Bacteroides

Classification

General Characteristics

Basic features

• Gram-negative bacilli Bacilli Shigella
• Pleomorphic: appear as either straight rods or coccobacilli
• 0.5–0.8 μm in diameter and 1.5–4.5 μm long
• Anaerobes Anaerobes Lincosamides, although tolerate exposure to oxygen
• Encapsulated Encapsulated Klebsiella
• Ferment carbohydrates Carbohydrates A class of organic compounds composed of carbon, hydrogen, and oxygen in a ratio of cn(H2O)n. The largest class of organic compounds, including starch; glycogen; cellulose; polysaccharides; and simple monosaccharides. Basics of Carbohydrates: 
  • Including complex plant polysaccharides Polysaccharides Basics of Carbohydrates indigestible to the host 
  • Allows for commensal/symbiotic relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship between the bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology and host
• Part of indigenous bacterial flora of mucosal surfaces, but opportunistic pathogens

Virulence factors Virulence factors Those components of an organism that determine its capacity to cause disease but are not required for its viability per se. Two classes have been characterized: toxins, biological and surface adhesion molecules that affect the ability of the microorganism to invade and colonize a host. Haemophilus

• Adherence to host tissue:
  • Fimbriae Fimbriae Thin, hairlike appendages, 1 to 20 microns in length and often occurring in large numbers, present on the cells of gram-negative bacteria, particularly enterobacteriaceae and Neisseria. Unlike flagella, they do not possess motility, but being protein (pilin) in nature, they possess antigenic and hemagglutinating properties. They are of medical importance because some fimbriae mediate the attachment of bacteria to cells via adhesins. Bacterial fimbriae refer to common pili, to be distinguished from the preferred use of ‘pili’. Escherichia coli: Long, hair-like projections
  • Lipopolysaccharide Lipopolysaccharide Lipid-containing polysaccharides which are endotoxins and important group-specific antigens. They are often derived from the cell wall of gram-negative bacteria and induce immunoglobulin secretion. The lipopolysaccharide molecule consists of three parts: lipid a, core polysaccharide, and o-specific chains (o antigens). When derived from Escherichia coli, lipopolysaccharides serve as polyclonal b-cell mitogens commonly used in laboratory immunology. Klebsiella (LPS):
    • Weakly endotoxic
    • Primary role is adherence to mucosal surfaces
• Protection from host immune response:
  • Superoxide dismutase Superoxide dismutase An oxidoreductase that catalyzes the reaction between superoxides and hydrogen to yield molecular oxygen and hydrogen peroxide. The enzyme protects the cell against dangerous levels of superoxide. Myeloperoxidase Deficiency and catalase Catalase An oxidoreductase that catalyzes the conversion of hydrogen peroxide to water and oxygen. It is present in many animal cells. A deficiency of this enzyme results in acatalasia. Nocardia/Nocardiosis: 
    • Neutralize oxygen radicals created by the immune system Immune system The body’s defense mechanism against foreign organisms or substances and deviant native cells. It includes the humoral immune response and the cell-mediated response and consists of a complex of interrelated cellular, molecular, and genetic components. Primary Lymphatic Organs 
    • Key for pathogenesis in areas of the body not free from oxygen
  • Capsule: 
    • Protects from complement-mediated phagocytosis Phagocytosis The engulfing and degradation of microorganisms; other cells that are dead, dying, or pathogenic; and foreign particles by phagocytic cells (phagocytes). Innate Immunity: Phagocytes and Antigen Presentation 
    • Leads to abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease formation
    • Polysaccharides Polysaccharides Basics of Carbohydrates on the capsule can be altered to evade the host immune response.
  • Conjugative transposons: aid in the transfer of antibiotic resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure
• Destruction of host tissue:
  • Hyaluronidase and chondroitin sulfatase:
    • Destroy brush border Brush border Tubular System enzymes Enzymes Enzymes are complex protein biocatalysts that accelerate chemical reactions without being consumed by them. Due to the body’s constant metabolic needs, the absence of enzymes would make life unsustainable, as reactions would occur too slowly without these molecules. Basics of Enzymes in the intestine
    • Make it harder for the host to absorb nutrients
    • More nutrients available for bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology
  • Enterotoxin Enterotoxin Substances that are toxic to the intestinal tract causing vomiting, diarrhea, etc. ; most common enterotoxins are produced by bacteria. Diarrhea:
    • Destroys tight junctions Tight junctions Cell-cell junctions that seal adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other. The Cell: Cell Junctions in the intestinal epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium: Histology
    • Leads to diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
  • Neuraminidase Neuraminidase An enzyme that catalyzes the hydrolysis of alpha-2, 3, alpha-2, 6-, and alpha-2, 8-glycosidic linkages (at a decreasing rate, respectively) of terminal sialic residues in oligosaccharides, glycoproteins, glycolipids, colominic acid, and synthetic substrate. Antivirals for Influenza: cleaves polysaccharides Polysaccharides Basics of Carbohydrates, freeing up glucose Glucose A primary source of energy for living organisms. It is naturally occurring and is found in fruits and other parts of plants in its free state. It is used therapeutically in fluid and nutrient replacement. Lactose Intolerance for bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology 

Pathogenesis

Reservoir Reservoir Animate or inanimate sources which normally harbor disease-causing organisms and thus serve as potential sources of disease outbreaks. Reservoirs are distinguished from vectors (disease vectors) and carriers, which are agents of disease transmission rather than continuing sources of potential disease outbreaks. Humans may serve both as disease reservoirs and carriers. Escherichia coli

• Large intestine Large intestine The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix: Anatomy of humans

Transmission and infection

Transmission and infection from the translocation of bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology from mucosal surfaces to other tissues may be due to:

• Blunt trauma
• Intestinal disease
• Penetrating wounds
• Abdominal surgery
• Ruptured appendix Appendix A worm-like blind tube extension from the cecum. Colon, Cecum, and Appendix: Anatomy

Diseases Caused by Bacteroides fragilis

Bacteroides fragilis (B. fragilis) is naturally found in the small intestines as part of the natural flora. B. fragilis is an opportunistic pathogen Opportunistic pathogen Moraxella that rarely infects the gastrointestinal system, more often causing disease when bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology escape Escape With constant immune mechanisms holding unstable tumor cells in equilibrium, tumor-cell variants may emerge. These cancer cells may express fewer antigens on their surfaces or lose their MHC class I expression.Variants may also protect themselves from T-cell attack via expression of IC molecules on their surfaces, like normal cells.Creation of an immunosuppressive state in the microenvironment is another way to grow without immunologic interference. Cancer Immunotherapy the small intestine Small intestine The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy. 

Diagnosis and Management

Diagnosis

• History:
  • Predisposing factors: 
    • Recent abdominal surgery
    • Trauma 
    • Malignancy Malignancy Hemothorax
    • Immunocompromised immunocompromised A human or animal whose immunologic mechanism is deficient because of an immunodeficiency disorder or other disease or as the result of the administration of immunosuppressive drugs or radiation. Gastroenteritis state
  • Known history of Bacteroides infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
• Physical exam:
  • Presence of pyogenic abscesses
  • Foul smell Smell The sense of smell, or olfaction, begins in a small area on the roof of the nasal cavity, which is covered in specialized mucosa. From there, the olfactory nerve transmits the sensory perception of smell via the olfactory pathway. This pathway is composed of the olfactory cells and bulb, the tractus and striae olfactoriae, and the primary olfactory cortex and amygdala. Olfaction: Anatomy is often associated with anaerobic infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease.
• Laboratory testing:
  • Appropriate tissue samples must be utilized to culture Bacteroides:
    • Blood cultures and fine-needle aspirates of infectious material
    • Requires an anaerobic environment to propagate
  • Defining laboratory characteristics:
    • Isolated as a single agent, but usually seen with other anaerobes Anaerobes Lincosamides
    • Gram –
    • Grows on blood agar Blood agar Nocardia/Nocardiosis and Bacteroides-bile-esculin (BBE) agar 
    • Kanamycin, vancomycin Vancomycin Antibacterial obtained from streptomyces orientalis. It is a glycopeptide related to ristocetin that inhibits bacterial cell wall assembly and is toxic to kidneys and the inner ear. Glycopeptides, and colistin-resistant 
    • Grows in 20% bile Bile An emulsifying agent produced in the liver and secreted into the duodenum. Its composition includes bile acids and salts; cholesterol; and electrolytes. It aids digestion of fats in the duodenum. Gallbladder and Biliary Tract: Anatomy
    • Catalase Catalase An oxidoreductase that catalyzes the conversion of hydrogen peroxide to water and oxygen. It is present in many animal cells. A deficiency of this enzyme results in acatalasia. Nocardia/Nocardiosis producing
    • Variably indole positive

Management

• Prevention:
  • Planned prophylactic antibiotics for abdominal surgeries
  • Antibiotic therapy if contamination from the colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix: Anatomy is suspected
• Treatment:
  • When present, the drainage of abscesses is the primary form of treatment
  • Given the polymicrobial nature of most infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease, antibiotic therapy should be directed to multiple anaerobes Anaerobes Lincosamides:
    • Antibiotic of choice for all anaerobic infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease is metronidazole Metronidazole A nitroimidazole used to treat amebiasis; vaginitis; trichomonas infections; giardiasis; anaerobic bacteria; and treponemal infections. Pyogenic Liver Abscess.
    • Effective antibiotics include: piperacillin Piperacillin Semisynthetic, broad-spectrum, ampicillin derived ureidopenicillin antibiotic proposed for pseudomonas infections. It is also used in combination with other antibiotics. Penicillins/ tazobactam Tazobactam A penicillanic acid and sulfone derivative and potent beta-lactamase inhibitor that enhances the activity of other anti-bacterial agents against beta-lactamase producing bacteria. Cephalosporins, meropenem Meropenem A thienamycin derivative antibacterial agent that is more stable to renal dehydropeptidase I than imipenem, but does not need to be given with an enzyme inhibitor such as cilastatin. It is used in the treatment of bacterial infections, including infections in immunocompromised patients. Carbapenems and Aztreonam 
    • Resistant to penicillin Penicillin Rheumatic Fever due to the production of beta-lactamase Beta-Lactamase Penicillins
    • Moxifloxacin Moxifloxacin A fluoroquinolone that acts as an inhibitor of DNA topoisomerase II and is used as a broad-spectrum antibacterial agent. Fluoroquinolones previously utilized; now, resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing reported in up to 57% of cases