Laboratory Diagnosis, Prevention and Treatment of Bacte rial Infection

(1)

Laboratory Diagnosis, Prevention and Treatment

of Bacterial Infection

Xiao-Kui Guo

(2)

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

laboratory data

.

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).

(3)

Specimen Selection, Collection, and

Processing

The quantity material must be adequate

Specimens are selected on the basis of signs and sy

mptoms, should be representative of the disease pro

cess

Contamination of the specimen must be avoided by

using only sterile equipment and aseptic precaution

s

The specimen must be taken to the laboratory and

examined promptly. Special transport media may b

e helpful.

Meaningful specimens to diagnose bacterial infectio

ns must be secured before antimicrobial drugs are

administered.

(4)

Microbiologic Examination

Culture:

Culture:Isolation of infectious agents frequently requires specialized media. NonselIsolation of infectious agents frequently requires specialized media. Nonsel ective (noninhibitory) media permit the growth of many microorganisms. Selective ective (noninhibitory) media permit the growth of many microorganisms. Selective media contain inhibitory substances that permit the isolation of specific types of mic media contain inhibitory substances that permit the isolation of specific types of mic roorganisms.

roorganisms.

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 carboh identification. Growth characteristics under various conditions, utilization of carboh ydrates and other substrates, enzymatic activity, immunoassays, and genetic probes ydrates and other substrates, enzymatic activity, immunoassays, and genetic probes are also used.

are also used.

Antimicrobial Susceptibility:

Antimicrobial Susceptibility: Microorganisms, particularly bacteria, are tested in v Microorganisms, particularly bacteria, are tested in v itro to determine whether they are susceptible to antimicrobial agents.

itro 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 sp ecific IgM antibodies may suggest or confirm a diagnosis.

ecific IgM antibodies may suggest or confirm a diagnosis.

Direct Examination and Techniques:

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(6)

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Artificial 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 usin g 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 pol pertussis (whooping cough) , typhoid and influenza. There is also an inactivated pol io 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: BCG

has 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, bi o-engineered vaccine, chemical vaccine, synthetic vaccine ), nucleic acid vaccine, i o-engineered vaccine, chemical vaccine, synthetic vaccine ), nucleic acid vaccine, i diotype vaccine, autovaccine, etc.

diotype vaccine, autovaccine, etc.

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.

(8)

Artificial passive immunity

Antitoxin

: e.g. Tetanus antitoxin and diphtheria antitox

in. It is raised in the horse .It is most important to give

an intented recipient of equine serum a prior test dose t

o exclude hypersensitivity subjects who may have been

sensitized by a previous dose of equine serum.

Pooled immunoglobulin

: It contains the normal repert

oire of antibodies for an adult, and can protect against h

epatitis A, and measles.

Specific immunoglobulin:

Preparations of specific im

munoglobulin are available for passive immunization a

gainst tetanus, hepatitis B, rabies, varicella-zoster.

Cytokine

(9)

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

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(12)

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.

(13)

General procedure for collecting and processing

specimens for aerobic and/or anaerobic bacterial culture

(14)

Agglutination test in which inert particles (latex beads or heat-killed

S aureu

s

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 ba

cteria.