Spheroplast-Mediated Carbapenem Tolerance in Gram-Negative Pathogens

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Antimicrobial Resistance

Background:

• Antibiotic tolerance is a key factor in treatment failure, yet remains understudied.
• Previous work demonstrated Vibrio cholerae tolerates beta-lactam antibiotics by forming cell wall-deficient spheroplasts.
• The prevalence of antibiotic tolerance among clinically significant Gram-negative pathogens is largely unknown.

Purpose of the Study:

• To investigate the prevalence and mechanisms of tolerance to the carbapenem antibiotic meropenem in clinically relevant Gram-negative pathogens.
• To determine if cell wall deficiency mediates meropenem tolerance in these bacteria.

Main Methods:

• Testing clinical isolates of Gram-negative pathogens (Enterobacter cloacae, Klebsiella aerogenes, Klebsiella pneumoniae, Escherichia coli) for meropenem tolerance.
• Assessing tolerance in both laboratory growth medium and human serum.
• Microscopic examination to identify morphological changes, specifically cell wall-deficient spheroplast formation.

Main Results:

• Clinical isolates of Enterobacter cloacae, Klebsiella aerogenes, and Klebsiella pneumoniae exhibited moderate to high tolerance to meropenem.
• Escherichia coli did not display significant tolerance to meropenem.
• Tolerance was consistently mediated by the formation of cell wall-deficient spheroplasts, which reverted to normal morphology upon antibiotic removal.

Conclusions:

• Carbapenem tolerance is prevalent among clinically significant bacterial species, particularly Klebsiella species and Enterobacter cloacae.
• The ability to form cell wall-deficient spheroplasts is a key mechanism for carbapenem tolerance.
• This widespread tolerance mechanism may contribute to treatment failures involving these common bacterial pathogens.