Origins of Resistance and Resistance

Transfer: Food-Producing Animals.

Chris Teale, AHVLA.

Origins of Resistance….

• MutationB h i h d t i d– Brachyspira hyodysenteriae and macrolide and pleuromutilin resistance.Campylobacter spp and fluoroquinolone– Campylobacter spp and fluoroquinolone resistance.

– Salmonella and fluoroquinolone– Salmonella and fluoroquinolone resistance

• No need for anything extraneous;• No need for anything extraneous; bacterial spontaneous mutations –then antimicrobial use selectsthen antimicrobial use selects resistant sub-population.

Transfer of Resistance.

• Rare or unusual mutations in l f i idAbattoir clones of organisms can provide

a useful means of tracing Abattoir Worker.

spread...• Denmark; cluster of 27 cases of• Denmark; cluster of 27 cases of

S. Typhimurium DT104 infection , ll ith t ti i thN all with same rare mutation in the

gyrase gene.Traced back to pigs Nurse.

on one farm.

Transfer of Resistance.

• Types of transfer.....– Direct contact.– Food borne spread.p– Secondary spread.

Origins of Resistance…..

• Acquisition of resistance h i b b t imechanisms by bacteria.

– Enzymes; may modify target or y y y gmodify antimicrobial.

– Aminoglycoside modifying enzymesAminoglycoside modifying enzymes in Salmonella.

– Strains from different– Strains from different epidemiological niches in contact provides opportunities for geneticprovides opportunities for genetic exchange.

Transfer of Resistance.

• AAC(3)IV– Aminoglycoside modifying enzyme.– Aminoglycoside acetyltransferase.g y y– Confers resistance to gentamicin

and apramycinand apramycin.– E. coli in calves → S. Typhimurium

in calves → E coli S Typhimuriumin calves → E. coli, S. Typhimurium, Kl. pneumoniae hospitals in BelgiumBelgium.

Evidence that AAC(3)IV emerged because ofEvidence that AAC(3)IV emerged because of veterinary use of apramycin rather than use of gentamicin in man:g

• -incidence of resistance in human and animal populations.AAC(3)IV id d i h h• -AAC(3)IV not widespread in other human

enterobacteriaceae.• -AAC(3)IV resistance gene linked to hphB• -AAC(3)IV resistance gene linked to hphB

gene encoding enzyme hygromycin B phosphotransferase, which confers resistance to the veterinary drug hygromycin B (also an aminoglycoside.....but is active as an anthelmintic).an anthelmintic).

Transfer of Resistance.

• AAC(3)II– Aminoglycoside modifying enzyme.– Aminoglycoside acetyltransferase.g y y– Confers resistance to gentamicin

but not apramycin.....but not apramycin.– Widespread in French hospitals in

the 1970s Limited diffusion tothe 1970s..... Limited diffusion to calves in western France.

Origins of Resistance......

• Salmonella Typhimurium DT 104.– tetR; unusual in Salmonellas....

mainly in Vibrio spp.– floR; first detected in a fish

pathogen.p g– Ampicillin resistance BLAcarb2; often

found in Pseudomonas spp.found in Pseudomonas spp.

Origins of Resistance…..

• Efflux pumps…– Activation of efflux pumps– Removal of antimicrobial from

bacterial cell.• Alternative metabolic pathways• Alternative metabolic pathways…

– Folate metabolism

Origins of Resistance….

• Many antimicrobials derived from bacteriabacteria.

• These possess resistance to the ti i bi l th dantimicrobial they produce.

• Therefore many resistance genes already exist in nature…

• Growth promoter avoparcin; DNA p p ;related to resistance cluster detected in product (Lu et al. 2004).p ( )

Strains of E. coli

POULTRY E. coli STRAINSHUMAN E. coli STRAINS

Scenarios;

Poultry strain colonises humans.

Poultry strain transiently colonises humansPoultry strain transiently colonises humans.

Poultry strain passes through human intestine.

Poultry strain transfers resistance to human strain while “passing through”.

12

Gene Transfer and Conjugation...

• vanA resistance gene – confers resistance to vancomycin and the formerresistance to vancomycin and the former growth promoter avoparcin.E f i f i l• Enterococcus faecium from animals given to human volunteers. Resistance gene transferred from animal E. faecium to human E. faecium, without any antibiotic use and during transient colonisation of the human intestine by the animal strain (Lester et al. 2004).

13

Common Epidemiological Pool.

• Same strain in:– Animals e.g. poultry– Meat produced from those animals.p– Humans

Exchange between the poolsExchange between the pools.• Direction of transfer?

– Prevalence in different hosts.– Exposure– Exposure.– Attribution rate.

14

– Vegetarians.

Evidence…. (EFSA Biohaz Opinion).

• Few studies describe clear evidence of direct transmission of ESBL E. coli from food-producing p ganimals or food to man.

• Data does exist regarding common clones of ESBL E. li i h d f d d i i l idicoli in humans and food-producing animals, providing

indirect evidence of transmission.• Limited evidence for spread of ESBL E coli via directLimited evidence for spread of ESBL E. coli via direct

contact with animals or indirectly via the environment. Nevertheless, people working with poultry have a higher i k f i t ti l i f ESBL E li (30% ltrisk for intestinal carriage of ESBL E. coli (30% poultry

farmers had ESBL bacteria; versus 5% general population Dierikx et al. 2010).p p )

General Bacterial Organisation:General Bacterial Organisation:

• The resistance gene.• The plasmid carrying the resistance gene.• The bacterial isolate.The bacterial isolate.

16

ESBLs hydrolyse the beta-lactam ring of penicillins and cephalosporins:penicillins and cephalosporins:

SS

H2O

NO

O OHNH

O

17

Overdevest Dutch retail Meat Survey:Overdevest Dutch retail Meat Survey:

• Chicken 89 samples• Beef 85 samplesBeef 85 samples• Pork 57 samples.• ESBL E. coli prevalence:

– Chicken 80%Chicken 80%– Beef 5%

P k 2%– Pork 2%

18

Overdevest et al.

• Compare genes, plasmids, bacterium.– Same gene (CTX-M-1, TEM-52) 30%– Same gene, same plasmid 19-20%g , p– Same gene, same plasmid, same strain of

E coli 11%E. coli 11%– c. 1 in 3 patients had a poultry-associated (PA) ESBL– c. 1 in 5 patients had a PA ESBL encoded by a PA

plasmid (pMLST)– c. 1 in 10 patients had a PA ESBL encoded by a PA

plasmid in a PA E coli strainplasmid in a PA E. coli strain

Overdevest – Conclusions.

• Extensive reservoir of ESBL genes in poultry, shown from on-farm studiesshown from on farm studies.

• Most E. coli strains containing the ESBL genes CTX-M-1 or TEM-52 belong to clustersCTX M 1 or TEM 52 belong to clusters containing isolates from both sources.

• Suggests contamination of chicken meat andSuggests contamination of chicken meat and appearance of ESBL genes in humans are related.

• Cross-transmission in hospitals in Holland controlled effectively, therefore acquisition from y, qfood more easily detected.

• Circumstantial evidence for an animal reservoir

20for a substantial part of ESBL genes in humans.

MRSA ST398.

• Rarer types of resistance again allow id i l i l t iepidemiological tracing....

• Portugal....g• Isolates resistant to clindamycin, but

susceptible to erythromycinsusceptible to erythromycin.• Plasmid; similar in a human clinical

isolate and an isolate from a pig.

MRSA ST398

• Livestock-associated MRSA.

G t l 2012Geenen et al.2012

ESBL E. coli......