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The staphylococci are spherical or ovoid cells usually arranged in grape-like clusters. Pairs and short chains are seen frequently in fluid media. They are non-spore forming, non-motile, non-capsule producing, and Gram-positive. White, yellow, or orange water-soluble pigments are formed. They are aerobic and facultative, liquefy gelatin, and ferment a number of carbohydrates to acid. These organisms are found in suppurative processes in man and animals.
Staphylococcus aureus is named for its golden yellow pigment. A similar species called Staphylococcus epidermidis produces a chalky white pigment. These pigments are most distinctive in colonies on solid media. The only other species now recognized is Staphylococcus saprophyticus, which grows on dead tissues. S. aureus and certain white-pigmented variants are distinguished from S. epidermidis on the basis of
They are facultative anaerobes that grow more rapidly and abundantly under aerobic conditions. Although they form no spores, they are somewhat resistant to drying, and can therefore remain alive for several months under favorable conditions in dust or elsewhere outside the body. One or both species are often present in the normal upper respiratory tract. The differential characteristics of staphylococci are presented in Table 1.
Table 1 Differential Characteristics of Staphylococcal Species
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The organism is resistant to the following:
Many staphylococci organisms resist 60`C for 1 hour and some resist 80`C for 30 min. The only other species of bacteria that resist these temperatures are the spore formers.
These organisms are exceeded in resistance only by spores and the mycobacteria. The mycobacteria have cell walls that are almost 20% wax. The Staphylococci can survive in dried exudate for weeks and months.
Staphylococci are very resistant to the action of disinfectant chemicals.
Staphylococci are resistant to the action of many available drugs.
Staphylococci are notorious for their speed and adaptability in developing resistance to antibiotics and other chemotherapeutic drugs. It has been estimated that 800 of all Staphylococci isolated are resistant to penicillin.
A few strains of S. aureus are encapsulated. They are virulent in animals, and capsular antibodies protect against experimental disease. Capsules may be formed in vivo more but are lost on cultivation. Encapsulated strains are not phage-typable and lack bound coagulase (clumping factor).
Species-specific carbohydrate of S. aureus and S. epidermidis (polysaccharides A and B, respectively) were recognized by Julianelle in 1935 and have now been identified as teichoic acids.
Strains of S. aureus frequently possess a surface component known as protein (or agglutinogen) A, the bulk of which is covalently linked to the peptidoglycan. Some of this protein is also released extracellularly.
The majority of nonencapsulated strains of S. aureus will clump when suspended in plasma or in fibrinogen.
A glycerol lipoteichoic acid is present. Several undefined antigens are involved in agglutination. (Please see Figure 2)
An extracellular enzyme which acts on citrated or oxalated plasma causing it to clot. There are seven immunologically distinct varieties of coagulase. They have no practical use in typing. The presence of the enzyme coagulase is the most definite in vitro indication of its pathogenicity for man.
Coagulase is found in two forms.
This enzyme elaborated by the organism enzyme dissolves fibrin clots. Most coagulase positive staphylococci have some Staphylokinase activity and is antigenic.
An enzyme which dissolves hyaluronic acid. Hyaluronic acid is part of the glue that holds cell matrices together. Hyaluronidase is used therapeutically to enhance the spread of injectable medicines.
All toxins are metabolic products elaborated by cells.These toxins are apparently not elaborated specifically to destroy the Tissues.
This hemolysin causes clear lysis of rabbit and sheep erythrocytes and kills rabbit and human leucocytes. These are usually elaborated from human strain of staphylococci. It is
dermonecrotic when injected into the skin of rabbits and lethal when injected intravenously into mice or rabbits in small doses.
This causes hot-cold lysis of sheep, human and ox erythrocytes, does not kill leucocytes. This is usually produced by animal strains. It is lethal for rabbits when injected intravenously in large doses.
It causes incomplete hemolysis of rabbit, sheep, human, guinea pig, ox, rat and horse erythrocytes. Its action on leucocytes is undetermined. It is usually produced by human strains. It is slightly dermonecrotic for rabbits and quinea pigs and lethal for rabbits.
This causes incomplete hemolysis of human, rabbit, horse, sheep, rat and quinea pig erythrocytes. This kills quinea pig, human, rabbit and mouse leucocytes. Edema and induration only in rabbits and guinea pigs. This hemolysin is usually elaborated by human strains of staphylococci.
This is immunologically different and instinct and is produced by S. epidermidis.
This is produced by most S. aureus strains.
This is elaborated by only a limited number of strains (approximately 500 of S. aureus strains). It is immunologically distinguishable from other staphylococcal toxins. A basic protein of high lysine content which is resistant to trypsin. It is not easily inactivated by heat. It is not formed in vivo, but acts when ingested with food.
causes a variety of dermatologic lesions. This toxin is relatively heat-stable and acid-labile protein and of is produced by approximately 50 of random isolates of S. aureus.
Strains are routinely identified by bacteriophage typing. For this purpose a selected set of lytic bacteriophages is divided into four host-range groups within each group are phages of different serologic types and morphology. It is thus possible to characterize a strain of staphylococcus as belonging to one of these groups and phage types.
Several media have been used for isolating S. aureus. They are polymyxin egg yolk, Vogel Johnson Agar, and Baird-Parker agar. Staphylococcus aureus ferments mannitol, while S. epidermidis and S. saprophyticus do not. Also, S. aureus can tolerate a high salt concentration of close to 10 per cent. Because of this property, mannitol salt agar is often used as a selective medium for the isolation of S. aureus from feces and other sources.
One of the enzymic properties often found in staphylococci is production of the enzyme penicillinase, which destroys penicillin.
Obviously any organism that can excrete this enzyme can protect itself from penicillin. The power to produce penicillinase is a result of genetic mutation. Penicillinase is a Beta-lactamase and can act on molecules like penicillin that contain the beta-lactamse ring.
Adaptive or Induced Enzymes. Sometimes staphylococci, are stimulated to produce penicillinase by contact with the drug, not by geneti mutation. Thus treatment with penicillin may, by itself, induce production of the enzyme.
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The degree of pathogenicity varies from innocuous strains through secondary invaders to the fully virulent forms. Pathogenicity of any bacteria depends as much on host factors as upon bacterial factors. Some hosts are especially vulnerable to infection such as: those recovering from virus infections, the very young whose defenses are not fully developed and the very old whose defenses are impaired due to debilitation. Also, immunologically deficient person eg. genetic deficiency transplantation therapy, irradiated persons, leukemia victims are susceptible to infection. Open wounds both accidental and surgical especially in burn patients, for many reasons such as: barriers (skin and mucus membranes) damaged or destroyed , injured tissue, stress, protein loss may be infected.
Some individuals are especially resistant to bacterial diseases such as: those vaccinated against the disease those recently recovered from the same or similar disease, strong healthy vigorous individuals, and genetically resistant to a certain diseases.
eg. Pustules, furuncles (boils), abscesses, carbuncles, paronychias, and wound infections.
eg. pneumonia, empyemia, cystitis, pyelonephritis, osteomyelitis, impetigo-contagiosa, meningitis.
- fulminating, profound toxemia and death within a few days,or common, longer duration, severe clinical disease, metastatic abscess formation in any or all parts of the body or may follow secondary to an access.
Not staph food poisoning! due to change in intestinal flora with staphylococci now predominating.
It causes mastitis in cows, causes suppurative conditions in wounds and causes lamb pyemia. Tick pyemia by the sheep tick (Ixodes ricinus) introduces S. aureus into the subcutaneous tissue leading to septicemia. Staphylococcosis in poultry causes septicemia, arthritis and 'bumble foot.
Describes chronic granulomatous infection of the udders of horses, cattle and pigs and also infection of the spermatic cord of horses following castration.
The hallmark of a staphylococcal infection is the obscess due to the limited invasive capacity of the bacteria and the host's response to these bacteria. Some of the infections caused by this organism are:
Staphylococci causes mastitis clinically in cattle. It can be in peracute, chronic and subclinical forms. Chronic and subclinical forms are most common.
Source of Infection.
The organisms can be transmitted from man, and other infected cows or contaminated milking machines.
Diagnosis of Mastitis in Cattle.
Bacteriological-Hotis test, culture on blood plate and microscopic examination. Other screening tests such as California Mastitis test. Strip cup method and Wisconsin mastitis test are also employed.
Control.
Proper management prevents spread of infection and one has to be careful in the use of milking machine. Sanitation is important.
Immunization.
Bacterin-toxoid are used in new herds but their effectiveness is still questionable.
Treatment.
Therapy with two antibiotics in combination with wide spectrum antibiotics is more effective as many strains are resistant to penicillin.
Staphylococci are normal inhabitants of skin, mouth, throat and nose. The normal skin barrier is one of the major resistant factors when this barrier is broken, resistance is lowered. Nasal carriers play an important role in the spread of virulent Staphylococci. Rarely do virulent forms come from pets and livestock.
Diagnosis. When taking specimens, the skin flora must be excluded. The following media are most commonly used:
l. Sheep blood agar plates.
Non-selective media allow the detection of hemolysis patterns, human blood may be used, but it is likely to contain antibodies.
2. Mannitol Salt Agar
Demonstrated fermentation of mannitol; 7.5% NaC is inhibitory for most other bacteria and pigment formation is often very good on this media.
3. Definitive test for human pathogenicity is the coagulase test.
All coagulase positive Staph are considered virulent and pathogenic.
4. Phage typing.
For epidemiological studies phage typing is used.
Prevention.
Good housekeeping ,aseptic technique when resistance barriers must be broken. Scrub everything often, and use disinfecting detergents. Keep known nasal carriers out of sensitive areas, i.e., nurseries, obstetric rooms, burn wards, operating teams.
The pneumococci are gram-positive, often lancet-shaped or arranged pairs, possessing a capsule of polysaccharide that permits easy "typing" with specific antisera. They are readily lysed by surface active agents, eg, bile salts. The organisms are normal inhabitants of the upper respiratory tract of humans and can cause pneumonia, sinusitis, otitis, and other infectious processes.
Types of Pneumococci: In humans, types l-8 are responsible for about 70% of cases of pneumococcal pneumonia and for more than half of all fatalities in pneumococcal bacteremia in children.
Immunity is type-specific and depends both on antibodies to SSS and on intact phagocytic function. Vaccines can induce antibody to specific SSS.
The neisserai are a group of gram-negative cocci, usually occurring in pairs. Some members of the group are normal inhabitants of the human respiratory tract. The gonococci and meningococci are human pathogens and typically exist as facultative intracellular parasites.
Humans are the only natural hosts. Meningitis is the commonest complication of meningococcemia. The infection begins very suddenly, with intense headache, vomiting and stiff neck and progresses to a coma within a few hours.
Gonorrhoeae is exclusively a sexually transmissible disease of humans. Gonococci exhibit several morphological types of colonies, but only piliated bacteria appear to be virulent.
Meningococci and gonococci grow best on media containing complex organic substances such as heated blood, hemin, and animal proteins and in an atmosphere containing 5 percent carbon dioxide. The organisms are rapidly killed by drying,sunlight, moist heat, and many disinfectants.
2. Which streptococcal species
are usually prevalent in mastitis in cows? 3. Define the
following: A. Hotis test B. CAMP test C. Strangles D. Streptokinase E. Scarlet fever 4. Describe the appearance of
alpha, beta, and gamma types of streptococci in
blood-agar plates. 5. List five extracellular
products of streptococci. What are their
characteristics. 6. What is the relationship of
pneumococci to streptococci? What is their normal
habitat? How do they resemble and differ from alpha-type
streptococci? Review Videos:
TV l36 & 420 1. Name several extracellular
enzymes produced by staphylococci. Describe properties of
each. 2. How are Staphylococci
identified in case of epidemics? 3. What tests are employed for
diagnosis of mastitis in cattle? 4. Elaborate on the different
types of hemolysins produced by these
organisms? 5. Differentiate between a
virulent staphylococcus and micrococcus 6. Define or identify the
following: a. Coagulase b. Hyaluronidase c. Enterotoxin d. Hot-cold lysis e.
Dermonecrotoxin
l. In what sorts of
infection are alpha-type streptococci found? How are they
transmitted? What is their usual habitat?
Questions
for Review
(Staphylococci)
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