Evaluation of various quinolone antimicrobial disks to screen for P1002 fluoroquinolone resistance in Salmonella spp.

Işın AKYAR1, 2, Aysel KARATAŞ2, Onur KARATUNA1, 2 1 Acıbadem University School of Medicine, Department of Medical Microbiology, Istanbul, Turkey 2 Acıbadem Labmed Clinical Laboratories, Istanbul, Turkey

1 (µg), (5 µg), (5 µg), Objectives Table 2. Zone diameters of various quinolone disks according to MIC for ciprofloxacin (10 µg), (10 µg), (10 µg), tested in clinical Salmonella isolates (n=198) It’s important to differentiate Salmonella isolates with low- garenoxacin (5 µg), (1 µg), (5 level fluoroquinolone (FQ) resistance (i.e. ciprofloxacin µg), (1 µg), (30 µg), MIC >0.06 mg/L) from wild type isolates because there is (2 µg), (2 µg), (10 µg), (5 clinical evidence that these isolates respond poorly to FQ µg), (5 µg), (10 µg). Escherichia treatment in systemic infections. EUCAST recently coli ATCC 25922 was used for quality control. recommended the use of 5 μg pefloxacin disk to screen for all currently defined FQ resistance mechanisms in Results Salmonella spp. The objective of this study was to investigate the correlation between ciprofloxacin MIC Ciprofloxacin susceptible (MIC ≤0.06 mg/L) isolates values and zone diameters of various quinolone constituted %84.3 (n=167), low-level resistant (MIC 0.12- antimicrobial disks to evaluate the performance of 0.5 mg/L) isolates constituted 11.6% (n=23), and high-level pefloxacin disk and possible utility of the other disks. resistant (MIC ≥1 mg/L) isolates constituted 4.0% (n=8) of Methods the study isolates (Figure 1). Among the tested antimicrobial disks the best correlation between Consecutive Salmonella isolates (n=198) from clinical ciprofloxacin MIC and range of zone diameters was samples (Table 1) were tested for ciprofloxacin MIC with observed for pefloxacin 5 µg (100% success in broth microdilution method at the range 0.002 – 2 mg/L. discriminating wild type isolates with MICs ≤0.06 mg/L from Disk diffusion test was performed on Mueller Hinton agar isolates with acquired resistance with MIC of >0.06 mg/L), plates (bioMérieux, France) with the following disks followed by nalidixic acid 30 µg (failure in discriminating (Bioanalyse, Turkey): (100 µg), ciprofloxacin 3.5% of the isolates) (Table 2).

Table 1. Serotypes of the clinical Salmonella isolates (n=198)

Salmonella enterica n (%) serovar Conclusion Enteritidis 90 (45.5) Gallinarum/Pullorum 64 (32.3) The high ciprofloxacin susceptibility rate (84.3%) among the study isolates caused a disproportionate distribution of wild type and non-wild type isolates included in the Typhimurium 11 (5.6) study, yet EUCAST’s recommended pefloxacin 5 µg disk performed excellently for Istanbul 4 (2.0) our isolate collection. Paratyphi B 2 (1.0) The traditional antimicrobials; nalidixic acid 30 µg and ciprofloxacin 5 µg used for the same purpose in the past, exhibited poor performance and caused overlapping of Nontypeable* 27 (13.6) wild type and non-wild type isolates (3.5% and 7.6%, respectively).

* Salmonella isolates which couldn’t be We tested various additional quinolone antimicrobials of which some are indicated typed with the antisera panel in use Figure 1. Distribution of the study Salmonella isolates (n=198) according to MIC for ciprofloxacin for veterinary use only, however none of them performed satisfactorily.