Evaluation of a simple method for testing aztreonam and ceftazidime-avibactam synergy in New Delhi metallo-beta-lactamase producing Enterobacterales.

NDM-producing carbapenem-resistant bacterial infections became a challenge for clinicians. Combination therapy of aztreonam and ceftazidime-avibactam is a prudent choice for these infections. However, there is still no recommendation of a practically feasible method for testing aztreonam and ceftazidime-avibactam synergy. We proposed a simple method for testing aztreonam and ceftazidime-avibactam synergy and compared it with reference broth micro-dilution and other methods. Carbapenem-resistant Enterobacterales clinical isolates were screened for the presence of the NDM gene by the Carba R test. NDM harbouring isolates were tested for aztreonam and ceftazidime-avibactam synergy by broth microdilution (reference method), E strip-disc diffusion, double disc diffusion, and disc replacement methods. In the newly proposed method, the MHA medium was supplemented with ceftazidime-avibactam (corresponding to an aztreonam concentration of 4µg/ml). The MHA medium was then inoculated with the standard inoculum (0.5 McFarland) of the test organism. An AZT disc (30 µg) was placed on the supplemented MHA medium, and the medium was incubated overnight at 37°C. Aztreonam zone diameter on the supplemented MHA medium (in the presence of ceftazidime-avibactam) was compared with that from a standard disc diffusion plate (without ceftazidime-avibactam), performed in parallel. Interpretation of synergy was based on the restoration of aztreonam zone diameter (in the presence of ceftazidime-avibactam) crossing the CLSI susceptibility breakpoint, i.e., ≥ 21 mm. Of 37 carbapenem-resistant NDM-producing isolates, 35 (94.6%) were resistant to aztreonam and tested synergy positive by the proposed method. Its sensitivity and specificity were 97.14% and 100%, respectively. Cohen's kappa value showed substantial agreement of the reference method with the proposed method (κ = 0.78) but no other methods. The proposed method is simple, easily interpretable, and showed excellent sensitivity, specificity, and agreement with the reference method. Therefore, the new method is feasible and reliable for testing aztreonam synergy with avibactam in NDM-producing Enterobacterales.

Evaluation of a rapid immunochromatographic test for the diagnosis of intestinal protozoan infections among patients attending a rural outreach outpatient department in Northern India.

Despite great efforts, intestinal protozoan infections remain a significant healthcare concern worldwide. Although many point-of-care (POC) tests are increasingly being used, microscopic examination of stool specimens remains the mainstay for their diagnosis, especially in resource-limited settings. We assessed the utility of rapid POC tests based on immunochromatography among patients from rural Northern India. A total of 78 patients were enrolled in the study. Out of nine specimens that tested positive for Giardia duodenalis on microscopy, an immunochromatographic test (ICT) could detect only five (55.55%). Entamoeba histolytica/dispar was demonstrated in two specimens on microscopy, both of which were missed by ICT. Its overall sensitivity, specificity, and positive and negative predictive value were 50%, 98.5%, 83.3%, and 93%, respectively. Its performance was considered unsatisfactory. Although ICT-based tests provide a relatively rapid and less labor-intensive alternative, they should be used to supplement and not replace stool microscopy.