Dear editor
In the recently published study1 to evaluate the use of aztreonam as an active empiric therapy against subsequent culture of Pseudomonas aeruginosa, empiric therapy failure using aztreonam is reported more common than on using β-lactam antibiotics in patients suffering P. aeruginosa infection. Though the study is interesting and revealing important findings regarding antibiotic use for treatment of P. aeruginosa infection, it should be accepted with caution as suggested by the authors1 repeatedly due to limited number of cases. In our observations on P. aeruginosa (95) and other pseudomonads (40) isolates from veterinary clinical cases we found that instead of generalizing the lesser efficacy of aztreonam in-depth studies are required. Although insignificant, aztreonam inhibited more numbers of extended spectrum β-lactamase (ESBL) producing (57) P. aeruginosa strains (56.1%) than most of the β-lactams including cefotaxime, ceftriaxone and piperacillin (53.3%). However, on non-ESBL producing (37) strains aztreonam inhibited 42.1% isolates, much less than cefepime (68%), ceftriaxone (50%) and piperacillin + tazobactam (61.1%). Therefore, it is suggested to use the two classes of antibiotics (aztreonam and β-lactams) judiciously based on antibiotic stewardship principle1 instead of following some general rule for infections with pseudomonads.
In the analysis, antibiotic sensitivity patterns, available in clinical epidemiology laboratory of the Institute, of the 82 ESBL producers pseudomonads including P. aeruginosa (57), P. alcaligenes (1), P. fluorescens (7), P. paucimobilis (8), P. pseudoalcaligenes (5), P. stutzeri (3), P. testosteronii (1) and 53 ESBL negative pseudomonads including P. aeruginosa (38), P. alcaligenes (1), P. diminuta (1), P. fluorescens (6), P. paucimobilis (2), P. pseudoalcaligenes (3), P. stutzeri (1), P. vesicularis (1) were included. All the isolates were associated with one or other clinical condition in animals and were tested for antibiotic sensitivity pattern using standard disc diffusion assay.2
The analysis of the data (Table 1) for sensitivity of P. aeruginosa included in the study for aztreonam, carbapenems (meropenem, imipenem, ertapenem), cefepime, cefotaxime, ceftriaxone, colistin, gentamicin, piperacillin + Tazobactam, tetracycline and tigecycline revealed ESBL negative P. aeruginosa (PA) isolates were more often (though statistically insignificant, P >0.05) resistant (57.9%) to aztreonam than the ESBL positive isolates (43.9%). However, significantly more number of the ESBL negative P. aeruginosa isolates resisted gentamicin (P <0.001) than ESBL positive isolates. The ESBL negative P. aeruginosa isolates were significantly more commonly resistant to aztreonam than to cefepime (P=0.04), colistin (P <0.001) and gentamicin (P=0.02) but less often than to tetracycline (P=0.025). The ESBL positive P. aeruginosa isolates were significantly (P <0.001) more often resistant to aztreonam than to colistin and gentamicin but less than to tetracycline. The ESBL and non-ESBL pseudomonads other than P. aeruginosa (NPA) had not differed significantly (P >0.05) in their sensitivity to any of the antibiotics, however, aztreonam inhibited 64% ESBL producers and only 46.7% of ESBL negative isolates. Though for most of the antibiotics, including aztreonam and cephalosporins, sensitivity of P. aeruginosa and NPA had not differed significantly (P >0.05), NPAs were significantly more often resistant to cefepime (P <0.001), colistin (P=0.02), but less often (P <0.001) to tetracycline and tigecycline.
Table 1.
Antibiotic sensitivity pattern of Pseudomonas aeruginosa and other pseudomonads isolated from clinical infections in animals
| Antibiotics tested | P. aeruginosa (N=95) | Other pseudomonads (N=40) | Total (N=135) | |||
|---|---|---|---|---|---|---|
| ESBL–ve (38) | ESBL+ve (57) | ESBL–ve (15) | ESBL+ve (25) | ESBL–ve (53) | ESBL+ve (82) | |
| Aztreonam | 42.1 | 56.1 | 46.7 | 64.0 | 43.4 | 58.5 |
| Carbapenems | 57.9 | 66.7 | 50.0 | 33.3 | 64.2 | 67.1 |
| Cefepime | 68.0 | 90.0 | 40.0 | 60.0 | 62.9 | 72.4 |
| Cefotaxime | 31.6 | 42.1 | 66.7 | 64.0 | 34.0 | 47.6 |
| Ceftriaxone | 50.0 | 49.1 | 66.7 | 84.0 | 54.7 | 53.7 |
| Colistin | 89.5 | 93.0 | 80.0 | 68.0 | 83.0 | 90.2 |
| Gentamicin | 68.4 | 94.7 | 93.3 | 88.0 | 75.5 | 92.7 |
| Piperacillin + Tazobactam | 61.1 | 53.3 | 64.3 | 78.9 | 62.0 | 60.9 |
| Tetracycline | 18.4 | 21.1 | 46.7 | 60.0 | 26.4 | 32.9 |
| Tigecycline | 28.9 | 42.1 | 80.0 | 72.0 | 43.4 | 51.2 |
Abbreviations: ESBL–ve, extended spectrum β-lactamase negative; ESBL+ve, extended spectrum β-lactamase positive.
The analysis on antibiotic sensitivity patterns of P. aeruginosa and NPA isolates from veterinary clinical cases indicated need of antibiotic sensitivity assay for judicious use of antibiotics in therapy ie, need to reinforce antimicrobial stewardship principles.1
Footnotes
Disclosure
The author reports no conflicts of interest in this communication.
References
- 1.Hogan M, Bridgeman MB, Min GH, Dixit D, Bridgeman PJ, Narayanan N. Effectiveness of empiric aztreonam compared to other beta-lactams for treatment of Pseudomonas aeruginosa infections. Infect Drug Resist. 2018;11:1975–1981. doi: 10.2147/IDR.S174570. [DOI] [PMC free article] [PubMed] [Google Scholar]
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