Group B Streptococci (Streptococcus agalactiae)• β hemolytic, with larger colonies and less hemolysis than group A Streptococci• Found in the vaginocervical tract of female carriers, and the urethral mucous membranes of male carriers as well as in the gastrointestinal (GI) tract• Transmitted sexually among adults and from an infected mother to her infant at birth• A leading cause of meningitis and septicemia in neonates, with a high mortality rate 51
Group B Streptococci (Streptococcus agalactiae)• Virulence factors: CAMP test – Hemolysin S.aureus – capsule polysaccharide – C5a peptidase – Various surface protein• Capsule polysaccharide: the serotype most frequently associated with neonatal infections is type III• Hemolysin known as the Christie, Atkins and Munch- Petersen (CAMP) factor lyses sheep or bovine red cells pretreated with β-toxin of S.aureus 52
Laboratory Identification• Specimens: blood, cervical swabs, sputum, or spinal fluid• Microscopy• Culture• Bacitracin disk test: resistantAvailable from http://medical-micro-case-study-grp- 5313.wikispaces.com/file/view/blood_agar_subculture.jpg/192093852/blood_agar_subculture.jpg [Accessed April 13, 2012]
Streptococcus pneumoniae (Pneumococcus)• Gram-positive diplococci (lancet shape)• α-hemolysis• Nonmotile• Encapsulated cocci• The most common cause of community acquired pneumonia and adult bacterial meningitis• An important cause of otitis media, sinusitis and mastoiditis 54
Epidemiology• An obligate parasite of humans• Found in the nasopharynx of many healthy individuals• Extremely sensitive to environmental agents• Susceptibility to the infection e.g. – Malnutrition – Alcoholism• Endogenous: the spread of S. pneumoniae residing in the nasopharynx of a carrier• Exogenous: by droplets from the nose of a carrier 55
Virulence Factors• Pili – Enable the attachment of encapsulated pneumococci to the epithelial cells of the upper respiratory tract – Express pili are more virulent• Choline-binding protein – A major adhesin allowing the pneumococcus to attach to carbohydrates on epithelial cells of the human nasopharynx 56
Virulence Factors 57• Capsule – Polysaccharide capsule is both antiphagocytic and antigenic – Antiphagocytic properties facilitating growth of the bacteria prior to the appearance of anti- capsular antibodies – Approximately 85 distinct capsular serotypes
Virulence Factors• Autolysins – LytA, B and C are peptidoglycan-hydrolyzing enzymes that are present in the bacterial cell wall and are normally inactive – However, these enzymes are readily activated (for example, by surface-active agents, β- lactam antibiotics, or stationary phase), resulting in cell lysis – Responsible for the release of intracellular virulence factors, pneumolysin 58
Virulence FactorsPneumolysin – Attack mammalian cell membranes – Binds to cholesterol with all cell types – Stimulates production of proinflammatory cytokines – Inhibits the activity of polymorphonuclear leukocytes – Activates complement 59
Clinical Significance• Pneumococcal pneumonia – A leading cause of death, especially in older adults – Frequently preceded by an upper or middle respiratory viral infection – Abruptly with a shaking chill and high fever – Cough with production of sputum pink to rusty in color – Pleuritic chest pain are common• Meningitis – The most common cause of adult bacterial meningitis – High mortality rate• Bacteremia/sepsis• Otitis media – The most common bacterial infection of children 60
Laboratory Identification• Specimen: nasopharyngeal swab, blood, pus, sputum, or spinal fluid• Microscopy• Culture on blood agar• Optochin disk test: sensitive 61
Prevention• There are two types of pneumococcal vaccine: – Pneumococcal polysaccharide vaccine (PPV) – Pneumococcal conjugate vaccine 62
Viridans streptococci • Commensal streptococci • S. salvarius and S.mitis : – Dominant members of normal flora in oral cavity and pharynx – Play important role to inhibit the colonization of many pathogens by production of bacteriocin and hydrogen peroxide • Cause dental plaque • Responsible for 50–70% of all cases of bacterial endocarditis • S. mutans, S. sanguis and S. mitis are responsible for dental cariesTooth decay and plaque forming by S. mutans 63
Enterococci• Gram positive cocci, some in chain or individual• Derives from their presence in the intestinal tract• Ability to grow in the presence of high concentrations of bile salts and sodium chloride• Most enterococci produce nonhemolytic or α-hemolytic colonies• Infection almost exclusively in hospitalized patients with significant compromise• The primary sites are the urinary tract and soft tissue sites adjacent to the intestinal flora 64
Flow chart for identification of Gram positive cocciAvailable from 65http://pmj.bmj.com/content/77/905/148/F2.large.jpg[Accessed April 13, 2012]
Gram Negative Cocci Neisseria Moraxella 66
Neisseria• Gram-negative, aerobic cocci• Nonmotile diplococci (kidney shape)• Classified as pyogenic cocci• Two species are pathogenic for humans: – Neisseria gonorrhoeae, the causal agent of gonorrhea – Neisseria meningitidis, a frequent cause of meningitis 67
Neisseria gonorrhoeae• Commonly called gonococcus• Frequently observed within the polymorphonuclear leukocytes• Usually transmitted during sexual contact or, more rarely, during the passage of a baby through an infected birth canal• Highly sensitive to dehydration 68
Structure• Unencapsulated, piliated, and nonmotile, and they resemble a pair of kidney beans• Pili – Enhance attachment of the organism to host epithelial and mucosal cell surfaces – Made of helical aggregates of repeating peptide subunits called pilin – Produce antigenically different pilin molecules 69
Structure• Lipooligosaccharide (LOS) – Capable of high-frequency variation of the LOS antigens presented on the cell surface• Porin (Por) proteins – Form pores in the surface through with some nutrient enter the cell• Opacity (Opa) proteins – The capacity to express up to 11 different Opa proteins – Adhesion of gonococci within colonies and attachment to host cells 70
Pathogenesis• Pili and Opa proteins facilitate adhesion of the gonococcus to epithelial cells of the urethra, rectum, cervix, pharynx, and conjunctiva• IgA protease that cleaves IgA1, helping the pathogen to evade immunity• The gonococcus requires iron for growth and survival• Expression of specific transport systems that remove and internalize the iron from human iron binding proteins including transferrin, lactoferrin and hemoglobin 71
Clinical SignificanceGenitourinary tract infections 72 – Male: • Typically presents with a yellow, purulent urethral discharge and painful urination – Female • Infection occurs in the endocervix and extends to the urethra and vagina • A greenish-yellow cervical discharge is most common • Often accompanied by intermenstrual bleeding • May progress to the uterus, causing salpingitis, pelvic inflammatory disease (PID), and fibrosis • Infertility occurs in approximately 20 percent of women with gonococcal salpingitis, as a result of tubal scarring.
Clinical SignificanceRectal infections – Prevalent in men who have sex with men – Characterized by constipation, painful defecation, and purulent dischargePharyngitis – Contracted by oral-genital contact – Show a purulent pharyngeal exudate 73
Clinical Significance 74 Ophthalmia neonatorum – Infection of the conjunctival sac is acquired by newborns during passage through the birth canals of infected mothers – If untreated, acute conjunctivitis may lead to blindness – To prevent, instillation of tetracycline, erythromycin or silver nitrate into conjunctival sacAvailable fromhttp://upload.wikimedia.org/wikipedia/commons/2/27/Gonococcal_ophthalmia_neonatorum.jpg [Accessed April 13, 2012]
Laboratory Identification• Specimens: pus, secretions from the urethra, cervix, rectum, conjunctiva and throat• In the male, the finding of numerous neutrophils containing gram negative diplococci in a smear of urethral exudate 75
Laboratory Identification• Staining: Gram stain• Culture: on enriched selective media e.g., modified Thayer- Martin in 5% CO2 at 37°C for 48 h• Oxidase test: positive• Carbohydrate fermentation: ferment glucose only 76
Epidemiology• Transmitted by sexual contact• The infection rate can be reduced by avoiding multiple sexual partners• Mechanical prophylaxis (condom) provides partial protection 77
Neisseria meningitidis• Commonly called meningococcus• The most frequent causes of meningitis• Close contact between individuals, such as occurs in schools, institutions, and military barracks 78
Structure• Nonmotile, gram-negative• diplococcus, shaped like a kidney bean• Pili allow attachment of the organism to the nasopharyngeal mucosa• polysaccharide capsule that enhances virulence by its antiphagocytic action• Vaccine; Antibodies to the capsule carbohydrate are bactericidal 79
Epidemiology• Transmission occurs through inhalation of respiratory droplets from a carrier• Risk factors include recent viral or Mycoplasma upper respiratory tract infection, active or passive smoking, and complement deficiency• In the United States is highest among infants younger than age 1 year 80
Pathogenesis• Colonizes the nasopharynx >> asymptomatic meningococcal pharyngitis >> disseminated disease by spreading through the blood (meningococcemia) >> meningitis and/or fulminating septicemia• Antiphagocytic properties of the meningococcal capsule aid in the maintenance of infection• LOS, released during autolysis and in outer membrane vesicles, is responsible for the toxic effects• Make an IgA protease that cleaves IgA1 and, thus, helps the pathogens to evade immunoglobulins 81
Clinical significance 82• Meningitis – The most common complication of meningococcemia – Acute inflammation with: • Thrombosis of blood vessels • Exudation of PMN leukocytes; the surface of brain is covered with a thick purulent exudates – Usually begins suddenly with intense headache, vomiting, stiff neck and sensitivity to bright lights, and progress to coma within a few hours
Septicemia• Cause a life-threatening septicemia in an apparently healthy individual in less than 12 h• Up to 30 percent of patients with meningitis progress to fulminant septicemia• Acute, fulminant meningococcal septicemia is seen mainly in very young children (the Waterhouse-Friderichsen syndrome)• Characterized by large, purple, blotchy skin hemorrhages, vomiting and diarrhea, circulatory collapse, adrenal necrosis, and death within 10 to 12 h 83
Laboratory identification• Specimens: blood and CSF• Staining: Gram stain• Culture: on chocolate agar at 37°C in 5%CO2• Oxidase test: positive• Carbohydrate fermentation: fermentglucose and maltose 84
Moraxella• Nonmotile, gram-negative coccobacilli (diplococci)• Aerobic, oxidase positive• Fastidious organisms that do not ferment carbohydrates• The most important pathogen in the genus is Moraxella catarrhalis (formerly, Branhamella catarrhalis)• Cause infections of the respiratory system, middle ear, eye, CNS, and jointsColonies of M. catarrhalis 85 in sputum
Moraxella catarrhalis pneumonia 86
References1. Cary Engleberg N, Dirita VJ, Dermody TS. Schaechter's mechanisms of microbial disease. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2013.2. Ryan KJ, George Ray C. Sherris Medical microbiology. 5th ed. New York: McGraw-Hill Companies, Inc; 2010.3. Levinson W. Review of Medical Microbiology & Immunology. 10th ed. New York: McGraw-Hill Companies, Inc; 2008.4. Greenwood D, Slack R, Peutherer J, Barer, M. Medical microbiology 17th ed. London: Churchill Livingstone Elsevier; 2007.5. Kayser FH, Bienz KA, Eckert J, Zinkernagel RM. Medical microbiology. 10th ed. Stuttgart: Georg Thieme Verlag; 2005.6. Brooks GF, Butel JS, Morse SA. Jawetz, Melnick, and Adelberg’s Medical microbiology. 23th ed. New York: McGraw-Hill Companies, Inc; 2004.7. Harvey RA, Cynthia Nau Cornelissen, Fisher BD. Lippincott’s Illustrated Reviews Microbiology. 3th ed. Lippincott Williams & wilkins, a wolters kluwer business; 2013. 87
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