# Results from the Survey of Antibiotic Resistance (SOAR) 2018–21 in Tunisia: data based on CLSI, EUCAST (dose-specific) and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints

## TL;DR

This study analyzed antibiotic resistance in bacteria causing respiratory infections in Tunisia, finding limited effective treatment options for Streptococcus pneumoniae.

## Contribution

The study compares antibiotic susceptibility using CLSI, EUCAST, and PK/PD breakpoints, revealing discrepancies in treatment guidance.

## Key findings

- Only 22.4% of S. pneumoniae isolates were penicillin-susceptible by CLSI/EUCAST low-dose breakpoints, but 89.7% by high-dose breakpoints.
- Ceftriaxone showed 100% susceptibility for both S. pneumoniae and H. influenzae according to CLSI and EUCAST guidelines.
- Most H. influenzae isolates were β-lactamase negative, with high susceptibility to most antibiotics except ampicillin and trimethoprim/sulfamethoxazole.

## Abstract

To determine the antibiotic susceptibility of community-acquired respiratory tract infection (CA-RTI) isolates of Streptococcus pneumoniae and Haemophilus influenzae collected in 2018–21 from two hospitals in Tunisia.

MICs were determined by CLSI broth microdilution, and susceptibility data were interpreted using CLSI, EUCAST (dose-specific) and pharmacokinetic/pharmacodynamic (PK/PD) breakpoints.

S. pneumoniae (n = 58) and H. influenzae (n = 71) isolates were collected; 22.4% of pneumococci were penicillin-susceptible by CLSI oral/EUCAST low-dose breakpoints, but 89.7% were susceptible by EUCAST high-dose/CLSI intravenous administration breakpoints. Susceptibility to ceftriaxone, levofloxacin and moxifloxacin was ≥91.4% by CLSI or PK/PD breakpoints which reduced to 82.8%–87.9% for amoxicillin, amoxicillin/clavulanic acid and cefotaxime. Tetracyclines, macrolides and trimethoprim/sulfamethoxazole were 41.4%–65.5% susceptible, with cefdinir and second-generation cephalosporins less active (24.1%–51.7% susceptible). EUCAST indicated ≥96.6% susceptibility only to high-dose ceftriaxone, moxifloxacin and high-dose levofloxacin. Most H. influenzae (66.2%) were β-lactamase negative, of which six and two isolates were ampicillin-resistant following EUCAST and CLSI criteria, respectively. Antibiotic susceptibility was ≥91.5% (CLSI) except for ampicillin (60.6%) and trimethoprim/sulfamethoxazole (77.5%). Susceptibility by EUCAST was lower than CLSI for most other antimicrobials, except for high dose amoxicillin/clavulanic acid (93.0% by EUCAST, 97.2% high dose PK/PD). Both CLSI and EUCAST showed 100% susceptibility to ceftriaxone.

Few therapeutic options with ≥90% susceptibility for the treatment of S. pneumoniae from CA-RTIs in Tunisia remain. Although H. influenzae isolates displayed higher susceptibility, only ceftriaxone provides 100% coverage for both species following CLSI and EUCAST guidelines. Continued surveillance is important for guiding empiric therapy.