Antibiotic resistance

and probiotics

P. Courvalin

The two types of resistanceThe two types of resistance

. Intrinsic or natural (insensitivity):- present in all the strains of the genus/species

- not transferable- defines the spectrum of activity of an antibiotic

. Acquired: - exogenous gene - mutation

Probiotics: Antibiotic multiresistance and safetyProbiotics: Antibiotic multiresistance and safety

. Pros: - co-administration with antibiotics

. Cons: - transfer of resistance to human bacterial pathogens

. directly

. indirectly via the commensal flora - acquisition of resistance from human commensals

- shortage of antibiotics in case of infection

Resistance mechanisms

Bacterial genome

Plasmid transfer by conjugation

Intra- and Inter-cellular mobility of Tn916

Tn916

plasmid

chromosome

Integration(Int)

Excision(Int + Xis)

Integration(Int)

Donor Recipient

Transfer(Tra)

Combinatorial genetics of antibiotic resistance

Vector

Bacteria

Plasmids

Transposons

Host

Mammals

Bacteria

Replicons

Potential for spread of resistance genesPotential for spread of resistance genes

. High: - gene carried by a mobile genetic element (self-transferable

plasmid or transposon)

. Low: - chromosomal gene(s) responsible for insensitivity - present in all the strains of the genus/species - absence of in vitro/in vivo transfer - absence of known acquired genes - genus/species specific gene - co-localisation with chromosomal genes - flanking sequences:

. house-keeping genes

. no mobile genetic element

Phenotype

SusceptibleResistant

Transferability

Yes No

Acquired genes

Yes No

Insensitivity or mutation

No convincing evidence Convincing evidence

OKNot OK

Algorithm for decision making

Antibiotic resistance in Bacillus clausiiAntibiotic resistance in Bacillus clausii

Resistance to No of resistant strains

PenicillinsCephalosporinsAminoglycosides(kanamycin, tobramycin, amikacin)

MacrolidesTetracyclinesChloramphenicolRifampicin

44

SIN

4T4

NR

Susceptible to carbapenems, co-trimoxazole, fluoroquinolones, gentamicin, glycopeptides, oxazolidinones, streptogramins

Risk assessment of resistance disseminationRisk assessment of resistance dissemination

. Identification of the resistance genes- cloning and deduced sequence comparison

. Characterisation of the biochemical mechanisms

. Elucidation of the genetic basis- co-localisation with a chromosomal gene

- sequence analysis of the flanking DNA

. Attempts of in vitro resistance transfer to:- Enterococcus faecalis and Enterococcus faecium- Bacillus subtilis

The aadD2 genomic environment

aadD2 blaI blaR blaZ ytrA gntR

ABC Transporter

12323073

4322 3552 3477 3097 1176 181

Antibiotic resistance in Bacillus clausiiAntibiotic resistance in Bacillus clausii

Resistance to Mechanism Known gene Genetic basis Presence inref. strains

Penicillins Inactivation No Chromosome +

Cephalosporins Inactivation No Chromosome +

Aminoglycosides Inactivation No Chromosome +(kanamycin, tobramycin, amikacin)

Macrolides Target modification No Chromosome +

Tetracyclines ? ? ? -

Chloramphenicol Inactivation No Chromosome -

Rifampicin Target modification Mutation Chromosome -

R genes - not located on a plasmid (Tc?) - not transferable in vitro

AcknowledgementsAcknowledgements

. Service de Microbiologie, CHU Côte de Nacre, CaenRoland Leclercq, Bülent Bozdogan, Sébastien Galopin

. Unité des Agents Antibactériens, Institut Pasteur, ParisGuy Gerbaud