Is Gram staining a diagnostic tool or a guide for optimal
empirical therapy?
In the article entitled ‘‘Gram stains have limited application in
the diagnosis of infected total knee arthroplasty’’, Zywiel et al.1
concluded that Gram staining for a suspected periprosthetic
infection after total knee arthroplasty is not recommended as a
diagnostic test due to its extremely low sensitivity (7%).
The authors addressed the difficulty of differentiating between
infectious and aseptic conditions based on the results presented in
their article, and concluded that Gram staining cannot reliably
identify infection after periprosthetic knee arthroplasty. Furthermore,
several investigators have suggested that the value of Gram
staining for diagnosing periprosthetic infection is questionable and
indeed that it is unsatisfactory as a diagnostic property.2,3 The
peer-reviewed ‘‘American Academy of Orthopaedic Surgeons
clinical practice guideline: the diagnosis of periprosthetic joint
infections of the hip and knee’’ also opposes the use of
intraoperative Gram staining to rule out periprosthetic joint
infection.4 The conclusion of Zywiel et al. is in line with this
guideline.
However, we wish to draw attention to the fact that Gram
staining nevertheless plays an irreplaceable role other than as a
diagnostic tool for patients with a suspected periprosthetic
infection, from two perspectives. Firstly, positive Gram stain
results are certainly helpful because detailed microbiological
information about the causative bacteria such as shape, size,
quantity, and grouping can be ascertained. Furthermore, this
information, combined with patient history and a physical
examination, can provide extra information for selecting optimal
antibiotics. Secondly, prosthetic joint infection is a challenging
clinical entity that typically requires extended hospitalization,
additional surgical procedures, and long courses of parenteral
antimicrobials.5–7 Cultures can often be negative because of prior
antimicrobial exposure,8,9 low numbers of organisms, or prolonged
duration of transportation to a microbiology laboratory.5 These
unique features of prosthetic joint infection rather emphasize the
value of microbiological information acquired from Gram staining.
In summary, Gram staining provides little information upon
which to base a diagnosis of periprosthetic knee arthroplasty
infection. However, positive Gram staining can help clinicians to
select appropriate antibiotics as initial or empirical therapy.
Clinicians should not overlook this aspect of Gram staining in the
ongoing search to uncover the microbiological cause of periprosthetic
knee arthroplasty infection.
Conflict of interest: No conflict of interest to declare