What is a Staph Infection?

Staphylococcal infections are infections caused by staphylococci, which are gram-positive cocci that cause purulent infections in humans and animals. Staphylococci belong to the family Micrococcus and Staphylococcus, and are named for their arrangement like grape bunches. Gram staining was positive. It mainly causes boils, boils, folliculitis, pneumonia, brain abscesses, liver abscesses, suppurative osteomyelitis, and wound infections. Staphylococci are widely distributed in nature, the vast majority are non-pathogenic, and only a few cause purulent infections in humans and animals. They can be divided into pathogenic Staphylococcus aureus and conditionally pathogenic Staphylococcus epidermidis, in addition to saprophytic grapes. Cocci. Staphylococcus aureus can produce a variety of exotoxins and enzymes, so it is highly pathogenic. It is a common bacterial infectious disease, mostly manifested as skin and soft tissue infections, which can also cause serious illness, life-threatening sepsis, endocarditis, pneumonia, meningitis, etc. In addition, it can also cause foreign body-related infections, urinary tract infections, Osteomyelitis, arthritis, enteritis, etc.

Basic Information

English name

staphylococcia

Visiting department

Internal medicine

Common causes

S. aureus is most pathogenic

Common symptoms

Sepsis, pneumonia

Causes of staphylococcal infections

Among the pathogenic staphylococci, Staphylococcus aureus is the most pathogenic, which is mainly related to its production of various toxins and enzymes and certain bacterial antigens. Epstaphylococcus and Staphylococcus do not produce toxins and enzymes that are toxic to the human body.

Toxin

(1) Hemolysin S. aureus can produce four different antigenic hemolysins, , , , and , all of which can produce complete hemolysis. Alpha hemolysin can still damage platelets, macrophages and leukocytes, contract vascular smooth muscle and cause ischemic necrosis.

(2) Leukocin kills or destroys leukocytes and macrophages, so that bacteria can still grow and reproduce in cells after being phagocytosed.

(3) Enterotoxin is an exotoxin that produces food poisoning. There are at least six types of A, B, C1, C2, D and E. Oral administration can cause vomiting and diarrhea in small amounts.

(4) Epidermal Dissolved Toxin This toxin can cause superficial division of the skin epidermis to produce bullous pemphigoid and other symptoms.

(5) The rash-producing toxin is produced by Staphylococcus aureus type 71 in phage group II, and it has a scarlet fever-like rash clinically.

(6) Other toxins such as toxic shock syndrome.

2. Enzyme

Staphylococcus can produce a variety of enzymes such as proteases, lipases, and hyaluronidases. The pathogenic effects of these enzymes are not clear, but they have the effect of destroying tissues and may promote the spread of infection to surrounding tissues. There are also several enzymes associated with pathogenicity and resistance.

(1) Plasma coagulase changes fibrinogen in the plasma into fibrin, deposits on the surface of the bacteria, hinders the phagocytosis of phagocytes, and facilitates the formation of infectious thrombus.

(2) -lactamase inactivates -lactam antibiotics.

(3) Hyaluronidase This enzyme can hydrolyze the matrix-hyaluronic acid between connective tissue cells of the human body to spread the infection.

(4) Lipolytic enzymes Staphylococcus aureus can produce several kinds of lipolytic enzymes, which act on the fats and oils on the surface of plasma and skin, which is beneficial for bacteria to invade human skin and subcutaneous tissues.

(5) Others include staphylokinase, catalase, and plasmin.

3. Cell antigen

(1) Some strains of S. aureus have obvious capsules, which increase the virulence, and the body can produce corresponding antibodies. Protein A (agglutinogen) is part of the S. aureus cell wall and is present in 90% of S. aureus. Protein A can bind to the Fc fragment of IgG, and has the function of anti- opsonin and anti-phagocytosis.

(2) Cell wall wall acid is a specific antigen. Staphylococcus aureus, epistasis and staphylococcus have different wall acid composition.

4. Regulation of virulence genes

The regulation of Staphylococcus aureus virulence genes is extremely complicated, which is affected by various environmental factors and bacterial products. At present, more researches are agr gene and sar gene, which can up-regulate the expression of bacterial secreted proteins and reduce the synthesis of cell wall-related proteins. Staphylococcus resistance: Staphylococcus is one of the most resistant pathogens. The bacterium of this genus has almost all currently known resistance mechanisms and can resist all antibacterials except vancomycin and norvancomycin. Drug resistance develops.

Clinical manifestations of staphylococcal infection

Staphylococcus aureus can cause skin and soft tissue infections, sepsis, pneumonia, endocarditis, meningitis, osteomyelitis, food poisoning, etc. In addition, it can also cause pericarditis, mastoiditis, sinusitis, otitis media, toxic shock syndrome Wait. In addition to causing septicemia and endocarditis, epistasis can also cause urinary tract and skin infections. Staphylococcus mainly causes urinary tract infections. Its clinical manifestations can be divided into two major types.

Disease caused by toxin

(1) Staphylococcus gastroenteritis Staphylococcus aureus contaminates starchy foods (such as leftovers, porridge, rice noodles, etc.), milk and dairy products, fish, meat, eggs and other foods, and can be large at room temperature (about 22 ° C) Breeding produces heat-resistant enterotoxin (exotoxin). At 100 ° C, 30 minutes can only kill Staphylococcus aureus without destroying the toxin, which can cause symptoms such as nausea, vomiting, upper and middle abdominal pain, and diarrhea. Vomiting is usually severe, and the vomit may be bile; diarrhea may be watery or thin. Most of the body temperature is normal or slightly elevated. Most patients recover quickly within a few hours to 1-2 days, and the course of the disease is self-limited. Previously, it was considered that the bacterial flora altered enteritis caused by the application of antibacterial drugs was pseudomembranous enteritis caused by Staphylococcus aureus, which has been rejected by most scholars. This enteritis is caused by the exotoxin of Clostridium difficile, and S. aureus is only a companion bacteria.

(2) The main clinical manifestations of toxic shock syndrome are high fever, shock, erythema rash, vomiting, diarrhea, and muscle pain, mucosal congestion, liver and kidney damage, disorientation, or altered consciousness. The onset of this syndrome is caused by the pyrogenic exotoxin C produced by S. aureus (phage I group), and has nothing to do with the bacteria themselves. Toxic shock syndrome is more common in young women, especially those with menstrual occlusion, but it also occurs in menopausal women, men and children. Although diagnosis can be established based on clinical manifestations, blood, vagina, nasal cavity, urine and other cultures still need to be performed to observe the presence of S. aureus and exclude the possibility of infection by other pathogens.

(3) Scald-like skin syndrome is generally thought to be caused by Group II phage-type Staphylococcus aureus, which can produce epidermal lytic toxins, causing diffuse erythema and blister formation on the skin of newborns and young infants, followed by large epidermal shedding . The inflammatory response in the affected area is slight, and only a small amount of pathogenic bacteria can be found. The syndrome is occasionally seen in adults, but the rash quickly peels off, and if properly treated, it heals quickly and has a low mortality rate.

2. Diseases caused by direct invasion or systemic spread of staphylococci

(1) Skin and soft tissue infections Most of the skin and soft tissue infections are caused by Staphylococcus aureus. A small number of pathogenic bacteria can be epistasis. The main pathogens are maggots, boils, folliculitis, pustules, impetigo, and pemphigus. , External otitis, wound infection, cavernous sinus thrombosis, blebitis, bedsore infection, perianal abscess and so on. When subcutaneous tissues and hair follicles are infected by S. aureus, ridge formation may occur, which is common in the neck, armpits, hips, and thighs, and recurrence is common. Scab mostly occurs behind the neck and back. It is a large induration with redness, swelling, pain, and multiple sinus drainage. Folliculitis is a superficial infection of Staphylococcus. Whiskers are an infection secondary to a foreign body hair reaction, most of which are caused by S. aureus. Newborns may suffer from skin abscesses, and occasionally severe pemphigoid, which may be severe throughout the body and mainly bullous. The skin lesions are blisters. After rupture, pus exudates and palate formation is called impetigo. Otitis and wound (surgery or trauma) infections are mostly caused by S. aureus. The latter can manifest as mild erythema, exudation of serous fluid, and even cellulitis and wound dehiscence. Cavernous sinus thrombosis is a rare and serious complication of S. aureus facial infection. Paronychia and blephaeritis are mainly caused by Staphylococcus aureus, while those with perianal abscess especially with anal fistula and pressure ulcer infection are mostly caused by intestinal bacteria, and the pathogenic bacteria are only a few.

(2) Staphylococcus sepsis is a common pathogen of sepsis. Most manifested as local pain and limited movement of large joints, but there were also people with septic arthritis. Migration damage and / or abscesses occurred in about 2/3 of the cases. The incidence was subcutaneous soft tissue abscess, pneumonia and pleurisy, suppurative meningitis, localized inflammation or abscess, joint abscess, liver abscess, sponge Sinus thrombosis, endocarditis, osteomyelitis (involving the spine, femur, tibia, radius or ulna, etc.), pericarditis, peritonitis, etc.

(3) Endocarditis can occur in the following cases: In the course of staphylococcal sepsis, normal or damaged valves can be involved; more than 2 months after the artificial heart valve device, sternal wound infection, urinary catheterization, Temporary bacteremia caused by tooth extraction, etc .; After pacemaker device (rare); Caused by intravenous fluids or intravenous drugs. Most of the endocarditis caused by Staphylococcus aureus has an acute course with rapid onset and signs of chills, high fever and toxemia. Because it often occurs in patients with normal heart, there may be no heart murmur early in the course of the disease, and then pathological murmur appears in the course of the disease. The original murmur may have significant changes in murmur. The aortic valve generally affects the right heart and tricuspid valve injectors. Skin and mucous membrane petechiae occur far less frequently than those caused by Streptococcus grass, and kidney, brain, and fundus embolisms are also uncommon. Cardiac insufficiency can occur early (about 30%). Migratory infections are more common, with 50% of patients having a purulent kidney infection, 40% with meningitis or brain abscess, and 30% with pneumonia, lung abscess, or pulmonary infarction. Eperostaphylococcal endocarditis can occur after the prosthetic valve device, and occasionally it also occurs in the heart with disease, such as rheumatic heart disease, congenital heart disease, arteriosclerotic heart disease, etc., most of its clinical course was subacute .

(4) Most of the pathogenic bacteria of Staphylococcus pneumoniae pneumonia are Staphylococcus aureus, the primary ones are rare, most of them are secondary to viral lung infections (measles, flu, etc.), or caused by the spread of blood. Infants are common in patients, and rare in adults. Babies are susceptible to S. aureus pneumonia after measles, which is characterized by rapid disease progression.

(5) Meningitis Staphylococcus meningitis is also mainly caused by S. aureus, which accounts for only 1% to 2% of various purulent meningitis. The disease is more common in young children under 2 years of age, but adults also account for a certain proportion. It occurs in all seasons, but it is more common in July, August, and September, which is related to more skin infections in summer and autumn.

(6) Urinary tract infections Staphylococcal urinary tract infections are mostly caused by staphylococci and staphylococcus sphaeroides, urinary tract infections of staphylococcal bacteria are common in patients with indwelling catheters, especially in patients with prostatectomy. Generally asymptomatic, the pathogen will disappear by itself after removal of the catheter, but in a few cases symptoms may also occur and require antibacterial treatment. Staphylococcal urinary tract infections are quite common in foreign countries and usually cause cystitis, but they can also affect the upper urinary tract and have been isolated from patients' kidney stones. Most strains can break down urea and are resistant to neomycin.

(7) Bone and joint infections with S. aureus can cause acute suppurative osteomyelitis, which is more common in children and men, and often involves the lower end of the femur and the upper end of the tibia, followed by the spine, humerus, ankle, wrist, pelvis, and radius. It can be a blood-borne infection, or it can be secondary to trauma or septic arthritis: first from the epiphyseal end, after the local formation of an abscess, it spreads to the proximal end to the subperiosteal or bone marrow cavity, causing subperiosteal abscess, or perforation Broken subcutaneously to form a subcutaneous abscess. About 10% of patients penetrate the joint capsule and cause septic arthritis. Those with chronic osteomyelitis forming sinus tract will not heal for years. The periosteal hyperplasia around the lesion forms the repair bone layer, called the cladding, which is one of the characteristics of suppurative osteomyelitis. The clinical manifestations showed a sudden chills, high fever, local muscle tension, the patient refused to move the affected limb, local tenderness in the bones, skin fever, and edema. Bone marrow aspiration culture can detect S. aureus. On X-ray examination, osteoporosis often occurred in the second to third week, and later periosteal hyperplasia, dead bone formation and new bone hyperplasia occurred; scanning with radionuclide strontium and fluorine revealed that the lesion was earlier than X-ray. Most of the acute lesions have a good prognosis after timely antibacterial treatment, and a few cases can occur repeatedly at the same site to form a chronic infection. Staphylococcus aureus causes purulent spondylitis to invade the lumbar spine, followed by the thoracic and cervical spine. Often with low fever, back pain, and radiation to both legs, local muscle cramps, restricted movement, and concurrent paravertebral abscesses. X-ray examination from 2 to 3 weeks can be seen in the spinal stenosis, bone destruction and hyperplasia later, the formation of bone bridges in the intervertebral disc, is the characteristic of the X-ray of the disease.

(8) Coagulase-negative staphylococci related to foreign body implantation account for about 50% of the pathogens of foreign body-associated infection, of which Staphylococcus is the main species. Intravascular catheters, continuous peritoneal dialysis tubes, body fluid shunting systems, artificial valves, artificial joints, cardiac pacing electrodes, artificial breasts, and implanted intraocular lenses can all be inducements for coagulase-negative staphylococcal infections. Clinical manifestations can be local or systemic infection symptoms, most of which are fever of unknown cause, which can be cured by removing foreign bodies, and can also lead to severe sepsis and death.

(9) Other staphylococci can still cause liver, spleen, kidney abscesses, abscesses around the kidney, pericarditis, empyema and so on.

Staphylococcal infection test

1. (blood, pus, sputum, cerebrospinal fluid, feces, secretions, etc.) smear or culture to find pathogenic bacteria.

2. The diagnosis of sepsis and endocarditis lies in the corresponding clinical manifestations and positive blood cultures. When both are suspected, it is advisable to take blood for culture 3 to 4 times before the application of antibacterial drugs. Those who have used antibacterial drugs every 1 to 2 hours must still take blood and culture 2 to 3 times a day at high fever. The blood volume can be 6 ~ 10ml, preferably blood clots for culture. The positive rate of 3 to 4 cultures can reach more than 95% to 98%. This refers to the pre-application of antibacterial drugs. If antibacterial drugs have been applied, the culture-positive rate will be reduced from more than 90% to about 40%. Blood culture is negative and the detection of pathogenic bacteria from a variety of purulent secretions (such as migrating abscesses, surgical wound pus, etc.), pleural effusion, ascites, etc. is also of diagnostic value.

3. It should be cautious when judging the positive blood culture of staphylococcus. If the same staphylococcus is obtained more than 2 times, although it is helpful to the diagnosis, the laboratory with conditions should do the analysis of plasmid and restriction enzyme digestion spectrum.

4. Cerebrospinal fluid in meningitis patients, sputum in patients with pneumonia, menstrual plugs and local abscesses, vagina, etc. in patients with toxic shock syndrome, local secretions in patients with osteomyelitis, stool and vomit from patients with food poisoning (and Corresponding food), etc. have the opportunity to isolate pathogenic bacteria. When clinically suspected of Staphylococcus aureus sepsis or endocarditis, and blood cultures are negative many times, serum teichoic acid antibodies can be tested (solid-phase radioimmunoassay or enzyme-linked immunosorbent assay).

5. Paravertebral abscess, X-ray examination from 2 to 3 weeks can see vertebral space stenosis, bone destruction and hyperplasia later, the formation of bone bridges in the intervertebral disc, are the characteristics of the X-ray of the disease.

Diagnosis of staphylococcal infections

The diagnosis of staphylococcal infections mainly depends on the clinical manifestations of various infections and smears or cultures of related specimens (blood, pus, sputum, cerebrospinal fluid, feces, secretions, etc.) to find the pathogenic bacteria. Skin, soft tissue infections such as pimple, palate, impetigo, blepharitis, folliculitis, and paronychia are easy to identify and generally do not cause misdiagnosis.

Differential diagnosis of staphylococcal infection

Golden grape infection should be distinguished from scarlet fever: Compared with the past, the incidence of scarlet fever has reduced the number of patients and typical cases, but increased atypical cases. The reason is that the virulence of streptococcus itself is not very strong, and it is still sensitive to penicillin and has no drug resistance, so the effect of treatment with penicillin is obvious.

Staphylococcal pneumonia should be distinguished from caseous pneumonia, Gram-negative bacillus pneumonia, lung abscess, and lung cancer.

Staphylococcal infection complications

Staphylococci can infect any part of the body, and the symptoms depend on the site of infection. Infections can range from mild to life threatening. In general, staphylococcal infections produce encapsulated pus, such as abscesses and pustules ( and ); staphylococci can spread through the blood and cause abscesses (such as the lungs) of internal organs and infections of the bones (osteomyelitis) and Infections of the endocardium and heart valves (endocarditis).

Staphylococcal infection treatment

General treatment

Prompt diagnosis and early application of appropriate antibacterial drugs are the main keys to the success of treating severe staphylococcal infections. In addition to antibacterial drugs, comprehensive measures such as improving the immune function of the human body, correcting water and electrolyte disturbances, rescuing septic shock, and protecting important organ functions such as the heart, lungs, kidneys, and liver should also be emphasized. Adrenal corticosteroids must be weighed and weighed before they are used. Unless there is severe toxemia and combined with effective antibacterial drugs, it is generally not appropriate. Human blood gamma globulin (gamma globulin) is suitable for patients with antibody-deficient diseases such as hypoglobulinemia.

2. Surgical treatment

Sufficient drainage of pus is often a prerequisite for treating certain staphylococcal infections with abscesses. Superficial infections such as scrofula, paronychia, and meibitis are cured quickly after puncture or incision and drainage, and generally do not require antibacterial drugs. Deep subcutaneous abscesses or osteomyelitis with abscess formation require incision and drainage. Pulmonary abscesses can be drained in position. These infections must be treated with antibacterial drugs. Multi-family liver abscess mainly depends on drug treatment, and large single-room abscesses are considered for surgical drainage when the effect of medical treatment is not satisfactory. When artificial heart valves or venous intubation are associated with staphylococcal infections, the valve must be replaced or the cannula removed. Antimicrobials alone cannot often control the infection. The medical treatment of acute staphylococcal endocarditis is not effective. Patients with repeated embolism or acute heart failure are surgical indications.

3. Antibacterial treatment

When patients with staphylococcal infection have systemic symptoms or local lesions are developing rapidly, they should be treated with active antibacterials immediately.

Prognosis of staphylococcal infection

Except for sepsis, endocarditis, meningitis, pneumonia, and toxic shock syndrome, the prognosis of uncomplicated staphylococcal skin and soft tissue infections, food poisoning, osteomyelitis, and urinary tract infections is good. Although Staphylococcus aureus food poisoning is rapid, vomiting and diarrhea are severe, but the recovery is fast. Since the application of antibacterial agents effective against S. aureus, cases of chronic osteomyelitis with sinus formation have been rare. Urinary tract infections caused by staphylococcal and staphylococcal bacteria rarely become a treatment problem. Although the scalded skin syndrome is more dangerous, most children recover smoothly after treatment. The prognosis of staphylococcal sepsis, endocarditis, meningitis, and pneumonia is poor. Although the treatment with effective drugs, the mortality rate is still high.

Staphylococcal infection prevention

To prevent the occurrence and spread of staphylococcal infections, the following points should be noted:

1. Strengthen labor protection, keep the skin clean and intact, and avoid trauma.

2. Timely and effective treatment of patients with staphylococcal infections, reasonable treatment of carriers, in order to remove and reduce the source of infection.

3. Strictly implement disinfection and isolation measures in neonatal rooms, burn wards, surgical wards, etc., and cut off the transmission channels.

4. Actively treat or control chronic diseases such as diabetes, blood diseases, liver cirrhosis, etc., especially those with granulocytopenia, and correct various immune defects to protect vulnerable groups. Staphylococcus-resistant vaccines can improve cell phagocytosis and the survival rate of staphylococcal infection models, and may be beneficial to prevent staphylococcal infections.