Gram-Negative Bacteria Lecture Notes PDF

Lecture-7 Gram-negative cocci Neisseria Gram– cocci in pairs (diplococci), catalase and oxidase positive, non motile, non hemolytic. The genus contains at least 30 spp. Two important spp. are pathogenic for human; N. gonorrhoeae (gonococcus), Diplococci in kidney shape and N. m...

Lecture-7 Gram-negative cocci Neisseria Gram– cocci in pairs (diplococci), catalase and oxidase positive, non motile, non hemolytic. The genus contains at least 30 spp. Two important spp. are pathogenic for human; N. gonorrhoeae (gonococcus), Diplococci in kidney shape and N. meningitidis (meningococcus), Diplococci in spherical shape. N. gonorrhoeae (gonococcus) Transmission N. gonorrhoeae causes gonorrhoea only in human. It is transmitted in horizontal by sexually from person to person. N. gonorrhoeae Pathogenesis and clinical finding Venereal disease (VD) Genital: In male are characterized by urethritis with yellow and creamy pus (purulent discharge) and painful urination with accompanied by dysuria, sometime leading to urethral stricture and infertility. In female, the primary infection is in endocervix and extends to urethra and vagina, causing a purulent vaginal discharge and cervicitis. It may then progress to causing salpingitis, which can result in sterility or ectopic pregnancy. Extra genital Proctitis (infection of rectum), stomatitis, infection of conjunctiva of newborn (ophthalmia nenatorum) is acquired from infected birth canal of mother. To prevent the infection instillation of tetracycline or erythromycin into conjunctiva sac of newborn. Lab Diagnosis microscopic: gram-ve stain smear of pus reveal many intracellular diplococci. Cultured: on Thayer-Martin medium, incubated under 5-10% CO2. Serologic test: ELISA. Control Antibiotics: penicillin G, sulfonamide, ciprofloxacin. No effective vaccine is available N. gonorrhoeae on Thayer-Martin medium N. meningitidis (meningococcus) Transmission: the natural reservoir is human and transmitted by airborne droplets to other person. Pathogencity and clinical feature The humans are natural host in nasopharynx and causes disease only in human. The organisms attach to epithelial cells of nasopharynx aid of pili, may be enter the bloodstream and spread to specific sites such as meninges, joints, disseminated through the body or it spread may be through sheath of olfactory nerve to meninges. The symptoms of meningococcal meningitis are fever, headache, stiff neck and increased level of PMNs in CSF. Lab Diagnosis microscopic: gram-ve stain smear of pus reveal many intracellular diplococci in PMN. Cultured: on Thayer-Martin medium,& chocolate agar incubated under5-10% CO2. Serologic test: latex agglutination test. Control Antibiotics: penicillin G, sulfonamide, ciprofloxacin. N. meningitidis Other Gram –ve Rods Bordetella B. pertussis and B. parapertussis are the human pathogens. The former causes the disease pertussis (whooping cough). Whooping cough is a highly contagious disease and a significant cause of morbidity and mortality worldwide. They are small, aerobic, encapsulated, coccobacilli that grow singly or in pairs. Pathogenesis &. Clinical significance Transmission of Bordetella is via droplets spread by coughing, , disease is most common children (ages one to five). B. pertussis binds to ciliated epithelium in the upper respiratory tract. The bacteria produce of toxins and other virulence factors that interfere with ciliary activity, eventually causing death of these cells. The incubation period for pertussis ranges from 1 to 3 weeks. The disease can be divided into two phases: catarrhal and paroxysmal. Catarrhal phase: This phase nonspecific symptoms (rhinorrhea, mild conjunctival infection, mild fever, and then progresses to include a dry, nonproductive cough). Paroxysmal phase: With worsening of the cough, the paroxysmal phase begins. The term whooping cough derives from the paroxysms of coughing followed by inspires rapidly. Large amounts of mucus may be produced. Treatment & Prevention Erythromycin is the drug of choice for infections. Pertussis vaccine is available that has had a significant effect on lowering the incidence of whooping cough. It contains proteins purified from B. pertussis, and is formulated in combination with diphtheria and tetanus toxoids (DPT). To protect infants who are at greatest risk of life- threatening B. pertussis disease, immunization is generally initiated when the infant is two months old. Pseudomonas P. aeruginosa, the primary human pathogen, is widely distributed in nature (soil, water, plants, and animals). It may colonize healthy humans without causing disease, it is also a significant opportunistic pathogen and a major cause of nosocomial (hospital-acquired) infections. It is motile by polar flagella, catalase and oxidase positive and obligatory aerobic. Nutritional requirements are minimal, can grow on a wide variety of organic substrates. This explains why the organism is responsible for many nosocomial infections. Pathogenesis &clinical significance P. aeruginosa produces numerous toxins and extracellular products that promote local invasion and dissemination of the organism. These may cause keratitis and, external otitis or swimmer's ear wound sepsis, UTI, pneumonia or cystic fibrosis, GTI, meningitis and brain abscesses. it can cause severe hospital-acquired infections, especially in immunocompromised hosts; it is often antibiotic resistant. Pseudomonas aeruginosa Helicobacter Helicobacter are curved or spiral organisms. motile by multiple polar flagella. H. pylori is microaerophilic, and produces urease. It causes acute gastritis and duodenal and gastric ulcers. H. pylori are unusual in their ability to colonize the stomach, where low pH normally protects against bacterial infection. Pathogenesis & Clinical significance Transmission of H. pylori is thought to be from person to person; the organism has not been isolated from food or water. Untreated, infections tend to be chronic, even lifelong. H. pylori colonizes gastric mucosal (epithelial) cells in the stomach, and duodenum or esophagus. The organism survives in the mucous layer that coats the epithelium, and causes chronic inflammation of the mucosa. the organism is non-invasive. Initial infection with H. pylori causes acute gastritis. Urease released by H. pylori produces ammonia ions that neutralize stomach acid in the vicinity of the organism, favoring bacterial multiplication.  Laboratory identification Noninvasive diagnostic tests include serologic tests (ELISA for serum antibodies to H. pylori). Invasive tests involve gastric biopsy specimens obtained by endoscopy. H. pylori can be detected in such specimens histologically, by culture, or by a test for urease.  Legionella Legionella are facultative intracellular parasites and fastidious, with a particular requirement for L- cysteine, In nature, Legionella cells are unencapsulated, relatively slender rods. Legionella cause respiratory tract infections. There are two distinctly different presentations: Legionnaires' disease (LD): This is an atypical, acute lobar pneumonia and Pontiac fever: This is an influenza- like illness. Brucella Brucella are primarily pathogens of animals. They are aerobic, facultative, intracellular parasites that can survive and multiply within host phagocytes. B. abortus causes brucellosis (undulant or malta fever) is a zoonosis. Pasteurella Pasteurella primarily colonize mammals and birds, pasteurella infections are considered zoonoses, which can cause either disease or asymptomatic infections. Pasteurellae are causes of acute, painful cellulitis , Soft tissue infections Anaerobic Gram-Negative Rods (Bacteroides) Bacteroides are anaerobic organisms slender rods or coccobacilli. B. fragilis causes peritonitis, abdominal abscesses, and bacteremia.