Research Article: Strong correlation of total phenotypic resistance of samples from household environments and the prevalence of class 1 integrons suggests for the use of the relative prevalence of intI1 as a screening tool for multi-resistance

Date Published: June 13, 2019

Publisher: Public Library of Science

Author(s): R. Lucassen, L. Rehberg, M. Heyden, D. Bockmühl, Andrew C. Singer.


One of the biggest challenges of health care systems worldwide is the increasing number of pathogenic bacteria resistant to a growing number of antibiotics. In this respect, class 1 integrons which are part of mobile genetic elements can confer several phenotypes including resistance to a broad range of antibiotic classes, heavy metals and biocides. They are linked to common resistance genes and have penetrated pathogenic and commensal bacteria likewise. Therefore its relative prevalence can be a proxy for antimicrobial resistance and anthropogenic pollution. Household environments are areas with a high influx of bacteria from humans, animals and foods, and biocides and detergents are frequently used. In this study we aimed to investigate the relative prevalence of class 1 integrons in household environments, in relation to the number of antibiotic and benzalkonium chloride resistant phenotypes of a sample point, for the validation of the relative prevalence of class 1 integrons as a screening tool for multi-resistance. Kitchen sink and bathroom sink U-bends, dishwasher, washing machines and toothbrushes of 28 households were probed. Copies /mL of class 1 integron integrase gene and 16SrDNA gene were determined by qPCR and bacteria of the respective sample were isolated on ampicillin selective agar plates, followed by the determination of the species and phenotypic resistance profiles. The relative prevalence of class 1 integrons in relation to 16SrDNA was calculated and correlated to phenotypic resistance. Our findings show a high relative prevalence of class 1 integrons in water reticulation systems of household environments and in particular shower U-bends. Furthermore, prevalence of class 1 integrons correlates strongly (rs = 0.95) with total phenotypic resistance at a sample point and suggest that a standardized assay determining the relative prevalence of class 1 integrons could be used as a useful screening tool in the assessment of multi-resistance in environmental samples.

Partial Text

One of the biggest challenges of health care systems worldwide is the increasing number of pathogenic bacteria resistant to a growing number of antibiotics. This process is even more critical since the number of new antibiotics developed, decreased from 19 between 1980 and 1984 to six between 2010 and 2014 [1]. Pseudomonas aeruginosa for example is a common cause for bloodstream, urinary tract, and surgical-site infections. In the United States 13% of health care–associated P. aeruginosa infections per year are multidrug resistant and 400 deaths per year are attributed to these infections [2]. Enterobacteriaceae resistant to cephalosporin antibiotics are responsible for 1700 deaths per year of health care–associated infections and some extended spectrum ß-lactamase (ESBL)-producing Enterobacteriaceae are resistant to nearly all antibiotics of the penicillin and cephalosporin classes [2]. This list of bacteria resistant to even the latest generation of antibiotics is growing. Causes of this antibiotic resistant crisis are the overuse and inappropriate prescription of antibiotics in healthcare and the extensive use as growth supplements in livestock [1]. Furthermore a role of biocides in this process has been discussed. Mechanisms by which biocides can effect antibiotic resistance are commonalities of target sites between biocides and antibiotics that lead to a selection of mutants and the emergence of cross-resistance, the co-selection and persistence of antibiotic-resistant strains by sub-inhibitory concentrations of biocides and antiseptics as well as the primary antibiotic and the selection of multidrug-resistant strains through polygamous mechanisms such as efflux pumps [3].

Previous studies established a link between the use of detergents and biocides (in particular QACs) and the occurrence of class 1 integrons. Furthermore class 1 integrons and resistant bacteria have been described to be present in the influx and efflux of WWTP and river sediments [4,5,19] but no studies on their distribution in households, particularly in relation to the simultaneous occurrence of phenotypic resistant and multi-resistant bacteria, are present. It has also been shown that washing machines, dishwashers and U-bends provide an aqueous environment with constant nutrient supply which promotes bacterial growth and the formation of biofilms [26,27]. Moreover, these environments have a substantial influx of bacteria from humans, animals or food origin, as well as biocides and detergents from cleaning, disinfecting and personal care products. Biocides and Detergents might create a highly selective environment for resistant bacteria and could promote their persistence.