DOCSLIB.ORG

The Genus Staphylococcus 19 171

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Genus Staphylococcus 19 171 43038_CH19_0171.qxd 1/3/07 3:53 PM Page 171 THE GENUS STAPHYLOCOCCUS 19 171 The Genus 19 Staphylococcus embers of the genus Staphylococcus are gram-positive spherical organisms about 1 micrometer in diameter. They M occur singly, in pairs, and in irregular clusters, and form yel- low, orange, or white colonies on agar media. They are salt tolerant and grow on ordinary bacteriological media as well as on the selective media used in this exercise. Up to three species of Staphylococcus are studied in this exercise. Cer- tain strains of Staphylococcus aureus are the cause of food poisoning and toxic shock syndrome. They also are the cause of boils and carbuncles. A second species, S. epidermidis, usually is a saprobe of the skin that is rarely involved in human infection. The third species, S. saprophyticus, is an opportunistic species that may cause urinary tract infections in women of childbearing years. In this exercise, staphylococcal species will be isolated from the body’s environment and their properties examined. A. Isolation of Staphylococci Species of Staphylococcus are tolerant to salt and, therefore, they can be PURPOSE: to isolate and selected out from a mixture of bacteria in a high-salt medium. In addition, identify staphylococcal species from the nasal cavity S. aureus ferments mannitol, an alcoholic derivative of the hexose mannose, and other environments. while S. epidermidis and S. saprophyticus do not. Therefore, if the differential medium contains mannitol, the two species may be differentiated from one another. In this section, we will use mannitol salt agar, a medium that is both selective and differential. The salt concentration is a high 7% to inhibit other organisms, and mannitol is available for fermentation to acid. The indicator phenol red is included in the medium to detect acid pro- duction. It will change from red to yellow in the presence of acid-producing S. aureus. No color change will occur with the other two species. S pecial Materials • Plates of mannitol salt agar • Sterile swabs • Tubes of sterile saline • Gram stain reagents • Nutrient agar slants 43038_CH19_0171.qxd 1/3/07 3:53 PM Page 172 172 19 THE GENUS STAPHYLOCOCCUS P rocedure 1. Select or prepare two plates of mannitol salt agar and, on the bottom sides, label them in the prescribed manner with your name, the date, and the name of the medium. Label one plate for a “nose swab” and the second for an environment of your choice. 2. Moisten a sterile swab in sterile saline solution, and swab the internal perimeter of the nose cavity. Apply the swab to one area of the appropriate Do not swab the nose too vigorously, to avoid mannitol salt agar plate, and place the swab in disinfectant. Perform the breaking one or more streak plate technique: Using a sterile loop, pass it a couple of times blood vessels. across the swabbed area and then streak into a second area of the plate to obtain isolated colonies, as described in Exercise 2A and directed by the ! instructor. Continue streaking into the third and fourth areas of the plate. Incubate the plate in the inverted position at 37° C for 24 to 48 hours, then refrigerate it. 3. Moisten a second swab, and attempt to isolate staphylococci from another environment. Consider a telephone receiver, a doorknob, the surface of a dollar bill, the area under your fingernail or behind your ear, or other source. If you wish to test a food sample, use the custard filling from a donut or a sample of hamburger meat or something similar. (If food is left out to “ripen” for a day or two, the chances of obtaining staphylococci will be greater.) Apply the swab to the second plate as in step 2, and con- tinue streaking with the loop to obtain isolated colonies. Incubate the plate as above. 4. Observe the plates for the presence of round opaque colonies that are white or pigmented. These are probably colonies of Staphylococcus species. S. aureus produces golden-yellow pigmented colonies, while the other species produce white colonies. Also, colonies surrounded by a yellow halo contain bacteria that fermented the mannitol and probably contain S. aureus. Where no color change to yellow has taken place, the colonies are possibly S. epidermidis or S. saprophyticus, since these species do not fer- ment mannitol. Another possibility is Micrococcus luteus, as noted below. A labeled representation of the plate indicating colony color and any color changes from mannitol fermentation may be entered in the Results section and Table 19.2. 5. The presence of staphylococci may be verified by performing the Gram stain technique on samples from isolated colonies. Typical clusters of gram-positive cocci should appear. Illustrations and your notes should be placed in the Results section. On occasion, Micrococcus luteus will be iso- lated on the medium. These bacteria also are gram-positive cocci but they occur in characteristic tetrads (clusters of four cells) or in cubical packets of eight cells (the sarcina configuration). The colonies on agar are bright yellow. 6. Other characteristics can be used to identify or differentiate between spe- cific species of Staphylococcus. However, to do this requires pure cultures of the isolated species. 43038_CH19_0171.qxd 1/3/07 3:53 PM Page 173 THE GENUS STAPHYLOCOCCUS 19 173 7. Obtain three nutrient agar slant tubes and label each tube with your Extra caution should be name. Also, label one tube A, another B, and the third C. These will be used observed when working to produce three pure cultures of Staphylococcus. with potential pathogens. 8. Based on colony color (pigmentation), mannitol fermentation results, and the purity of the colony based on Gram staining, select three separate ! colonies to pure culture. One colony should be positive for mannitol fer- mentation (yellow halo). Identify this colony as isolate A. The other two should be white colony isolates that cannot ferment mannitol (no yellow halo). Identify these colonies as isolates B and C. 9. Sterilize your inoculation loop and transfer a loopful of colony isolate A to the agar slant labeled A. Streak the loop up the length of the agar, being care- ful not to gouge the agar (Exercise 1). Repeat the process with a sterile loop from colonies B and C to slants B and C. Incubate the three slants at 37ºC for 24 to 48 hours. If they will not be used until the following week, they can be refrigerated after 48 hours. B. Differentiation between Staphylococcal Species Each of the three species of Staphylococcus has specific characteristics that PURPOSE: to distinguish can be used to separate it from the other two species. S. aureus has the abil- between species of Staphylococcus based on ity to produce coagulase, an enzyme that clots blood plasma and enhances biochemical characteristics. its virulence by providing resistance to phagocytosis. The species also produces DNase to digest DNA and is sensitive to the antibiotic novo- biocin. Of the three species, only S. saprophyticus is resistant to novobiocin (Table 19.1). In this exercise, the three samples of isolated staphylococci from Part A will be tested for coagulase and DNase activity as well as sensitivity to novobiocin. TABLE 19.1 Characteristics of Staphylococcal Species CHARACTERISTIC S. AUREUS S. EPIDERMIDIS S. SAPROPHYTICUS Colony color Golden-yellow White White Acid production Yes No No from mannitol Coagulase production Yes No No DNase activity Yes No No Novobiocin sensitivity Yes Yes No 43038_CH19_0171.qxd 1/3/07 3:53 PM Page 174 174 19 THE GENUS STAPHYLOCOCCUS S pecial Materials • Isolated staphylococci from Part A • Tubes containing 0.5 ml of coagulase plasma • DNase test agar • 1 N HCl • Mueller-Hinton agar • 30 µg Novobiocin discs • Sterile forceps P rocedure Obtain the three slant cultures (isolates A, B, and C) that you made in the previous lab period. I. Coagulase Activity 1. Obtain three tubes of coagulase plasma and label them with your name. Then, label one tube A, one B, and one C. 2. Inoculate coagulase tube A with a heavy loopful of bacteria from slant A. Sterilize the loop and repeat the transfers for slants B and C to coagulase tubes B and C. 3. Observe the tubes at intervals designated by the instructor. Incubation can continue for up to 24 hours. Coagulase activity is determined by tilting each coagulase tube to the side and noting the presence of a solid immov- able clot (Figure 19.1). If the plasma still flows, clot formation and coagu- lase activity have not taken place. 4. Enter your results in the Results section, using (+) for coagulase activity and (–) for lack of activity. Include the time for clotting, if known. II. DNA Digestion 1. Obtain a DNase test agar plate and divide the bottom of the plate into three sections. Label each section with a colony designation (A, B, or C), and “DNA test.” Make sure your name also is on the plate. 2. Aseptically make a single line of inoculation of each staph isolate (A, B, and C) in its respective sector on the DNase test agar plate. 3. Incubate the plate in the inverted position for 24 to 48 hours at 37ºC. A The first species is unable to clot the plasma because it cannot produce coagulase. FIGURE 19.1 B The second species produces The coagulase test performed with two species coagulase and clots the plasma. of staphylococci. 43038_CH19_0171.qxd 1/3/07 3:53 PM Page 175 THE GENUS STAPHYLOCOCCUS 19 175 4. Test for DNA digestion by flooding the plate with 1N hydrochloric acid (HCl). DNA will normally react with HCl and form a very fine precipitate, which will give a cloudy appearance to the agar after several minutes.
Load more

Recommended publications
  • Laboratory Exercises in Microbiology: Discovering the Unseen World Through Hands-On Investigation
    City University of New York (CUNY) CUNY Academic Works Open Educational Resources Queensborough Community College 2016 Laboratory Exercises in Microbiology: Discovering the Unseen World Through Hands-On Investigation Joan Petersen CUNY Queensborough Community College Susan McLaughlin CUNY Queensborough Community College How does access to this work benefit ou?y Let us know! More information about this work at: https://academicworks.cuny.edu/qb_oers/16 Discover additional works at: https://academicworks.cuny.edu This work is made publicly available by the City University of New York (CUNY). Contact: [email protected] Laboratory Exercises in Microbiology: Discovering the Unseen World through Hands-On Investigation By Dr. Susan McLaughlin & Dr. Joan Petersen Queensborough Community College Laboratory Exercises in Microbiology: Discovering the Unseen World through Hands-On Investigation Table of Contents Preface………………………………………………………………………………………i Acknowledgments…………………………………………………………………………..ii Microbiology Lab Safety Instructions…………………………………………………...... iii Lab 1. Introduction to Microscopy and Diversity of Cell Types……………………......... 1 Lab 2. Introduction to Aseptic Techniques and Growth Media………………………...... 19 Lab 3. Preparation of Bacterial Smears and Introduction to Staining…………………...... 37 Lab 4. Acid fast and Endospore Staining……………………………………………......... 49 Lab 5. Metabolic Activities of Bacteria…………………………………………….…....... 59 Lab 6. Dichotomous Keys……………………………………………………………......... 77 Lab 7. The Effect of Physical Factors on Microbial Growth……………………………... 85 Lab 8. Chemical Control of Microbial Growth—Disinfectants and Antibiotics…………. 99 Lab 9. The Microbiology of Milk and Food………………………………………………. 111 Lab 10. The Eukaryotes………………………………………………………………........ 123 Lab 11. Clinical Microbiology I; Anaerobic pathogens; Vectors of Infectious Disease….. 141 Lab 12. Clinical Microbiology II—Immunology and the Biolog System………………… 153 Lab 13. Putting it all Together: Case Studies in Microbiology…………………………… 163 Appendix I.
    [Show full text]
  • LAB 2: Staining and Streaking Protocols for Simple Stain, Gram Stain, Streak Plate Technique and Culture Maintenance
    LAB 2: Staining and Streaking Protocols for Simple stain, Gram Stain, Streak Plate Technique and Culture Maintenance Lab 2a: INTRODUCTION To Staining Live specimens are difficult to see with the bright field microscope. The contrast between a cell, which is primarily water, and the background, which is water, is poor. Staining is used to increase contrast and can be employed to provide information about the chemistry of a specimen. Stains, or dyes, are salts in which one of the ions is colored. In a basic stain, the color is in the positively charged ion. In an acidic stain the color is in the negatively charged ion. Bacterial surfaces have a slight negative charge. Thus, there is an affinity between a positively charged color ion and the negatively charged bacterial cell. In the Direct or Positive Staining Procedure a cell takes up a positively charged dye and becomes stained. Methylene blue, crystal violet, and safranin, are all basic dyes. In the Indirect or Negative Staining Procedure, a cell is immersed in a negatively charged dye. As the cell will repel the dye, the cell appears clear in a background of color. Nigrosine is an example of an acidic stain. Staining procedures that use one dye to increase contrast between specimen and background are simple staining procedures. Complex staining procedures employ a series of stains and chemical reagents to increase contrast and reveal information about the specimen. Any staining procedure that allows differentiation of one type of bacterium from another is a differential staining procedure. For all staining procedures, it is first required that cells be fixed to the slide.
    [Show full text]
  • Medical Bacteriology
    LECTURE NOTES Degree and Diploma Programs For Environmental Health Students Medical Bacteriology Abilo Tadesse, Meseret Alem University of Gondar In collaboration with the Ethiopia Public Health Training Initiative, The Carter Center, the Ethiopia Ministry of Health, and the Ethiopia Ministry of Education September 2006 Funded under USAID Cooperative Agreement No. 663-A-00-00-0358-00. Produced in collaboration with the Ethiopia Public Health Training Initiative, The Carter Center, the Ethiopia Ministry of Health, and the Ethiopia Ministry of Education. Important Guidelines for Printing and Photocopying Limited permission is granted free of charge to print or photocopy all pages of this publication for educational, not-for-profit use by health care workers, students or faculty. All copies must retain all author credits and copyright notices included in the original document. Under no circumstances is it permissible to sell or distribute on a commercial basis, or to claim authorship of, copies of material reproduced from this publication. ©2006 by Abilo Tadesse, Meseret Alem All rights reserved. Except as expressly provided above, no part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without written permission of the author or authors. This material is intended for educational use only by practicing health care workers or students and faculty in a health care field. PREFACE Text book on Medical Bacteriology for Medical Laboratory Technology students are not available as need, so this lecture note will alleviate the acute shortage of text books and reference materials on medical bacteriology.
    [Show full text]
  • Characterization of the Lactobacillus Isolated from Different Curd Samples
    African Journal of Biotechnology Vol. 11(79), pp. 14448-14452, 2 October, 2012 Available online at http://www.academicjournals.org/AJB DOI: 10.5897/AJB11.310 ISSN 1684–5315 © 2012 Academic Journals Full Length Research Paper Characterization of the Lactobacillus isolated from different curd samples Renuka Goyal, Harish Dhingra*, Pratima Bajpai and Navneet Joshi Department of Biotechnology and Microbiology, Mody Institute of Technology and Science, Faculty of Arts, Science and Commerce, Lakshmangarh—332311, Distt.-Sikar, Rajasthan, India. Accepted 16 February, 2012 Lactic acid bacteria are commonly found in the fermented dairy products. Lactobacillus is a genus of lactic acid bacteria and described as heterogeneous group of regular, non-spore forming, gram- positive, rod shaped, non-motile bacteria and absence of catalase enzyme. The aim of this study was to isolate Lactobacillus from different curd samples. A total of 14 curd samples were collected from the local areas of Gurgaon (Haryana) and Lakshmangarh (Rajasthan). From these, 28 isolates were obtained by growing on de Man, Rogosa and Sharpe (MRS) agar medium and characterised by their phenotypic characteristics. The Lactobacillus isolates also possess homofermentative and heterofermentative characteristics. Key words: Lactobacillus, curd, microorganism INTRODUCTION Microorganisms are important in dairy products. One of carbohydrates to organic acids (lactic acid and acetic the most important groups of acid producing bacteria in acids) in the food during their development. the food industry is the lactic acid bacteria, which are Among all lactic acid bacteria, the genus Lactobacillus used in making starter culture for dairy products. has some beneficial characteristics which make it useful Genus Lactobacillus contains over 110 species, which for the industrial applications.
    [Show full text]
  • Development of a Standardized Protocol for Optochin Susceptibility Testing Using Total Lab Automation
    Hindawi BioMed Research International Volume 2017, Article ID 4174168, 7 pages https://doi.org/10.1155/2017/4174168 Research Article Identification of Streptococcus pneumoniae: Development of a Standardized Protocol for Optochin Susceptibility Testing Using Total Lab Automation Irene Burckhardt,1 Jessica Panitz,1 Florian Burckhardt,2 and Stefan Zimmermann1 1 Department for Infectious Diseases, Microbiology and Hygiene, University Hospital of Heidelberg, Heidelberg, Germany 2EPIET Alumni Network (EAN), Heidelberg, Germany Correspondence should be addressed to Irene Burckhardt; [email protected] Received 5 January 2017; Accepted 22 February 2017; Published 19 March 2017 Academic Editor: Gyorgy¨ Schneider Copyright © 2017 Irene Burckhardt et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Purpose. Optochin susceptibility is one parameter used in the laboratory to identify Streptococcus pneumoniae.However,asingle standardized procedure does not exist. Optochin is included neither in the current EUCAST breakpoint tables nor in the CLSI performance standards for antimicrobial susceptibility testing. We wanted to establish an evidence-based protocol for optochin testing for our Total Lab Automation. Methods. We tested seven different agars and four different reading time points (7 h, 12h, 18 h, and 24 h). To accommodate for serotype diversity, all tests were done with 99 different strains covering 34 different serotypes of S. pneumoniae. We calculated a multivariable linear regression using data from 5544 inhibition zones. Results. Reading was possible for all strains at 12 h. Agar type and manufacturer influenced the size of the inhibition zones by up to 2 mm and they varied considerably depending on serotype (up to 3 mm for serotype 3).
    [Show full text]
  • Exercise 4 ASEPTIC TECHNIQUE & STREAK PLATE PREPARATION
    Exercise 4 ASEPTIC TECHNIQUE & STREAK PLATE PREPARATION Introduction In order to make laboratory studies with pure microbial cultures, microbiologists must start with sterile culture media and must be able to prevent contamination of this media. At the same time, they must be able to inoculate media with the desired pure cultures without introducing any other organisms. The procedure utilized to accomplish this is referred to as aseptic technique and is essential to any microbiology laboratory. Remember that all culture media must be sterile prior to inoculation. Media samples that appear to be contaminated with unknown cultures (are already supporting growth) must be discarded and not used for laboratory exercises. Transfer Instruments In order to inoculate a tube or plate with a desired microbial culture, students will use some type of transfer instrument, usually a wire loop or a pipette. If a wire loop or needle is being used, it must be sterilized (heated to redness by flaming) before and after making the microbial transfer. This heating destroys any living forms on the surface of the needle or loop, thus preventing unwanted contamination. To sterilize the loop or needle, hold it in the hottest part of the flame at an angle that will distribute heat to the entire length of the wire. After the loop or needle is sterilized in this manner, it must be allowed to cool briefly before being used to pick up the desired culture. Remember that contact with hot metal will kill bacteria. When using a wire loop to transfer bacteria from cultures grown on solid media it is recommended that students avoid filling the loop.
    [Show full text]
  • Laboratory Methods for the Diagnosis of Meningitis Caused by Neisseria Meningitidis, Streptococcus Pneumoniae, and Haemophilus Influenzae WHO Manual, 2Nd Edition
    WHO/IVB.11.09 Laboratory Methods for the Diagnosis of Meningitis caused by Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae WHO MANUAL, 2ND EDITION Photo: Jon Shadid/UNICEF WHO/IVB.11.09 Laboratory Methods for the Diagnosis of Meningitis caused by Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae WHO MANUAL, 2ND EDITION1 1 The first edition has the WHO reference WHO/CDS/CSR/EDC/99.7: Laboratory Methods for the Diagnosis of Meningitis caused by Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae, http://whqlibdoc.who.int/hq/1999/WHO_CDS_CSR_EDC_99.7.pdf © World Health Organization 2011 This document is not a formal publication of the World Health Organization. All rights reserved. This document may, however, be reviewed, abstracted, reproduced and translated, in part or in whole, but not for sale or for use in conjunction with commercial purposes. The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted lines on maps represent approximate border lines for which there may not yet be full agreement. The mention of specific companies or of certain manufacturers’ products does not imply that they are endorsed or recommended by the World Health Organization in preference to others of a similar nature that are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguished by initial capital letters. All reasonable precautions have been taken by the World Health Organization to verify the information contained in this publication.
    [Show full text]
  • Pure Culture Techniques
    Microbiology BIOL 275 PURE CULTURE TECHNIQUES I. OBJECTIVES • To demonstrate good aseptic technique in culture transfer or inoculation and in handling sterile materials. • To demonstrate skill in isolation of organisms from a mixed culture using selective and differential media. • To isolate microorganisms from a wide variety of sources and describe their colonial morphology. II. INTRODUCTION Most environments carry a mixed microbial population. To fully appreciate the contribution of each group of organisms to the ecology of the mass, one must first dissect this mixed culture to obtain single colonies. The single colony is transferred (picked) to a fresh medium to obtain a larger, homogeneous culture that may be studied and characterized by a variety of techniques. One such technique is called aseptic technique. Microbiologists and health workers use this technique to prevent contamination of cultures from outside sources and to prevent the introduction of potential disease agents into the human body (infection can occur through contamination of your hands and clothing with material from your bacterial cultures). Aseptic Techniques Aseptic techniques (also called sterile techniques) are defined as the processes required for transferring a culture from one vessel to another without introducing any additional organisms to the culture or contaminating the environment with the culture. The following conditions must exist for aseptic technique to be successful: 1. The work area must be wiped with an antiseptic to reduce the number of potential contaminants. 2. The transfer instruments must be sterile. 3. The work must be accomplished quickly and efficiently to minimize the time of exposure during which contamination of the culture or laboratory worker can occur.
    [Show full text]
  • Microbiological Profile of Asyptomatic Bacteriuria in Pregnancy Abstract
    Research iMedPub Journals Critical Care Obstetrics and Gynecology 2016 http://www.imedpub.com/ Vol.2 No.5:26 ISSN 2471-9803 DOI: 10.4172/2471-9803.1000134 Microbiological Profile of Asyptomatic Bacteriuria in Pregnancy Anu Mary Bose*, Sreekumary PK and Sobha Kurian Pulikkottil Department of Microbiology, Government Medical College Kottayam, Kerala, India *Corresponding author: Anu Mary Bose, Department of Microbiology, Government Medical College Kottayam, Kerala, India, Tel: + 919746559119; E-mail: [email protected] Received date: October 07, 2016; Accepted date: October 20, 2016; Published date: October 30, 2016 Copyright: © 2016 Bose AM et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Citation: Bose AM, Sreekumary PK, Pulikkottil SK. Microbiological profile of asyptomatic bacteriuria in pregnancy. Crit Care Obst&Gyne. 2016, 2:26. as persistently and actively multiplying bacteria in significant numbers i.e., 105 bacteria per ml within the urinary tract Abstract without any obvious symptoms [1-5]. It is also known as Covert bacteriuria. Females are more susceptible for these infections Background: Asymptomatic bacteriuria is the presence of because of the short length of urethra along with proximity to actively multiplying bacteria within the urinary tract in the warm, moist anal canal [4]. Sexual intercourse facilitates the absence of any symptoms. Anatomical and physiological ascent of bacteria into bladder. The pregnant females are two changes make women more susceptible to UTI in pregnancy. times more commonly affected than age matched non pregnant females.
    [Show full text]
  • Streaking Microbiology Dr.Heba Shehab
    Streaking microbiology Dr.Heba Shehab In microbiology, streaking is a technique used to isolate a pure strain from a single species of microorganism, often bacteria. Samples can then be taken from the resulting colonies and a microbiological culture can be grown on a new plate so that the organism can be identified, studied, or tested. History: The modern streak plate method has progressed from the efforts of Robert Koch and other microbiologists to obtain microbiological cultures of bacteria in order to study them. The dilution or isolation by streaking method was first developed by Loeffler and Gaffky in Koch's laboratory, which involves the dilution of bacteria by systematically streaking them over the exterior of the agar in a petri dish to obtain isolated colonies which will then grow into quantity of cells, or isolated colonies. If the agar surface grows microorganisms which are all genetically same, the culture is then considered as a microbiological culture. Technique Streaking is rapid and ideally a simple process of isolation dilution. The technique is done by diluting a comparatively large concentration of bacteria to a smaller concentration. The decrease of bacteria should show that colonies are sufficiently spread apart to effect the separation of the different types of microbes. Streaking is done using a sterile tool, such as acotton swab or commonly an inoculation loop. Aseptic techniques are used to maintain microbiological cultures and to prevent contamination of the growth medium.There are many different types of methods used to streak a plate. Picking a technique is a matter of individual preference and Streaking microbiology Dr.Heba Shehab can also depend on how large the number of microbes the sample contains.
    [Show full text]
  • The Microscopic Examination of Milk Characterization of Milk Bacteria and Cells
    The Microscopic Examination of Milk Characterization of Milk Bacteria and Cells The microscope has been used to observe and count bacteria and somatic cells in raw milk since the early 1900’s. It has proven to be a valuable tool to the dairy industry. The milk smear procedure in use today is outlined in detail in the most recent edition of Standard Methods for the Examination of Dairy Products (i.e., SMEDP, 17th ed) and other references. For somatic cell counting, the Direct Microscopic Somatic Cell Count (DMSCC) is considered an official reference method used for regulatory purposes for direct milk counts and/or for calibration of approved electronic instruments. The regulatory procedure for somatic cells is outlined in detail in the most recent FDA 2400 Form. With the exception of the type of cells counted, the 2400 form procedure can be used for bacteria as well. While the Direct Microscopic Clump Count (DMCC) for bacteria is not considered an official test for bacteria counts, it is used throughout the dairy industry to estimate bacteria colony forming units (i.e., “clumps”) in raw milk samples taken from the farm, the tank truck or the plant storage facility. The DMCC is most widely used to screen incoming raw milk supplies (i.e., tank-trucks) to determine whether the milk has an acceptable or legal bacterial load and has become accepted in some states as a legal method for rejection of unacceptable milk. In addition to providing estimated counts of bacteria and somatic cells, the direct microscopic method has also been used as a trouble-shooting guide in attempts to identify the general types of bacteria present in a milk sample.
    [Show full text]
  • Purification, Biochemical Characterization, and Implications
    ASTROBIOLOGY Volume 15, Number 4, 2015 ª Mary Ann Liebert, Inc. DOI: 10.1089/ast.2014.1242 Purification, Biochemical Characterization, and Implications of an Alkali-Tolerant Catalase from the Spacecraft-Associated and Oxidation-Resistant Acinetobacter gyllenbergii 2P01AA N. Muster, I. Derecho, F. Dallal, R. Alvarez, K.B. McCoy, and R. Mogul Abstract Herein, we report on the purification, characterization, and sequencing of catalase from Acinetobacter gyl- lenbergii 2P01AA, an extremely oxidation-resistant bacterium that was isolated from the Mars Phoenix spacecraft assembly facility. The Acinetobacter are dominant members of the microbial communities that inhabit spacecraft assembly facilities and consequently may serve as forward contaminants that could impact the integrity of future life-detection missions. Catalase was purified by using a 3-step chromatographic pro- cedure, where mass spectrometry provided respective subunit and intact masses of 57.8 and 234.6 kDa, which were consistent with a small-subunit tetrameric catalase. Kinetics revealed an extreme pH stability with no loss 7 - 1 - 1 6 - 1 in activity between pH 5 and 11.5 and provided respective kcat/Km and kcat values of *10 s M and 10 s , which are among the highest reported for bacterial catalases. The amino acid sequence was deduced by in-depth peptide mapping, and structural homology suggested that the catalases from differing strains of A. gyllenbergii differ only at residues near the subunit interfaces, which may impact catalytic stability. Together, the kinetic, alkali-tolerant, and halotolerant properties of the catalase from A. gyllenbergii 2P01AA are significant, as they are consistent with molecular adaptations toward the alkaline, low-humidity, and potentially oxidizing conditions of spacecraft assembly facilities.
    [Show full text]