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Listeria monocytogenes Infection of the Brain
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Effect of subinhibitory concentrations of ampicillin on Listeria monocytogenes

Ángel Rodríguez-Villodres1, José Antonio Lepe1, Jesús Blázquez2

  • 1Clinical Unit of Infectious Diseases, Microbiology and Preventive Medicine, University Hospital Virgen del Rocío, Seville, Spain; Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/University of Seville, Seville, Spain.

Enfermedades Infecciosas Y Microbiologia Clinica (English Ed.)
|April 28, 2019
PubMed

Insights

Subinhibitory ampicillin concentrations cause Listeria monocytogenes to form aggregates and exhibit heteroresistance. This may explain ampicillin treatment failures in central nervous system (CNS) listeriosis.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Pharmacology

Background:

  • Listeria monocytogenes causes severe meningoencephalitis with high mortality.
  • Ampicillin is the primary treatment for listeriosis, but achieves low concentrations in the central nervous system (CNS).

Purpose of the Study:

  • To investigate the effects of subinhibitory ampicillin concentrations on Listeria monocytogenes morphology, growth, and survival.
  • To determine the non-inhibitory concentration (NIC), minimum inhibitory concentration (MIC), and MIC/NIC ratio for L. monocytogenes.

Main Methods:

  • Gram staining and Live/Dead staining were used to assess bacterial morphology and viability.
  • Determination of NIC, MIC, and MIC/NIC ratio for ampicillin against L. monocytogenes strains.

Main Results:

  • Subinhibitory ampicillin concentrations induced the formation of L. monocytogenes aggregates.
  • Over 90% of cells within these aggregates remained viable.
  • L. monocytogenes strains displayed intermediate heteroresistance to ampicillin, with a MIC/NIC ratio of 4.

Conclusions:

  • Intermediate heteroresistance and aggregate formation in L. monocytogenes may contribute to ampicillin treatment failure in CNS infections.
  • Further research is needed to confirm the clinical implications of these findings.
Keywords:
AggregatesAgregadosAmpicilinaAmpicillinConcentraciones subinhibitoriasHeteroresistanceHeterorresistenciaListeria monocytogenesSubinhibitory concentrations

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