Cationic peptide antimicrobials induce selective transcription of micF and osmY in Escherichia coli

Cationic antimicrobial peptides, such as polymyxin and cecropin, activated transcription of osmY and micF in growing Escherichia coli independently of each other. The micF response required the presence of a functional rob gene. It is intriguing that in this and other assays an identical response profile was also seen with hyperosmotic salt or sucrose gradient, two of the most commonly used traditional food preservatives. The osmY and micF transcription was not induced by hypoosmotic gradient, ionophoric peptides, uncouplers, or with other classes of membrane perturbing agents. The antibacterial peptides did not promote transcription of genes that respond to macromolecular or oxidative damage, fatty acid biosynthesis, heat shock, or depletion of proton or ion gradients. These and other results show that the antibacterial cationic peptides induce stasis in the early growth phase, and the transcriptional efficacy of antibacterial peptides correlates with their minimum inhibitory concentration, and also with their ability to mediate direct exchange of phospholipids between vesicles. The significance of these results is developed as the hypothesis that the cationic peptide antimicrobials stress growth of Gram-negative organisms by making contacts between the two phospholipid interfaces in the periplasmic space and prevent the hyperosmotic wrinkling of the cytoplasmic membrane. Broader significance of these results, and of the hypothesis that the peptide mediated contacts between the periplasmic phospholipid interfaces are the primary triggers, is discussed in relation to antibacterial resistance.

Osmotic stress in viable Escherichia coli as the basis for the antibiotic response by polymyxin B

Cationic antimicrobial peptides, such as polymyxin B (PxB), below growth inhibitory concentration induce expression of osmY gene in viable E. coli without leakage of solutes and protons. osmY expression is also a locus of hyperosmotic stress response induced by common food preservatives, such as hypertonic NaCl or sucrose. High selectivity of PxB against Gram-negative organisms and the basis for the hyperosmotic stress response at sublethal PxB concentrations is attributed to PxB-induced mixing of anionic phospholipid between the outer layer of the cytoplasmic membrane with phospholipids in the inner layer of the outer membrane. This explanation is supported by PxB-mediated rapid and direct exchange of anionic phospholipid between vesicles. This mechanism is consistent with the observation that genetically stable resistance against PxB could not be induced by mutagenesis.

Comparison of MIDI Sherlock system and pulsed-field gel electrophoresis in characterizing strains of methicillin-resistant Staphylococcus aureus from a recent hospital outbreak

An outbreak of methicillin-resistant Staphylococcus aureus infections at the University of Utah Health Sciences Center occurred over a 7-month period. While the isolates phenotypically appeared to be similar in gross morphology and have similar Vitek antibiotic susceptibility patterns, two additional methods of strain characterization were evaluated to enhance the epidemiological investigation: pulsed-field gel electrophoresis and gas chromatography with the MIDI Sherlock system. Sherlock uses gas chromatography to qualitatively and quantitatively analyze the cellular fatty acid composition of organisms and creates two-dimensional plots based on principal-component analysis to define groups of closely related organisms. All isolates were also evaluated by digesting their chromosomal DNAs with the low-frequency-cutting enzyme SmaI and separating the restriction fragments by contour-clamped homogeneous electric field gel electrophoresis. Sample preparation for this pulsed-field gel electrophoresis included a novel cell lysis procedure involving achromopeptidase, greatly reducing the turnaround time. Isolates tested were recovered from the following: 45 suspected outbreak patients, 6 hospitalized patients believed to be unrelated to the outbreak, 6 patients from outside the hospital, and one health care practitioner implicated in the outbreak. Of 45 phenotypically similar suspect strains, 43 clustered tightly on the Sherlock two-dimensional plot. All outbreak patient isolates were also identical by pulsed-field gel electrophoresis with the exception of the same two outliers identified by Sherlock. In this epidemiologic investigation, we found an excellent correlation between the Sherlock and pulsed-field gel electrophoresis results for strain characterization of methicillin-resistant S. aureus.

Differentiation of Erwinia carotovora ssp. carotovora and E. carotovora ssp. atroseptica on the basis of cellular fatty acid composition

The cellular fatty acids of Erwinia carotovora were analyzed by gas–liquid chromatography with a fused-silica capillary column. All strains contained, in decreasing order of amount present, 9-hexadecenoic acid (16:1), hexadecanoic acid (16:0), 9-octadecenoic acid (18:1), dodecanoic acid (12:0), 3-hydroxytetradecanoic acid (3-OH-14:0), and tetradecanoic acid (14:0). In addition some strains contained a small amount of 13, 15, 17, and 18 carbon saturated fatty acids. Strains of E. carotovora ssp. atroseptica (Eca) and E. carotovora ssp. carotovora (Ecc) from potato could be differentiated on the basis of three different fatty acid ratios. The Ecc strains had ratios of >3.71 for 12:0/14:0, <4.87 for 16:0/12:0, and <2.70 for 16:1/18:1, while the Eca strains had contrasting values for each of the ratios. Non-potato strains of E. carotovora including strains that were neither Ecc nor Eca on the basis of biochemical reactions were more variable in fatty acid composition than the potato strains, but the fatty acid ratios were generally of the Ecc type.

Contribution to the taxonomy of the turkey coryza agent: cellular fatty acid analysis of the bacterium

Gas-liquid chromatography was used to analyze bacterial cellular fatty acids to elucidate the relatedness of the turkey coryza (TC) bacterium to Alcaligenes spp., Bordetella spp., and other gram-negative bacteria. The results indicated that the TC bacterium is not closely related to Alcaligenes faecalis or any of the reference strains of Alcaligenes and Bordetella studied. Most urease-positive bacterial isolates obtained from the upper respiratory tract of turkeys were identified as Bordetella bronchiseptica. It is suggested that Bordetella avium is a suitable designation for the TC bacterium formally called Bordetella-"like" and A. faecalis type I. It is also suggested that the nonpathogenic bacterium previously identified as type II A. faecalis be designated B. avium-like until further taxonomic studies are available. Furthermore, it is proposed that the term turkey coryza be used to refer to the disease induced by this bacterium.

Evaluation of medical-psychiatric consultation

This report describes four approaches to the evaluation of hospital psychiatric consultation. These are: 1) a survey of actual consultation use; 2) a house staff attitudinal survey; 3) a patient chart review; and 4) a patient questionnaire. The findings of this project and those previously reported are: 1) The psychiatric consultation is under-utilized and a large number of house staff find it not useful. 2) The psychiatric and non-psychiatric house staff view the functions of consultation in markedly different ways. 3) A high percentage of written consultation reports are too vague to determine if the needs of the referring physician were met. 4) Patients usually respond positively to psychiatric consultation. The implications of these findings are discussed in this report.