Anaerobic Techniques
For anaerobic bacteria, the susceptibility to doxycycline can be determined by a standardized test method5. The MIC values obtained should be interpreted according to the criteria provided in Table 1.

Table 1: Susceptibility Test Interpretive Criteria for Doxycycline and Tetracycline  Bacteria* Minimal Inhibitory Concentration
(mcg/mL) Zone Diameter
(mm) Agar Dilution
(mcg/mL)
 S I R S I R S I R
*
Organisms susceptible to tetracycline are also considered susceptible to doxycycline. However, some organisms that are intermediate or resistant to tetracycline may be susceptible to doxycycline
†
The current absence of resistance isolates precludes defining any results other than "Susceptible". If isolates yielding MIC results other than susceptible, they should be submitted to a reference laboratory for further testing.
‡
Gonococci with 30 mcg tetracycline disk zone diameters of <19 mm usually indicate a plasmid-mediated tetracycline resistant Neisseria gonorrhoeae isolate. Resistance in these strains should be confirmed by a dilution test (MIC ≥ 16 mcg/mL) 
Acinetobacter spp.         
  Doxycycline ≤4 8 ≥16 ≥13 10–12 ≤9 - - -
  Tetracycline ≤4 8 ≥16 ≥15 12–14 ≤11 - - -
Anaerobes         
  Tetracycline - - - - - - ≤4 8 ≥16
Bacillus anthracis*†         
  Doxycycline ≤1 - - - - - - - -
  Tetracycline ≤1 - - - - - - - -
Brucella species*†         
  Doxycycline ≤1 - - - - - - - -
  Tetracycline ≤1 - - - - - - - -
Enterobacteriaceae         
  Doxycycline ≤4 8 ≥16 ≥14 11–13 ≤10 - - -
  Tetracycline ≤4 8 ≥16 ≥15 12 –14 ≤11 - - -
Franciscella tularensis*†         
  Doxycycline ≤ 4 - - - - - - - -
  Tetracycline ≤ 4 - - - - - - - -
Haemophilus influenzae         
  Tetracycline ≤2 4 ≥8 ≥29 26–28 ≤25 - - -
Mycoplasma pneumoniae†         
  Tetracycline - - - - - - ≤2 - -
Nocardiae and other aerobic Actinomyces species*†         
  Doxycycline ≤1 2–4 ≥8 - - - - - -
Neisseria gonorrhoeae‡         
  Tetracycline - - - ≥38 31–37 ≤30 ≤0.25 0.5–1 ≥2
Streptococcus pneumoniae         
  Tetracycline ≤2 4 ≥8 ≥ 23 19–22 ≤ 18 - - -
Vibrio cholerae         
  Doxycycline ≤4 8 ≥16 - - - - - -
  Tetracycline ≤4 8 ≥16 - - - - - -
Yersinia pestis         
  Doxycycline ≤4 8 ≥16 - - - - - -
  Tetracycline ≤4 8 ≥16 - - - - - -
Ureaplasma