Demeclocycline hydrochloride microbiology

# Microbiology
The tetracyclines are primarily bacteriostatic and are thought to exert their antimicrobial effect by the inhibition of protein synthesis. The tetracyclines, including demeclocycline, have a similar antimicrobial spectrum of activity against a wide range of gram-negative and gram-positive organisms. Cross-resistance of these organisms to tetracyclines is common.
Demeclocycline 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:
Bacillus anthracis
Listeria monocytogenes
Staphylococcus aureus
Streptococcus pneumoniae
AEROBIC GRAM-NEGATIVE MICROORGANISMS:
Bartonella bacilliformis
Brucella species
Calymmatobacterium granulomatis
Campylobacter fetus
Francisella tularensis
Haemophilus ducreyi
Haemophilus influenzae
Neisseria gonorrhoeae
Vibrio cholerae
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 especially recommended:
Acinetobacter species
Enterobacter aerogenes
Klebsiella species
Shigella species
OTHER MICROORGANISMS:
Actinomyces israelii
Borrelia recurrentis
Chlamydia psittaci
Chlamydia trachomatis
Clostridium species
Entamoeba species
Fusobacterium fusiforme
Mycoplasma pneumoniae
Propionibacterium acnes
Rickettsiae
Treponema pallidum subspecies pallidum
Treponema pallidum subspecies pertenue
Ureaplasma urealyticum

## 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 method (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of demeclocycline hydrochloride or tetracycline powder.1 The MIC values should be interpreted according to the following criteria:
For organisms other than Haemophilus species, Neisseria gonorrhoeae and Streptococcus species:2
A report of "Susceptible" indicates that the pathogen is likely to be inhibited by usually achievable concentrations of the antimicrobial compound in blood. 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 usually achievable concentrations of the antimicrobial compound in the blood are unlikely to be inhibitory and that 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 demeclocycline or tetracycline powder should provide the following MIC values:2
Diffusion Techniques
Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure requires the use of standardized inoculum concentrations.2 This procedure uses paper disks impregnated with 30-mcg tetracycline (as a class disk) or a 30-mcg demeclocycline hydrochloride disk to test the susceptibility of microorganisms to demeclocycline.
Reports from the laboratory providing results of the standard single-disk susceptibility test with either a 30-mcg tetracycline-class disk or a 30-mcg demeclocycline disk should be interpreted according to the following criteria:
For organisms other than Haemophilus species, Neisseria gonorrhoeae and Streptococcus species:2
Interpretation should be as stated above for results using dilution techniques. Interpretation involves correlation of the diameter obtained in the disk test with the MIC for demeclocycline hydrochloride or tetracycline.
As with standardized dilution techniques, diffusion methods require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures. For the diffusion technique, the 30-mcg demeclocycline hydrochloride disk or the 30-mcg tetracycline-class disk should provide the following zone diameters in these laboratory test quality control strains:2
- E. coli, ATCC 25922          18 to 25mm
- H. influenzae, ATCC 49247    14 to 22mm
- N. gonorrhoeae, ATCC 49226   30 to 42mm
- S. aureus, ATCC 25923        24 to 30mm
- S. pneumoniae, ATCC 49619    27 to 31mm