APP 1 Chapitre Flashcards
True or false
Staphylococci are Gram-positive cocci that form grapelike clusters. They include Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus saprophyticus (which almost exclusively causes urinary tract infections), and numerous others.
Encounter with staph?
Organisms grow on the surface of humans and survive on inanimate surface. During a lifetime, ~90% of humans are colonized at some point with S aureus in their external nares or skin.
Entry of staph?
Carriage of staphylococci usually occurs after direct, skin-to-skin contact with another carrier. Infection may also occur after penetration of a contaminated object through the skin.
Spread and Multiplication of staph?
Commensal staphylococci (eg, S epidermidis) are colonizers of normal skin and rarely cause deeper infection unless they are physically introduced into deeper tissues in association with an intravenous catheter or other artificial device. Virulent staphylococci (ie, S aureus) may cause skin and mucous membrane infections, from which organisms may disseminate to almost any organ or tissue.
Damage of S aureus?
S aureus is pyogenic (“pus forming”), except in toxic shock syndrome, which may occur with nonpyogenic infection. Staphylococci cause skin and soft tissue infections (such as furuncles, abscesses, and necrotizing fasciitis), pneumonia, food poisoning, and toxin-induced diseases (toxic shock and scalded skin syndromes). If the organisms enter the bloodstream, they may cause osteomyelitis, kidney abscesses, or endocarditis.S aureus produces microbial surface components recognizing adhesive matrix molecules (MSCRAMMs), including peptidoglycan, teichoic acids, protein A, clumping factor, and others. They also secrete virulence factors such as hemolysins, leukocidins, superantigens, and other exotoxins.
Diagnosis of staph?
Staphylococci have a characteristic appearance on Gram stain, and they are easily isolated on most laboratory media.
Treatment of staph?
Most strains produce β-lactamase (an enzyme that breaks down penicillin). Consequently, antistaphylococcal penicillins or cephalosporins are used. However, some strains express penicillin-binding protein 2a, which also makes the organism resistant to the above-mentioned agents (methicillin-resistant S aureus or MRSA). Drainage of abscesses and supportive therapy for hypotension and shock are also critical, nonantimicrobial elements of care.
Prévention staph?
There is no vaccine against staphylococci.
What is staph aureus?
STAPHYLOCOCCUS AUREUS (Gram-positive cocci) are the most common of the pyogenic, or pus-producing, bacteria that cause human diseases. They colonize the anterior nares of 30%-40% of individuals and may be present on other mucous membranes and the skin.
Diseases caused by staph aureus?
Skin and soft tissue infections
Furuncles, carbuncles, paronychia (nail infections)
Wound infections (traumatic, surgical)
Cellulitis
Impetigo (also caused by streptococci)
Bacteremia (frequently with metastatic abscesses)
Endocarditis
Central nervous system infections
Brain abscess
Meningitis (rare)
Epidural abscess
Pulmonary infections
Embolic
Aspiration
Musculoskeletal infections
Osteomyelitis
Arthritis
Genitourinary tract infections
Renal abscess
Lower urinary tract infection
Toxin-related diseases
Toxic shock syndrome
Necrotizing pneumonia
Scalded skin syndrome
Extreme pyrexia syndrome
Food poisoning (gastroenteritis)
Why can staph aureus survive in almost any environnement?
Staphylococcus aureus is a large (1 μm in diameter) Gram-positive coccus that grows in grapelike clusters. It is one of the hardiest of the non–spore-forming bacteria and can survive for long periods on dry, inanimate objects. It is also relatively heat resistant. These properties permit S aureus to survive in almost any environment in which humans coexist.
Staphylococcus epidermidis
The most ubiquitous Staphylococcus species is Staphylococcus epidermidis, which is found on the skin and mucous membranes of most people and only infrequently causes disease in healthy individuals. This organism causes numerous infections in hospitals and in patients with implanted artificial devices (eg, -intravenous catheters, vascular grafts, and artificial joints).
S aureus
S aureus generally causes more serious infections, including pneumonia, bone and joint infections, endocarditis, sepsis, and severe life-threatening TSS. The species name aureus means “golden” and refers to carotenoid pigmentation of S aureus colonies (other species colonies are white, but occasionally, S aureus colonies are also white)
Staphylococcus saprophyticus
Staphylococcus saprophyticus is unique in that it causes only urinary tract infections.
Staphylococcus lugdunensis,
A fourth species, Staphylococcus lugdunensis, is an uncommon cause of aggressive endocarditis. The genus Staphylococcus contains other species that occasionally cause disease; those species are described in standard microbiological texts.
Caracteristics (coagulase and colonies and common) of 4 species of staph?
2 tests to identify strains?
Within a species of staphylococci, individual strains can be identified by differences in their resistance to a panel of antibiotics and by using a procedure called phage typing or, more commonly, pulsed field gel electrophoresis. Phage typing, which is rarely done today, involves determining the sensitivity of a strain to a variety of standard bacteriophages. Pulsed field gel electrophoresis involves isolating staphylococcal DNA, treating the DNA with restriction enzymes that cut the DNA only rarely, and then resolving those DNA fragments in agarose gels. The newer molecular techniques for typing staphylococci based on the DNA sequence of the bacterial chromosome provide greater discrimination than phage typing between outbreak-related and non–outbreak-related strains and, as shown in the cases cited in this chapter, showed the relatedness of the organisms.
Where are staph found?
Staphylococci share their environment with that of human beings. They live on people and survive on inanimate objects and surfaces (fomites), such as bedding, clothing, and doorknobs. Humans are the major reservoir for S aureus. The organisms frequently colonize the anterior nares and are found in ~30% of healthy individuals. However, studies of individuals over time have found that up to 90% of people are eventually colonized in the nares with S aureus at some point in their lives. The organisms can also be found transiently on the skin, oropharynx, and vagina and in feces. Staphylococci are well equipped to colonize the skin because they grow at high salt and lipid concentrations. They make enzymes, referred to as lipases and glycerol ester hydrolases, that degrade skin lipids.
Cell surface proteins for staph aureus?
The ability of S aureus to colonize the skin and mucosal surfaces has been associated with bacterial cell surface proteins—the MSCRAMMs (microbial surface components recognizing adhesive matrix molecules)—that bind to a variety of host extracellular matrix proteins. Fibronectin-binding proteins (FnbpA and FnbpB) have been identified on the surface of S aureus. Fnbp’s allow the bacteria to invade epithelial and endothelial cells and to attach to exposed fibronectin in wounds, which may make FnbpA and FnbpB important virulence factors for the invasion of deeper tissues. S aureus also has MSCRAMMs for collagen binding, called CNAs. They are important components of connective tissue, bones, and joints. Other MSCRAMMs, called clumping factors A and B, are present for fibrinogen binding and experimentally have been shown to be important in clot formation and endocarditis. These proteins are responsible for the clumping seen in the slide coagulase test.
Who gets more staph aureus?
Staphylococci spread from person to person, usually through direct contact or aerosols associated with upper respiratory viral or bacterial infections. It is important to remember that S aureus is an important secondary pathogen associated with patients recovering from influenza and parainfluenza (croup) infections. Infants may become colonized with S aureus shortly after birth, acquiring the organism from people in their immediate surroundings. Some people will become carriers for prolonged periods, while others will harbor the organisms only intermittently. For unknown reasons, people in certain occupations, including physicians, nurses, and other hospital workers, are more prone to colonization. Also, certain patient groups, including diabetics, patients on hemodialysis, and chronic intravenous drug abusers, have a higher carriage rate than does the general population.
Entry?
S aureus and most other bacteria do not usually penetrate into deep tissues unless the skin or the mucous membranes are damaged or actually cut. Skin damage may be caused by burns, accidental wounds, lacerations, insect bites, surgical intervention, or associated skin diseases. If present in very large numbers, some bacteria, including S aureus, are able to enter spontaneously and cause disease. This scenario occurs in cases of poor hygiene or prolonged moisture of the skin, which permits the growth of large numbers of organisms. It is not known if these infections are caused by spontaneous penetration or if the organisms enter through inapparent cuts and abrasions.
Spread and multiplication?
The survival of S aureus in tissues depends on several factors: the number of entering organisms, the site involved, the speed with which the body mounts an inflammatory response, and the immunological status of the host. When the inoculum is small and the host is immunologically competent, infections by these and other organisms are usually stopped. Nonetheless, staphylococci possess a particularly complex but effective pathogenic strategy, and even healthy persons may be unable to combat S aureus. Luckily, the area of inflammation most often remains localized, and the organisms can be contained.
True or false most local staphylococcal infections lead to the formation of a collection of pus called an abscess. Abscesses in the skin are called boils or, in medical parlance, furuncles. Multiple interconnected abscesses are called carbuncles. Alternatively, staphylococci can spread in the subcutaneous or submucosal tissue and cause a diffuse inflammation called cellulitis. In most cases, these skin infections are caused by S aureus and not by the other staphylococcal species.
True
How does an abcess develop?
The development of an abscess is a complex process that involves both bacterial and host factors (Fig. 11-4). The early events are characteristic of an acute inflammatory reaction, with a rapid and extensive influx of leukocytes (eg, neutrophils). Chemotactic factors, derived both from bacteria and complement, are made in large amounts. However, some staphylococci not only survive this onslaught but are even capable of killing and lysing many of the neutrophils that have entered the infection area by the production of cytolysins. The lysed neutrophils pour out large amounts of lysosomal enzymes, which damage surrounding tissue.
The development of an abscess is a complex process that involves both bacterial and host factors. S aureus infections cause a rapid and extensive influx of leukocytes (eg, neutrophils). Chemotactic factors, derived both from bacteria and complement, are made in large amounts. S aureus secretes coagulase that causes formation of clots. Protein A is released where it may bind antibodies reducing opsonization. S aureus lyse neutrophils and red blood cells that have entered the infection area by the production of cytolysins (leukocidins and hemolysins). The lysed neutrophils pour out large amounts of lysosomal enzymes, which damage surrounding tissue.