Microbiology

• Gram-Negative Bacteria


  • Hemophilus
  • Bortedetella
  • Brucella
• Haemophilus influenzae


  • Causes meningitis in unvaccinated children
  • Causes upper and lower respiratory tract infections in children and in adults
• Factor X


  Acts physiologically as hemin
• Factor V


  Nicotinamide adenine dinucleotide (NAD)
• Most H. influenzae organisms in the normal microbiota of the upper respiratory tract are not encapsulated and are referred to as nontypeable (NTHi)
• The somatic antigens of H. influenzae consist of outer membrane proteins. Lipooligosaccharides (endotoxins) share many structures with those of neisseriae
• Diseases of H. influenzae type b

  • Otitis media in children
  • Meningitis: in children between the age of 6 months to 3 years
  • Acute epiglottitis
  • Septic arthritis
  • Sepsis: Children between 6 months to 3 years
• Ampicillin resistance is transmitted by a plasmid from strain to strain of Haemophilus influenzae
• Hib capsule vaccine


  • Purified type b capsule, was effective only in generating antibodies in children older than 18 months
  • Women in the eighth month of pregnancy, resulting in increased antibody secretion in breast milk (passive immunization)
• Haemophilus ducreyi


  • Causes the sexually transmitted disease (STD) chancroid
  • Causes a painful genital ulcer, painful swollen inguinal lymph nodes
  • The lymph nodes become matted and will rupture, releasing pus

  
• Chancroid


  Painful genital ulcer
• Syphilis (Treponema pallidum)


  Painless, and no pus
• Bordetella pertussis


  • Causes whooping cough
  • Gram-negative coccobacilli
  • Capsulated
  • Strict aerobe, oxidase and catalase positive
  • Grows on Bordet-Gengou medium (potato-blood-glycerol agar) that contains penicillin G, 0.5 μg/mL

  
• Pathogenesis of whooping cough

  1. Tracheal cytotoxin

  2. Filamentous hemagglutinin (FHA): a pili involve in binding with ciliated epithelial cells of the bronchi

  3. Pertussis toxin: exotoxins: B subunit (Bind) and A subunit (A for Action). It overactivate cAMP which promotes lymphocytosis and sensitization to histamine

  4. Adenylate cyclase toxin (ACT): Synthesizes the messenger cAMP, impairs chemotaxis and generation of H2O2 and superoxide. Inhibits phagocytosis and clear the bacteria

  5. Tracheal cytotoxin: destroys the ciliated epithelial cells, resulting in impaired clearance of bacteria, mucus, and inflammatory exudate

  
• Whooping Cough


  • Highly contagious disease
  • Transmission: via respiratory secretions on the hands or in an aerosolized form
  • Incubation period: one week
  • 3 stages of the disease: Catarrhal stage, Paroxysmal stage, Convalescent stage
• Not typical cough may occur, e.g. chronic cough for more than 1 week in adolescents and adults
• B. pertussis is now a frequent cause of chronic unexplained cough in adolescents and adults
• Other causes of chronic cough to exclude

  • Asthma
  • Post-nasal drip (allergic rhinitis)
  • Acid-reflux
• Diagnosis of whooping cough

  • Blood test: The white blood count is high (16,000–30,000/μL), with an absolute lymphocytosis
  • Specimens: Nasopharyngeal (NP) with Dacron swab not cotton. Bordet-Gengou medium
  • PCR and serology (ELISA)
• Vaccination for whooping cough

  • It is combined with the formalin-inactivated tetanus and diphtheria toxoids to form the DTaP (Diptheria-Tetanus- acellular Pertussis)
  • The usual schedule is administration of doses at 2, 4, 6, and 15–18 months of age and a booster dose at 4–6 years of age
• Brucellae


  • Obligate parasites of animals and humans
  • Intracellular
  • All the names of Brucella species are based on the animal they infect
• Brucella species


  • Brucella melitensis (goats)
  • Brucella abortus (causes abortions in cows)
  • Brucella suis (pigs)
  • Brucella canis (dogs)
• Brucellosis


  Undulant fever, Malta fever
• Transmission of Brucellosis


  Direct contact with infected animal meat or aborted placentas, or ingestion of infected milk products
• Pathogenesis and Pathology of Brucellosis

  1. Portal of entry to bloodstream via lymphatic channels and regional lymph nodes

  2. Infected organs: Osteomyelitis, meningitis, or cholecystitis

  3. B. melitensis infection is more acute and severe than other species

  4. Placentas and fetal membranes of cattle, swine, sheep, and goats contain erythritol, a growth factor for brucellae. The proliferation of organisms in pregnant animals leads to placentitis and abortion in these species

  
• Clinical Findings of Brucellosis

  • Incubation period: 1 to 4 weeks
  • Malaise, fever, weakness, aches, and sweats
  • The fever (undulant fever) usually rises in the afternoon; it falls during the night and is accompanied by drenching sweat
  • Chronic stage may develop
• Diagnostic Laboratory Tests for Brucellosis


  • Specimens: blood and bone marrow
  • Culture: Trypticase-soy medium with or without 5% sheep blood, Brain–heart infusion medium, Chocolate agar. Incubation : 8–10% CO2 at 35–37°C and should be observed for 3 weeks
  • Serology: IgM: rise during the first week, peak at 3 months. IgG: rise during the first week, peak at 6-8 week
  • Agglutination test: Rose Bengal Test. IgG agglutinin titers above 1:80 indicate active infection
  • ELISA assays: IgG, IgA, and IgM antibodies. More sensitive