Bacteria Unit 4 2018 Past Paper PDF

UNIT 4: BACTERIA Bacteria ▪ Bacteria are unicellular and most multiply by binary fission ▪ Bacterial species are differentiated by ▪ morphology, ▪ chemical composition, ▪ nutritional requirements, ▪ biochemical activities, and ▪ source of energy.  What are bacteria? Single...

UNIT 4: BACTERIA Bacteria ▪ Bacteria are unicellular and most multiply by binary fission ▪ Bacterial species are differentiated by ▪ morphology, ▪ chemical composition, ▪ nutritional requirements, ▪ biochemical activities, and ▪ source of energy.  What are bacteria? Single celled organisms ✔ Very small E. Coli O157:H7 can make you very sick. ✔ Need a microscope to see ✔ Can be found on most materials and Streptococcus can surfaces cause strep throat. ◦ Billions on and in your body right now This E. coli helps you digest food. USDA NIFSI Food Safety in the Classroom© University of Tennessee, Knoxville 2006 Size, shape and arrangement of bacterial cells Most bacteria are 0.2 um in diameter and 2-8 um in length. The three basic bacterial shapes are coccus (spherical), bacillus (rod-shaped), and spiral (twisted), however pleomorphic bacteria can assume several shapes. Arrangement of Cocci Cocci may be oval, elongated, or flattened on one side. Cocci may remain attached after cell division. These group characteristics are often used to help identify certain cocci.  cocci Cocci that remain in pairs after dividing are called diplococci. Cocci that divide in multiple planes and form grape like clusters or sheets are called staphylococci. Cocci that remain in chains after dividing are called streptococci. Cocci that divide in two planes and remain in groups of four are called tetrads. Binary Fission Bacteria Bacilli Bacilli only divide across their short axis thus forming fewer groupings. Bacillus is a shape (rod shaped or cylindrical) NB: there is also a genus of bacteria with the name Bacillus Bacilli Most bacilli appear as single rods. Diplobacilli appear in pairs. Streptobacilli appear in chains after division. after division. Some bacilli are so short and fat that they look like cocci and are referred to as coccobacilli.  Spiral bacteria Spiral bacteria have one or more twists. Vibrios look like curved rods. Spirilla have a helical shape and fairly rigid bodies. Spirochetes have a helical shape and flexible bodies. Spirochetes move by means of axial filaments, which look like flagella contained beneath a flexible external sheath. SPIROCHETE :AXIAL FILAMENT Spiral Bacteria Spirillum is the bacteria of a genus of Gram-negative bacteria Staphylococcus Staphylococcus is a gram positive spherical cell, usually arrange in grapelike irregular clusters. They grow rapidly on many types of media producing pigments that varies from white to deep yellow Staphylococcus has at least 40 species. The three most frequently encountered species are Staphylococcus aureus, Staphylococcus epidermidis and Staphylococcus saprophyticus Staphylococcus - Toxic shock syndrome Most S. aureus strains isolated from patient with toxic shock syndrome produce a toxin call toxic shock syndrome toxin-1 This toxin is associated with fever, shock, and multiple involvement, including a skin rash Staphylococcus - Clinical Findings A staphylococcus infection may appear as: ◦ Pimple ◦ Hair follicle infection or abscess Staphlococcus infection can also result from direct contamination of wound e.g. post operation wound or infection following trauma Stapylococcus aureus may also cause 1. endocarditis, 2. osteomyelitis, or 3. meninigitis Streptococcus Streptococci are gram positive spherical bacteria that characteristically form pairs or chains Some are members of the normal flora; others are associated with important human diseases such as sore throat Streptococcus There are many species of streptococcus. Those of clinical importance include: S. pyogenes (group A), S. agalactiae (group B) S. pneumoniae (pneumococcus) Streptococcus Streptococcus pyogenes; The individual cocci are spherical or ovoid and are arranged in chains The length of the chains vary widely and are conditioned by environmental factors Most group A strains produce capsule  Streptococcus - Clinical Finding A variety of disease conditions are associated with S. pyogenes these include: Cellulitis – an acute, rapidly spreading infection of the skin and subcutaneous tissues Bacteraemia/ sepsis- infection of traumatic or surgical wounds with streptococci results in bacteraemia Rheumatic fever– one of the most serious disease conditions associated with S. pyogenes as it damages the heart muscles and valves Streptococcus agalactiae The group B streptococci. Typically gram positive Part of the normal flora of the vagina and the lower intestinal tract. Streptococcus agalactiae - Clinical Findings Group B streptococcal infection during the first month of life may present as: sepsis, meningitis or respiratory distress syndrome Intravenous ampicillin given to mothers who carry group B streptococcus prevents the colonization of their infants and group B streptococcal disease  Streptococcus pneumoniae S. pneumoniae are gram positive diplococci, often lancet shape or arrange in chains S. pneumoniae are normal flora of the the upper respiratory tract May cause pneumonia, sinusitis, otitis, bronchitis, bacteremia and other infections Escherchia coli These are gram negative rods (baccili) They are normal flora of the intestine An isolate from urine can be quickly identified as E. coli by it haemolysis on blood agar Clinical Findings E. coli is the most common form of urinary tract infection Symptoms and signs include urinary frequency, dysuria, hematuria, pyrexia E. coli may also be associated with diarrheal diseases. Microscopic picture of E. coli  Shigella Another e.g. of bacilli Shigella are non-motile gram negative bacilli Shigella species are closely related to E.coli Shigella are facultative anaerobes but grow best aerobically.  Clinical Findings Shigella infections are almost always limited to the gastrointestinal tact; blood stream invasion is quite rare Shigella are highly communicable After an incubation period of (1-2 days) there is a sudden onset of abdominal pain, fever and watery diarrhea The diarrhea has been attributed to to an exotoxin acting in the small intestine  Clinical findings cont After a day or so later the infection involves the ileum and colon and the number of stool increases 2-5 days fever and diarrhea subside spontaneously In children and elderly loss of water and electrolytes may lead to dehydration, acidosis or even death  Vibrios Vibrios are among the most common in surface waters worldwide They are curved aerobic rods and are motile They posses a polar flagellum V. cholerae serogroups O1 and O139 cause cholera in humans Vibrios  Pathogenesis V. cholerae is pathogenic only for humans A person with normal gastric acid may have to ingest 10 or more V. cholerae to become infected when the vehicle is water, because the organism is susceptible to acid When the vehicle is food fewer organisms are need to cause an infection.  Pathogenesis continue Any medication or condition that decreases the stomachs acidity make the person more susceptible to infection with V. cholerae Cholera is a non invasive infection Vibrio cholerae  Clinical findings About 60% of infection with V. cholerae are asymptomatic The incubation period is 1-4 days There is a sudden onset of nausea and vomiting and profuse diarrhea with abdominal cramps Stool which resembles “rice water” contain mucus, epithelial cells and large no. of vibrios There is rapid loss of fluid and electrolytes The mortality rate without treatment is between 25%- 50% Specimen for culture stool  Treponema Pallidum These are slender spirals gram negative organisms The organisms are actively motile The long axis of the spiral is most times straight but may sometimes bend They do not stain well with aniline dyes, but they can be seen in tissues when stained by a silver impregnation method. T. Pallidum is the agent responsible for causing syphilis Treponeme a  Treponemea Pathogenesis Infection with T. pallidum is limited to humans Usually transmitted by sexual contact Produces legions on the skin or mucus membrane of genitalia In 10-20% of case, the primary lesion is intrarectal, perianal, or oral Spirochetes multiply at the site of entry and some spread to the lymph node and then reach the blood stream  Treponemea Clinical Findings Incubation period 2-10wks In 2-10 wks after infection a papule develops at the site of infection and breaks down to form an ulcer (“hard chancre”) The inflammation is characterize by a predominance of lymphocytes and plasma cells This primary lesion always heal spontaneously.  Treponemea Clinical Findings cont 2-10 wks secondary lesions appear. These consist of a red maculo-papular rash any where on the body Both primary and secondary legions are rich in spirochetes, and highly infectious Syphilitic infection may remain subclinical; patient may pass through the primary or secondary (or both) without symptoms yet develop tertiary legions.  Laboratory Tests Specimen – tissue fluid from legions or blood serum Test include: Dark –Field examination Immunofluorence Serologic tests for syphilis  Leptospirae The agent causing leptospirosis Leptospirae are tightly coiled, thin, flexible spirochetes They are motile (best seen under dark-field microscope) It does not stain readily but can be impregnated with silver Leptospirae grow best under aerobic conditions at 28- 30 degree celcius The spirochete is very delicate in dark –field view it may appear only as a chain on minute cocci Darkfield Microscope and Image  Leptospirae Pathogenesis Leptosprires are often found in water and enters the body through breaks in the skin (cuts and abrasions) and mucus membranes (mouth, nose, conjunctivae) Incubation period 1-2 wks After incubation there is a febrile onset during which spirochetes are present in the blood stream They often attach themselves in organs such as the liver and the kidney Symptoms: jaundice hemorrhage and nitrogen retention The illness is biphasic after improvement, the second phase develops presenting as “ aseptic meningitis” with intense headache stiff neck Laboratory Test Specimens – include blood, CSF, urine (should be collected with great care to avoid contamination) Test 1. Dark-field examinations or thick smears stained by the giemsa technique 2. Culture 3. Serology Cross section of spirochete cell Spirochetes APPENDAGES OF VARIOUS SPECIES OF BACTERIA ▪ Cell surface appendages (aka filamentous appendages) are proteinaceous tubular or fibrous structures found on the surface of bacterial cells. ▪ They extend from the surface of the bacterial cell wall ▪ Have many functions such as locomotion, attachment, adhesion and assisting in genetic exchange. Appendages of Bacteria The THREE types of cell surface appendages are present on bacteria. The classification is based on the relative length of the appendages, composition and function. The three cell surface appendages of bacteria are (1). Flagella (2). Fimbriae (3). Pili FLAGELLA The most important function of flagella is to assist in locomotion. Flagella can also act as a sensory organ to detect temperature and the presence of certain chemicals. present in prokaryotes and eukaryotes, both are entirely different in their structure, formation and mechanism of propulsion. FIMBRIAE Bristle-like short fibres occur on the surface of some bacteria. Enable the bacterial cell to stick to the surface of host cells Help in the formation of pellicles or biofilms. (Pellicle: thin sheet of cells on the surface of a liquid).  PILI Pili are long hair like tubular micro-fibres like structures present on the surface of some Gram negative bacteria. Comparatively shorter than flagella and longer than fimbriae. Many classes of pili based on their structure and function. APPENDAGES OF VARIOUS SPECIES OF BACTERIA INCLUSIONS OF VARIOUS SPECIES OF BACTERIA Inclusion bodies are nuclear or cytoplasmic aggregates of stainable substances, usually proteins. Typically represent sites of viral multiplication in a bacterium or a eukaryotic cell, and Usually consist of viral capsid proteins. Inclusion bodies have a non-unit lipid membrane researchers have recovered folded protein from inclusion bodies.  INCLUSION BODIES Sulfur granules are especially common in bacteria that use hydrogen sulfide as an electron source. When genes from one organism are expressed in another, the resulting protein sometimes forms inclusion bodies. Many bacteria store excess carbon in the form of polyhydroxyalkanoates or glycogen. See notes section for more details Distinguishing Features of Stains THE SIMPLE STAIN simple staining procedure involving only one stain. methylene blue, Gram safranin, and Gram crystal violet. Basic stains, such as methylene blue, Gram safranin, or Gram crystal violet are useful for staining most bacteria. Methylene Blue DIFFERENTIAL STAINS Differential Staining is a staining process which uses more than one chemical stain. Using multiple stains can better differentiate between different microorganisms or structures/cellular components of a single organism.  DIFFERENTIAL STAINING Differential staining is used to detect abnormalities in the proportion of different white blood cells in the blood. The process or results are called a WBC differential. This test is useful because many diseases alter the proportion of certain white blood cells. By analyzing these differences in combination with a clinical exam and other lab tests, medical professionals can diagnose disease.  DIFFERENTIAL STAINING Differential staining eg: the Gram stain. Gram staining uses two dyes: Crystal violet and Fuchsin or Safranin (the counterstain) to differentiate between Gram-positive bacteria (large Peptidoglycan layer on outer surface of cell) and Gram-negative bacteria. DIFFERENTIAL STAINING SPECIAL STAINING Special staining is performed to visualize selected tissue elements, entities and microorganisms. Based on classical dye staining methods, special stains technique provide valuable information in the evaluation of numerous abnormal or disease conditions.  SPECIAL STAINS An example of special stain technique highlights the flagella of bacteria by coating the flagella with dyes or metals to increase their width. Flagella so stained can then be observed. A special stain technique is used to examine bacterial spores. SPECIAL STAINING EXAMPLE