bsp; I R S I R
a The current absence of resistant isolates precludes defining any results other than “Susceptible.” Isolates yielding MIC results suggestive of “Nonsusceptible” category should be submitted to reference laboratory for further testing.
b Tigecycline has decreased in vitro activity against Morganella spp., Proteus spp. and Providencia spp.
c Agar dilution
Staphylococcus aureus (including methicillin-resistant isolates) ≤0.5a - - ≥19 - -
Streptococcus spp. other than S. pneumoniae ≤0.25a - - ≥19 - -
Streptococcus pneumoniae
≤0.06a - - ≥19 - -
Enterococcus faecalis (vancomycin-susceptible isolates) ≤0.25a - - ≥19 - -
Enterobacteriaceaeb ≤2 4 ≥8 ≥19 15-18 ≤14
Haemophilus influenzae
≤0.25a - - ≥19 - -
Anaerobesc ≤4 8 ≥16 n/a n/a n/a
A report of “Susceptible” indicates that the pathogen is likely to be inhibited if the antimicrobial compound 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 that 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 reaches the concentrations usually achievable; other therapy should be selected.
Quality Control
As with other susceptibility techniques, the use of laboratory control microorganisms is required to control the technical aspects of the laboratory standardized procedures.1,2,3,4 Standard tigecycline powder should provide the MIC values provided in Table 5. For the diffusion technique using the 15 mcg tigecycline disk the criteria provided in Table 5 should be achieved.
Table 5. Acceptable Quality Control Ranges for Susceptibility Testing QC organism Minimum Inhibitory
Concentrations (mcg/mL) Disk Diffusion
(zone
diameters in mm)
ATCC = American Type Culture Collection
a Agar dilution
Staphylococcus aureus
ATCC 25923 Not Applicable 20-25
Staphylococcus aureus
ATCC 29213 0.03-0.25 Not Applicable
Escherichia coli ATCC 25922 0.03-0.25 20-27
Enterococcus faecalis
ATCC 29212 0.03-0.12 Not Applicable
Streptococcus pneumoniae
ATCC 49619 0.016-0.12 23-29
Haemophilus influenzae
ATCC 49247 0.06-0.5 23-31
Bacteroides fragilisa
ATCC 25285 0.12-1 Not Applicable
Bacteroides thetaiotaomicrona
ATCC 29741 0.5-2 Not Applicable
Eubacterium lentuma
ATCC 43055 0.06-0.5 |
