In vitro susceptibility of Listeria monocytogenes isolated from human blood and cerebrospinal fluid

Abstract

The in vitro susceptibility of 156 strains of Listeria monocytogenes isolated since 1958 from human cerebrospinal fluid or blood to twelve antibiotics was determined by an agar dilution technique. Erythromycin (0.05), trimethoprim (0.2), netilmicin (0.2), and penicillin (0.2) were the most active drugs on weight basis (MIC90 0.05–0.2 μg/ml). Ampicillin and imipenem had MICs for 90% of the strains of 0.4 μg/ml. Ceftazidime was inactive (MIC90 > 100 μg/ml). Comparison of susceptibility pattern between strains isolated in different years showed that the antimicrobial susceptibility of L. monocytogenes has not changed during the last 25 years. The minimal bactericidal concentration (MBC) of penicillin was determined by a macro tube dilution method in ten recent isolates. Penicillin was bactericidal for all the strains with a MBC of 0.4–3.1 μg/ml, i.e. one to three two‐fold dilutions above the MIC of 0.2–0.8 μg/ml, which means that no tolerant strains were found.

Antibiotic susceptibility of Listeria monocytogenes in Denmark 1958–2001

“…Our results show that the MIC measurements for penicillin and ampicillin did not change during the period examined and they are in good accordance with other studies (5, 7, 10–13). Our MIC measurements for gentamicin are also in accordance with other studies (see e.g.…”

“…Our study shows that in vitro susceptibility of L. monocytogenes , when isolated from cases of human infection, has not changed during the last decades in Denmark. Earlier studies from Sweden and Denmark, and a recent study from Austria encompassing strains of L. monocytogenes from four European countries, also conclude that susceptibility has not changed (5, 7, 11). None of these studies including our own revealed any multiresistant strains, nor did two studies of 621 and 513 strains from human infections in the UK during the periods 1987–90 and 1990–95 (12, 13).…”

Antimicrobial susceptibilities of Corynebacterium species and other non-spore-forming gram-positive bacilli to 18 antimicrobial agents

“…The dissociated susceptibility of L. monocytogenes to cephalothin and cefuroxime has been described previously, and this organism is also resistant to ceftazidime (11). Our results show an increase in the MICs of ampicillin for L. monocytogenes in comparison with those given in other reports (21). Although the inoculum size and the media used to determine antimicrobial susceptibility in L. monocytogenes seem to affect the results (11), a careful follow-up of the susceptibilities over time should be carried out.…”

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).…”