Introduction: emerging antimicrobial resistance mechanisms in the zoonotic foodborne pathogens Salmonella and Campylobacter

The interaction between prior antimicrobial drug exposure and resistance in human Salmonella infections

OBJECTIVES

The use of antimicrobial drugs for food animals selects for resistant non-typhoid Salmonella strains, but human consumption of antimicrobial drugs may also increase the risk of subsequent infection. The aim of this study was to determine the risk of salmonellosis attributable to human consumption of antimicrobial drugs in a case-control study of 22 602 laboratory-confirmed Salmonella infections, diagnosed in Denmark between 1997 and 2005.

METHODS

A population registry-based case-control study, using several Danish databases: the National Prescription Database; the National Registry for Enteric Pathogens; the Civil Registry System; and the Integrated Database on Labour Market Research.

RESULTS

Exposure to trimethoprim, sulphonamides, broad-spectrum penicillins, tetracyclines and fluoroquinolones, during the year prior to diagnosis, was associated with an increased risk of non-typhoid Salmonella infection. Overall, the highest risk was associated with the prior use of fluoroquinolones. This risk increased as the time window of exposure approached the infection date. Previous use of fluoroquinolones was associated with an odds ratio (OR) of 4.55 [95% confidence interval (CI): 3.78-5.47] for Salmonella serotypes other than Salmonella Typhimurium or Salmonella Enteritidis, an OR of 2.21 (95% CI: 1.70-2.86) for Salmonella Typhimurium and an OR of 2.07 (95% CI: 1.76-2.42) for Salmonella Enteritidis. In particular for fluoroquinolones, there was an interaction between the pathogen resistance pattern and a history of antibiotic drug use.

CONCLUSIONS

The increasing use of antibiotics, particularly fluoroquinolones, is likely to result in increased incidence of foodborne infections with drug-resistant Salmonella.

Isolation and identification of a Paenibacillus polymyxa strain that coproduces a novel lantibiotic and polymyxin

A new bacterial strain, displaying potent antimicrobial properties against gram-negative and gram-positive pathogenic bacteria, was isolated from food. Based on its phenotypical and biochemical properties as well as its 16S rRNA gene sequence, the bacterium was identified as Paenibacillus polymyxa and it was designated as strain OSY-DF. The antimicrobials produced by this strain were isolated from the fermentation broth and subsequently analyzed by liquid chromatography-mass spectrometry. Two antimicrobials were found: a known antibiotic, polymyxin E1, which is active against gram-negative bacteria, and an unknown 2,983-Da compound showing activity against gram-positive bacteria. The latter was purified to homogeneity, and its antimicrobial potency and proteinaceous nature were confirmed. The antimicrobial peptide, designated paenibacillin, is active against a broad range of food-borne pathogenic and spoilage bacteria, including Bacillus spp., Clostridium sporogenes, Lactobacillus spp., Lactococcus lactis, Leuconostoc mesenteroides, Listeria spp., Pediococcus cerevisiae, Staphylococcus aureus, and Streptococcus agalactiae. Furthermore, it possesses the physico-chemical properties of an ideal antimicrobial agent in terms of water solubility, thermal resistance, and stability against acid/alkali (pH 2.0 to 9.0) treatment. Edman degradation, mass spectroscopy, and nuclear magnetic resonance were used to sequence native and chemically modified paenibacillin. While details of the tentative sequence need to be elucidated in future work, the peptide was unequivocally characterized as a novel lantibiotic, with a high degree of posttranslational modifications. The coproduction of polymyxin E1 and a lantibiotic is a finding that has not been reported earlier. The new strain and associated peptide are potentially useful in food and medical applications.