bacteriology 4

Non-Spore-Forming Gram-Positive Bacilli

• Corynebacterium C. diphtheriae

DiseaseDiphteria Opportunistic infections by other

Corynebacterium species (dipheroids)

Properties• Club-shaped also V- or L-shaped

• Beaded appearance

• Methachromatic granules (Albert staining)

• Nonmotile • no capsule

• Facultative anaerobic.

• Classified in CNM group.

Biotypes(based on colony shape, biochemical properties and virulence)

GravisMitisIntermediusBelfanti

Clinical finding• Common diphtheria (Nasopharyngitis)Incubation period of 2–5 days.

Fibrinous exudate “pseudomembrane”

Sore throat, fever, Enlargement of neck lymph nodes and neck edema. Irregulatory of cardiac rhythm, difficulties with vision, speech and swallowing.

Corrosion of myelin sheaths in the central and peripheral nervous system leading to degenerating motor control

Clinical finding

• Cutanous diphtheria (a secondary infection)

• Antibody production: Blocking the fragment B and so preventing entry into the cell.

Transmission• Humans the only natural host

• C. diphtheriae reside in the upper respiratory tract

• Transmitted by airborn droplet

• Infection at the site of a pre-existing skin lesion

Pathogenesis

• Invasivness

• Exotoxin

Invasivness

• Cord factorA glycolipid inhibits eukaryotic cell oxidation.

• NuraminidaseRemoves N-acetyl nuraminic acid from musine

membranes.

Exotoxin (Encoded by gen tox from a temperate phage)

Fragment B. Binding of the toxin

Fragment A. Enzymatic activity

A

B

Nicotinamide adenine dinucleotide phosphate (NAD)

Exotoxin (A fragment)

Nicotinamide ADPReaction with EF2

ADP-EF2Protein synthesis

inhibition

Testing immunity(Schick’s test)

• Intradermal injection (0.1 mL):

I. Cause inflammation (4-7 days later): No antitoxin in patient

II. No inflammation: Antitoxin is present (Immune person)

Laboratory diagnosis• Microscopic observation (differentiation from streptococcal and

vansant nasopharyngitis)

• Isolating the organismLoffler’s mediuma tellurite plateTinsdal medium

• Demonstrating toxin productionAnimal inoculationEleck testELISA

• PCR to detect tox gene

Treatment• Tracheostomy in children (to prevent croup)

• Antitoxin20000-100000 unit (Intra muscular)

• Penicillin or erythromycin

Prevention• VaccinationA combination of diphtheria toxoid, tetanus toxoid,

and killed pertusis organism.

Given at 2, 4 an 6 months of age, with a booster at 1 and 6 years of age and then each 10 years afterward. (DPT or DT)

The toxoid is prepared by treating the exotoxin with 0.3% formaldehyde.

Listeria monocytogenes

• Small rod like “chinese character” • No capsule, Facultative aerobic.• Tumbling movement. Movement in 25 c• Growing in 4c• Small and smooth colony on blood with a

narrow zone of beta-hemolysis• Biochemical tests: Fermentation, Catalase +

Oxidase +

Disease

• Meningitis and sepsis in

1. The fetus or newborn as a result of transmission across the placenta or during delivery.

2. Immunosuppressed adults (especially renal transplant patients)

• The infected mother: asymptomatic or influenzalike illness/ Abortion

Transmission

• The organism is distributed worldwide in animals, plants and soil.

• Transmission to human by contact with animals or their feces

unpasteurized milk contaminated vegetables. Endogenously from gasterointestinal tract.

Pathogenesis

Internalin E-cadherinPhagocytosis

into epithelial cells

PhagocytiosisBy

macrophages and

hepatocytes

Phagolysosome formation

(acidic condition)

Lysteriolysin OsecretionRelease from phagolysosome

Inducing actin polymerization in cytoplasm

Forming filopods

Lab. diagnosis

• Microscopic observation: Diphtheroids

• Isolation by culture: Blood and CSF samples on blood agar

Colonies: Small, gray colonies with a narrow zone of beta hemolysis

Treatment• PenicillinResistant are rare

Prevention

• Cell-mediated immunity is active but no immunization

• Limiting the exposure of immunosuppressed patients to potential sources

Spore-forming gram-positive bacilli

• Bacillus (Aerobic) B. antheracis, B.cereus

• Clostridum (Anaerobic) C. tetani, C. botulinum, C. perfringens,

C. difficile

Bacillus anthracis

• DiseaseAnthrax (common in animal but rare in

humans).

Properties

• A large rod with square ends. • Frequently in chains• A unique anti-phagocytic capsule is composed

of D-glutamate.• Non-motile (other members of the genus are

motile.)

Transmission

• Spores persist in soil for years. Infection from animal products (hides, bristles and wool), contact with sick animal.

• Portals of entry: skin, mucous membranes, and respiratory tract.

Clinical findings

• A typical lesion: A painless ulcer with black, necrotic eschar. Local edema.

• Untreated cases progress to bacteremia and death.

• Woolsorter’s disease (pulmonary anthrax) is a life threatening pneumonia (by inhalation of spores).

Pathogenesis• Invasiveness• Exotoxin

• Anthrax toxin, has 3 components:- Protective antigen- Lethal factor: In the presence of protective antigen is

rapidly fatal for mice. The action is unknown- Edema factor (an exotoxin): An adenylate cyclase

dependent on protective antigen for its binding and entry into the cell.

Lab. diagnosis

• Samples: Exudate, Blood, sputum. • Direct smear: Large rods in chains. Spores not

seen in smears of exudate.• Culture and biological/biochemical tests

(Sensitivity to penicillin (String of pearls test), Fermentation, gelatin hydrolysis, Motility)

• No serological tests are useful

Prevention

• Preventing soil contamination

• Sterilizing dead animals and animal products .

• Protecting persons at risk of exposure with special clothes.

• Vaccination with cell-free vaccine for persons at high risk.

Treatment

• Penicillin No resistant strain isolated

• Motile• No capsule• Saprophyte

Bacillus cereus

Bacillus cereus

• Disease Food poisoningRare infections: Meningitis, Osteomyelitis, …

• TransmissionSpores on grains survive during steaming and rapid

frying. Spore germinated when rice is kept warm.Portal of entry is the gastrointestinal tract.

Pathogenesis• B. cereus produces 2 enterotoxins. Their actions

is unclear.

Clinical findings1. Emetic syndromeA short incubation period (4 hours) with nausea and

vomiting similar to staphylococcal food poisoning.

2. Diarrheal syndromeInvolves a long incubation period (18 hours) with diarrhea

and resembles clostridial gastroenteritis.

Lab. diagnosis

• Not usually done

TreatmentNo antibiotic is given. Only symptomatic treatment

PreventionGrains (specially rice) should not be reheated

ClostridiumsAn aerobic bacteria

Clostridiums tetaniPeritricus flagellaTerminal spore

• DiseaseTetanus (Lockjaw)

Clinical findings

• Incubation period: 4-5 days – several weeks• Violent muscle spasms in the site of infection and

then jaw)• Lockjaw (trismus) due to rigid contraction of the

jaw muscles, which prevents the mouth from opening: a characteristic known as “risus sardonicus”’.

• Low blood pressure• Respiratory failure

Neonatal tetanus

TransmissionSpores are widespread in soil. The portal of entry is a wound site.Germination of spores is favoured by necrotic

tissue and poor blood supply in the wound.

Pathogenesis

• Tetanus toxin (tetanospasmin)It is carried intra-axonally (retrograde) to the

central nervous system, where it binds to ganglioside receptors and blocks release of inhibitory mediators (e.g. glycine, Gamma-aminobutiric acid) at spinal synapses leading to hyper reflection and spastic paralysis.

Diagnosis

• History of wound and clinical picyure• There is no microbiologic or serologic diagnosis.• Organisms are rarely isolated from the wound site.

Treatment• Antitoxin does have a low effect• Penicillin• Respiratory support• Muscle relaxants

Prevention

• Immunization with toxoid in childhood (2, 4, 6, 12 months ages) and every 10 years thereafter.

• When trauma occurs deeply:1. Wound should be cleaned and debrided.2. Tetanus toxoid booster should be given.3. Tetanus immune globulin should be given.4. Penicillin administered.

Clostridium botulinum

• Disease•Transmission•Pathogenesis•Clinical findings•Laboratory diagnosis•Treatment•Prevention

Transmission

• In soil ---> Alkaline vegetables/meat ---> canned/vacuum-packed ---> Spore germination ---> Toxin production ---> ingestion

Pathogenesis

• Botulinus toxinObserving from the gut ---> Carrying via the

blood to peripheral nerve synapses ---> Blocking release of acetylcholine ---> Paralysis

Clostridium perfringens

• Disease: Gas Gangrene / Food Poisoning• Transmission• Pathogenesis• Clinical findings• Laboratory diagnosis• Treatment• Prevention

Transmission

• Soil, vegetative cells are members of normal flora in colon and vagina.

• Is associated with war wounds.

Pathogenesis and clinical findings

• Alpha toxin: Lecithinase• Glycogen metabolism: Gas in tissues:

Crepitation

• TreatmentPenicillinWounds should be debridedH2O2

Crepitation

Lab diagnosis

• Smear of tissue and exudate samples: large positive rods.

• Cultured anaerobically identified with fermentation reactions

Food poisoning• Transmission: Soil and food. Survives cooking and

grows to large numbers in reheated food, especially meat.

• Pathogenesis: An enterotoxin (a protein in the spore coat)

• Clinical findings: Incubation: 8-16 hours, then watery diarrhea with

cramps and little vomiting. Resolves in 24 hours.

Treatment and prevention

• Treatment: Symptomatic – No antimicrobial drugs

• Prevention: cooking well

Clostridium difficile

DiseaseTransmissionPathogenesisClinical FindingLaboratory diagnosisTreatmentPrevention

Disease

• Antibiotic-associated pseudomembranous colitis

TransmissionIt is a part of normal flora of gasterointestinal

tract (3%)

Pathogenesis

• Antibiotic (Clindamycin and ampicillin) supress drug-sensitive normal flora, allowing C. difficile to multiply: produce toxin.

• Toxin mechanism is unclear

Clinical findings

• Diarrhea• Pseudomembranes (yellow-white plaques) on

the colonic mucosa.• Visualised by sigmoidoscopy.

Lab diagnosis

• Toxin detectable in stool affecting on cell cultured cells.

• Inhibition of cytotoxicity by specific antibody.

Treatment

• Withdrew the antibiotic• Oral vancomycin instead along with fluids.