Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Doctorat en sciences médicales / info:eu-repo/semantics/nonPublished

Colistin, also known as polymyxin E, is antibiotics active against most of Gram-negative bacteria. In the pas decade, emergency of multidrug-resistant bacteria led to increase of colistin administration as a last resort antibiotic for human infections. The first plasmid-mediated colistin resistance gene mcr-1 was identified in 2015 in animals in China and after first detection, additional mcr genes: mcr-2, mcr-3, mcr-4, mcr-5, mcr-6, mcr-7 a mcr-8 were described throughout the world. The aim of this thesis was to clarify whether there is horizontal transmission colistin resistance encoded by the mcr genes in gram-negative bacteria isolated from the environment, animals and their breeding and food. The mcr-1 gene was detected in 2 strains Escherichia coli isolated from waste water. The mcr-4 gene was detected in 1 strain Shewanella putrefaciens isolate obtained from the lake. The environment is the most important source and way of spreading this type of resistance in the Czech Republic.

This study deals with the nature and characteristics of the Gram negative bacterial flora of the intestine of the domestic pigeon. Columba livia was selected for this study because of the abundance of this species around the Classroom building on the University of the Pacific campus.

Aerobic Gram negative bacteria such as Pseudomonas putida were reported to possess class A ATCases and to have a M.W. of 360 kD. The nucleotide sequence of the P. putida pyrBC was determined to answer this question once and for all. The expected regulatory gene was not found. It is shown that the P. putida pyrB gene is overlapped by pyrC by 4 bp. The P.putida pyrB is 1005 bp (335 aa) in length and the pyrC is 1275 bp (425 aa) long. Both of these genes complement E. coli mutants with their respective genotypes. Another finding borne out from the sequence is an effector binding site at the N-terminus of pyrB of P. putIda. The binding site shows that effectors compete with carbamoylphosphate for the active site. In this dissertation, it is shown that the ATCase of P.putida is a trimer of M.W. of 109 kD (3 x 36.4 kD) and that the gene encoding pyrB is overlapped by the pyrC gene which encodes DHOase. It is also shown that the pyrBC encoded enzymes copurify as a dodecameric complex with a M.W. of 484 kD.

Central nervous system (CNS) infection with Morganella morganii is very rare. We describe a 38-year-old female patient with frontal brain abscess caused by M morganii who was unsuccessfully treated. We also review all reported cases of Morganella CNS infections with an emphasis on treatment modalities and outcomes. Aggressive surgical management and appropriate antimicrobial therapy can lead to cure, but the mortality rate for these infections remains high.

This study describes the biochemical activity and antimicrobial susceptibility patterns (antibiograms) of 104 gram-negative bacteria, represented by six species of bacilli, isolated from ten macaws of the genus Ara. Bacterial samples were acquired from fecal matter of six different species of macaws, ages one to three years, housed in a variety of locations. Bacteria from these samples were cultured onto selective media for classification. Identification and biochemical characterization were accomplished with the API 20E system. Escherichia (E.) coli accounted for 78% (81/1 04) of the total number of isolates. Antimicrobial susceptibility testing was done using the Kirby-Bauer method. Biotype and antimicrobial susceptibility data gathered in this study correspond with data of studies done on pigeons and llamas. These data show specific E. coli biotypes as members of the microflora of macaws.

No description available.

We tested 42 strains of amikacin-resistant gram-negative bacilli with amikacin in combination with six beta-lactam antibiotics using the checkerboard and time kill curve techniques. Synergism was demonstrated with time-killing curve in 43-68% of the strains tested. Ceftazidime plus amikacin was the most active combination by the checkerboard technique, while amikacin-cefoperazone was the most active combination by the time-killing curve technique against Pseudomonas aeruginosa. Discrepancies were found between the results of the two methods used.

<P> Type II Secretion (T2S) and type IV pilus (T4P) systems in Gram-negative bacteria share many features that suggest a common ancestral origin. This study examined the role of the minor pilins FimU, PilV, PilW, PilX and PilE, as well as the putative adhesin PilYl in both the T4P and T2S systems, and elucidated the role of these proteins in pilus assembly. Genetic analysis of the major pilin cluster and the minor pilin operon revealed that the major pilin alleles are associated with a specific set of minor pilins, and that unrelated strains of the same major pilin type have identical minor pilin genes, suggesting that the two gene clusters were horizontally acquired as a 'pilin island'. We observed that the minor pilins required a specific stoichiometric ratio for proper assembly, as overexpression either completely abolished, or significantly reduced twitching motility in mutant backgrounds. We demonstrated that the minor pilins were incorporated into the pilus fibre, and that they were dependent on PilA for surface localization. The T4P minor pilins were also shown to play a role in the secretion of effectors through the T2S system, as elastase and haemolytic phospholipase C secretion was reduced in minor pilin mutants, while overexpression of FimU or PilX significantly increased secretion of T2S exoproteins. Therefore, the minor pilins may participate in T2S substrate recognition. We found that PilYl was not essential for assembly in the absence of retraction, but that its absence caused changes in the levels of other T4P biogenesis proteins, namely FimU, PilW, PilF and PilQ secretin multimers. Finally we show that the minor pilin, PilX functions as a strain-specific factor, potentially through specific interactions with non-conserved residues of PilQ that are necessary to induce opening of the secretin. </p> / Thesis / Doctor of Philosophy (PhD)