8 - Laboratory Diagnosis, Prevention and Treatment...

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Unformatted text preview: Laboratory Diagnosis, Prevention and Treatment Laboratory of Bacterial Infection Xiao-Kui Guo Manifestations of Infection: Signs and symptoms vary Manifestations according to the site and severity of infection. Diagnosis requires a composite of information, including history, physical examination, radiographic findings, and laboratory data. laboratory Microbial Causes of Infection: Infections may be Microbial caused by bacteria, viruses, fungi, and parasites. The pathogen may be exogenous (acquired from environmental or animal sources or from other persons) or endogenous (from the normal flora). Specimen Selection, Collection, and Processing Processing The quantity material must be adequate Specimens are selected on the basis of signs and Specimens symptoms, should be representative of the disease process process Contamination of the specimen must be avoided by Contamination using only sterile equipment and aseptic precautions precautions The specimen must be taken to the laboratory and The examined promptly. Special transport media may be helpful. be Meaningful specimens to diagnose bacterial Meaningful infections must be secured before antimicrobial drugs are administered. drugs Microbiologic Examination Microbiologic Culture:Isolation of infectious agents frequently requires specialized media. Isolation Nonselective (noninhibitory) media permit the growth of many microorganisms. Selective media contain inhibitory substances that permit the isolation of specific types of microorganisms. types Microbial Identification: Colony and cellular morphology may permit preliminary identification. Growth characteristics under various conditions, utilization of carbohydrates and other substrates, enzymatic activity, immunoassays, and genetic probes are also used. probes Antimicrobial Susceptibility: Microorganisms, particularly bacteria, are tested in vitro to determine whether they are susceptible to antimicrobial agents. vitro Serodiagnosis:A high or rising titer of specific IgG antibodies or the presence of high specific IgM antibodies may suggest or confirm a diagnosis. specific Direct Examination and Techniques: Direct examination of specimens reveals Direct gross pathology. Microscopy may identify microorganisms. Immunofluorescence, immuno-peroxidase staining, and other immunoassays may detect specific microbial antigens. Genetic probes identify genus- or species-specific DNA or RNA sequences. RNA Artificial active immunity Artificial Vaccines are antigens prepared from pathogens that can raise a Vaccines protective immune response, yet do not cause illness. These prepared antigens will stimulate both B cells and T cells and help to create memory cells that can later mount a vigorous immune response to an encounter with the real pathogen. response Toxoids: a modified form of the toxin that preserves its antigenicity but has lost its toxicity. This has been spectacularly successful with tetanus and diphtheria. toxicity. Inactivated vaccines: The production of protective antibodies is stimulated by using the killed (inactivated) organisms This is done as a routine with vaccines against pertussis (whooping cough) , typhoid and influenza. There is also an inactivated polio vaccine. inactivated Attenuated live vaccines : The approach is to use suspensions of living organisms that are reduced in their virulence (attenuated) but still immunogenic. This strategy has yielded: BCG, mumps, measles , and rubella vaccines (now combined); the live has virus polio vaccine. virus Special vaccines: polysaccharide vaccine, subunit vaccine, ( conjugate vaccine, bio-engineered vaccine, chemical vaccine, synthetic vaccine ), nucleic acid vaccine, idiotype vaccine, autovaccine, etc. idiotype Artificial passive immunity Artificial Antitoxin: e.g. Tetanus antitoxin and diphtheria Antitoxin e.g. antitoxin. It is raised in the horse .It is most important to give an intented recipient of equine serum a prior test dose to exclude hypersensitivity subjects who may have been sensitized by a previous dose of equine serum. serum. Pooled immunoglobulin: It contains the normal It repertoire of antibodies for an adult, and can protect against hepatitis A, and measles. against Specific immunoglobulin: Preparations of specific immunoglobulin are available for passive immunization against tetanus, hepatitis B, rabies, varicella-zoster. varicella-zoster. Cytokine Cytokine Active-passive immunity Active-passive involves giving both a vaccine to provide involves long-term protection (preventive infection) and immune globulin to provide immediate protection (therapeutic and preventive infectious disease). infectious stop stop 人人人人人人人人人人人人人人人人 区区区区 区区区区 区区区区区区 区区区区区区 区区区区 区区 区区区区区区区区 区区区区区区 区区 2~4 区 区区区区 区区区区区区 区区区区 ~ 区区 区区 2~3 区 区区区区 区区 区区区区区区区 DI = duration of illness, DH = duration of hospitalization, B/BF = blood/body fluid precautions, D/S = drainage/secretion precautions, E = enteric precautions, C = contact isolation, S = strict isolation, R = respiratory isolation, TB = tuberculosis isolation, U = universal precautions. isolation, General procedure for collecting and processing specimens for aerobic and/or anaerobic bacterial culture specimens Agglutination test in which inert particles (latex beads or heat-killed S aureus Cowan 1 strain with protein A) are coated with antibody to any of a aureus variety of antigens and then used to detect the antigen in specimens or in isolated bacteria. isolated ...
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