Infectious Diseases II
ii.
Sensitivity and specificity
| (a) | For species identification: Greater than 90% |
|---|---|
| (b) | For resistance genes: 100% (currently only available for mecA - methicillin resistance; van |
A/B - vancomycin resistance; Klebsiella pneumoniae carbapenemase [KPC] - carbapenem
resistance)
iii.
Application: Earlier escalation or de-escalation of antimicrobial agents
iv.
Studies have shown an earlier time to pathogen identification and antibiotic de-escalation. One
study found no difference in mortality, LOS, or cost when multiplex PCR was combined with
antibiotic stewardship.
Mechanism
Direct detection from positive blood culture medium using nanoparticle technology
ii.
Nucleic acid extraction and array hybridization
Most-developed commercially available product with resistance gene detection
Sensitivity and specificity: 93%β100%
| d. | Studies: Currently, most studies are limited to in vitro evaluations, which showed high levels |
|---|
of accuracy and decreased time to pathogen and resistance mechanism identification. Limited
clinical evidence; however, two small single-center studies have evaluated the use of Nanosphere
technology to augment clinical decisions. These studies showed a decrease in time to appropriate
antibiotic, in addition to decreased LOS and overall cost.
Mechanism
Microbiological media used to identify different microorganisms by color production
ii.
Growth media use enzyme substrates that release colored dyes on hydrolysis, with a wide
range of enzymes that can be targeted
iii.
Potential advantage of being able to detect polymicrobial growth
Sensitivity and specificity: 95%β100%
Limitations
Many different companies make different chromogenic agar media (Brilliance, chromID,
CHROMagar). Slight differences in sensitivity and specificity were seen in studies; however,
all were within acceptable ranges.
ii.
Time to identification is longer than with other rapid diagnostic tests.
iii.
Different manufacturersβ chromogenic agar produces different colors for positive identification.
Readers of chromogenic agar should be sufficiently trained and familiar with the product used
by the local institution.
| d. | Application |
|---|
Isolation of S. aureus from other Staphylococcus spp.
ii.
Detection of methicillin resistance among S. aureus
iii.
Detection of vancomycin resistance
iv.
Detection of specific Enterobacterales: Salmonella, E. coli O157, extended-spectrum
Ξ²-lactamase (ESBL) production
Differentiation of different Candida spp.
vi.
Detection of KPC
Studies: Many clinical studies have shown significant advantages over conventional culture media.
With the advent of newer technology and shorter detection times, the clinical applicability of
chromogenic media may be limited. However, few microbiology laboratories have implemented
rapid diagnostic methods because of the considerable upfront costs. Centers where chromogenic
media are being used may continue to rely on this technology.