In vitro Susceptibility of <i>Listeria monocytogenes</i>: Comparison of the E Test with the Agar Dilution Test

Abstract

In vitro susceptibility testing was performed on 66 strains of Listeria monocytogenes. Recently obtained clinical isolates from Austria, France, Norway and Switzerland and 17 reference strains from three type culture collections were tested against ampicillin, gentamicin, trimethoprim-sulfamethoxazole, ampicillin-sulbactam, meropenem, and first-, second-, third- and fourth-generation cephalosporins. All isolates were susceptible to ampicillin, gentamicin, and trimethoprim-sulfamethoxazole, ampicillin-sulbactam, and meropenem and more than 86% of the minimal inhibitory concentration E test values were within plus/minus one dilution step of the agar dilution test. In vitro susceptibility of L. monocytogenes has not changed markedly during the last decades; the level of susceptibility of old reference strains did not differ from that of recently encountered clinical isolates. The E test seems to be a suitable method for Listeria.

Antimicrobial Resistance of Listeria monocytogenes Strains Isolated from Humans in France

“…The prevalence of acquired resistance in France determined from the largest collection of clinical isolates to date remains low, similar to reported results of previous epidemiological studies in other countries (14,15,19,22,25,31). This contrasts with the higher prevalence of resistance reported for food and environmental Listeria species, possibly overstated due to the existence of a larger reservoir of resistance in Listeria innocua than in L. monocytogenes (6).…”

“…However, some studies have recently reported an increased rate of resistance to one or several clinically relevant antibiotics in environmental isolates (1,6,7,21,33,37) and less frequently in clinical strains (3,9,26,31). Yet, this probably remains a marginal phenomenon for clinical strains, although only a limited number of studies have focused on the evaluation of antimicrobial resistance in Listeria (14,15,19,22,25,31).…”

Contribution of Penicillin-Binding Protein Homologs to Antibiotic Resistance, Cell Morphology, and Virulence of Listeria monocytogenes EGDe

“…In general, L. monocytogenes is susceptible to a wide range of antibiotics, including penicillins, aminopenicillins, and carbapenems (5,11). Clinicians treating patients suspected of having L. monocytogenes infection normally utilize ampicillin or benzylpenicillin, either alone or in combination with an aminoglycoside (30).…”

Antimicrobial Activities against 84 Listeria monocytogenes Isolates from Patients with Systemic Listeriosis at a Comprehensive Cancer Center (1955-1997)

“…Penicillin and ampicillin are bactericidal against most strains of L. monocytogenes; however, in the preferred intracellular milieu, these microorganisms become more recalcitrant and on May 9, 2018 by guest http://jcm.asm.org/ even highly effective drugs are rendered bacteriostatic at best (7,9,15). The lack of in vivo bactericidal antilisteric effect becomes important in the treatment of systemic opportunistic infections in patients with compromised adaptive cellular immunity (10,20).…”

“…These antimicrobials can achieve greater than 99.9% bacterial killing with no evidence of bacterial regrowth (3,7,13,14). However, no measurable antilisteric effect of ciprofloxacin in intracellular cell culture experiments (17) cautions against therapeutic intervention.…”