Andreas Hoefer

Klebsiella pneumoniae sequence type 11 from companion animals bearing ArmA methyltransferase, DHA-1 β-lactamase, and QnrB4.

ABSTRACT Seven Klebsiella pneumoniae isolates from dogs and cats in Spain were found to be highly resistant to aminoglycosides, and ArmA methyltransferase was responsible for this phenotype. All isolates were typed by multilocus sequence typing (MLST) as ST11, a human epidemic clone reported worldwide and associated with, among others, OXA-48 and NDM carbapenemases. In the seven strains, armA was borne by an IncR plasmid, pB1025, of 50 kb. The isolates were found to coproduce DHA-1 and SHV-11 β-lactamases, as well as the QnrB4 resistance determinant. This first report of the ArmA methyltransferase in pets illustrates their importance as a reservoir for human multidrug-resistant K. pneumoniae.

A naturally occurring SNP in plasmid pB1000 produces a reversible increase in antibiotic resistance.

ABSTRACT ColE1 plasmids are small mobilizable replicons that play an important role in the spread of antibiotic resistance in Pasteurellaceae. In this study, we describe how a natural single nucleotide polymorphism (SNP) near the origin of replication of the ColE1-type plasmid pB1000 found in a Pasteurella multocida clinical isolate generates two independent plasmid variants able to coexist in the same cell simultaneously. Using the Haemophilus influenzae Rd KW20 strain as a model system, we combined antibiotic susceptibility tests, quantitative PCRs, competition assays, and experimental evolution to characterize the consequences of the coexistence of the pB1000 plasmid variants. This coexistence produced an increase of the total plasmid copy number (PCN) in the host bacteria, leading to a rise in both the antibiotic resistance level and the metabolic burden produced by pB1000. Using experimental evolution, we showed that in the presence of ampicillin, the bacteria maintained both plasmid variants for 300 generations. In the absence of antibiotics, on the other hand, the bacteria are capable of reverting to the single-plasmid genotype via the loss of one of the plasmid variants. Our results revealed how a single mutation in plasmid pB1000 provides the bacterial host with a mechanism to increase the PCN and, consequently, the ampicillin resistance level. Crucially, this mechanism can be rapidly reversed to avoid the extra cost entailed by the increased PCN in the absence of antibiotics.

Highly Tigecycline-Resistant Klebsiella pneumoniae Sequence Type 11 (ST11) and ST147 Isolates from Companion Animals

ABSTRACT In this study, we characterized two tigecycline-resistant Klebsiella pneumoniae isolates from dog urine samples. The isolates were genetically unrelated, belonging to sequence type 11 (ST11) and ST147, both classically related to human isolates. To the best of our knowledge, this is the first identification of tigecycline-resistant isolates from animals. We unveil here the worrisome circulation among animals of bacterial clones resistant to this last-resort antibiotic.

Compensatory evolution facilitates the acquisition of multiple plasmids in bacteria

The coexistence of multicopy plasmids is a common phenomenon. However, the evolutionary forces promoting these genotypes are poorly understood. In this study, we have analyzed multiple ColE1 plasmids (pB1000, pB1005 and pB1006) coexisting within Haemophilus influenzae RdKW20 in all possible combinations. When transformed into the naïve host, each plasmid type presented a particular copy number and produced a specific resistance profile and biological cost, whether alone or coexisting with the other plasmids. Therefore, there was no fitness advantage associated with plasmid coexistence that could explain these common plasmid associations in nature. Using experimental evolution, we showed how H. influenzae Rd was able to completely compensate the fitness cost produced by any of these plasmids. Crucially, once the bacterium has compensated for a first plasmid, the acquisition of new multicopy plasmid(s) did not produced any extra biological cost. We argue therefore that compensatory adaptation pave the way for the acquisition of multiple coexisting ColE1 plasmids. Importance Antibiotic resistance is a major concern for human and animal health. Plasmids play a major role in the acquisition and dissemination of antimicrobial resistance genes. In this report we investigate, for the first time, how plasmids are capable to cohabit stably in populations. This coexistence of plasmids is driven by compensatory evolution alleviating the cost of a first plasmid, which potentiates the acquisition of further plasmids at no extra cost. This phenomenon explains the high prevalence of plasmids coexistance in wild type bacteria, which generates multiresistant clones and contributes to the maintenance and spread of antibiotic resistance genes within bacterial populations.