examprepare

Chapter 8

Disease of upper respiratory tract

streptococci---1. a large and diverse group of encapsulated, nonmotile, gram-possitive cocci. 2. they cause streptococcal sore throat喉咙痛, scarlet fever猩红热, and other diseases. 3. the bacteria divide in one plane and cling紧贴 together to form chains of various lengths. This is apparent in streptococci grown in liquid media, but may not be obvious in solid media.

Classification of streptococci
1. by J. H. Brown in 1919, divides streptococci into hemolytic溶血的 group (blood-disgesting), depending on how they affect red blood cells in blood agar.
Alpha-hemolytic streptococci turn blood agar an olive-green color as they partially destroy red blood cells in the medium;
Beta-hemolytic strptococci are surrounded by clear, colorless zones due to the complete destruction of reb blood cells and thus cause no change in blood agar.
Nonhemolytic streptococci have no effect on red blood cells and thus cause no change in blood agar.
2. by Rebecca Lancefield in 1933, bases on variants of a specific carbohydrate, the C substance, in cell walls of streptococci.
Groups A through O streptococci have been distinguished,.
Most streptococci diseases in humans are caused by species of group A streptococci;

Streptococcus pyogenes唾液链球菌---
1. cause streptococcal pharyngitis链球菌咽炎. generally known as strep throat.
2. the streptococci reach the upper respiratory tract within airborne droplets of mucus expelled by infected persons during coughing and sneezing打喷嚏.
3. patients experience a sore throat, high fever, coughing, swollen肿胀的 lymph nodes and tonsils扁桃腺, and a fiery red火热的红色 "beefy" appearance to pharyngeal咽的 tissues owing to tissue erosion. Primarily children suffer this disease, many cases complicated by an infection of the middle ear, otitis media耳炎(可有疼痛、发热、听力异常、听力丧失、耳鸣和眩晕)
4. the pathogenicity of S. pyogenes is enhanced by a substance called M protein. this protein anchored in the cell wall and cell memberane, encourages adherence to the pharyngeal tissue and retards phagocytosis减速吞噬作用.
5. Over 80 types of M protein exist, immunity to streptococcal disease requires a person to produce antibiodies against all 80 types.
6. S. pyogenes commonly present in the human nose and throat, and transmission to many other tissues is possible.


Scarlet fever(猩红热)---
1. is strep throat accompanied by a skin rash皮疹.the rash develops as a pink-red blush, apparent on the neck, chest, and soft-skin areas of the arms.
2. it results from blood leaking through the walls of capillaries damaged by a toxin---erthrogenic (red-forming) toxin, is produced only by strains of S. pyogenes that carry a prophage 前噬菌体that encodes the toxin.

Rheumatic fever风湿热---
1. most common in young school-age children. caused by specific M serotypes of group A streptococci.
2. characterized by fever and inflammation炎症 of the small blood vessels. Joint pain is common, most significant long-range effect is permanent scaring and distortion of the heart valves, a condition called rheumatic heart disease.
3. rheumatic heart disease , the damage arise from a reaction of the body's antibodies to streptococci antigens抗原 crossreacting with antigens on heart tissues. another magnifestation of this reaction may develop in the kidney, where the condition is called glomerulonephritis.
4. Rheumatic fever declines in the U.S. due to antibiotic reatment, and the strains cause the disease. in developing nations, this remains a serious problem.

Erysipelas丹毒--- streptococci cause diease in open wounds or skin abrasions.

Necrotizing fasciitis坏死性筋膜炎---invasive group A streptococci containing other specific prophage invade and infect the fascia纤维组织片或带 over the muscles and beneath the skin, the phage-encoded tosins cause this condition.

Puerperal sepsis/ childbed fever产后脓毒病---The tissue of the uterus becomes infected during the birth process. promoted Ignaz Semmelweis to institute hand washing in the hospital maternity wards.

Streptococci pneumonia肺炎---infection on the lower respiratory tract.

Septicemia败血病 ---"blood poisoning," a disease now know to be due to several organisms, including streptococci, one of Louis Pasteur's daughter died of this died of this.

Treatment of streptococcal disease
1. with antibiotics such as penicillin and erythromycin.
2. however, widespread resistance to antibiotics has been notices, indicating that many strains of S. pyogenes carry prophages having antinbiotic resistance genes.

Diphetheria白喉---
1. recoginzed by French pathologist Pierre F. Bretonneau in 1826.
2. the name means "membrane", a reference to the exudate渗出液 that appears in the throats of patients.
3. in 1883, Edwin Klebs observed a bacterium in material from a patient's throat, and next year Friederich Loeffler cultivated the organism and gave this a name Corynebacterium diphtheriae 白喉杆菌because it resembles a club (coryne is "club")

Corynebacterium diphtheriae白喉杆菌---
1. is gram-positive, nonmotile bacillus containing numerous metachromatic granules巴-恩二氏小体 that show up with a methylene blue stain as cytoplasmic dots.
2. the bacteria remain close to one another after multiplying and form a palisade 木栅 layer, a picket支柱, 警戒哨-fence arrangment.
3. Diphtheria is acquired by inhaling respiratory droplets from an infected person into the upper repiratory tract near tonsils.
4. Initial symptoms include a sore throat and moderate fever.
5. The bacteria produce a potent有力 exotoxin 外毒素that inhibits protein synthesis in epithelial cells, the cube like cells that line the skin and body cavities such as the respiratory tract. As dead tissue accumulates with mucus, white blood cells, and fibrous material, a leathery pserudomembrane on the tonsiles or pharynx. Respiratory blockage and death may follow, especially in children. In adults, the toxin often spreads to the bloodstream, where it causes neck swelling, heart damage, and destruction of the fatty sheaths surrounding nerves.
6. Treatment: both antibiotics (penicillin or erythromycin) for the bacteria and antitoxins to neutralize the toxins.
7. less case in the U.S., more cases in Asia.
8. Immunization against diphtheria may be rendered by an injection of diphtheria toxoid 类毒素contained in the diphtheria-tetanus-acellular 白喉病破伤风非细胞 pertusis vaccine.类毒素: 经过处理的细菌外毒素，已失其毒性，但仍能与抗毒素结合或促使抗毒素形成. The toxoid induces促使 the immune system to produce antitoxins that circulate in the bloodstream throughout the person's life.
9. 1961, V. J. Freeman discovered that a prophage integrated into the bacterial chromosome contains the genetic code for diphtheria exotoxin production. Strains of C. diphtheriae lacking the phage are harmless, but they may become toxigenic 产生毒素的 if the gene-carry bacteriophage infects them. The same phage is carried by cells of C. ulcerans, a related species found primarily in cattle家养牲畜,牛.

Pertussis

posted by C-T @ 4:44 AM