Dissemination of Multiresistant Bacteria : Their Selection, Transmission, Virulence and Resistance

Multiresistant bacteria are an emerging threat in modern medicine. Consumption of antimicrobial agents among humans, animals and in agriculture causes a selection of resistance genes. Dissemination of bacteria carrying resistance genes occurs both globally and locally, and hospital settings pose a special risk for spread when staff, environment and vulnerable patients interact. The overall aim of this thesis was to analyse underlying factors that facilitate the dissemination of multiresistant pathogenic bacteria in hospital settings. Clusters of resistant bacteria from six occasions were investigated. Vancomycin-Resistant Enterococci (VRE), Methicillin-Resistant Staphylococcus pseudintermedius (MSRP), ESBL-producing Escherichia coli and Klebsiella pneumoniae, and carbapenemase-producing Pseudomonas aeruginosa were analysed by a range of methods, from cultures on broth to PCR and whole genome sequencing. Type of resistance, clonality, virulence factors, mobile genetic elements, epidemiology, survival in the environment, and patient history were examined variously depending on study. The results showed that VRE resistance genes can be acquired during treatment with vancomycin. Furthermore, contamination of the hospital environment could quickly cause an outbreak, when patients are frequently relocated and exposition to contaminated rooms increase. Resistant bacteria emerging among companion animals, such as the dog-associated MRSP, can pose a zoonotic threat, when a virulent clone finds a new niche in humans. The ability of Gram-negative bacteria to survive in a hospital environment is probably better than expected, given the right prerequisites; incorrect use of sinks enabled the spread of ESBL-producing K. pneumoniae and carbapenemase-producing P. aeruginosa. Additionally, the survival on hospital associated materials was longer for ESBL-producing E. coli than the AmpC-producing counterpart, which could tell part of why ESBL-producing E. coli is increasing. Hence, the survival in the environment calls for consideration when choosing materials and equipment for hospitals and nursing homes. Exchange of bacteria occurs continuously between humans and our surroundings. Outbreaks of multiresistant bacteria are rare in Sweden but expose the weaknesses in healthcare when occurring. The organization, materials and equipment of hospitals facilitate the dissemination of resistant bacteria, as does animals and humans around us and even the genes in our own microbiota