An Arsenal of Multiple Antimicrobial Resistance, Toxins, and Virulence Factors in Gram-Negative Bacterial Isolates from Food – A Formidable Combination!

Abstract

Background

Infectious diseases caused by pathogenic members of the family Enterobacteriaceae cause mortality and morbidity in humans. These are mediated mainly via toxins or virulence factors in combination with multiple antimicrobial resistance (MAR) against antimicrobials intended to treat infections. Resistance can be transferred to other bacteria, possibly also in association with other resistance determinants and/or virulence properties. Food-borne bacterial infections are one of the major causes of infections in humans. The level of scientific information about foodborne bacterial infections in Ethiopia is very limited at best.

Methods

Bacteria were isolated from commercial dairy foods. These were cultured in appropriate media for identification at the family level (Enterobacteriaceae) based on Gram-negative, catalase-positive, oxidase-negative, and urease-negative phenotypes, followed by testing for the presence of virulence factors and resistance determinants to various antimicrobial classes using phenotypic and molecular tests.

Results

Twenty Gram-negative bacteria isolated from the foods were found to be resistant to almost all antimicrobials belonging to the phenicol, aminoglycoside, fluoroquinolone, monobactam, and β-lactam classes. All of them were multiple-drug-resistant. The resistance to the β-lactams was due to the production of β-lactamases and were also mostly resistant to some of the β-lactam/β-lactamase inhibitor combinations. Some isolates also contained toxins.

Conclusion

This small-scale study demonstrated the presence, in the isolates, of high levels of virulence factors and resistance to major antimicrobials that are in clinical use. Most treatment being empirical, there can be not only a high degree of treatment failure but also the likelihood for further development and dissemination of antimicrobial resistance. Since dairy foods are animal products, there is an urgent need to control animal-food-human transmission mechanisms, restrict antimicrobial use in animal agriculture, and improve clinical treatment from the usual empirical treatment to more targeted and effective treatment.

Keywords:

• dairy isolates
• gram-negative bacteria
• multiple antimicrobial resistance
• virulence
• β-lactamase inhibitor

Acknowledgments

No special funding was received for this study. The availability of AHRI facilities for this work is gratefully acknowledged. We thank Seble Worku for supplying/providing some reagents.

Disclosure

The authors declare no conflicts of interest in this work.