Laboratory Diagnosis, Prevention and TreatmentLaboratory Diagnosis, Prevention and Treatment of Bacterial Infection of Bacterial Infection

Xiao-Kui GuoXiao-Kui Guo

Manifestations of Infection:Manifestations of Infection: Signs and symptoms vary Signs and symptoms vary according to the site and severity of infection. Diagnosis according to the site and severity of infection. Diagnosis requires a composite of information, including requires a composite of information, including history, history, physical examination, radiographic findings, and physical examination, radiographic findings, and laboratory datalaboratory data..

Microbial Causes of Infection:Microbial Causes of Infection: Infections may be Infections may be caused by bacteria, viruses, fungi, and parasites. The caused by bacteria, viruses, fungi, and parasites. The pathogen may be exogenous (acquired from pathogen may be exogenous (acquired from environmental or animal sources or from other persons) environmental or animal sources or from other persons) or endogenous (from the normal flora). or endogenous (from the normal flora).

Specimen Selection, Collection, and Specimen Selection, Collection, and ProcessingProcessing

The quantity material must be adequateThe quantity material must be adequateSpecimens are selected on the basis of signs and sySpecimens are selected on the basis of signs and symptoms, should be representative of the disease prmptoms, should be representative of the disease processocessContamination of the specimen must be avoided by Contamination of the specimen must be avoided by using only sterile equipment and aseptic precautiousing only sterile equipment and aseptic precautionsnsThe specimen must be taken to the laboratory and The specimen must be taken to the laboratory and examined promptly. Special transport media may examined promptly. Special transport media may be helpful.be helpful.Meaningful specimens to diagnose bacterial infectiMeaningful specimens to diagnose bacterial infections must be secured before antimicrobial drugs arons must be secured before antimicrobial drugs are administered.e administered.

Microbiologic ExaminationMicrobiologic Examination

Culture:Culture:Isolation of infectious agents frequently requires specialized media. NonseIsolation of infectious agents frequently requires specialized media. Nonselective (noninhibitory) media permit the growth of many microorganisms. Selective lective (noninhibitory) media permit the growth of many microorganisms. Selective media contain inhibitory substances that permit the isolation of specific types of mimedia contain inhibitory substances that permit the isolation of specific types of microorganisms.croorganisms.Microbial Identification:Microbial Identification: Colony and cellular morphology may permit preliminary Colony and cellular morphology may permit preliminary identification. Growth characteristics under various conditions, utilization of carboidentification. Growth characteristics under various conditions, utilization of carbohydrates and other substrates, enzymatic activity, immunoassays, and genetic probehydrates and other substrates, enzymatic activity, immunoassays, and genetic probes are also used.s are also used.Antimicrobial Susceptibility:Antimicrobial Susceptibility: Microorganisms, particularly bacteria, are tested in Microorganisms, particularly bacteria, are tested in vitro to determine whether they are susceptible to antimicrobial agents.vitro to determine whether they are susceptible to antimicrobial agents.Serodiagnosis:Serodiagnosis:A high or rising titer of specific IgG antibodies or the presence of spA high or rising titer of specific IgG antibodies or the presence of specific IgM antibodies may suggest or confirm a diagnosis.ecific IgM antibodies may suggest or confirm a diagnosis.Direct Examination and Techniques: Direct Examination and Techniques: Direct examination of specimens reveals grDirect examination of specimens reveals gross pathology. Microscopy may identify microorganisms. Immunofluorescence, imoss pathology. Microscopy may identify microorganisms. Immunofluorescence, immuno-peroxidase staining, and other immunoassays may detect specific microbial amuno-peroxidase staining, and other immunoassays may detect specific microbial antigens. Genetic probes identify genus- or species-specific DNA or RNA sequences.ntigens. Genetic probes identify genus- or species-specific DNA or RNA sequences.

Artificial active immunityArtificial active immunity

Toxoids:Toxoids: a modified form of the toxin that preserves its antigenicity but has lost its 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. This has been spectacularly successful with tetanus and diphtheria.

Inactivated vaccines:Inactivated vaccines: The production of protective antibodies is stimulated by usin The production of protective antibodies is stimulated by using the killed (inactivated) organisms This is done as a routine with vaccines against g the killed (inactivated) organisms This is done as a routine with vaccines against pertussis (whooping cough) , typhoid and influenza. There is also an inactivated polpertussis (whooping cough) , typhoid and influenza. There is also an inactivated polio vaccine.io vaccine.

Attenuated live vaccines :Attenuated live vaccines : The approach is to use suspensions of living organisms The approach is to use suspensions of living organisms that are reduced in their virulence (attenuated) but still immunogenic. This strategy that are reduced in their virulence (attenuated) but still immunogenic. This strategy has yielded: BCGhas yielded: BCG,, mumps, measles , and rubella vaccines (now combined); the live mumps, measles , and rubella vaccines (now combined); the live virus polio vaccine.virus polio vaccine.

Special vaccines:Special vaccines: polysaccharide vaccine, subunit vaccine, ( conjugate vaccine, bi polysaccharide vaccine, subunit vaccine, ( conjugate vaccine, bio-engineered vaccine, chemical vaccine, synthetic vaccine ), nucleic acid vaccine, io-engineered vaccine, chemical vaccine, synthetic vaccine ), nucleic acid vaccine, idiotype vaccine, autovaccine, etc.diotype vaccine, autovaccine, etc.

Vaccines are antigens prepared from pathogens that can raise a Vaccines are antigens prepared from pathogens that can raise a protective immune response, yet do not cause illness. These protective immune response, yet do not cause illness. These prepared antigens will stimulate both B cells and T cells and help prepared antigens will stimulate both B cells and T cells and help to create memory cells that can later mount a vigorous immune to create memory cells that can later mount a vigorous immune response to an encounter with the real pathogen.response to an encounter with the real pathogen.

Artificial passive immunityArtificial passive immunity

AntitoxinAntitoxin: e.g. Tetanus antitoxin and diphtheria antitox: e.g. Tetanus antitoxin and diphtheria antitoxin. It is raised in the horse .It is most important to give in. It is raised in the horse .It is most important to give an intented recipient of equine serum a prior test dose tan intented recipient of equine serum a prior test dose to exclude hypersensitivity subjects who may have been o exclude hypersensitivity subjects who may have been sensitized by a previous dose of equine serum.sensitized by a previous dose of equine serum.

Pooled immunoglobulinPooled immunoglobulin: It contains the normal repert: It contains the normal repertoire of antibodies for an adult, and can protect against hoire of antibodies for an adult, and can protect against hepatitis A, and measles.epatitis A, and measles.

Specific immunoglobulin:Specific immunoglobulin: Preparations of specific im Preparations of specific immunoglobulin are available for passive immunization amunoglobulin are available for passive immunization against tetanus, hepatitis B, rabies, varicella-zoster.gainst tetanus, hepatitis B, rabies, varicella-zoster.

Cytokine Cytokine

Active-passive immunityActive-passive immunity

involves giving both a vaccine to provide involves giving both a vaccine to provide long-term protection (preventive infection) long-term protection (preventive infection) and immune globulin to provide immediate and immune globulin to provide immediate protection (therapeutic and preventive protection (therapeutic and preventive infectious disease).infectious disease).

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区别要点区别要点 人工主动免疫人工主动免疫 人工被动免疫人工被动免疫

免疫物质免疫物质 抗原抗原 抗体或细胞因子等抗体或细胞因子等

免疫出现时间免疫出现时间 慢，慢， 2~42~4周周 快，立即快，立即

免疫维持时间免疫维持时间 长，数年长，数年 ~~数月数月 短，短， 2~32~3周周

主要用途主要用途 预防预防 治疗或紧急预防治疗或紧急预防

人工主动免疫与人工被动免疫的区别

DI = duration of illness, DH = duration of hospitalization, B/BF = blood/body fluid DI = duration of illness, DH = duration of hospitalization, B/BF = blood/body fluid precautions, D/S = drainage/secretion precautions, E = enteric precautions, C = precautions, D/S = drainage/secretion precautions, E = enteric precautions, C = contact isolation, S = strict isolation, R = respiratory isolation, TB = tuberculosis contact isolation, S = strict isolation, R = respiratory isolation, TB = tuberculosis isolation, U = universal precautions.isolation, U = universal precautions.

General procedure for collecting and processing General procedure for collecting and processing

specimens for aerobic and/or anaerobic bacterial culturespecimens for aerobic and/or anaerobic bacterial culture

Agglutination test in which inert particles (latex beads or heat-killed Agglutination test in which inert particles (latex beads or heat-killed S aureuS aureuss Cowan 1 strain with protein A) are coated with antibody to any of a variet 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 isolated by of antigens and then used to detect the antigen in specimens or in isolated bacteria.acteria.