Lyme disease was reproduced in specific pathogen-free beagle dogs by exposure to Borrelia burgdorferi-infected ticks (Ixodes dammini). Seroconversion and disease frequency were higher after exposure to infected adult ticks than to infected nymphs. Young pups developed clinical disease more readily than older dogs. The incubation period lasted 2-5 months. Acute recurrent lameness with fibrinopurulent arthritis was the dominant clinical sign. Dogs recovered but developed persistent mild polyarthritis. B. burgdorferi persisted in recovered dogs for at least 1 year. Isolation of B. burgdorferi and detection by polymerase chain reaction was most successful from skin biopsies at the site of the tick bite. Antibody to B. burgdorferi antigens was first detected by ELISA and Western blots by 4-6 weeks after exposure. High serum levels persisted during 17 months of observation. In contrast to infection from ticks, inoculation of dogs with cultured B. burgdorferi resulted in seroconversion with a shorter duration of antibody persistence and no clinical disease.

The genetic features of the antimicrobial resistance of a multidrug resistant Klebsiella pneumoniae strain harboring bla NDM-1 were investigated to increase our understanding of the evolution of NDM-1. The strain, KPX, came from a Taiwanese patient with a hospitalization history in New Delhi. Complete DNA sequencing was performed; and the genes responsible for antimicrobial resistance were systematically examined and isolated by library screening. KPX harbored two resistance plasmids, pKPX-1 and pKPX-2, which are 250-kb and 141-kb in size, respectively, with bla NDM-1 present on pKPX-1. The plasmid pKPX-1 contained genes associated with the IncR and IncF groups, while pKPX-2 belonged to the IncF family. Each plasmid carried multiple antimicrobial resistance genetic determinants. The gene responsible for resistance to carbapenems was found on pKPX-1 and that for resistance to aztreonam was found on pKPX-2. To our surprise, we discovered that bla NDM-1 exists on pKPX-1 as multiple copies in the form of tandem repeats. Amplification of bla NDM-1 was found to occur by duplication of an 8.6-kb unit, with the copy number of the repeat varying from colony to colony. This repeat sequence is identical to that of the pNDM-MAR except for two base substitutions. The copy number of bla NDM-1 of colonies under different conditions was assessed by Southern blotting and quantitative PCR. The bla NDM-1 sequence was maintained in the presence of the antimicrobial selection; however, removal of antimicrobial selection led to the emergence of susceptible bacterial populations with a reduced copy number or even the complete loss of the bla NDM-1 sequence. The dynamic nature of the NDM-1 sequence provides a strong argument for judicious use of the broad-spectrum antimicrobials in order to reduce the development and spread of antimicrobial resistance among pathogens.

In order to determine the prevalence of methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) colonization among adults in community settings in Taiwan and identify its risk factors, we conducted the present study. For a 3-month period, we enrolled all adults who attended mandatory health examinations at three medical centers and signed the informed consent. Nasal swabs were taken for the isolation of S. aureus. For each MRSA isolate, we performed multilocus sequence typing, identification of the staphylococcal cassette chromosome mec, tests for the presence of the Panton-Valentine leukocidin gene, and tests for drug susceptibilities. Risk factors for MRSA colonization were determined. The results indicated that the MRSA colonization rate among adults in the community settings in Taiwan was 3.8% (119/3,098). Most MRSA isolates belonged to sequence type 59 (84.0%). Independent risk factors for MRSA colonization included the presence of household members less than 7 years old (P < 0.0001) and the use of antibiotics within the past year (P ‫؍‬ 0.0031). Smoking appeared to be protective against MRSA colonization (P < 0.0001).Before the late 1990s, nearly all methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) infections occurred in patients with specific risk factors who were in health care facilities (31). However, the emergence of MRSA infections among previously healthy persons in community settings (without exposure to health care facilities) was noted thereafter (6, 31). Therefore, MRSA infections are now classified as health care-associated MRSA (HA-MRSA) infections and community-associated MRSA (CA-MRSA) infections (38).Strains responsible for CA-MRSA infections differ from those for HA-MRSA infections in several phenotypic and genetic features (1, 28). CA-MRSA strains carry type IV or V staphylococcal cassette chromosome mec (SCCmec) elements, are usually Panton-Valentine leukocidin (PVL) producing, and are not multidrug resistant; HA-MRSA strains carry type I, II, or III SCCmec elements, are usually not PVL producing, and are multidrug resistant (15,22,28).Initially, CA-MRSA infections were mostly reported in young children (36). However, as CA-MRSA infections became more common, infections were reported among people of all ages and contributed to the increase of communityassociated S. aureus infections with significance (25,29,36). MRSA colonization is an important risk factor for subsequent MRSA infection (30), so several studies in the United States have characterized the MRSA colonization rate in a community setting (13,16). These studies demonstrated that the nasal colonization rates among healthy children increased from In Taiwan, MRSA strains of sequence type 59 (ST59), determined by multilocus sequence typing (MLST) and carrying type IV or V SCCmec elements, were recently found to be the major strains of CA-MRSA (5, 7, 27). Other studies demonstrated that these CA-MRSA strains were responsible for the rapid increase in the number of CA-MRSA infections among children and adults ...

BackgroundOur understanding of the factors influencing the emergence, dissemination and global distribution of epidemic clones of bacteria is limited. ST59 is a major epidemic clone of community-associated MRSA in East Asia, responsible for extensive morbidity and mortality, but has a much lower prevalence in other parts of the world. The geographic origin of ST59 and its international routes of dissemination are unclear and disputed in the literature.ResultsTo investigate the origin and spread of the ST59 clone, we obtained whole genome sequences of isolates from four continents, sampled over more than a decade, and carried out a time-scaled phylogeographic analysis. We discover that two distinct ST59 clades emerged concurrently, in East Asia and the USA, but underwent clonal expansion at different times. The East Asia clade was strongly enriched for gene determinants associated with antibiotic resistance, consistent with regional differences in antibiotic usage. Both clones spread independently to Australia and Europe, and we found evidence of the persistence of multi-drug resistance following export from East Asia. Direct transfer of strains between Taiwan and the USA was not observed in either direction, consistent with geographic niche exclusion.ConclusionsOur results resolve a longstanding controversy regarding the origin of the ST59 clone, revealing the major global source and sink populations and routes for the spread of multi-drug resistant clones. Additionally, our findings indicate that diversification of the accessory genome of epidemic clones partly reflects region-specific patterns of antibiotic usage, which may influence bacterial fitness after transmission to different geographic locations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-016-1022-0) contains supplementary material, which is available to authorized users.

Genetic determinants of ablaNDM-1-positive, multidrug-resistant bacterial isolate that caused active infection was investigated by DNA sequencing. Two plasmids, pKOX_NDM1 and pKOX-R1, were identified for theKlebsiella oxytocastrain E718. Sequence annotation revealed ablaNDM-1gene in pKOX_NDM1 and two extended-spectrum β-lactamase producers (blaCTX-M-3andblaSHV-12) and a wide array of resistance genes in pKOX-R1. These findings highlight the difficulty in treating multidrug-resistant bacterial infections and the potential danger of emerging resistant enterobacteria.