Evaluation of phenotypic carbapenem inactivation methods among carbapenem resistant gram-negative bacteria isolated from blood culture specimens and their synergy testing

: Carbapenem-resistant Enterobacterales (CRE) are a significant public health threat due to their resistance to antibiotics, leading to serious infections, increased healthcare expenses, and higher mortality rates. Accurate identification of CRE is essential for effective treatment and infection control. Phenotypic methods like the modified Carbapenemase Inactivation Method (mCIM) and the EDTA-Carbapenem Inactivation Method (eCIM) are practical approaches for identifying production carbapenemase. As a result, the current study aims to analyse the efficacy of phenotypic carbapenem inactivation approaches in detecting carbapenem-resistant Gram-negative bacteria isolated from blood culture specimens, as well as the synergy of ceftazidime-avibactam and aztreonam in treating such infections. This laboratory based prospective study was adopted to evaluate the efficacy of phenotypic carbapenem inactivation methods in detecting carbapenem-resistant Gram-negative bacteria isolated from blood culture specimens and assess the synergy of ceftazidime-avibactam and aztreonam in treating these infections. : Gram-negative bacteria isolated from positive blood cultures were evaluated for carbapenemase activity using mCIM and eCIM, respectively. Synergy testing was conducted using ceftazidime-avibactam and aztreonam to evaluate potential therapeutic benefits. Among 383 blood cultures, 153 (39.94%) were MDROs, predominantly (57.5%). Of these, 123 (81%) were carbapenem-resistant. The mCIM and eCIM tests identified 67 (54%) serine carbapenemase and 54 (45.5%) metallo beta-lactamases. Synergy testing with ceftazidime-avibactam and aztreonam showed positive results in 43 (68.25%) of the 63 CZA-resistant isolates. : The study confirms that mCIM and eCIM tests effectively detect carbapenemase production in blood culture isolates, identifying 54% serine carbapenemases and 45.5% metallo beta-lactamases. Additionally, synergy testing with ceftazidime-avibactam and aztreonam demonstrated a 68.25% success rate in CZA-resistant isolates, indicating a promising treatment option for these resistant infections.