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Unformatted text preview: Laboratory Diagnosis, Prevention and Treatment
of Bacterial Infection Xiao-Kui Guo Manifestations of Infection: Signs and symptoms vary
according to the site and severity of infection. Diagnosis
requires a composite of information, including history,
physical examination, radiographic findings, and
Microbial Causes of Infection: Infections may be
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
The quantity material must be adequate
Specimens are selected on the basis of signs and
symptoms, should be representative of the disease
Contamination of the specimen must be avoided by
using only sterile equipment and aseptic
The specimen must be taken to the laboratory and
examined promptly. Special transport media may
Meaningful specimens to diagnose bacterial
infections must be secured before antimicrobial
drugs are administered.
drugs Microbiologic Examination
Culture:Isolation of infectious agents frequently requires specialized media.
Nonselective (noninhibitory) media permit the growth of many microorganisms.
Selective media contain inhibitory substances that permit the isolation of specific
types of microorganisms.
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.
Antimicrobial Susceptibility: Microorganisms, particularly bacteria, are tested in
vitro to determine whether they are susceptible to antimicrobial agents.
Serodiagnosis:A high or rising titer of specific IgG antibodies or the presence of
specific IgM antibodies may suggest or confirm a diagnosis.
Direct Examination and Techniques: Direct examination of specimens reveals
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 Artificial active immunity
Vaccines are antigens prepared from pathogens that can raise a
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.
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.
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.
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
virus polio vaccine.
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
Antitoxin: e.g. Tetanus antitoxin and diphtheria
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
Pooled immunoglobulin: It contains the normal
repertoire of antibodies for an adult, and can protect
against hepatitis A, and measles.
Specific immunoglobulin: Preparations of specific
immunoglobulin are available for passive
immunization against tetanus, hepatitis B, rabies,
Cytokine Active-passive immunity
involves giving both a vaccine to provide
long-term protection (preventive infection)
and immune globulin to provide immediate
protection (therapeutic and preventive
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
variety of antigens and then used to detect the antigen in specimens or in
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- Fall '11