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Legionella strains used in this study are listed in Table 1; they include 40 L. pneumophila and 26 non-L. pneumophila strains. L. gormanii and L. wadsworthii isolates resulted in no visible growth after 96 h incubation in BYE broth. The cumulative percentages, MIC50, and MIC90 values for the other 60 Legionella isolates, inhibited by different concentrations of the tested antimicrobials, are shown in Table 2. MIC50 and MIC90 values for macrolides were 0.062 and 0.25 mg/L, respectively, for AZM (range 0.031–0.5 mg/L); and 0.125 and 0.5 mg/L, respectively, for ERM (range 0.031–0.5 mg/L). MIC50 and MIC90 values for fluoroquinolones were 0.031 and 0.031 mg/L, respectively, for CIP and LEV (range 0.004–0.062 mg/L); and 0.031 and 0.062 mg/L, respectively, for MOX (range 0.004–0.125 mg/L). MIC50 and MIC90 values for tetracycline drugs were 8 and 16 mg/L, respectively, for DOC (range 0.5–16 mg/L); and 4 and 8 mg/L, respectively, for MIN (range 0.5–8 mg/L). MIC50 and MIC90 values for CTX were 4 and 8 mg/L, respectively (range 0.062–16 mg/L). With a MIC90 of 0.031 mg/L, CIP and LEV were the most active drugs, while DOX (MIC90 of 16 mg/L) was the least effective.

Table 1

List of Legionella strains used in this study

L. pneumophila (40)
Non-L. pneumophila (26)
SerogroupNo. of strainsSpeciesNo. of strains
12 L. adelaidensis 
L. rubrilucens 
L. gormanii 
L. shakespearei 
L. feeleii 
L. wadsworthii 
L. quateirensis 
14 17   
L. pneumophila (40)
Non-L. pneumophila (26)
SerogroupNo. of strainsSpeciesNo. of strains
12 L. adelaidensis 
L. rubrilucens 
L. gormanii 
L. shakespearei 
L. feeleii 
L. wadsworthii 
L. quateirensis 
14 17   
Table 2

Cumulative distribution of MICs for 60 environmental Legionella isolates

 Cumulative % of strains inhibited at indicated concentrations of antimicrobials (mg/L)
Drugs0.0040.0080.0160.0310.0620.1250.250.5124816
AZM    30.0 55.0 58.3 78.3 100      
CTX     8.3 10.0  11.7 16.7 30.0 68.3 95.0 100 
CIP 1.7 8.3 40.0 91.7 100         
DOC        1.7 3.3  33.3 83.3 100 
ERM    1.7 5.0 60.0 88.3 100      
LEV 1.7 15.0 45.0 96.7 100         
MIN      1.7  6.7 16.7 33.3 71.7 100  
MOX 1.7 5.0 36.7 68.3 98.3 100        
 Cumulative % of strains inhibited at indicated concentrations of antimicrobials (mg/L)
Drugs0.0040.0080.0160.0310.0620.1250.250.5124816
AZM    30.0 55.0 58.3 78.3 100      
CTX     8.3 10.0  11.7 16.7 30.0 68.3 95.0 100 
CIP 1.7 8.3 40.0 91.7 100         
DOC        1.7 3.3  33.3 83.3 100 
ERM    1.7 5.0 60.0 88.3 100      
LEV 1.7 15.0 45.0 96.7 100         
MIN      1.7  6.7 16.7 33.3 71.7 100  
MOX 1.7 5.0 36.7 68.3 98.3 100        

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