# Identification and Antibiotic Resistance of Isolates from Poultry Meat and Poultry Meat By-Products Exhibiting Characteristic Salmonella Morphology on Chromogenic Agar

## TL;DR

This study found that chromogenic agar used to detect Salmonella in poultry meat often gives false positives and that many of the non-Salmonella bacteria found are resistant to multiple antibiotics.

## Contribution

The study reveals the low selectivity of chromogenic agar for Salmonella detection and highlights widespread antibiotic resistance in non-Salmonella isolates from poultry meat.

## Key findings

- Only 7% of isolates with Salmonella-like morphology were actual Salmonella.
- 66 non-Salmonella isolates showed multiple antibiotic resistances, mostly with MDR or XDR phenotypes.
- The study emphasizes the need for improved control measures in poultry meat production to prevent antibiotic-resistant bacteria spread.

## Abstract

Background/Objectives: The main objective of this research work was to identify and determine the antibiotic resistance of the false-positive isolates on chromogenic agar when analyzing Salmonella in chicken meat. Methods: A total of 234 samples of chicken meat (carcasses, cuts and preparations) were studied using buffered peptone water for primary enrichment, Rappaport–Vassiliadis soy broth for secondary enrichment and Salmonella Chromogen Agar Set as a selective solid medium. Colonies with a morphology characteristic of Salmonella (one isolate per sample) were identified by matrix-assisted laser desorption ionization and time-of-flight mass spectrometry (MALDI-TOF). Results: Colonies with a characteristic morphology of Salmonella were detected in 71 samples. Only five isolates (7.0% of the total) corresponded to the genus Salmonella. Other genera detected were Hafnia (three isolates; 4.2% of the total), Escherichia (22; 31.0%), Klebsiella (19; 26.8%), Proteus (6; 8.5%) and Pseudomonas (16; 22.5%). The 66 isolates of these last five genera were tested for susceptibility to a panel of 42 antibiotics of clinical importance by disc diffusion. All isolates presented multiple resistances, to between 4 and 29 antibiotics, all of them having a multi drug-resistant (MDR) phenotype except for one Pseudomonas strain, with an extensively drug-resistant (XDR) phenotype. Conclusions: These results highlight the low selectivity of this method, with the specific culture media under test, for the detection of Salmonella in poultry meat. The considerable prevalence of antibiotic resistance observed suggests a need to improve control measures throughout the poultry meat production chain to prevent this food from becoming a reservoir of bacteria with resistance to multiple antibiotics.