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Background The emergence of macrolide and tetracycline resistance within Pasteurella multocida isolated from feedlot cattle and the dominance of ST394 in Australia was reported recently. Objectives To establish the genetic context of the resistance genes in P. multocida 17BRD-035, the ST394 reference genome, and conduct a molecular risk assessment of their ability to disperse laterally. Methods A bioinformatic analysis of the P. multocida 17BRD-035 genome was conducted to determine if integrative conjugative elements (ICEs) carrying resistance genes, which hamper antibiotic treatment options locally, are in circulation in Australian feedlots. Results A novel element, ICE- Pmu ST394, was characterized in P. multocida 17BRD-035. It was also identified in three other isolates (two ST394s and a ST125) in Australia and is likely present in a genome representing P. multocida ST79 from the USA. ICE- Pmu ST394 houses a resistance module carrying two variants of the bla ROB gene, bla ROB-1 and bla ROB-13, and the macrolide esterase gene, estT. The resistance gene combination on ICE- Pmu ST394 confers resistance to ampicillin and tilmicosin, but not to tulathromycin and tildipirosin. Our analysis suggests that ICE- Pmu ST394 is circulating both by clonal expansion and horizontal transfer but is currently restricted to a single feedlot in Australia. Conclusions ICE- Pmu ST394 carries a limited number of unusual antimicrobial resistance genes but has hotspots that facilitate genomic recombination. The element is therefore amenable to hosting more resistance genes, and therefore its presence (or dispersal) should be regularly monitored. The element has a unique molecular marker, which could be exploited for genomic surveillance purposes locally and globally. [ABSTRACT FROM AUTHOR]

Antimicrobial-resistant Klebsiella pneumoniae is one of the predominant pathogens in healthcare settings. However, the prevalence and resistome of this organism within residential aged care facilities (RACFs), which are potential hotspots for antimicrobial resistance, remain unexplored. Here, we provide a phenotypic and molecular characterization of antimicrobial-resistant K. pneumoniae isolated from RACFs. K. pneumoniae was isolated from urine, faecal and wastewater samples and facility swabs. The antimicrobial susceptibility profiles of all the isolates were determined and the genomic basis for resistance was explored with whole-genome sequencing on a subset of isolates. A total of 147 K. pneumoniae were isolated, displaying resistance against multiple antimicrobials. Genotypic analysis revealed the presence of beta-lactamases and the ciprofloxacin-resistance determinant QnrB4 but failed to confirm the basis for the observed cephalosporin resistance. Clonal spread of the multidrug-resistant, widely disseminated sequence types 323 and 661 was observed. This study was the first to examine the resistome of K. pneumoniae isolates from RACFs and demonstrated a complexity between genotypic and phenotypic antimicrobial resistance. The intra-facility dissemination and persistence of multidrug-resistant clones is concerning, given that residents are particularly vulnerable to antimicrobial resistant infections, and it highlights the need for continued surveillance and interventions to reduce the risk of outbreaks. [ABSTRACT FROM AUTHOR]

Many bacteria are able to survive in the presence of antibiotics in part because they possess pumps that can remove a broad range of small molecules; here, the structure of one such pump, AcrAB-TolC, is determined using X-ray crystallography and cryo-electron microscopy. AcrAB-TolC efflux pump structure Many bacteria are able to survive in the presence of antibiotics and other toxic compounds because they possess versatile energy-dependent transmembrane pumps. For example, the AcrAB-TolC efflux pump, which spans the inner and outer membranes of the bacterium, is able to transport a broad range of structurally unrelated small molecules/drugs out of some Gram-negative bacteria. The pump is comprised of an outer-membrane channel (TolC), a secondary transporter (AcrB; located in the inner membrane), and AcrA, a periplasmic protein that acts as a bridge for these two integral membrane proteins. In this paper, the authors solve an X-ray crystal structure of AcrB bound to AcrZ (a small protein that appears to alter the substrate preferences of AcrB) and a cryo-EM structure of the entire 771 kDa efflux pump. The capacity of numerous bacterial species to tolerate antibiotics and other toxic compounds arises in part from the activity of energy-dependent transporters. In Gram-negative bacteria, many of these transporters form multicomponent 'pumps' that span both inner and outer membranes and are driven energetically by a primary or secondary transporter component.sup.1,2,3,4,5,6,7. A model system for such a pump is the acridine resistance complex of Escherichia coli.sup.1. This pump assembly comprises the outer-membrane channel TolC, the secondary transporter AcrB located in the inner membrane, and the periplasmic AcrA, which bridges these two integral membrane proteins. The AcrAB-TolC efflux pump is able to transport vectorially a diverse array of compounds with little chemical similarity, thus conferring resistance to a broad spectrum of antibiotics. Homologous complexes are found in many Gram-negative species, including in animal and plant pathogens. Crystal structures are available for the individual components of the pump.sup.2,3,4,5,6,7 and have provided insights into substrate recognition, energy coupling and the transduction of conformational changes associated with the transport process. However, how the subunits are organized in the pump, their stoichiometry and the details of their interactions are not known. Here we present the pseudo-atomic structure of a complete multidrug efflux pump in complex with a modulatory protein partner.sup.8 from E. coli. The model defines the quaternary organization of the pump, identifies key domain interactions, and suggests a cooperative process for channel assembly and opening. These findings illuminate the basis for drug resistance in numerous pathogenic bacterial species., Author(s): Dijun Du [sup.1] , Zhao Wang [sup.2] , Nathan R. James [sup.1] , Jarrod E. Voss [sup.1] , Ewa Klimont [sup.1] , Thelma Ohene-Agyei [sup.3] , Henrietta Venter [sup.4] [...]