GRAM POSITIVE BACILLI Bacillus Corynebacteria Listeria, etc.
-
Upload
arline-dean -
Category
Documents
-
view
220 -
download
0
Transcript of GRAM POSITIVE BACILLI Bacillus Corynebacteria Listeria, etc.
Clinically important Gram positive bacilli
Spore forming• BacillusNon spore forming• Corynebacterium• ListeriaBacilli w/ branching filaments• Actinomyces • Nocardia
Bacillus anthracis
• Large bacilli of 1-3 m• Single or paired in
clinical isolates• In vitro – prominent
capsule• Highly resistant spores
Anthrax
Virulence factors• Capsule (antiphagocytic)• Toxin (oedema & death)
Cutaneous anthraxAbout 20% mortality
Cutaneous anthraxAbout 20% mortality
Gastrointestinal anthraxHigh mortality
Gastrointestinal anthraxHigh mortality
Inhalation anthraxHigh mortality
Inhalation anthraxHigh mortality
Anthrax - Diagnosis
• Specimen– Aspirate or swab from cutaneous lesion– Blood culture– Sputum
• Laboratory investigation– Gram stain– Culture– Identification of isolate
Anthrax – treatment and prevention
• Penicillin• Tetracycline /chloramphenicol
• Erythromycin,Clindamicin• Prevention
– Vaccination of animal herds– Proper disposal of carcasses
• Active immunisation with live attenuated bacilli
Bacillus cereus
• Large, motile, saprophytic bacillus• Heat resistant spores• Pre formed heat and acid stable toxin (Emetic
syndrome)• Heat labile enterotoxin (Diarrhoeal disease)• Lab diagnosis – Demonstation of large number
of bacilli in food
Gastroenteritis
Gastroenteritis
Bacillus cereus clinical presentation
Incubation period < 6 hoursSevere vomitingLasts 8-10 hours
Incubation period > 6 hoursDiarrhoea
Lasts 20-36 hours
EMETIC FORM DIARRHOEAL FORM
CORYNEBACTERIA
• Causes localized inflammation (pseudomembrane, greyish white exudate ) and generalized toxaemia
• Prevalent in baby’s after 3-6 months, very high in young children
Morphology
• Gram+ve/ palisade/Chinese letter arrangement
• Irregular swellings at one end -club shaped.• Corynebacteria tend to pleomorphism in
microscopic and colonial morphology.
Culture characteristics
• On blood agar Small granular & gray with irregular edges and may have small zones of hemolysis.
• Also grow on Loeffler's serum slope• On blood telurite agar (black colonies)
Important species
• Corynebacterium diphtheriae• Normal flora of nasopharynx in about 10%
– Some may cause Diphtheria• Diptheroids
– Normal flora of skin, contaminants of samples– Can cause disease in ‘compromised’ host
• C. ulcerans C. haemolyticum C. jeikeium
Epidemiology
• Rare in developed countries/ • Disease of third world countries• Still highly prevalent in the former Soviet
Union.• Spread through droplets.• Nasal carriers are very dangerous
Types of Diphtheria
• Faucial• Laryngeal• Nasal• Conjunctival• Vulvovaginal• Otitic• Cutaneous around the mouth and the nose
Pathology
• Toxin is absorbed in the mucus membrane and causes destruction of epithelium and causes a superficial inflammatory response.
• Necrotic epithelium becomes embedded in exuding fibrin and red and white cells, with bacteria.
• Grayish pseudomembrane is formed over the tonsils and pharynx and larynx.
Pathology
• Removal of pseudomembrane - capillary damage and bleeding..
• Regional lymphadenopathy with marked edema of the neck within the membrane bacilli produce toxin.
• This results in distant toxic damage - parenchymatous degeneration, fatty infiltration & necrosis in heart muscle liver kidney & adrenals.
Diagnosis• Direct smear - Albert's stain• Culture - Loffler's serum slope/blood agar/blood
telurite agar
Check the toxigenicity• Animal inoculation - Guinea pigs/rabbits - Death
within 96 hrs• Elek’s test
Management
1. Patients – Isolation of the patient– Bed rest– Antibiotic treatment
(Penicillin/erythromycin/teracycline/rifampicin/clindamycin )– Antitoxins (horse serum)
2. Contacts– Immunize (toxoid)– Prophylactic antibiotic – erythromycin– Swab nose and throats of contacts
3. Community – immunization
DIPHTHERIA
DIAGNOSIS
Clinical suspicionSwab for cultureToxin production
TREATMENT
PenicillinAnti-diphtheretic serum
Maintaining airwaySupportive
PREVENTION
Immunization(toxoid)
Clinical Manifestations
• Listeriosis is a serious disease for humans, with a mortality greater than 25 percent.
• Two main clinical manifestations, sepsis and meningitis.
Characteristics
• Small, gram-positive rods, which are sometimes arranged in short chains.
• Flagella are produced at room temperature rather than at 37° C.
• A particular property of L monocytogenes is the ability to multiply at low temperatures. Bacteria therefore can accumulate in contaminated food stored in the refrigerator.
Pathogenesis
• Listeria monocytogenes is presumably ingested with raw, contaminated food.
• An invasion factor secreted by the pathogenic bacteria enables them to penetrate host cells of the epithelial lining.
• Normally, the immune system eliminates the infection before it spreads. If the immune system is compromised, however, systemic disease may develop.
Pathogenesis
• Listeria monocytogenes multiplies not only extracellularly but also intracellularly within macrophages after phagocytosis and even within parenchymal cells which are entered by induced phagocytosis.
• Survival within the phagosomes and eventual escape into the cytoplasm are mediated by a toxin, which also acts as a hemolysin.
Host immune response
• Because it multiplies intracellularly, L monocytogenes is largely protected against humoral immune factors such as antibodies,
• The effective host response is cell- mediated, involving both CD4+ (T-helper) cells and direct lysis of infected cells by CD8+ (cytotoxic) T lymphocytes.
Epidemiology
• Listeria species are found in living and nonliving matter. Various foodstuffs of vegetable and animal origin are sources of infection.
• Most human cases of listeriosis develop in immunocompromised hosts: newborns, old people, cancer patients, and transplant recipients.
• Outbreaks of listeriosis are due mainly to a common source of contaminated food.
• Listeriosis also may be transmitted congenitally across the placenta. The immunocompetent mother suffers at worst a brief, flu-like febrile illness, but the fetus, whose defense system is still immature, becomes seriously ill.
Diagnosis
• Listeria monocytogenes is implicated when monocytosis is observed in the peripheral blood as well as the cerebrospinal fluid.
• Early diagnosis may be obtained by finding pleocytosis with Gram-positive rods in a Gram stain of smears of the cerebrospinal fluid.
• Final proof is obtained by culture. • Serologic tests are highly unreliable.
Control
• Hygienic food processing and storage may reduce the risk of listeriosis.
• Individuals in high-risk groups (i.e., immuno-compromised individuals and pregnant women) should avoid uncooked food or should at least marinate salads for a long time in a vinegar-based dressing to kill adherent bacteria.
• Antimicrobial agents are the mainstay of treatment. Most of the common antibiotics, except cephalosporins, are active against L monocytogenes in vitro. High doses for prolonged periods are indicated.
Erysipelothrix Rhusiopathiae
• Clinical Manifestations• The most common human infection by E
rhusiopathiae is erysipeloid, a well-defined, violet or wine-colored inflammatory lesion of the skin of the fingers or hand .
• Itching is typical. Infrequently, septicemia develops, followed by various organ manifestations such as endocarditis or arthritis without fever.
Erysipelothrix Rhusiopathiae
• Structure and Classification• Erysipelothrix rhusiopathiae is a slender, Gram-
positive rod similar to L monocytogenes. • They grow on routine culture media under aerobic
conditions, but preferentially in a CO2 atmosphere. • In contrast to L monocytogenes, they are nonmotile,
nonhemolytic, and catalase negative. • The production of H2S is highly indicative.
Erysipelothrix Rhusiopathiae
• Pathogenesis• A minor skin injury may facilitate the penetration of E
rhusiopathiae after contact with infected material. After an incubation of 1 to 4 days the local lesion develops; spontaneous recovery occurs in 2 to 3 weeks. Septicemia has been observed without previous local lesions so that an oral infection is assumed. Endocarditis may develop in a few cases.
Erysipelothrix Rhusiopathiae
• Epidemiology• Erysipelothrix rhusiopathiae is found in mammals,
poultry, and fish. • Individuals who have occupational exposure to such
animals (i.e., farmers, veterinarians, slaughterhouse workers, and fish handlers) are at risk.
Erysipelothrix Rhusiopathiae
• Diagnosis• Since there is no wound, a swab is not useful.
Bacteria can be cultured from a biopsy of the progressing, inflamed edge of the lesion.
• Blood culture is indicated in the setting of sepsis and endocarditis.
• Control• Penicillin is the drug of choice to treat serious
infections. Since local skin infection is self-limited, therapy is not essential.
ACTINOMYCETES(FACULTATIVELY ANAEROBES)
• Fermentative gp: Actinomyces, Arcanobacterium and Rothia
• Oxidative gp : Actinomadura (actinomycetoma), Nocardia (nocardiosis), Streptomyces and related species.
6. Actinomyces israelii
• Has branching filaments• Facultative anaerobes• Normal flora of oral cavity• Causes ‘Actinomycosis’ characterised by
multiple abscess and granuloma formation• Tissue destruction, fibrosis and sinus
formation
ACTINOMYCOSIS
• Mostly in cervico-facial region• Endogenous infection• Can get
– Thoracic actinomycosis (aspiration)– Pelvic actinomycosis (IUCD)– Rarely haematogenous spread
• Treatment– Surgical– Long term penicillin
Diagnosis
• Specimens – open biopsy, aspiration material
• Sulphur granules (yellowish myecelial masses)
• The discharge should mix with sterile saline in a universal bottle and allow to stand, particles will separate out.
7.Nocardia asteroides
• Branched, strictly aerobic bacillus• Environmental saprophytes (exogenous
infection)• Lightly acid-fast • Uncommon causes of opportunistic
pulmonary disease• Causes primary post-traumatic or post-
inoculation lung disease