Unusual antibiotic resistance pattern among blood culture isolates of Salmonella Paratyphi A

  • Rajan Prabhurajan Department of Microbiology, Research Laboratory for Oral and Systemic Health, Sree Balaji Dental College and Hospital, Bharath Institute of Higher Education and Research (BIHER), Chennai, India
  • R Mary Esther Selvam Department of Microbiology, ESIC Hospital, Chennai, Tamil Nadu, India
  • Kesavaram Padmavathy Department of Microbiology, Research Laboratory for Oral and Systemic Health, Sree Balaji Dental College and Hospital, Bharath Institute of Higher Education and Research (BIHER), Chennai, India
Keywords: DSC, ESBL, enteric fever, NAR, NAS, pefloxacin, Salmonella Paratyphi A

Abstract

Introduction: With increasing fluoroquinolone resistance, extended spectrum cephalosporins are recommended for the treatment of invasive Salmonella infections. However, Extended spectrum beta-lactamases (ESBL) producing Salmonella Paratyphi A causing enteric fever is on the rise and constitutes a major therapeutic challenge. Hence, we aimed to assess the incidence of ESBL production, fluoroquinolone resistance in S. Paratyphi A and to compare the fluoroquinolone resistance detection methods.

Methodology: Seventeen blood-culture isolates of S. Paratyphi A were tested for susceptibility to ampicillin, chloramphenicol, co-trimoxazole, streptomycin and tetracycline (ACCuST), fluoroquinolones, azithromycin and ceftriaxone by disk diffusion method. We compared and correlated between disk diffusion of ciprofloxacin and pefloxacin with ciprofloxacin MIC. Combined disk test was employed to determine ESBL production.

Results: In this study, 13(76.5%) isolates were nalidixic acid resistant (NAR), 16 (94.1%) were pefloxacin resistant, while 7 (41.2%), 9 (52.9%) exhibited resistance and intermediate susceptibility to ciprofloxacin respectively. The MIC50, MIC90 of ciprofloxacin was 1 µg/mL, 2 µg/mL respectively. Among the NAR, 76.92% were DSC (MIC 0.5-1 µg/mL) and 23.08% had an MIC of 2-4 µg/mL. Of note, 4 isolates with DSC were NAS. Of the 17 S. Paratyphi A isolates, 14 (82.4%) were ESBL producers and 11 (64.7%) isolates were ceftriaxone susceptible.

Conclusions: Multidrug resistant (AmpRChlRSxtR) S. Paratyphi A with combined resistance to fluoroquinolones and ESBL production is a cause of concern. We found S. Paratyphi A isolates with a relatively unusual phenotype: nalidixic acid susceptible but exhibited DSC; pefloxacin susceptible but ciprofloxacin resistant. Of note one multidrug resistant (AmpRChlRSxtR) isolate, an ESBL producer exhibited resistance to azithromycin, cephalosporins and fluoroquinolones but was susceptible to carbapenems and streptomycin.

Author Biography

Kesavaram Padmavathy, Department of Microbiology, Research Laboratory for Oral and Systemic Health, Sree Balaji Dental College and Hospital, Bharath Institute of Higher Education and Research (BIHER), Chennai, India

Assistant Professor, Dept of Microbiology

Published
2021-04-30
How to Cite
1.
Prabhurajan R, Selvam RME, Padmavathy K (2021) Unusual antibiotic resistance pattern among blood culture isolates of Salmonella Paratyphi A. J Infect Dev Ctries 15:579-583. doi: 10.3855/jidc.12336
Section
Brief Original Articles