GRAM POSITIVE RODS

Dr Hamed Al-Zoubi

Ass. Prof. / Department of Microbiology

Bacterial infections of GIT

• Corynebacterium

• Bacillus cereus and anthracis

• Clostridium

Corynebacterium

• Aerobic, non motile GPR, club shape, Chinese letters L V shapes

• 1 - C. diphtheria

• 2 - Others: low pathogenic ability e.g diphtheroids (skin, urogenital and commensals)

Corynebacterium

• C. diphtheria:

• Virulence and pathogenesis:

• Local invasion

• heat stable exotoxin

bacteriophage tox gene

A and B parts:

Inhibit EF2 and protein synthesis leading to cell necrosis and death

• Clinically: • Transmission by respiratory route , skin contact

• Incubation 1-10 days, infectivity 2-4 weeks if untreated or 4 days if treated

1 Local inflammation in nasal, oral, pharyngeal, laryngeal areas <thick adherent green psuedomembrane < airway obstructionand death

2 systemic:

• Toxin tropism to brain, heart and adrenal glands

• Paralysis, heart failure low platelets

6

This child has diphtheria resulting in a thick gray

coating over back of throat. This coating can

eventually expand down through airway and, if not

treated, the child could die from suffocation CDC

• Diagnosis:

Swab:Not from the membrane.. and tell the lab:

• Blood agar

• Loeffler medium for chromogenic granules

• Tensdale agar: has K tellurtite medium • reduction by bacteria

• tellurium precipitation

• black colonies

• Toxin detection ELEK test or PCR

• Treatment: start ASAP

antitoxin, penicillin plus gentamicin

• Prevention: toxoid vaccine DIPHTHERIA TETANUS AND PERTUSIS ( DTP) 2m,3m,4m,1y,6y

• BACILLUS: GPR, aerobic, spore centrally located

• 1- Anthracis • Non motile, glutamic acid capsule

• Plasmid toxin: increase vascular permeability and shock

• Zoonosis

• Inhalation: hemorrhagic pneumonia and sepsis

• Ingestion: bloody diarrhea and death

• skin scratch: vesicles that rupture leaving malignant black eschar

2 --Bacillus cereus :

• Motile but no capsule

• food poisoning by enterotoxin

Cases in which vomiting, occurring within 1-6 h of ingestion, is the main symptom.

• Caused by preformed toxin, which is a low molecular weight, heat- and acid-stable toxin that can withstand intestinal proteolytic enzymes (similar to s. aureus).

A diarrhoeal form of food poisoning, occurring 8-24 h after ingestion of spores

• caused by heat labile enterotoxins formed in the intestine.

• Bacillus diagnosis: • blood agar: (medusa head) grey wavy with

projections

• Gram stain:

String of pearls

Appears G neg

in old culture

• TREATMENT

• Anthrax: penicillin

• Cereus:

Symptomatic : fluids

If antibiotic needed: Cindamycin or erythromycin

• Prevention : Human vaccines for Anthrax

Cellualr antigen from culture supernatan

Anthrax genetically engineered antigen

Clostridium

• Characteristics:

• Gram positive anaerobic rods (appear as gram negative in old cultures)

• Spore forming, dust water soil...

• Anaerobics

• May appear G neg in old culture

• C. Botulinum and Tetanus : neurotoxins

• C. Perfringens and Difficile: enterotoxins

Clostridium botulinum

• Seven main types A-G: A, B and E are the commonest

• Each secretes antigenically distinct but functionally similar toxin (very potent)

• The toxin (heat labile):

1. Preformed in food that is badly preserved and processed (hygiene and heat) > food borne botulism (canned, smoked..)

2. Spores ingestion e.g Honey > germinate in the gut > toxin production > infantile or (intestinal) botulism

Clostridium botulinum

Spores:

• Oval and subterminal

Clostridium botulinum

• Pathogenesis:

Neurotoxin production > stomach absorption > circulation >

neuromuscular junction (NMJ) > inhibition of acetylcholine release

at the NMJ > flaccid descending motor paralysis

Clostridium botulinum

• Clinically (food borne and wound botulism ):

Incubation period 12-48hrs in food borne

Early: nausea, vomiting, weakness, dizziness but no fever

Late: double vision, difficulty in swallowing, speaking and respiratory failure (descending motor paralysis)

• Infantile: weakness, altered cry, loss of appetite , loss of head control, Floppy child syndrome and sudden infant death syndrome

Clostridium botulinum • Diagnosis:

• Isolating the organism or toxin from gastric aspirates, blood or stool

• Detecting Toxin in the food

• n.b: toxin-antitoxin approach

• Alert the lab

Clostridium botulinum Treatment:

• Gastric wash

• Antitoxin (A, B, E)

• Supportive: ICU and respiratory support, wound cleaning and debridement

Prevention:

• Proper cooking and heating of food?

• Avoid suspicious canned food

• Proper processing, preservation and canning of food

• vaccine

Clostridium perfringens: • It causes gas gangrene and food poisoning (HL)

• subterminal spores

• Toxins:

• Alpha toxin (phospholipase C, lecithinase): Degrades lecithin in mammalian cell membrane leading to cell lysis

• Other toxins: collagenase, proteinase, hyaluronidase

• Identification: Nagler agar: based on neutralisation of alpha toxin by a specific antitoxin

Clostridium tetani

• Widely distributed in the environment especially in the soil

• Gram positive, motile anaerobic rods (GNR in old culture)

• Spore forming: round terminal (drumstick, tennis racket)

• Not commonly seen due to vaccine (DTP)

Clostridium tetani • Not commonly seen due to vaccine (DTP)

• Produce two plasmid coded exotoxins:

1. Tetnospasmin:

• Neurotoxin

• Heavy (binding ) and light chain (neurotoxic part)

• One antigenic toxin

2. Tetanolysin (haemolysin): pathogenesis not clearly known but ? RBCs haemolysis

produced when spores germinate and vegetative cells grow in necrotic tissues. The organism multiplies locally and symptoms appear remote from the infection site

Clostridium tetani • Pathogenesis: Spastic paralysis

inhibition of the inhibitory neurotransmitter

gamma aminobutyric acid (GABA) > loss of inhibitory action on

motor and autonomic neurons> uncontrolled muscle contractions (spasms) >

Clostridium tetani / pathogenesis

Clostridium tetani Clinically (tetanus):

• Mode of transmission:

• Spores > wound contamination(low oxygen) > germination to bacilli that secrete the toxins

• Incubation period: 3days – 3 weeks

Source:

• Infected wound and abscesses (~65%), eg, wood or metal, thorns...)

• Chronic skin ulcers are the source in approximately 5% of cases

• in the remainder of cases, no obvious source is identified (cryptogenic)

Clostridium tetani 1. Local:

Muscles spasm and pain at/near injury site

2. Generalised:

• Trismus (locked jaw): may bite the tongue

• Opisthotonus: flexion and adduction of the arms, clenching of the fists, extension of the lower extremities

• spasm is stimulated by noise and light

• the patient is afebrile, has intact sensation

• Meningitis, seizures and coma

Clostridium tetani

Clostridium tetani Diagnosis:

1. Clinical (very useful):

Sign and symptoms

Vaccination history

History of a trauma

2. Wound smear staining: may help

3. Culture

4. Toxin-antitoxin test in mice

Clostridium tetani • Treatment:

• Wound debridement

• Treat in In a dark quite room

• Sedation, Muscle relaxant (e.g diazepam) and artificial ventilation

• Antibiotics:

may be given to kill any vegetative forms

metronidazole

• Tetanus immunoglobulin TIG

• Vaccination:

• Toxoid vaccine: formalin inactivated

• VACCINE as per vaccination program and a booster every 10 years

C. difficile • Secrete toxins A (enterotoxin) and B (cytotoxin).

> exotoxins that cause inflammation and mucosal damage.

• Most common cause of nosocomial diarrhea.

• Colonizes the colon of up to 3% of healthy adults and it increases to 15 – 25% of debilitated and antibiotic-treated hospitalized adults.

• present in environment.

• Spread primarily on hands of HCW.

Risk factors

1. Antimicrobial exposure

2. Acquisition of C. difficile

3. Advanced age

4. Underlying illness

5. Immunosuppression

6. Tube feeds / Enema..

All are Modifiable but not 3.

1 & 2 are major

Clinical picture and Complications

• Asymptomatic colonization

• Diarrhea (mild to severe)

• Colitis +/- pseudomembranes (endoscopy)

• Toxic megacolon (radiology)

• Colonic perforation/peritonitis

• Sepsis and acute abdomen without diarrhea

Diagnosis

• Clinically

• Enzyme-linked immunosorbent assay (ELISA) for toxins A and B

• Endoscopy (pseudomembranous colitis)

Management

• Resuscitate the patient; fluids, electrolytes

• Isolate the patient: Private room or cohorting

• Stop antibiotics and the just in case ones.

• Daily monitoring.

• ANTIBIOTICS: metronidazole / and or vancomycin

The End