Chemical Communication of Antibiotic Resistance by a Highly Resistant Subpopulation of Bacterial Cells

Abstract

The overall antibiotic resistance of a bacterial population results from the combination of a wide range of susceptibilities displayed by subsets of bacterial cells. Bacterial heteroresistance to antibiotics has been documented for several opportunistic Gram-negative bacteria, but the mechanism of heteroresistance is unclear. We use Burkholderia cenocepacia as a model opportunistic bacterium to investigate the implications of heterogeneity in the response to the antimicrobial peptide polymyxin B (PmB) and also other bactericidal antibiotics. Here, we report that B. cenocepacia is heteroresistant to PmB. Population analysis profiling also identified B. cenocepacia subpopulations arising from a seemingly homogenous culture that are resistant to higher levels of polymyxin B than the rest of the cells in the culture, and can protect the more sensitive cells from killing, as well as sensitive bacteria from other species, such as Pseudomonas aeruginosa and Escherichia coli. Communication of resistance depended on upregulation of putrescine synthesis and YceI, a widely conserved low-molecular weight secreted protein. Deletion of genes for the synthesis of putrescine and YceI abrogate protection, while pharmacologic inhibition of putrescine synthesis reduced resistance to polymyxin B. Polyamines and YceI were also required for heteroresistance of B. cenocepacia to various bactericidal antibiotics. We propose that putrescine and YceI resemble "danger" infochemicals whose increased production by a bacterial subpopulation, becoming more resistant to bactericidal antibiotics, communicates higher level of resistance to more sensitive members of the population of the same or different species.

Communication is Key: Do Bacteria use a Universal ‘Language‘ to Spread Resistance?

“…Given that polyamines are being produced and utilized by most of the bacterial species, it could be speculated that the excessive secretion of putrescine can communicate resistance to antibiotic-sensitive cells from species other than B. cenocepacia. Interestingly, this notion was supported by the protection of Pseudomonas aeruginosa PAO1 from the action of polymyxin B by putrescine released from B. cenocepacia in direct coculture [7]. Putrescine secretion was stimulated by the exposure to polymyxin B as a result of the overexpression of the ornithine decarboxylase enzyme, supporting its role in response to the antibiotic.…”

“…Recently, putrescine released from bacteria was shown to directly communicate antibiotic resistance between different bacterial cells within the same or different species [7]. Putrescine released in excess from a highly resistant subset of the population of the extremely antibiotic-resistant environmental bacterium Burkholderia cenocepacia [7].…”

“…Putrescine released in excess from a highly resistant subset of the population of the extremely antibiotic-resistant environmental bacterium Burkholderia cenocepacia [7]. Given that polyamines are being produced and utilized by most of the bacterial species, it could be speculated that the excessive secretion of putrescine can communicate resistance to antibiotic-sensitive cells from species other than B. cenocepacia.…”

“…Putrescine secretion was stimulated by the exposure to polymyxin B as a result of the overexpression of the ornithine decarboxylase enzyme, supporting its role in response to the antibiotic. Putrescine could be involved in similar communication of resistance against other antibiotics, especially bactericidal antibiotics such as the fluoroquinolone norfloxacin, the b-lactam ceftazidime and rifampicin [7].…”

“…The filtered supernatant of an overnight culture of a highly resistant subpopulation of B. cenocepacia in polymyxin B communicated higher-level resistance to physically less distant polymyxin-resistant mutant of B. cenocepacia and three different E. coli strains. This volatile-dependant protection was proposed to be attributed to the overexpression of putrescine in response to polymyxin B [7], owing to the volatile nature of polyamines [16].…”