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Anaerobic Gram-Negative Bacilli: Genus Identification, Chemical Tests, and Diagnosis

This lecture focuses on the identification, chemical tests, and differentiation of Bacteroides, Prevotella, Fusibacterium, and Porphyromonas. It also covers the symptoms, diagnosis, and treatment of different species.

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Anaerobic Gram-Negative Bacilli: Genus Identification, Chemical Tests, and Diagnosis

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  1. Objectives • By the end of this lecture the student must be: • A) Identify the genus Bacteroides, Prevotella, Fusibacterium and Porphyromonas • B) describe the chemical tests for this genus • C) Differentiate between different sps. • D) List and match the symptoms, diagnosis and treatment for different sps.

  2. Anaerobic Gram negative bacilli • Gram negative rods, Anaerobic, Non-spore forming • Over 24 genera of Gram-negative anaerobic bacilli • The most important genera: • Bacteroides, Prevotella, Fusibacterium and Porphyromonas • B. fragilis, B. melaningenicus (now P. melaningenicus) and B. corrodensare the most important species • They predominant components of the florae of mucous membranes • B. fragilisgroup are the predominant in the colon (1011/g of feaces) • Anaerobes outnumber aerobes by 1000:1 in the large intestine • They play an important role in almost all intra-abdominal infections • 60% of female carry it in their vagina • P. melaningenicusand B. corrodensoccur primarily in oral cavity

  3. Anaerobic Gram negative bacilli • Opportunistic pathogens • Cause serious infections • Infections are generally polymicrobial • Transmission • Endogenous spread to normally sterile tissues or fluids • Bacteroides infections can develop in all body sites, including the CNS, the head, the neck, the chest, the abdomen, the pelvis, the skin, and the soft tissues • Predisposing factors • Any condition predisposing to anaerobic infections such as diabetes • Surgical/Trauma patients and chronic diseases • Human and animal bites • Decreased redox potential: Local tissue necrosis, impair blood supply and growth of facultative anaerobes (E. coli) at the site contribute to anaerobic infection • E. coli utilize O2 therefore reduce it to level allow anaerobic to grow

  4. Anaerobic Gram-Negative Infections • CNS Infections • Brain abscess and meningitis • Brain abscesses are commonly caused by adjacent chronic infections in ears, mastoids, sinuses, oropharynx, teeth or lungs • Head and neck Infections • Chronic otitis media; sinusitis; mastoiditis; tonsillar,peritonsillar, and retropharyngeal abscesses; cervical lymphadenitis • Dental infections, include periodontal disease, gingivitis, localized periodontitis, pericoronitis, endodontitis, periapical and dental abscesses and post-extraction infection • Pleuropulmonary Infections • 90% of patients with community-acquired aspiration pneumonia • B. fragilisis found in 25% of lung abscesses • Intra-abdominal Infections • Secondary peritonitis, Appendicitis and Abdominal abscesses

  5. Anaerobic Gram-Negative Infections • Gynecoloical Infections • Bacterial vaginosis; soft tissue perineal, tubo-ovarian, pelvic and vulvar abscesses; endometritis; salpingitis; pelvic cellulitis; intrauterine device–associated infection; septic abortion and postsurgical obstetric and gynecologic infections • Skin and Soft Tissues Infections • Infected cutaneous ulcers, secondary diaper rash • Cutaneous and subcutaneous abscesses, breast abscesses • Necrotizing fasciitis, necrotizing synergistic cellulitis, gas gangrene • Osteomyelitis and septic arthritis • Bacteremia (5-15%)

  6. Bacteroides Virulence Factors • Polysaccharide capsule • Antiphagocytic and adhesive • Lipopolysaccharide • Stimulates leucocytes migration and chemotaxis • Agglutinins • Enhance adherence • Histolytic enzymes • Tissues destruction, inactivates Immunogloublins • Oxygen tolerance • Catalase and superoxide dismutase • Beta-lactamases • Inactivates penicillins

  7. Diagnosis • Direct-needle aspiration is the best method of obtaining a culture • Specimens obtained from normally sterile sites, such as blood or spinal, joint, or peritoneal fluids • Bacteroides can be isolated anaerobically on blood agar containing kanamycin and vancomycin to inhibit unwanted bacteria and incubated anaerobiacally • Treatment • Directed at all major aerobic and anaerobic pathogens • Clindamycin, cefoxitin and cefotetan • Almost sensitive to metronidazole, carbapenems, chloramphenicol and combinations of penicillin/β-lactamase inhibitors

  8. Prevention and Control • Avoiding conditions that reduce the redox potential of the tissues • Preventing the introduction of anaerobes of the normal flora to wounds, closed cavities, or other sites prone to infection • Surgical intervention, abscesses drainage and antibiotic treatment • Prophylactic therapy are used when medical procedure disrupt the mucosa or if disruption of mucosa causing trauma • No vaccines are available

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