Assessing the In-Vitro Effectiveness of Ceftazidime-Avibactam Against Carbapenem-Resistant Gram-Negative Bacteria: Insights from a Pakistani Cross-Sectional Study

In the relentless global battle against antimicrobial resistance, researchers are continuously scouting for viable alternatives to combat the rise of multidrug-resistant pathogens. One recent investigative study, conducted at the Microbiology Department of Indus Hospital in Karachi, Pakistan, has scrutinized the efficacy of a promising antibiotic combination, ceftazidime-avibactam (CAZ-AVI), against carbapenem-resistant gram-negative bacteria—a formidable group of pathogens notorious for their resistance and clinical challenges. This study, encompassing clinical isolates obtained over nearly two years, provides a meticulous evaluation of CAZ-AVI’s potential as a therapeutic agent amid increasing resistance trends globally.

Carbapenem-resistant organisms pose a significant threat due to their ability to evade the most potent beta-lactam antibiotics, making infections caused by these pathogens exceedingly difficult to treat. This scenario has intensified the need for novel antibiotics or antibiotic combinations capable of bypassing these resistance mechanisms. Ceftazidime-avibactam emerges as one such combination, pairing the well-established third-generation cephalosporin ceftazidime with avibactam, a non-beta-lactam beta-lactamase inhibitor that can inhibit a broad spectrum of beta-lactamases, including class A and some class D enzymes. This mechanism potentially revitalizes ceftazidime’s efficacy by protecting it from enzymatic degradation.

The Karachi-based study employed a cross-sectional, observational design, analyzing 158 isolates of carbapenem-resistant gram-negative rods collected consecutively from outpatient, emergency, and inpatient clinical samples. These bacteria were subjected to precise identification through API® ID strips, a method guaranteeing accurate species-level identification critical for understanding the spectrum of resistance patterns across different pathogens. Their susceptibility to carbapenems and CAZ-AVI was thoroughly tested using the Kirby-Bauer disk diffusion assay, a gold standard technique in antimicrobial susceptibility testing.

Among the 158 carbapenem-resistant isolates, 58% were identified as Enterobacterales—a large order comprising many clinically important genera such as Klebsiella and Escherichia—and the remaining 42% constituted Pseudomonas aeruginosa, a notoriously adaptable pathogen with intrinsic and acquired resistance mechanisms. This distribution underscores the diverse bacterial populations responsible for carbapenem resistance in the clinical setting, highlighting the need for tailored therapeutic approaches.

A crucial finding of this research was the notably low susceptibility rate to CAZ-AVI among these resistant isolates, with only 11% demonstrating susceptibility. This alarming trend suggests that even novel antibiotic combinations like CAZ-AVI face significant hurdles when confronting carbapenem-resistant strains, necessitating careful stewardship and region-specific resistance monitoring. Interestingly, within the susceptible subset, Klebsiella spp. and Escherichia coli each represented about a quarter of these strains, with the majority being Pseudomonas aeruginosa. This distribution hints at species-specific variations in resistance mechanisms or differing prevalence of beta-lactamases susceptible to avibactam inhibition, posing important questions for future molecular investigations.

The demographic and clinical characteristics of patients harboring CAZ-AVI susceptible isolates offered insightful patterns. The majority were in the 26–50 years age bracket, suggesting a working-age population is predominantly affected by these infections in this context. Gender-wise, females predominated among susceptible cases, and nearly half were inpatients, affirming the clinical complexity and the broad healthcare impact of these resistant infections. Furthermore, urinary tract infections emerged as the primary clinical source of CAZ-AVI susceptible strains, indicating potential niches where CAZ-AVI might still retain clinical utility.

These findings underscore the critical importance of local antimicrobial surveillance to inform therapeutic decisions. Regional variability in resistance patterns can profoundly influence the effectiveness of antibiotic regimens. In Pakistan, the low susceptibility rate to CAZ-AVI signals caution in relying solely on this agent for treating carbapenem-resistant infections and highlights the necessity for integrated strategies combining antimicrobial stewardship with infection prevention and control measures.

From a molecular perspective, the modest susceptibility rates observed may be attributable to the prevalence of carbapenemases such as metallo-beta-lactamases (MBLs), which avibactam does not inhibit effectively. This mechanism underscores a vexing challenge for the clinical use of CAZ-AVI in settings where MBL producers are prevalent. Ongoing research into overcoming this resistance, including the development of novel inhibitors or combination therapies targeting MBLs, remains a critical need.

This study’s design, involving consecutive and non-probability sampling in a major tertiary care center, offers a pragmatic snapshot of real-world resistance trends. While the Kirby-Bauer method provides widely accepted phenotypic susceptibility data, future studies might benefit from integrating molecular detection of resistance genes to correlate phenotypic resistance with genetic determinants, thereby enhancing understanding and guiding targeted interventions.

Given the escalating threat of antimicrobial resistance globally, the findings from this Pakistan-based research reflect a microcosm of broader challenges. The limited efficacy of even advanced antibiotic combinations like CAZ-AVI underpins the urgency for novel drug discovery, investment in rapid diagnostic technologies, and robust antimicrobial stewardship programs. Collaborative global efforts addressing these multifaceted challenges will be pivotal in reinvigorating the dwindling arsenal against resistant bacterial pathogens.

In conclusion, the low in-vitro susceptibility of carbapenem-resistant gram-negative bacteria to ceftazidime-avibactam in this Pakistani cohort raises critical concerns about the drug’s current clinical utility in similar settings. These insights emphasize the need for continuous, localized resistance surveillance to optimize antibiotic use and for stringent policies to curb the spread of resistant bacteria. The battle against superbugs demands a multipronged approach, blending innovative pharmacology with rigorous public health strategies to sustain effective antimicrobial therapeutics for the future.

News Publication Date: 25-Mar-2025

Web References:
http://dx.doi.org/10.14218/JERP.2025.00001
https://www.xiahepublishing.com/journal/jerp