Infection and drug resistance
Trimethoprim-Sulfamethoxazole and Azithromycin Resistance in Salmonella and Shigella: Genotype-Phenotype Concordance and Integron-MDR Association
By Pourmahdi-Torghabeh N, Izadi N, Boroumand Alipour M and 2 others.
Abstract
Background
Rising antimicrobial resistance in Salmonella and Shigella narrows therapeutic options, especially resistance to first-line agents like trimethoprim‑sulfamethoxazole and azithromycin.
Methods
We retrospectively analyzed 156 archived clinical isolates (Shigella n=108; Salmonella n=48) originally recovered from stool specimens collected between January 2017 and December 2020. Isolates were re-evaluated in a blinded manner using phenotypic susceptibility testing and PCR detection of dfrA1, sul1, ermB, mphA, and class 1 integron (IntI1).
Results
S. sonnei was the predominant species (50.6%). Among Shigella and Salmonella isolates, resistance to trimethoprim-sulfamethoxazole and azithromycin was observed in 97.2% and 67.6% versus 16.7% and 20.8%, respectively. dfrA1 was detected in 97.2% of Shigella and 10.4% of Salmonella, while sul1 was detected in 58.3% and 14.8%, respectively. mphA was detected in 58.3% of Shigella but was absent in Salmonella, whereas ermB was detected in 0.04% and 58.3%, respectively. The PPV and NPV of ermB for phenotypic azithromycin resistance were 33.3% and 100%, respectively (κ=0.25, P<0.008). 20 Salmonella and two Shigella isolates harboring resistance-associated determinants were susceptible to azithromycin, while five Salmonella isolates with related genotypes remained susceptible to trimethoprim-sulfamethoxazole. MDR was observed in 55.6% of Shigella and 4.2% of Salmonella and was associated with IntI1 (χ2=31.99, P<0.001; Cramer's V=0.45).