Doxycycline monohydrate microbiology

# Microbiology
The tetracyclines are primarily bacteriostatic and are thought to exert their antimicrobial effect by the inhibition of protein synthesis. The tetracyclines, including doxycycline, have a similar antimicrobial spectrum of activity against a wide range of gram-positive and gram-negative microorganisms. Cross-resistance of these microorganisms to tetracyclines is common.
Doxycycline has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.
Aerobic Gram-Positive Microorganisms:
Because many strains of the following groups of gram-positive microorganisms have been shown to be resistant to tetracyclines, culture and susceptibility testing are recommended.
Bacillus anthracis
Listeria monocytogenes
Staphylococcus aureus
- Doxycycline is not the drug of choice in the treatment of any type of staphylococcal infection.
Up to 44 percent of strains of Streptococcus pyogenes and 74 percent of Streptococcus faecalis have been found to be resistant to tetracycline drugs. Therefore, tetracyclines should not be used to treat streptococcal infections unless the microorganism has been demonstrated to be susceptible.
Streptococcus pneumoniae
Aerobic Gram-Negative Microorganisms:
Bartonella bacilliformis
Haemophilus ducreyi
Brucella species
Haemophilus influenzae
Calymmatobacterium granulomatis
Neisseria gonorrhoeae
Campylobacter fetus
Vibrio cholerae
Francisella tularensis
Yersinia pestis
Because many strains of the following groups of gram-negative microorganisms have been shown to be resistant to tetracyclines, culture and susceptibility testing are recommended:
Acinetobacter species
Klebsiella species
Enterobacter aerogenes
Shigella species
Escherichia coli
Anaerobic Microorganisms:
Actinomyces israelii
Fusobacterium fusiforme
Clostridium species
Other Microorganisms:
Borrelia recurrentis
Rickettsiae
Chlamydia psittaci
Treponema pallidum
Chlamydia trachomatis
Treponema pertenue
Mycoplasma pneumoniae
Susceptibility Tests:
- Dilution Techniques:
Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized procedure. Standardized procedures are based on a dilution method1,3 (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of tetracycline powder. The MIC values should be interpreted according to the following criteria:
Microorganisms that are susceptible to tetracycline are generally susceptible to doxycycline.
A report of Susceptible indicates that the pathogen is likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable. A report of Intermediate indicates that the result should be considered equivocal, and, if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug is physiologically concentrated or in situations where high dosage of drug can be used. This category also provides a buffer zone which prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of Resistant indicates that the pathogen is not likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable; other therapy should be selected.
Standardized susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures. Standard tetracycline powder should provide the following MIC values: