Antibiotic susceptibility, serotyping and determination of minimum inhibitory concentrations of imipenem and meropenem in relation to 88 strains of Pseudomonas aeruginosa isolated in northern Lebanon
We studied the susceptibility of 88 non-repetitive clinical isolates of Pseudomonas aeruginosa by the agar diffusion method. Serotyping of the strains is determined by the slide agglutination technique using specific antisera, polyvalent and monovalent. The minimum inhibitory concentration (MIC) of imipenem and meropenem was determined by the E-test method. Finally we analyzed the different resistance phenotypes observed in the study.
The results of serotyping showed that serotype O11 was the most common (N = 14, P = 16%) followed by serotype O7 (N = 11, P = 12.5%) and serotype O2 (N = 10, P = 11.36%).
The strains isolated in broncho-alveolar secretions were the most resistant to antibiotics.
The level of susceptibility of 88 strains to ticarcillin and ticarcillin-clavulanate was 66% and 67.1% respectively. The susceptibility to Piperacillin and Piperacillin - Tazobactam was 72.73% and 80.7% respectively. With regard to carbapenems, we tested imipenem and meropenem and the susceptibility was 78.4% and 87.51% respectively.
Regarding anti-pyocyanic cephalosporins, we observed that the susceptibility to ceftazidim was 77.37% and that of Cefepim was 80.67%.
Susceptibility to aminoglycosides showed good activity for amikacin with an 87.53% susceptibility.
By analyzing the MIC values obtained, we observed that for sensitive strains, values of meropenem were lower than those for imipenem.
Five strains had intermediate susceptibility to imipenem while they were sensitive to meropenem. Finally 14 strains were resistant to imipenem whereas only 9 were resistant to meropenem.
By analyzing the different resistance phenotypes observed in this study, we can report that there were 50 different resistance phenotypes.
Based on these results, we concluded that the major phenotype observed was the phenotype of resistance to fosfomycin (13 strains).
There was one isolated resistance phenotype to imipenem (one strain) and another strain that showed an intermediate susceptibility phenotype to this antibiotic.
* N: Number of strains
** P: Percentage
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