Phenotypic Detection of β-Lactamase-Producing Bacterial Pathogens and Antimicrobial Resistance Patterns in Bloodstream Infections at a Tertiary Care Hospital: A Cross-Sectional Study

Background: Bloodstream infections (BSIs) are considered great morbid and mortal events worldwide, especially in critically ill and immunocompromised patients in the hospital setting and are among the most serious infectious conditions encountered in clinical practice. If they are not diagnosed quickly and treated appropriately, these infections can rapidly develop into sepsis, septic shock and multiorgan dysfunction. The challenge of treating bloodstream infections is growing worldwide as more bacteria have become multidrug-resistant, especially those that are β-lactamase resistant, making the majority of standard antimicrobial therapies ineffective. Clinically important resistance mechanisms developed as an extension of β-lactamases are extended-spectrum β-lactamases (ESBLs), AmpC β-lactamases, metallo-β-lactamases (MBLs), and carbapenemases, and they have restricted therapeutic choices and negatively affected patient outcomes. Bacteriological profile of BSI, antimicrobial susceptibility pattern and phenotypically characterisation of the mechanism of resistance to β-lactam antibiotics in bacterial pathogens recovered from BSI. Material and Methods: This is a cross-sectional observational study performed in the Department of Microbiology of a Tertiary care hospital. Samples of blood were obtained from patients who had clinical suspicions of bloodstream infection and processed for isolation and identification of bacterial pathogens following standard microbiological procedures. Antimicrobial susceptibility testing was done by the Kirby–Bauer disc diffusion method according to the guideline set by the Clinical and Laboratory Standards Institute (CLSI). The phenotypic detection of ESBL production, production of AmpC β-lactamase and metallo-β-lactamase and carbapenemase activity were performed with the Double Disc Synergy Test and E-test. Results: A gram-negative bacillary bloodstream infection was found to be the most common pathogens, and Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter species were isolated as the major pathogens. Staphylococcus aureus and enterococci were also important pathogens, as they are gram positive. Significant levels of multidrug resistance were observed in gram-negative isolates, which were highly resistant to the cephalosporins, fluoroquinolones, and carbapenems. The presence of ESBL, AmpC β-lactamase, metallo-β-lactamase and carbapenemase-producing organisms was confirmed by phenotypic screening. Comparative evaluation showed perfect agreement between double disc synergy test and E-test for the detection of metallo-β-lactamase. Conclusion: The study underscores the significant burden of bloodstream pathogens with multiple resistance mechanisms that are specific to the β-lactam group, specifically Gram-negative bacilli with β-lactamase-mediated resistance mechanisms. Screening for the presence of resistance determinants and active surveillance of antimicrobials is crucial in optimizing antimicrobial therapy and preventing spread of resistance pathogens.

Keywords: The bloodstream infections, antimicrobial resistance, β-lactamase, ESBL, AmpC, metallo-β-lactamase, carbapenemase, and multidrug resistance.