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Milner D.S.,University of Nottingham | Till R.,University of Nottingham | Cadby I.,University of Birmingham | Lovering A.L.,University of Birmingham | And 5 more authors.
PLoS Genetics | Year: 2014

Bdellovibrio bacteriovorus invade Gram-negative bacteria in a predatory process requiring Type IV pili (T4P) at a single invasive pole, and also glide on surfaces to locate prey. Ras-like G-protein MglA, working with MglB and RomR in the deltaproteobacterium Myxococcus xanthus, regulates adventurous gliding and T4P-mediated social motility at both M. xanthus cell poles. Our bioinformatic analyses suggested that the GTPase activating protein (GAP)-encoding gene mglB was lost in Bdellovibrio, but critical residues for MglABd GTP-binding are conserved. Deletion of mglABd abolished prey-invasion, but not gliding, and reduced T4P formation. MglABd interacted with a previously uncharacterised tetratricopeptide repeat (TPR) domain protein Bd2492, which we show localises at the single invasive pole and is required for predation. Bd2492 and RomR also interacted with cyclic-di-GMP-binding receptor CdgA, required for rapid prey-invasion. Bd2492, RomRBd and CdgA localize to the invasive pole and may facilitate MglA-docking. Bd2492 was encoded from an operon encoding a TamAB-like secretion system. The TamA protein and RomR were found, by gene deletion tests, to be essential for viability in both predatory and non-predatory modes. Control proteins, which regulate bipolar T4P-mediated social motility in swarming groups of deltaproteobacteria, have adapted in evolution to regulate the anti-social process of unipolar prey-invasion in the "lone-hunter" Bdellovibrio. Thus GTP-binding proteins and cyclic-di-GMP inputs combine at a regulatory hub, turning on prey-invasion and allowing invasion and killing of bacterial pathogens and consequent predatory growth of Bdellovibrio. © 2014. Source

Kautz M.J.M.,University of Delaware | Dvorzhinskiy A.,University of Delaware | Frye J.G.,Bacterial Epidemiology and Antimicrobial Resistance Research Unit | Stevenson N.,University of Delaware | Herson D.S.,University of Delaware
Applied and Environmental Microbiology | Year: 2013

Salmonella infection causes a self-limiting gastroenteritis in humans but can also result in a life-threatening invasive disease, especially in old, young, and/or immunocompromised patients. The prevalence of antimicrobial and multidrug-resistant Salmonella has increased worldwide since the 1980s. However, the impact of antimicrobial resistance on the pathogenicity of Salmonella strains is not well described. In our study, a microarray was used to screen for differences in gene expression between a parental strain and a strain of Salmonella enterica serovar Enteritidis with reduced susceptibility (SRS) to the widely used antimicrobial sanitizer dodecyltrimethylammonium chloride (DTAC). Three of the genes, associated with adhesion, invasion, and intracellular growth (fimA, csgG, and spvR), that showed differences in gene expression of 2-fold or greater were chosen for further study. Real-time reverse transcriptase PCR (real-time RT-PCR) was used to confirm the microarray data and to compare the expression levels of these genes in the parental strain and four independently derived SRS strains. All SRS strains showed lower levels of gene expression of fimA and csgG than those of the parental strain. Three of the four SRS strains showed lower levels of spvR gene expression while one SRS strain showed higher levels of spvR gene expression than those of the parental strain. Transmission electron microscopy determined that fimbriae were absent in the four SRS strains but copiously present in the parental strain. All four SRS strains demonstrated a significantly reduced ability to invade tissue culture cells compared to the parental strains, suggesting reduced pathogenicity of the SRS strains. © 2013, American Society for Microbiology. Source

Jackson C.R.,Bacterial Epidemiology and Antimicrobial Resistance Research Unit | Fedorka-Cray P.J.,Bacterial Epidemiology and Antimicrobial Resistance Research Unit | Davis J.A.,Bacterial Epidemiology and Antimicrobial Resistance Research Unit | Barrett J.B.,Bacterial Epidemiology and Antimicrobial Resistance Research Unit | And 3 more authors.
Journal of Applied Microbiology | Year: 2010

Aims: In this study, mechanisms of antimicrobial resistance and genetic relatedness among resistant enterococci from dogs and cats in the United States were determined. Methods and Results: Enterococci resistant to chloramphenicol, ciprofloxacin, erythromycin, gentamicin, kanamycin, streptomycin, lincomycin, quinupristin/dalfopristin and tetracycline were screened for the presence of 15 antimicrobial resistance genes. Five tetracycline resistance genes [tet(M), tet(O), tet(L), tet(S) and tet(U)] were detected with tet(M) accounting for approx. 60% (130/216) of tetracycline resistance; erm(B) was also widely distributed among 96% (43/45) of the erythromycin-resistant enterococci. Five aminoglycoside resistance genes were also detected among the kanamycin-resistant isolates with the majority of isolates (25/36; 69%) containing aph(3′)-IIIa. The bifunctional aminoglycoside resistance gene, aac(6′)-Ie-aph(2″)-Ia, was detected in gentamicin-resistant isolates and ant(6)-Ia in streptomycin-resistant isolates. The most common gene combination among enterococci from dogs (n = 11) was erm(B), aac(6′)-Ie-aph(2″)-Ia, aph(3′)-IIIa, tet(M), while tet(O), tet(L) were most common among cats (n = 18). Using pulsed-field gel electrophoresis (PFGE), isolates clustered according to enterococcal species, source and antimicrobial gene content and indistinguishable patterns were observed for some isolates from dogs and cats. Conclusion: Enterococci from dogs and cats may be a source of antimicrobial resistance genes. Significance and Impact of the Study: Dogs and cats may act as reservoirs of antimicrobial resistance genes that can be transferred from pets to people. Although host-specific ecovars of enterococcal species have been described, identical PFGE patterns suggest that enterococcal strains may be exchanged between these two animal species. © 2009 The Society for Applied Microbiology. No claim to US Government works. Source

Thitaram S.N.,Bacterial Epidemiology and Antimicrobial Resistance Research Unit | Frank J.F.,University of Georgia | Siragusa G.R.,Poultry Microbiological Safety and Processing Research Unit | Siragusa G.R.,Eurofins | And 9 more authors.
International Journal of Food Microbiology | Year: 2016

Clostridium difficile is commonly associated with a spectrum of disease in humans referred to as C. difficile-associated disease (CDAD) and use of antimicrobials is considered a risk factor for development of disease in humans. C. difficile can also inhabit healthy food animals and transmission to humans is possible. As a result of the complexity and cost of testing, C. difficile is rarely tested for antimicrobial susceptibility. A total of 376 C. difficile strains (94 each from swine and dairy feces, and 188 from beef cattle feces) were isolated from healthy food animals on farms during studies conducted by the National Animal Health Monitoring System. Using the Etest (AB Biodisk, Solna, Sweden), samples were tested for susceptibility to nine antimicrobials implicated as risk factors for CDAD (linezolid, amoxicillin-clavulanic acid, ampicillin, clindamycin, erythromycin, levofloxacin, metronidazole, rifampicin, and vancomycin). Vancomycin was active against all isolates of C. difficile (MIC90 = 3.0 μg/ml) while almost all isolates (n = 369; 98.1%) were resistant to levofloxacin. With the exception of vancomycin, resistance varied by animal species as follows: linezolid (8.5% resistance among swine versus 2.1 and 1.1% resistance among dairy and beef, respectively), clindamycin (56.4% resistance among swine versus 80% and 90.9% resistance among dairy and beef, respectively), and rifampicin (2.1% and 0% resistance among swine and dairy cattle isolates, respectively versus 14.3% resistance among beef isolates). Regardless of species, multiple drug resistance was observed most often to combinations of clindamycin and levofloxacin (n = 195; 51.9%) and ampicillin, clindamycin and levofloxacin (n = 41; 10.9%). The reason for the variability of resistance between animal species is unknown and requires further research. © 2016. Source

Ladely S.R.,U.S. Department of Agriculture | Meinersmann R.J.,Bacterial Epidemiology and Antimicrobial Resistance Research Unit | Plumblee J.R.,Bacterial Epidemiology and Antimicrobial Resistance Research Unit | Fedorka-Cray P.J.,North Carolina State University1060 William Moore DriveRaleigh 27607North Carolina
Journal of Food Safety | Year: 2016

To determine if Campylobacter isolation method influenced antimicrobial susceptibility results, the minimum inhibitory concentrations (MIC) of nine antimicrobials were compared for 291 pairs of Campylobacter isolates recovered from chicken carcass rinse samples using direct plating and an enrichment method. Among the isolates 64.1% were C. jejuni, 35.7% were C. coli, and 0.2% were C. lari. Direct plating yielded significantly less (P<0.05) C. coli (21.3%) compared to sample enrichment (50.2%). Antimicrobial resistance was most common for tetracycline (41.4%), nalidixic acid (26.3%), and ciprofloxacin (25.9%). Significantly more (P<0.05) C. coli were resistant to nalidixic acid, ciprofloxacin, gentamicin, azithromycin, and erythromycin as compared to C. jejuni isolates. Nonparametric bootstrap analysis of antimicrobial MICs showed no significant differences between direct plating and the enrichment method for any of the antimicrobials tested. These data indicate that bacterial isolation method can bias Campylobacter species recovery. However, isolation method did not significantly affect antimicrobial susceptibility results of C. jejuni or C. coli recovered from broiler carcasses. Practical Applications: To monitor trends in food safety and public health, antimicrobial susceptibility testing of Campylobacter derived from poultry products and infected patients has become common practice in both regulatory food safety and public health programs. Various methods have been employed for Campylobacter recovery including direct plating for enumeration of contamination levels and enrichment protocols for detection of low numbers or injured cells. This study was conducted to determine if the method of Campylobacter isolation from chicken carcass rinsate, direct plating or enrichment, influences antimicrobial susceptibility testing results. © 2016 Wiley Periodicals, Inc. Source

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