BACTERIA

· Bacteria are single-celled microorganisms

· Bacteria are prokaryotic organisms, meaning they lack a true nucleus and membrane-bound organelles

· They are among the most abundant and diverse organisms on Earth

· Found in various environments, including soil, water, air, and the bodies of plants & animals.

· They lack a true nucleus and membrane-bound organelles

· They play vital roles in various ecosystems and have a significant impact on human health

CHARACTERISTICS

· Some major characteristics of bacteria are:

1. Prokaryotic Cells:

• Bacteria are prokaryotes, which means they lack a nucleus and other membrane-bound organelles found in eukaryotic cells.

• Their genetic material, a single circular DNA molecule.

• Genetic material located in the cytoplasm in an area called the nucleoid.

2. Unicellular Organisms:

• Bacteria exist as single-celled organisms.

• Each bacterial cell is capable of carrying out all the functions necessary for its survival, reproduction, and metabolism independently.

3. Cell Wall:

• Bacteria have a cell wall that surrounds the cell membrane.

• The cell wall provides structural support and protection against changes in the external environment.

• Composition of the cell wall varies different in every bacterial species.

• On the basis of cell wall bacteria are classified as –

Ø Gram-positive or

Ø Gram-negative.

4. Diverse Shapes:

• Bacteria exhibit a wide range of shapes, including –

Ø Spherical shape (cocci)

Ø Rod-shaped (bacilli)

Ø comma (vibrios)

Ø Spiral-shaped (spirilla or spirochetes).

• Some bacteria may also have complex shapes or forms such as filamentous or branching structures.

5. Flagella and Pili:

• Flagella are whip-like structures that allow bacteria to move in liquids, while pili are thin, hair-like appendages that aid in adherence to surfaces.

6. Metabolic Diversity:

• They can be categorized as –

Ø Autotrophs: capable of synthesizing their own organic compounds from inorganic sources.

Ø Heterotrophs: obtain organic compounds from external sources.

7. Reproduction:

• Bacteria reproduce asexually through a process called binary fission.

BINARY FISSION: bacterial cell divides into two identical daughter cells, allowing for rapid population growth.

• Some bacteria can also exchange genetic material through processes like conjugation, transformation, and transduction, contributing to genetic diversity and adaptation.

8. Ubiquity and Abundance:

• Bacteria are ubiquitous and can be found in almost every environment on Earth, including soil, water, air, and the bodies of plants and animals.

• They are among the most abundant and diverse organisms on the planet.

MEDICALLY IMPORTANT BACTERIA

GRAM POSITIVE BACTERIA

A. GRAM POSITIVE COCCIAM POSITIVE COCCI .RAM POSITIVE COCCI GRAM POSITIVE COCCI .

STAPHYLOCOCUS AUREUS

# Morphology:

· Gram-positive bacteria.

· It appears in clusters resembling grapes when viewed under a microscope.

· Size: 1 µm in diameter.

· Motility: They are Non-motile

· Non-spore-forming

· Capsulated: Non-capsulated.

· Facultative Anaerobic

# Pathogenesis:

· Staphyl. Aureus is an important pyogenic organism.

· Thick creamy pus is formed in staphyl. Infection.

Ø Source of infection – Contaminated food, patient with septic lesion, infected blood or body fluid, etc.

Ø Mode of transmission – Staphy. aureus are most often transmitted by direct or indirect content, inhalation, ingestion & inhalation.

Ø Route of transmission – respiratory tract, GI tract, etc.

Ø Incubation period – about 2-6 hours in food born staphylococcus aureus.

· Disease may be classified as

• Cutaneous infection: It Include postules, boils, abcesses, burn & wound.

• Deep infection: It Include Osteomyelitis, tonsilitis, pharyngitis, sinusitis, meningitis.

• Food poisoning: It may follow 2-6 hours after ingestion contaminated food.

• Nosocomial infection: It refers hospital acquired disease.

• Skin exoflative disease: commonly seen in children. Example – staphylococcus scalded skin syndrome (SSSS).

• Toxic shock syndrome: women’s are commonly affect.

# Lab diagnosis:

Ø Specimen:

• Common samples include pus, wound swabs, sputum, blood, urine, or other body fluids.

Ø Microscopy:

• After gram stain Gram-positive cocci in clusters seen.

Ø Culture:

• Grow on culture media such as nutrient agar, macconkry agar, blood agar, milk agar & mannitol salt agar.

• Incubate at 37*C for overnight.=

Ø Biochemical reaction:

• Coagulase test – positive

• Phosphatase test – positive

• Catalase test – positive

• Oxidase test – negative

Ø Antibiotic susceptibility testing:

• Susceptibility is determined by various method such as disk-diffusion.

STREPTOCOCCUS PYOGENES

# Morphology

· Gram-positive bacteria

· Shape: spherical or oval

· Size: About 0.5 to 1.0 µm in diameter.

· Arrangement: Arrange in chain.

· Capsule: Some strains of possess capsule.

· Motility: Non-motile

· Spore: Non-sporing

# Pathogenesis

• Streptococcus pyogenes produce pyogenic infection that spread locally along with lymphatic & blood stream.

Ø Source of infection – Contaminated food, lesion, infected blood or body fluid such as saliva, wound, or nasal secretions, etc.

Ø Mode of transmission – transmitted by direct or indirect content, ingestion & inhalation.

Ø Route of transmission – respiratory tract, GI tract, etc.

Ø Incubation period – about 3 to days.

A. SUPPRATIVE INFECTION:

1) RESPIRATORY INFECTION –

• Sore throat (acute tonsillitis and/or pharyngitis) is the most common streptococcal diseases.

• Tonsillitis is more common in older children and adults.

2) Skin & soft tissue infection –

• Strep. Pyogenes causes subcutaneous infection of skin lymphangitis & cellulitis.

• It include wound & burn.

• It may lead to fetal septicemia.

• Strep. Pyogenes is also known as ‘FLASH EATING BACTERIA’.

• Bacterial infection such as Erysipelas & impetigo.

3) Streptococcal toxic shock syndrome –

• TSS is a condition in which the entire organ system is collapse, leading to death.

4) Genital infection –

• Aerobic & Anerobic streptococci are normal inhabitant of female genital tract.

• Important causative agent of puerperal sepsis.

5) Other supprative infection

• Strep. Pyogenes may cause abscess in internal organ such as brain, lungs, liver & kidney.

B. NON-SUPPRATIVE INFECTION:

# Lab diagnosis

Ø Specimen:

• Throat swab

• Wound swab

• Pus

• CSF

• Blood

Ø collection & transport:

• Specimen should be collected on sterile container.

• Pike’s medium is used for transport

Ø Microscopy:

• Gram staining - Gram positive bacteria seen in chain formation.

Ø Culture:

• Best grow in blood agar at 37®C for 24-48 hours in presence of 5 – 10% CO2.

Ø Colony morphology:

• Colony of strep. Pyogenes are-

Shape – round

Size- 0.5-1mm

Surface – smooth

Color – grey

Opacity – translucent

Ø Biochemical reaction:

• Camp test – negative

• Catalase – negative

• PYR test – positive

Ø Serological test:

• Anti streptolysin o (ASO) is most widely used

Ø Antigen detection test:

• ELISA

• Agglutination test

Ø Molecular method:

• Polymerase chain reaction

Ø Antibiotic susceptibility testing:

• Oral penicillin V or amoxicillin

B. GRAM POSITIVE BACILLIRAM POSITIVE COCCI .

BACILUS ANTHRAX

# Morphology

· Gram positive bacilli

· Non-acid-fast

· Non-motile

· Size: 3- 10 µm

· Shape: rod shaped

· Spore forming bacillus

# Pathogenesis

Ø Source of infection – Contaminated food & water, contaminated animal product, air droplet.

Ø Mode of transmission – transmitted by direct or indirect content, ingestion & inhalation.

Ø Route of transmission – respiratory tract, GI tract, etc.

Ø Incubation period – about 1 to 7 days.

· Anthrax is primarily a disease of animal like cattle & sheep, less often of horse & swine.

· Direct spread of disease from animal to animal is rare.

· Anthrax is usually septicemia but may sometimes be localized.

HUMAN ANTHRAX:

· Human are occasionally secondary infected from disease animal.

· There are three clinical type of infection based on route of infection.

1. Cutaneous infection:

• Entry of spore through the skin.

• Face, neck, hand & back are commonly affected site.

• Commonly seen in farmer or person handling carcasses.

2. Pulmonary infection:

• Pulmonary anthrax is due to inhalation of the dust or filament of wool from infected animal, particular seen in wool facories.

• Also called wool sorter’s disease.

3. Intestinal infection:

• It is rare & seen in person who take improper cooked infected meat.
  

# Lab diagnosis

Ø Specimen:

• Throat swab

• Fluid

• Pus

• Sputum

• Blood

Ø collection & transport:

• Specimen should be collected on sterile container.

Ø Microscopy:

• Gram staining - Gram positive bacilli seen.

Ø Culture:

• Best grow in nutrient agar at 37®C for 24-48 hours.

Ø Colony morphology:

• After growth medusa head appearance colonies appear.

Ø Molecular method:

• Polymerase chain reaction

Ø Antibiotic susceptibility testing:

• Ciprofloxacin

• Doxycycline

GRAM NEGATIVE BACTERIA

C. GRAM NEGATIVE COCCIGRAM NEGATIVE COCCI .

NEISSERIA MENINGITIDIS

# Morphology

· Gram negative cocci

· Shape: spherical or oval cocci

· Size:0.6- 0.8 µm in size

· Motility: non-motile

· Flagella: non-flagellated

· Spore: non-sporing

· Arrangement: in pairs (diplococcic)

# Pathogenesis

Ø Source of infection – droplets of respiratory secretions.

Ø Mode of transmission – transmitted by kissing, sneezing or coughing.

Ø Route of transmission – respiratory tract

Ø Incubation period – about 3 to 4 days.

· N. meningitidis causes pyogenic meningitis in all ages.

· Meningococci are strict human pathogens, Common in children and young adults.

· The other bacterial agents responsible for pyogenic meningitis include H. influenzae and Str. pneumoniae.

· The organism may spread along the perineural sheath of the olfactory nerve, through the cribriform plate to the subarachnoid space or through the blood stream.

# Lab diagnosis

Ø Specimen:

• CSF

• Blood

• Nasopharyngeal swab

Ø collection & transport:

• Specimen should be collected on sterile container.

• Lumbar puncture for CSF & vein puncture for blood.

Ø Microscopy:

• Gram staining - Gram negative diplococci seen.

Ø Culture:

• Inoculated on blood agar or chocolate agar.

• The plate is incubated at 35-36°C under 5- 10% CO2.

• Colonies appear after 18- 24 hours.

Ø Colony morphology:

• In solid media colonies appear

Shape – round

Size - 1mm

Surface – convex

Color – grey

Opacity – translucent

Ø Biochemical reaction:

• Catalase test – positive

• Oxidase test – negative

Ø Molecular method:

• Polymerase chain reaction

Ø Slide Agglutination

• Direct slide agglutination of the organism may be done with specific antisera.

Ø Antibiotic susceptibility testing:

• penicillin

D.GRAM NEGATIVE BACILLI

ESCHRICHIA COLI (E.COLI)

# Morphology

· Gram negative bacilli

· Shape: rod shapes bacteria

· Size: 1- 2 µm in size

· Motility: some strain of bacteria are motile

· Flagella: some bacteria are motile

· Spore: non-sporing

# Pathogenesis

Ø Source of infection – contaminated food and water

Ø Mode of transmission – transmitted direct contact with infected person and animal

Ø Route of transmission – ingestion, inhalation, etc.

Ø Incubation period – about 2 to 4 days.

· There are four major types of clinical syndromes which are caused by Esch. coli:

1. Urinary tract infection

2. Diarrhoea

3. Pyogenic infections

4. Septicaemia

# Lab diagnosis

Ø Specimen:

• Midstream urine

Ø collection & transport:

• Specimen should be collected on sterile container.

• Send it to the laboratory with minimum delay.

Ø Microscopy:

• Gram negative bacilli seen

Ø Culture:

• Inoculated on mac-conkey agar

• The plate is incubated at 37°C for 24-48 hours

• Colonies appear after 18- 24 hours.

Ø Colony morphology:

• In solid media colonies appear

Shape – circular

Size – 2-3mm

Surface – smooth

Edge – entire

Color – pink due to lactose fermentation

Opacity – opaque

Ø Biochemical reaction:

• Catalase test – positive

• Oxidase test – negative

• Indole test – positive

• Methyl red – positive

• VP – negative

• Citrate - negative

Ø Molecular method:

• Polymerase chain reaction

Ø Antibiotic susceptibility testing:

• Antimicrobial susceptibility testing can be performed to determine the most effective antibiotics for treating the infection.

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