A is the major protein in the cell wall. It binds to the Fc portion of IgG at the complement- binding site, thereby preventing the activation of complement. As a consequence, no C3b is produced, and the opsonization and phagocytosis of the organisms are greatly reduced. The coagulase-negative staphylococci do not produce protein A. Antigenic Structure (2) Teichoic acids -they mediate adherence of the staphylococci to mucosal cells. Lipoteichoic acids play a role in the induction of septic shock by inducing cytokines such as interleukin-1 (IL-1) and tumor necrosis factor (TNF) from macrophages (3) Polysaccharide capsule - there are 11serotypes based on the antigenicity of the capsular polysaccharide, but types 5 and 8 cause 85% of infections. The capsule is poorly immunogenic, which has made producing an effective vaccine difficult. (4) The peptidoglycan of S. aureus has endotoxin-like properties, it can stimulate macrophages to produce cytokines and can activate the complement and Coagulation cascades. This explains the ability of S. aureus to cause the clinical findings of septic shock yet not possess endotoxin.  Enzymes and Staphylococcus aureus Toxins All staphylococci produce catalase, whereas no streptococci do (catalase degrades H2O2 into O2 and H2O). Catalase is an important virulence factor. Bacteria that make catalase can survive the killing effect of H2O2 within neutrophils. S. aureus is distinguished from the others primarily by coagulase production. Coagulase is an enzyme that causes plasma to clot by activating prothrombin to form thrombin. Thrombin then catalyzes the activation of fibrinogen to form the fibrin clot. S. epidermidis and S. saprophyticus are often referred to as coagulase-negative staphylococci. Staphyloxanthin -imparts a golden color to its colonies. This pigment enhances the pathogenicity of the organism by inactivating the microbicidal effect of superoxides and other reactive oxygen species within neutrophils. S. epidermidis does not synthesize this pigment and produces white colonies. Enzymes and Staphylococcus aureus Toxins Hemolysins -α-toxin is a pore-forming cytotoxin that lyses the cytoplasmic membranes by direct insertion into the lipid bilayer to form transmembrane pores (Staph. aureus). The β-toxin is toxic for many kinds of cells, including human red blood cells. The δ-toxin - disrupts biologic membranes and may have a role in S. aureus diarrheal diseases. The γ-hemolysin is a leukocidin that lyses Enterotoxin causes food poisoning white blood cells characterized by prominent vomiting and watery, nonbloody diarrhea. It acts as a superantigen within the gastrointestinal tract to stimulate the release of large amounts of IL-1 and IL-2 from macrophages and helper T cells, respectively. Enterotoxin is heat- resistant. It is resistant to stomach acid and to enzymes in the stomach and jejunum. There are six immunologic types of enterotoxin, types A–F  Enzymes and Toxins Staphylococcus aureus Exfoliative causes “scalded skin” syndrome in young children. It is “epidermolytic” and acts as a protease that cleaves desmoglein in desmosomes, leading to the separation of the epidermis at the granular cell layer.  Enzymes and Toxins Staphylococcus aureus P-V leukocidin is a pore-forming toxin that kills cells, especially white blood cells, by damaging cell membranes. The two subunits of the toxin assemble in the cell membrane to form a pore through which cell contents leak out. Approximately 2% of clinical isolates of S. aureus produce P-V leukocidin and is encoded by mobile phage. Toxic shock syndrome toxin (TSST) causes toxic shock, TSST is produced locally by S. aureus in the vagina, nose, or other infected site. The toxin enters the bloodstream, causing a toxemia. Approximately 5% to 25% of isolates of S. aureus carry the gene for TSST. Toxic shock occurs in people who do not have antibody against TSST  Coagulase-negative staphylococci ✔Coagulase-negative staphylococci do not produce exotoxins. ✔Coagulase-negative staphylococci do not cause food poisoning or toxic shock syndrome. ✔Coagulase-negative staphylococci cause pyogenic infections. For example, S. epidermidis is a Prominent cause of pyogenic infections on prosthetic implants such as heart valves and hip joints, and S. saprophyticus causes urinary tract infections, especially cystitis.  Transmission Humans are the reservoir for staphylococcii, particularly S epidermidis, are members of the normal microbiota of the human skin and respiratory and gastrointestinal tracts. The nose is the main site of colonization of S. aureus, and approximately 30% of people are colonized People who are chronic carriers of S. aureus in their nose have an increased risk of skin infections caused by S. aureus. Staphylococci are found regularly on clothing,.. bed linens, and other fomites in human environments. The skin, especially of hospital personnel and patients, is also a ⮚ Hand common contactsite is anofimportant mode S. aureus of transmission, and handwashing decreases transmission. colonization. ⮚ S. aureus is also found in the vagina of approximately 5% of women ⮚ S. saprophyticus is found primarily on the mucosa of the genital tract in young women and from that site can ascend into the urinary bladder to cause urinary tract infections Clinical Findings The important clinical manifestations caused by S. aureus can be divided into two groups: pyogenic (pus-producing) and toxin-mediated. S. aureus is a major cause of skin, soft tissue, bone, joint, lung, heart, and kidney infections. Pyogenic diseases are the first group described, and toxin- mediated diseases are the second group Staphylococcus aureus: Pyogenic Diseases Skin infections- PRIMARY INFECTION Furuncle Furuncle- skin infection that typically develops in a hair follicle, sebaceous gland, or sweat gland. The infected patient is often a carrier of the Staphylococcus. No surgical or antimicrobial treatment is needed Skin infections- PRIMARY INFECTION Carbuncle The lesion of furuncle, known as a carbuncle, occurs most often on the back of the neck, but it may involve other skin sites. Carbuncles are serious lesions that may result In bloodstream invasion (bacteremia). Impetigo Staphylococcus aureus has been long known as a secondary invader in group A streptococcal pustular impetigo. Strains of S aureus that produce exfoliatin cause a characteristic form called bullous impetigo, characterized by blisters containing many staphylococci in the superficial layers of the skin. Staphylococcus aureus: Pyogenic Diseases Deep Lesions Septicemia (sepsis) can originate from any localized lesion, especially wound infection, or as a result of intravenous drug abuse Endocarditis may occur on normal or prosthetic heart valves, especially right sided endocarditis (tricuspid valve) in intravenous drug users. (Prosthetic valve endocarditis is often caused by S. epidermidis.) Osteomyelitis and septic arthritis may arise either by hematogenous spread from a distant infected focus or be introduced locally at a wound site. S. aureus is a very common cause of these diseases, especially in children. S. aureus is the most common cause of Postsurgical wound infections. Pneumonia can occur in postoperative patients or following viral respiratory infection, especially influenza. Staphylococcal pneumonia often leads to empyema or lung abscess. Conjunctivitis typically presents with unilateral burning eye pain, hyperemia of the conjunctiva, and a purulent discharge. The organism is transmitted to the eye by contaminated fingers.. Abscesses can occur in any organ when S. aureus circulates in the bloodstream (bacteremia). These abscesses are often called “metastatic abscesses”because they occur by the spread of bacteria from the original site of infection, often in the skin Staphylococcus aureus: Toxin-Mediated Diseases Staphylococcal food poisoning-is a gastrointestinal illness caused by eating foods contaminated with toxins produced by the bacterium. ✔can contaminate food by people who carry it ✔can also be found in unpasteurized milk and cheese products ✔Because Staph is salt tolerant, it can grow in salty foods like ham Symptoms: vomiting nausea stomach cramps Diarrhea Vomiting is typically more prominent than diarrhea The illness cannot be passed to other people and typically lasts for only 1 day. Severe illness is rare. Staphylococcus aureus: Toxin-Mediated Diseases Toxic shock Syndrome (TSS)- was first described Treatment in children but came to public attention during Aggressive Therapy -antibiotics the early 1980s, when hundreds of cases were Blood Transfusions reported in young women using intravaginal Corticosteroids tampons. Electrolyte replacements Ventilator if lungs are damaged Toxic shock syndrome is characterized by fever; hypotension; a diffuse, macular, sunburn-like rash that goes on to desquamate; and involvement of three or more of the following organs: liver, kidney, gastrointestinal tract, central nervous system, muscle, or blood. high fever vomiting Diarrhea Sore throat muscle pain. Pathogenesis of staphylococcal toxic shock syndrome Staphylococcus aureus: Toxin-Mediated Diseases Scalded Skin Syndrome (SSS) also known as Ritter von Ritterschein disease- results from the production of toxin exfoliatin , SSS characterized by red blistering skin that looks like a burn or scald. The disease is most common in neonates and children less than 5 years of age. Symptoms: Fussiness (irritability) Tiredness Fever Redness of the skin Fluid-filled blisters that break easily and leave an area of moist skin that soon becomes tender and painful Large sheets of the top layer of skin may peel away electrolyte imbalance can occur Hair and nails can be lost Treatment may include: Intravenous antibiotic therapy Fluids to prevent dehydration Nasogastric feeding Use of skin creams or ointments and bandages Pain medicines Laboratory diagnosis A. Specimens One or more of the following specimens should be collected to confirm a diagnosis: Pus from abscesses, wounds, burns, etc. is much preferred to swabs. Sputum from patients with pneumonia (e.g. postinfluenzal or ventilator-associated pneumonia); bronchoscopic specimens, e.g. bronchoscopic lavage, are increasingly used in critically ill patients. Faeces or vomit from patients with suspected food poisoning, or the remains of implicated Foods Blood from patients with suspected BSI such as septic shock, osteomyelitis or endocarditis. Mid-stream urine from patients with suspected cystitis or pyelonephritis. Anterior nasal and perineal swabs (moistened in saline or sterile water) from suspected carriers; nasal swabs should be rubbed in turn over the anterior walls of both nostrils.  Diagnostic Laboratory Tests A. Specimens F. Molecular typing techniques have been used to B. Smears document the spread of epidemic disease- Typical staphylococci appear as gram-positive cocci in clusters producing clones of S aureus. Pulsed-field gel in Gram-stained smears of pus or sputum electrophoresis and multilocus sequence typing are highly discriminatory. G. API TestAPI Staph strip consists of 20 microtubes containing The dehydrated substrates. These microtubes are inoculated with a bacterial suspension, prepared in API Staph Medium, that reconstitutes the tests. During incubation, metabolism C. Culture produces color changes that are either spontaneous or Specimens planted on blood agar plates give rise to typical revealed by the addition of reagents. colonies in 18 hours at 37°C. S aureus but not other The reactions are read according to the Reading Table and the staphylococci ferment mannitol. identification is obtained by referring to the Analytical Profile Index or using the identification software D. Catalase Test is used to detect the presence of cytochrome oxidase enzymes. All staphylococci produce catalase, whereas no streptococci do E. Coagulase Test S. aureus is coagulase-positive TREATMEN T Most boils and superficial staphylococcal abscesses resolve spontaneously without antimicrobial therapy. Those that are more extensive, deeper, or in vital organs require a combination of surgical drainage and antimicrobials for optimal outcome. Penicillins and cephalosporins are active against S aureus cell wall peptidoglycan and vary in their susceptibility to inactivation by staphylococcal β-lactamases. Penicillin G is the treatment of choice for susceptible strains The penicillinase-resistant penicillins (methicillin, nafcillin, oxacillin) and first-generation cephalosporins are now used because of the high frequency of penicillin resistance (>80%). For MRSA strains resistant to these agents or in patients with β-lactam hypersensitivity, the alternatives are vancomycin, clindamycin, or erythromycin. Synergy between cell wall-active antibiotics and the aminoglycosides is present when the staphylococcus is sensitive to both types of agents. Such combinations are often used in severe systemic infections when effective and rapid bactericidal action is needed, particularly in compromised hosts.  Prevention of bacterial diseases The most important preventive measure in hospitals is washing the hands thoroughly before medical and nursing procedures. Intranasal application of antibiotics (mupirocin) is a method of reducing bacterial counts in carriers. COAGULASE-NEGATIVE STAPHYLOCOCCI (CoNS)  COAGULASE-NEGATIVE STAPHYLOCOCCI (CoNS) Staphylococcus epidermidis and many other species of CoNS are normal commensals of the skin, anterior nares, and ear canals of humans. Common colonizers of the skin Colonize implanted medical devices Polysaccharide mediates attachment to plastics and between CoNS cells Staphylococcus epidermidis often forms biofilms on intravascular catheters and leaches out to cause bacteremia and catheter related sepsis Coagulase negative staphylococcal biofilm. A. Staphylococcus epidermidis cocci are shown attached to the surface of a plastic catheter and are starting to produce extracellular polysaccharide biofilm. B. After 48 hours the bacteria are fully embedded in the slime glycocalyx.  COAGULASE-NEGATIVE STAPHYLOCOCCI (CoNS) Staphylococcus saphrophyticus Staphylococcus saphrophyticus’ usual habitat is the gastrointestinal tract, and from that location the organism gains access to the urinary tract. S saphrophyticus causes urinary infections in young women. The infection process is aided by surface adhesins to uroepithelial cells and factors aiding survival in urine like the production of a urease. Most CoNS now encountered are resistant to penicillin, and many are also methicillin-resistant. Eradication of CoNS from prosthetic devices and associated tissues with chemotherapy alone is very difficult unless the device is also removed.  Staphylococci vs Streptococci Catalase + Catalase - THANK YOU!