Collateral sensitivity interactions between antibiotics depend on local abiotic conditions

Abstract

9Mutations conferring resistance to one antibiotic can increase (cross resistance) or 10 decrease (collateral sensitivity) resistance to others. Drug combinations displaying 11 collateral sensitivity could be used in treatments that slow resistance evolution. 12However, lab-to-clinic translation requires understanding whether collateral effects 13 are robust across different environmental conditions. Here, we isolated and 14 characterized resistant mutants of Escherichia coli using five antibiotics, before 15 measuring collateral effects on resistance to other antibiotics. During both isolation 16 and phenotyping, we varied conditions in ways relevant in nature (pH, temperature, 17 bile). This revealed local abiotic conditions modified expression of resistance against 18 both the antibiotic used during isolation and other antibiotics. Consequently, local 19 conditions influenced collateral sensitivity in two ways: by favouring different sets 20 of mutants (with different collateral sensitivities), and by modifying expression of 21 collateral effects for individual mutants. These results place collateral sensitivity in 22 the context of environmental variation, with important implications for translation 23 to real-world applications. 24 exposed to the same antibiotic sometimes acquire collateral sensitivity to another 48 antibiotic, and sometimes do not 10,11 . This can be explained by different mutations, 49 which vary in their phenotypic effects on resistance, spreading in different replicate 50 populations 11,12,14,15 . However, we know from past work that phenotypic effects of 51 antibiotic resistance mechanisms also vary strongly depending on local 52 environmental conditions [16][17][18] . For example, bile can upregulate efflux pumps 19 , zinc 53 can reduce the activity of aminoglycoside degrading enzymes 20 , and high 54 temperature can modulate the effects of rifampicin-resistance mutations on growth 55 in the absence of antibiotics 21 . This raises the possibility that local environmental 56 conditions could influence both the emergence of collateral sensitivity (by affecting 57 which of the possible pathways to resistance are most strongly selected during 58 antibiotic exposure) and its expression (by modifying the phenotypic effects of 59 resistance alleles when bacteria are exposed to a second antibiotic). To date, 60 research on collateral sensitivity interactions has focused on testing many 61 combinations of antibiotics 5,6,9,14 , multiple strains 10 , or many replicate populations 62 for individual antibiotic combinations 11 . Therefore, the role of local abiotic 63 conditions in the emergence and expression of collateral sensitivity interactions 64 remains unclear. Answering this question would improve our understanding of the 65 robustness of collateral sensitivity across different populations and environments. 66This would in turn boost our ability to predict pathogen responses to treatment 67 regimens that exploit collateral sensitivity interactions. 68 69To address these gaps in our knowle...

Evolutionary instability of collateral susceptibility networks in ciprofloxacin resistant clinical Escherichia coli strains

“…This is supported by reports using E. coli MG1655 (2) and Streptococcus pneumoniae (54) where this link was not observed. Taken together with a recent report demonstrating that collateral networks are dependent on environmental factors (17), our data support that collateral responses measured for combinations of host strains and newly acquired resistance determinants across non-standardized growth conditions serve as poor references for accurate predictions. To that end, future clinical application of collateral responses requires careful considerations of evolutionary stability, impact of biotic and abiotic factors on quantification and predictions of collateral effects as well as pharmacodynamics and pharmacokinetics of drug-bacteria combinations.…”

“…Taken together, these reports allow for careful optimism for future use of collateral networks as an antimicrobial resistance management strategy. However, with few exceptions (3) (17), the current body of literature rests on newly acquired resistance determinants upon which collateral networks are identified and characterized relative to a susceptible wild-type (WT) in an optimal environment as baseline. Thus, robust predictions of collateral networks are contingent on the evolutionary stability of the initial association between resistance determinants and bacterial hosts.…”