In vitro extracellular and intracellular activities of clavulanic acid and those of piperacillin and ceftriaxone alone and in combination with tazobactam against clinical isolates of Legionella species

Abstract

The activities of ceftriaxone, piperacillin, tazobactam, clavulanic acid, and combinations of ceftriaxone or piperacillin with tazobactam against 22 clinical Legionella isolates were measured by broth microdilution and macrodilution methods and in macrophages. The broth microdilution MICs that inhibited 90%o of strains tested were 2 and 1 ,ug/ml for ceftriaxone and tazobactam, respectively. Broth macrodilution MICs were 8 and 1 ,ug/ml, respectively, for the two LegioneUla pneumophila strains tested with piperacillin and were 0.25 and 0.5 ,ug/ml, respectively, for clavulanate. No significant intracellular anti-L. pneumophila activity was observed for ceftriaxone (32 ,ug/ml), piperacillin (32 ,ug/ml), tazobactam alone (16 ,Ig/ml), clavulanate alone (2 ,ig/ml), or tazobactam in combination with ceftriaxone (ceftriaxone/tazobactam at 32/4 and 16/16 ,ug/ml) or piperacillin (32/4 ,ig/ml). Erythromycin (1 ,ug/ml) was active against intracellular L. pneumophila in the same macrophage model of infection. It is very unlikely that tazobactam or clavulanate, alone or in combination with f-lactam antimicrobial agents, will be effective for the treatment of Legionnaires' disease in humans.Contrary to expectations, the ,-lactamase inhibitor clavulanic acid has been shown to be active against extracellular and intracellular Legionella pneumophila and in murine models of L. pneumophila infection (28, 33-36, 38, 39). This has led to the evaluation of the activities of other P-lactamase inhibitors against L. pneumophila. Recently, Collins and colleagues (1) reported that tazobactam, with or without piperacillin, is active against extracellular Legionella species. We tested tazobactam alone and in combination with either ceftriaxone or piperacillin to confirm the findings of Collins and colleagues and to determine whether these antimicrobial agents were active against intracellular L. pneumophila. The activity of clavulanic acid alone was also determined. We demonstrate that both tazobactam and clavulanic acid are active against extracellular, but not intracellular, L. pneumophila. MATERIALS AND METHODSBacteria and growth media. All legionellae studied were clinical isolates. These strains were identical to those used in prior studies and comprised 2 strains each of Legionella dumoffli, Legionella longbeachae, Legionella micdadei, 1 strain of Legionella bozemanii, and 15 strains of L. pneumophila (9,12

Isolation on Chocolate Agar Culture of Legionella pneumophila Isolates from Subcutaneous Abscesses in an Immunocompromised Patient

“…The quantitative MIC was 0.016 g/ml. Our results showed a lower MIC than previous reports by Edelstein et al and Collins et al, which showed MICs between 0.12 and 1 g/ml and between 0.03 and 2 g/ml, respectively, reinforcing the effectiveness of these antibiotics against extracellular forms (4,5).…”

Antibiotic Resistance of Legionella pneumophila in Clinical and Water Isolates—A Systematic Review

“…There was only one paper, Jia et al [ 53 ], which used the Broth Microdilution method with the ECOFF interpretation criteria [ 54 ]. Classifying the results according to year or a period of years, it was observed that a significant number of papers from the 1980s and 1990s (18/37; 48.6%) used the Broth Microdilution method according to previously published protocols, such as Edelstein et al [ 55 , 56 , 57 , 58 ], Hoogkamp-Korstanje [ 59 ] and Jones et al [ 60 ] ( Table S1 raw data; Figure 2 and Figure 3 ). Looking at the studies published in the time period 2000–2019, it is interesting to note that 17/57 articles used the Broth Microdilution method, as recommended by the CLSI, but then applied methods cited by older publications instead of the CLSI-recommended method for the interpretation of the results.…”

Intraphagocytic growth induces an antibiotic-resistant phenotype of Legionella pneumophila

“…In general, conclusions that an antibiotic is bactericidal against intracellular L. pneumophila have been based on the absence of regrowth or very slow regrowth of the bacterium after drug removal from tissue culture wells of infected phagocytes and continued incubation (20,21,28,43). Although such studies demonstrate the ability of the antibiotic to penetrate and concentrate within various types of phagocytic cells, i.e., macrophage-like cells (e.g., U937 cells) or professional phagocytic cells, they do not give any indication of the level of resistance of the intracellular bacterium.…”