Overview of Bacterial Infections

Overview of Bacterial Infections

• Bacteria are classified as gram-positive or gram-negative based on their cell wall structure.
• Gram-positive bacteria have a thick peptidoglycan layer in their cell wall. Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane.
• Staphylococcus aureus is a gram-positive coccus arranged in clusters.
• It is catalase-positive and coagulase-positive.
• It is a facultative anaerobe.
• Common sources of infection include the nose, throat, skin, and under the nails.
• Transmission occurs via contact with pus from infected wounds, skin-to-skin contact with infected people or objects used by infected people (towels, sheets, clothing, or athletic equipment).
• Diseases caused by S. aureus include bacteremia, infective endocarditis, pneumonia, meningitis, skin and soft tissue infections, food poisoning.
• Major bone and joint infections (osteomyelitis and septic arthritis) are also caused.
• Urinary tract infection and Scalded skin syndrome (neonatal and children under 4 years old) are also caused.
• Antibiotic resistance, including Methicillin-Resistant Staphylococcus aureus (MRSA), is widespread.
• First-line treatment for serious invasive MRSA infections is currently glycopeptide antibiotics (vancomycin and teicoplanin).

Streptococcus pyogenes

• Gram-positive cocci arranged in chains.
• Catalase-negative.
• Transmission occurs through inhalation of respiratory droplets, skin contact with infectious lesions, and contact with contaminated objects or surfaces.
• Diseases caused include streptococcal pharyngitis and tonsillitis, scarlet fever, mild skin infection (impetigo), invasive infection (including erysipelas), acute superficial cellulitis, deeper subcutaneous cellulitis, and streptococcal toxic shock syndrome (TSS).

Other Gram-Positive Cocci - Streptococcus pneumoniae

• Bacteria causes pneumonia, otitis media, sinusitis, and meningitis.

Streptococcus viridans

• Causes dental caries, bacteremia, and subacute bacterial endocarditis.
• Once in the bloodstream, the organism infects the degenerated heart valve.
• The organism can transmitted through birth canal, and causes Neonatal septicaemia, Neonatal Meningitis and Neonatal pneumonia.

Clostridium

• Gram-positive bacilli.
• Obligate anaerobe.
• Clostridium botulinum produces botulinum toxin in food or wounds, leading to botulism.
• Clostridium perfringens causes a broader spectrum of illnesses, including food poisoning, cellulitis, fasciitis, necrotic enteritis, and gas gangrene.
• Clostridium tetani causes tetanus.
• Clostridium difficile causes antibiotic-associated diarrhea.

Gram-Negative Bacteria

• Diverse group of bacteria. Categorized by different criteria including cell shape, oxygen requirements, and metabolic capabilities.
• Examples like Escherichia coli, Klebsiella pneumoniae, Salmonella, and Neisseria.

Escherichia coli

• Gram-negative bacilli.
• Facultative anaerobe.
• Ferments lactose.
• Commonly found in the human lower intestine.
• Some serotypes cause enteropathogenic or uropathogenic infections.
• Uropathogenic E. coli can also cause urinary tract infections.
• Certain serotypes cause neonatal meningitis.

Klebsiella pneumoniae

• Gram-negative bacilli.
• Facultative anaerobic.
• Non-motile.
• Causes diseases like pneumonia, urinary tract infections, septicemia, wound infections, and meningitis.

Salmonella

• Gram-negative bacilli.
• Facultative anaerobe.
• Doesn't ferment lactose.
• Frequently found in contaminated animal or human feces.
• Some serotypes cause typhoid fever.

Neisseria

• Gram-negative diplococci.
• Oxidase-positive and aerobic.
• Two major pathogens are N. meningitidis and N. gonorrhoeae.
• N. gonorrhoeae is associated with sexually transmitted genitourinary infections, including gonorrhea.
• N. meningitidis causes meningitis.

Helicobacter pylori

• Gram-negative spiral (helical) shaped bacilli.
• Typically found in the stomach.
• Four to six unipolar flagella help the bacteria penetrate the stomach's mucus lining.
• Infection can be asymptomatic, cause gastritis, ulcers in the stomach or duodenum.
• Associated with certain stomach cancers.