Bacteriology Series (part 2) = Gram +ve Bacilli

gram negative

2007

This is an by copyright after embargo allowed publisher’s PDF of an article published in

2009

The interest in the TonA protein, now called FhuA, has endured since the beginnings of phage genetics and molecular biology. The functions of this energy-coupled transporter and receptor in the outer membrane of Escherichia coli cells are fascinating. The historical perspective of this protein presented here is not intended to provide a comprehensive account of the structure and function of FhuA but rather attempts to explain how this protein has attracted interest for so long. The seminal work published by Salvador E. Luria and Max Delbrück (51) in 1943 is considered the beginning of modern bacterial genetics (12). In this publication, they reported their fluctuation test, which demonstrates that in bacteria, genetic mutations arise in the absence of selection rather than as a response to selection. They isolated virus-resistant mutants of Escherichia coli B, ascribed this virus resistance to mutations in the host cells prior to infection by the phage, and presented a means for quantitatively calculating mutation rates. The virus they used was later named phage T1, and the mutations that conferred resistance were subsequently designated tonA and tonB (ton derived from T one). It was later found that a phage morphologically and serologically distinct from T1, named T5, cannot infect tonA mutants but can infect tonB mutants; i.e., phage T5 requires only the tonA-encoded function but not the tonB-encoded function. Members of the "phage group" surrounding Luria and Delbrück were interested in genetics, reproduction, and multiplication. They studied, as the most simple system, phages and E. coli host cells, mutants, phage morphology, serology, adsorption, lysis, and burst size, but not biochemistry (12, 14). The prejudice against biochemistry began to dissolve during the postdoctoral studies of Wolfhard Weidel, a biochemist by training, on phage adsorption and infection in Delbrück's laboratory. Delbrück's enthusiasm for Weidel's studies was evident in his report to the Caltech president, in which he referred to Weidel's work as "the most startling finding of the year" (66). Weidel's findings were included in the 1950 report on viruses of the Division of Biology of the California Institute of Technology. They were published in 1951 (68) after he was back in Germany at the Max Planck Institute of Biology in Tübingen, where he continued his work on phage adsorption, first with phages T2, T4, and T6 and then mainly with phage T5. His first achievement was the isolation of membrane frac

We studied the molecular mechanism of resistance in extended-spectrum b-lactamase (ESBL)producing Klebsiella pneumoniae isolated from a neonatal intensive care unit (NICU) of one of the hospitals in North India. A total of 3000 clinical samples were collected from a NICU (January 2009 to February 2011), of which 523 strains were K. pneumoniae positive and 262 of them were ESBL-producing K. pneumoniae strains. All of the ESBL-producing clinical isolates were susceptible to carbapenems. However, the majority of the clinical isolates (30-96 %) were resistant to a wide range of antibiotics including antibiotic/inhibitor combinations. The MIC values confirmed that these isolates were highly resistant to cephalosporins and aztreonam. In the 262 ESBL-producing K. pneumoniae isolates, 15 different enterobacterial repetitive intergenic consensus (ERIC)-PCR-typed phylogenetic groups were identified and reconfirmed by PFGE. Characterization of plasmids from each representative member of these phylogenetic groups revealed the presence of three plasmids of different sizes. Conjugation experiments confirmed the presence of different resistance markers only on the 154 kb plasmid. PCR amplification and sequence analysis revealed that bla CTX-M-3 , bla TEM-1 , bla SHV-1 , bla OXA-1 and armA were the predominant resistance markers. Plasmid-replicon typing showed that IncI1-Ic and IncFIA-FIB types are the most prevalent. This study shows the co-existence of multiple ESBL-encoding genes and their polyclonal dissemination among K. pneumoniae clinical isolates in the NICU of a North Indian hospital. %paper no. mic075762 charlesworth ref: mic075762& Environmental and Evolutionary Microbiology Abbreviations: ERIC, enterobacterial repetitive intergenic consensus; ESBL, extended-spectrum b-lactamase; MBL, metallo-b-lactamase; NICU, neonatal intensive care unit. A supplementary table is available with the online version of this paper.

The American Journal of Medicine, 1980

Evaluation of 612 episodes of gram-negative bacteremia over a loyear period demonstrated its progressively increasing frequency. This increase was associated with an increasing proportion of patients with more severe underlying disease, increasing patient age, increasing frequency of cardiac surgery and manipulative procedures, and increasing frequency of treatment with antibiotics, corticosteroids and antimetabolites in patients with bactere~mia. Fatality rates paralleled the severity of the host's underlying disease as noted in previous reports. The urinary tract was the most frequent source of bacteremia, but in 30 per cent of the patients, predominantly those with more severe underlying disease, the original source could not be identified. Of all blood cultures obtained in these patients, 72 per cent were positive. Bacteremia was of low magnitude with 77 per cent of the patients having quantitative blood cultures with less than 10 gram-negative bacilli per milliliter of blood. Kscherichia coli was the most frequent etiologic agent followed in frequency by Klebsiella-KnterobacterSerratia species, Pseudomonas aeruginosa, Proteus and Providencia species, and species of Bacteroides. Sixteen per cent of the bacteremias were polymicrobic. K and O-antigen typing of Kscherichia coli and capsular typing of K. pneumoniae demonstrated that a large number of serologic types of these strains were responsible for bacteremia. Over-all, bacteremia caused by multiple species of bacteria was associated with higher fatality rates, but no significant differences in fatality rates could be demonstrated for bacteremias caused by individual species of gram-negative bacilli when comparisons were made between patients wtth underlying diseases of similar severity. The presence or type of K-antigen did not influence the lethality of Esch. coli infectiona Although some O-antigen types, 0:4,0:6 and 6~8, were associated with higher fatality rates than other O-antigen types, "rough" or autoagglutinable Ekh. coli were as lethal as smooth strains. These findings indicate that bacterial factors, other than andbiodc resistance, have little influence on the outcome of gram-negative bacteremia and that gram-negative bacilli function primarily as "opportunistic" pathogens.

Microbiology questions , 2018

Microbes, also called microorganisms, are minute living things that individually are usually too small to be seen with the unaided eye. The group includes bacteria, fungi (yeasts and molds), protozoa, and microscopic algae. It also includes viruses, those noncellular entities sometimes regarded as straddling the border between life and nonlife. Today we understand that microorganisms are found almost everywhere (Ubiquitous). Yet not long ago, before the invention of the microscope, microbes were unknown to scientists. Thousands of people died in devastating epidemics, the causes and transmission of which were not understood. Entire families died because vaccinations and antibiotics were not available to fight infections. We tend to associate these small organisms only with uncomfortable infections, with common inconveniences such as spoiled food, or with major diseases such as AIDS. Though only a minority of microorganisms are pathogenic (disease-producing), practical knowledge of microbes is necessary for medicine and the related health sciences. For example, hospital workers must be able to protect patients from common microbes that are normally harmless but pose a threat to the sick and injured. However, the majority of microorganisms actually help maintain the balance of life in our environment. Marine and freshwater microorganisms form the basis of the food chain in oceans, lakes, and rivers. Soil microbes help break down wastes and incorporate nitrogen gas from the air into organic compounds, thereby recycling chemical elements among soil, water, living organisms, and air. Certain microbes play important roles in photosynthesis, a food and oxygengenerating process that is critical to life on Earth. Humans and many other animals depend on the microbes in their intestines for digestion and the synthesis of some vitamins that their bodies require, including some B vitamins for metabolism and vitamin K for blood clotting. Microorganisms also have many commercial applications. They are used in the synthesis of such chemical products as vitamins, organic acids, enzymes, alcohols, and many drugs. For example, microbes are used to produce acetone and butanol, and the vitamins B 2 (riboflavin) and B 12 (cobalamin) are made biochemically. The process by which microbes produce acetone and butanol was discovered in 1914 by Chaim Weizmann, a Russian-born chemist working in England. With the outbreak of World War I in August of that year, the production of acetone became very important for making cordite (a smokeless form of gunpowder used in munitions). Weizmann's discovery played a significant role in determining the outcome of the war. The food industry also uses microbes in producing, for example, vinegar, sauerkraut, pickles, soy sauce, cheese, yogurt, bread, and alcoholic beverages. In addition, enzymes from microbes can now be manipulated to cause the microbes to produce substances they normally don't synthesize, including cellulose, digestive aids, and drain cleaner, plus important therapeutic substances such as insulin. Industrially microbial enzymes may even have helped produce your favorite pair of jeans Designer Jeans: Made by Microbes? Denim blue jeans have been popular ever since Levi Strauss and Jacob Davis first made them for California gold miners in 1873. Now, companies that manufacture blue jeans are turning to microbiology to develop environmentally sound production methods that minimize toxic wastes and the associated costs. Soft, Faded Jeans A softer, faded denim is made with enzymes called cellulases from Trichoderma fungus. They digest some of the cellulose in the cotton. Unlike many chemical reactions, enzymes usually operate at safe temperatures and pH. Moreover, enzymes are proteins, so they are readily degraded for removal from wastewater. Fabric Cotton production requires large tracts of land, pesticides, and fertilizer, and the crop yield depends on the weather. However, bacteria can produce both cotton and polyester with less environmental impact. Gluconacetobacter xylinus bacteria make cellulose by attaching glucose units to simple chains in the outer membrane of the bacterial cell wall. The cellulose microfibrils are extruded through pores in the outer membrane, and bundles of microfibrils then twist into ribbons. Bleaching Peroxide is a safer bleaching agent than chlorine and can be easily removed from fabric and wastewater by enzymes. Researchers at Novo Nordisk Biotech cloned a mushroom peroxidase gene in yeast and grew the yeasts in washing machine conditions. The yeast that survived the washing machine were selected as the peroxidase producers. Revision Question 1 a. Describe some of the destructive and beneficial actions of microbes. UNIT 2: Naming and Classifying Microorganisms 2.0 GENERAL OBJECTIVES At the end of this unit, you should be able to: i Explain why scientific names are used. ii. List the major taxa. iii. Differentiate culture, clone, and strain. iv. List the major characteristics used to differentiate the three kingdoms of multicellular Eukarya. v. Define protist. vi. Differentiate eukaryotic, prokaryotic, and viral species. vii. Recognize the system of scientific nomenclature that uses two names: a genus and a specific epithet. viii. Differentiate the major characteristics of each group of microorganisms. ix. List the three domains. x. Identify the major groups of microorganism xi. State the major characteristics which set each group apart from others xii. Identify important genera within the appropriate group. 2.1. Nomenclature Living organisms are grouped according to similar characteristics (classification), and each organism is assigned a unique scientific name. The rules for classifying and naming, which are used by biologists worldwide, are discussed. Scientific Nomenclature In a world inhabited by millions of living organisms, biologists must be sure they know exactly which organism is being discussed. We cannot use common names, because the same name is often used for many different organisms in different locales. For example, there are two different organisms with the common name Spanish moss, and neither one is actually a moss. Plus, common names can be misleading and are in different languages. A system of scientific names was developed to solve this problem. Every organism is assigned two names, or a binomial. These names are the genus name and specific epithet (species), and both names are printed underlined or italicized. The genus name is always capitalized and is always a noun. The species name is lowercase and is usually an adjective. Because this system gives two names to each organism, the system is called binomial nomenclature. Let's consider some examples. Our own genus and specific epithet are Homo sapiens (HŌ-mō SĀ-pē-enz). The genus means man; the specific epithet means wise. A mold that contaminates bread is called Rhizopus stolonifer (RĪ-zō-pus stō-LON-i-fer). Rhizo-(root) describes rootlike structures on the fungus; stolo-(a shoot) describes the long hyphae.