This kind of test is called a PCR, or polymerase chain reaction, and it uses small samples of DNA to detect patterns that indicate the presence of certain bacteria, viruses, or infections.
One PCR instrument can test stool samples for presence of C. That same instrument can use a nasal swab to test for MRSA. Another instrument allows for testing of the respiratory virus panel based on a nasal swab. It can also detect the stool parasites Giardia , Cryptosporidium , and E. This instrument reduces the time it takes the result to get to the doctor.
A traditional stool culture can take days to be resulted once received in the lab, but the BD MAX can get the same results within 24 hours. Automated molecular instruments can also provide much faster results for some sexually transmitted diseases just hours after they are run on the instrument, rather than patients having to wait days for traditional cultures to yield a result.
Yes, PCR automation saves time, but identifying the causative agent of an illness is just one step in determining how it should be treated. Many specimens must still be cultured to determine their susceptibility — to find out which antibiotics will kill off the offending bacteria. This process is called susceptibility testing. One method of S. For this test, the surface of a large culture plate is swabbed with the pathogenic organism and small discs of antibiotics are placed on the plate.
She explained that using antibiotics incorrectly can wipe out populations of very susceptible bacteria and can leave more resistant strains behind. Susceptibility testing informs the clinician of the antibiotics that can be used, as well as those drugs that the bacteria is resistant to. This provides a range of responses to determine the most effective treatment, even if it means testing more than one drug.
Barrante recalls her own experience with severe illness as a child, and how it inspired her to get into the field of Microbiology. TMCC is offering in-person classes and services, masks are required for all individuals. For more information, visit coronavirus. This lab should give you the background information and techniques you will need to successfully perform biochemical tests in order to identify unknown bacterial samples. The micro lab website, your textbook, the web and assorted books available in lab will be the reference materials necessary for you to successfully complete the next several weeks of lab work.
View Flowchart ». Staphylococcus species are normal flora widespread over the body surface. They are also important pathogens. Some of the most common diseases caused by Staphylococcus species include: impetigo, toxic shock syndrome, bacteremia, endocarditis, folliculitis furuncle boils , and osteomyelitis bone abscesses.
Many species of Staphylococcus have the ability to form biofilms which can then colonize structures such as medical catheters, stents, heart valves, prostheses, shunts, and valves. The clinically significant species are generally separated into coagulase-positive staphs S. Many members of the Streptococcus genus are normal flora to the mouth, nose, and throat. The genus Streptococcus is a complex group causing a wide range of diseases such as: rheumatic fever, impetigo, pharyngitis, laryngitis, toxic shock syndrome, scarlet fever, and endocarditis.
Streptococci are often classified based on hemolysis which can be seen by their reaction on blood agar. Alpha hemolytic species produce alpha-hemolysin which reduces hemoglobin red to methemoglobin green causing a brownish or greenish zone around the colony. Beta hemolytic species produce a hemolysin that forms a clear zone around the colony, indicating complete lysis of red blood cells.
Gamma hemolytic species are non-hemolytic, having no apparent effect on red blood cells. The Gram negative enterics are important both as natural flora in the intestinal tract and as pathogens of disease in the gastrointestinal tract and other sites. Four main families with numerous genera and species comprise the Gram negative enteric: Enterobacteriacea, Pseuodmonadaceae, Vibrionaceae, and Camplyobacteraceae.
You will only be working with organisms from the first two families. We have included the basic procedure for doing many common biochemical tests below. You will find more specific procedures for specific biochemical test on the following pages.
You will need to look up the individual test for a more detailed description, including the biochemical basis of each test. Blood agar is used to support the growth of fastidious organisms and to determine the type of hemolysis destruction of red blood cell walls an organism produces.
The hemolytic response can be dependent upon the type of blood. Sheep blood is commonly used, but some organisms require rabbit or bovine blood. The coagulase test detects the presence of free and bound staphylcoagulase.
This enzyme is excreted extracellularly by human strains of Staph. The mechanism of action is unknown.
The formation of a clot in the bottom of the tube is considered a positive result. The clot will not move as you tilt the tube. Unclotted plasma will flow in the tube. Bacitracin differential disks are used to presumptively identify Group A, beta-hemolytic streptococci from other beta-hemolytic streptococci.
The combination of SXT sensitivity increases the accuracy of the results. Recent studies of nontypable H influenzae strains have shown that bactericidal antibody to outer membrane proteins develops in infants in response to otitis media caused by these organisms.
Normal adults generally have both bactericidal and opsonizing antibodies directed against nontypable H influenzae. Although levels of opsonizing antibody may be low in adults who develop acute nontypable H influenzae infection, substantial levels of bactericidal activity are present in serum at the time infection is diagnosed. It is not clear why this should occur.
In some instances a blocking effect by secretory IgA in bronchial secretions might be responsible. Alternatively, the extensive structural damage to the bronchi and lungs that predisposes to serious nontypable H influenzae infection may allow proliferation of the bacteria unchecked by normal serum defense mechanisms.
Haemophilus organisms spread directly among individuals without a known contribution from environmental sources or animal reservoirs. Nontypable H influenzae strains are found in the nasopharynx of many healthy subjects, depending upon the frequency and intensity with which they are sought.
By contrast, type b H influenzae is found only in 1 to 2 percent of healthy children, and its spread to previously uncolonized children in the early years is associated with a substantially increased risk of infection. Families and day care centers are important sources for dissemination of these organisms.
Haemophilus influenzae meningitis cannot be distinguished on the basis of clinical presentation, physical examination, or cerebrospinal fluid abnormalities from meningitis due to other common bacterial pathogens. Detection of capsular material in the cerebrospinal fluid by counter immunoelectrophoresis is helpful in cases in which the Gram stain is not conclusive; this technique is especially important in patients who have received enough antibiotic to suppress the growth of organisms in cultures of cerebrospinal fluid, but not enough to be curative.
The bacteriologic diagnosis of pneumonia or acute febrile purulent tracheobronchitis due to H influenzae is made by finding myriad small, somewhat pleomorphic, Gram-negative coccobacilli in Gram-stained sputum Fig. Blood cultures may be positive in 10 to 15 percent of patients with pneumonia and are negative in those with acute febrile tracheobronchitis. Endocarditis due to H parainfluenzae tends to be associated with large vegetations that embolize to large arteries such as femoral or carotid, causing a limb to turn blue and cool, or producing a stroke.
The etiologic diagnosis of endocarditis is, of course, established by blood culture. Recent studies have suggested that many isolates previously identified as H parainfluenzae are, in fact, H paraphrophilus.
Chancres due to H ducreyi are tender, somewhat irregular, and slightly indurated; they may be confused with primary syphilitic chancres, traumatic lesions of the penis especially with bacterial superinfection , fixed drug eruptions, or ulcerated herpetic lesions.
The diagnosis is established by culturing the causative organism on Mueller-Hinton agar supplemented with 5 percent sheep blood and incubating it for 96 hours in a CO 2 -enriched atmosphere. Outbreaks of serious infection due to type b H influenzae can be prevented by vaccination or prophylactic therapy.
Initial trials of vaccination with type b H influenzae PRP were disappointing, because this polysaccharide in its pure form is not immunogenic in infants, the group most at risk of infection. Later studies showed that injection of PRP conjugated to a protein, such as diphtheria toxoid, that serves as an adjuvant results in good antibody responses in infants. Clinical trials with these vaccines have been successful, and preparation of PRP linked to outer membrane proteins or ribosomes are currently in widespread use.
Once an outbreak of type b H influenzae infection has been documented, infants and toddlers who are in intimate contact with colonized or infected individuals have a greatly increased, albeit still small, likelihood of developing serious infection. The use of rifampin prophylaxis to prevent or eradicate nasopharyngeal colonization has been recommended. This measure is controversial, however, because if widely applied it might encourage the emergence of rifampin-resistant organisms, and also because the cost to prevent each potential case of meningitis is high.
The mainstay of therapy for H influenzae infection used to be ampicillin, since isolates were uniformly susceptible to 0. In most medical centers, 25 to 30 percent of type b isolates and a somewhat smaller percentage of nontypable isolates are now resistant to penicillin or ampicillin; in some centers, 50 to 60 percent of type b H influenzae isolates are ampicillin resistant.
Chloramphenicol was long considered the drug of choice for meningitis caused by a penicillin-resistant H influenzae strain, and it is still highly effective. Third-generation cephalosporins, such as ceftriaxone or cefotaxime, are effective against H influenzae and penetrate the meninges well; these drugs are useful in treating H influenzae meningitis.
The addition of corticosteroids may reduce the incidence of complications such as deafness. In addition to the above-named drugs, tetracycline and sulfa drugs are effective in treating upper and lower respiratory infections caused by Haemophilus. Erythromycin should not generally be used to treat H influenzae infections; many isolates are resistant, and documentation of susceptibility in routine clinical laboratories is subject to error. The spread of soft chancre due to H ducreyi is best prevented by use of a condom during sexual intercourse.
All isolates are susceptible in vitro to erythromycin, and excellent clinical results have been obtained. Turn recording back on. National Center for Biotechnology Information , U. Show details Baron S, editor. Search term. Chapter 30 Haemophilus Species Daniel M.
General Concepts Clinical Manifestations Type b Haemophilus influenzae can cause meningitis, epiglottitis, bacteremia, and cellulitis. Structure, Classification, and Antigenic Types Haemophilus species are Gram-negative coccobacilli similar in ultrastructural features to other pathogenic bacilli. Pathogenesis Type b H influenzae colonizes the nasopharynx, and may penetrate the epithelium and capillary endothelium to cause bacteremia.
Host Defenses Serum antibody to the capsule in the case of typable H influenzae or to somatic antigens is bactericidal and promotes phagocytosis. Diagnosis Respiratory secretions and cerebrospinal fluid must be cultured on chocolate agar.
Introduction The genus Haemophilus includes a number of species that cause a wide variety of infections but share a common morphology and a requirement for blood-derived factors during growth that has given the genus its name.
Clinical Manifestations Haemophilus species cause a variety of clinical syndromes Fig. Figure Clinical presentation of Haemophilus infections. Structure, Classification, and Antigenic Types Haemophilus species are Gram-negative coccobacilli that share common ultrastructural features with other Gram-negative bacilli.
Pathogenesis The pathogenesis of H influenzae infections is not completely understood, but the presence of the type b polysaccharide capsule is a major factor in virulence.
Meningitis The pathogenesis of meningitis due to type b H influenzae has been well studied. Cellulitis and Epiglottitis Cellulitis and epiglottitis are discussed together because their pathogenesis is probably quite similar. Respiratory Disease Nontypable H influenzae is a major pathogen that colonizes the human respiratory tract. Figure Gram-stained sputum showing profuse Gram-negative coccobacilli with no other bacterial forms present original magnification X Brazilian Purpuric Fever In the past few years, a syndrome of fulminating illness with substantial mortality characterized by nausea, vomiting, hemorrhagic skin lesions, fever, prostration, and shock has been recognized under the name Brazilian purpuric fever.
Miscellaneous Type b H influenzae use to be a relatively common cause of septic arthritis in children and results from hematogenous dissemination. Host Defenses For many years it was believed that bactericidal antibody directed against PRP capsule of type b H influenzae was entirely responsible for host resistance to infection. Figure Macrophage or polymorphonuclear leukocyte phagocytosing H influenzae coated with antibodies specific for the capsule and somatic antigen.
Epidemiology Haemophilus organisms spread directly among individuals without a known contribution from environmental sources or animal reservoirs.
Diagnosis Haemophilus influenzae meningitis cannot be distinguished on the basis of clinical presentation, physical examination, or cerebrospinal fluid abnormalities from meningitis due to other common bacterial pathogens. Control Outbreaks of serious infection due to type b H influenzae can be prevented by vaccination or prophylactic therapy.
Branhamella catarrhalis , and Neisseria gonorrhoeae. Antimicrob Agents Chemother , Efficacy of Haemophilus influenzae type b polysaccharide-diphtheria toxoid conjugate vaccine in infancy.
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J Clin Microbiol. Antimicrobial resistance among respiratory isolates of Haemophilus influenzae , Moraxella catarrhalis , and Streptococcus pneumoniae in the United States. Antimicrob Agents and Chemother. Infect and Immun, p. Serotype and ampicillin susceptibility of Haemophilus influenzae causing systemic infections in children: 3 years of experience.
Nontypable Haemophilus influenzae : a review of clinical aspects, surface antigens, and the human immune response to infection. Outer membrane protein and lipooligosaccharide analysis of paired nasopharyngeal and middle ear isolates in otitis media due to nontypable Haemophilus influenzae : pathogenic and epidemiological observations.
Immunity to Haemophilus influenzae type b in young adults: correlation of bactericidal and opsonizing activity of serum with antibody to polyribosylribitol phosphate and lipooligosaccharide before and after vaccination.
Pneumonia and acute febrile tracheobronchitis due to Haemophilus influenzae. Ann Intern Med. The risk of subsequent transmission of Haemophilus influenzae type b disease among children in day care.
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