Interactions between antibiotic resistance in soil microbial communities and coupled elemental cycles

Michael S. Strickland, Brian Badgley, Jeb Barrett, Katharine KnowltonVirginia Tech

@strickm27 www.stricklandresearch.net

McKenna (2013)

The age of antibiotic resistance

The burden of antibiotic resistance

•80% of U.S. antibiotic sales are for livestock (FDA 2011, Sarmah et al 2006)• 32.6 million lbs

•Globally, use is predicted to increase by 67% in the next 20y (Van Boeckel et al 2015)

• 40-95% of administered antibiotic is excreted! (Toth et al 2011)

• 13-31 million lbs of antibiotics enter the environment.

What are the consequences of antibiotic inputs on soil microbial composition and function?

Antibiotic effects on soil microbes• Bacterial community compositional shifts towards groups

indicative of resistance• Increase in antibiotic resistance gene (ARGs) abundance• Maintenance of antibiotic resistance may increase

metabolic demands

Schimel et al. (2007)

Focused on dairy operations

Antibiotic

Examining antibiotic effects• Nationwide observation of paired manure exposed

and reference sites.

Assessed soil parameters, bacterial community composition, ARG abundance and activity, mass specific respiration

High input

Reference siteGoogle Earth (2016)

Wepking et al. (In Review)

Change in bacterial community composition

• Increase in relative abundance of Firmicutes and -Proteobacteria𝛾• Environmental indicators of ARGs (Berendonk et al.

2015)• 25-fold increase in Acinetobacter

CDC (2013)

Change in ARG abundance

• ampC was ~400% greater under high inputs

• tetO was ~3,000% greater

Total ARG abundanceARG copies g soil-1

Implications for function

• 2-fold increase in mass specific respiration• Back of the envelope - ~4 metric ton ha-1 y-1 increase in

respired C

Conclusions• Cattle inputs can markedly shift bacterial

community composition and ARG abundance

• The maintenance of antibiotic resistance may have implications for ecosystem functions

• Can the maintenance of antibiotic resistance be directly linked to ecosystem function?

PirlimycinControl

Cephapirin+ No manure

S.C.A.R.E.

650 g manure m-2 month-1

562 kg manure year-1

S.C.A.R.E. Results• Still analyzing 13C data

Pul

se-c

hase

(May

201

5)

Pul

se-c

hase

(May

201

6)

July

201

5

Exp

. Sta

rt (O

ct 2

014)

S.C.A.R.E. Results

• Choice of antibiotic → 3.9 to 6.5 metric tons of C ha-1 y-1 difference.

Conclusions• Cattle inputs can markedly shift bacterial

community composition and ARG abundance

• The maintenance of antibiotic resistance may have implications for ecosystem functions

• Can the maintenance of antibiotic resistance be directly linked to ecosystem function?

• Antibiotic treatment regimes can induce change in soil respiration.

• Antibiotic effects can manifest rapidly and are dependent on the type of antibiotic administered.

• We must also be concerned with the effect antibiotics have on soil microbial communities and the ecosystem processes that these communities regulate.

Antibiotics and antibiotic resistance can have ecosystem implications

Thank you!

Strickland Lab:Carl WepkingKevan MinnickSteve McBrideJosh Franklin

Steffany YamadaBethany Avera

Brian BadgleyKatharine Knowlton

Jeb BarrettMatt HedinPartha Ray

Crystal Smitherman

Grant no. 2013-67019-21363

All the on-site personnel that sent soil!

@strickm27 www.stricklandresearch.net

ARG activity

Microbial function

Parameter weights

ARG activity

Fungi

Firmicutes

Total ARGs