Overview of Bacterial Infections

Overview of Bacterial Infections

• Bacteria are classified as gram-positive or gram-negative.
• Gram-positive cocci are arranged in clusters, are catalase-positive, and coagulase-positive.
• Gram-positive cocci are also arranged in chains. These are catalase-negative.
• Staphylococcus aureus is a facultative anaerobe found in healthy carriers. Transmission is skin-to-skin, contact with pus, and contact with objects.
• Diseases caused by S. aureus include bacteremia, endocarditis, pneumonia, meningitis, skin and soft tissue infections, food poisoning, and major bone infections.

Staphylococcus Aureus

• Gram positive cocci arranged in grape-like clusters
• Catalase-positive
• Coagulase-positive
• Facultative anaerobe

Sources of Infection

• Healthy carriers harbor bacteria in the nose, throat, skin, and under the nails.

Mode of Transmission

• Contact with pus from an infected wound
• Skin-to-skin contact with an infected person
• Contact with objects used by an infected person (e.g., towels, sheets, clothing, or athletic equipment)

Diseases Caused by Staphylococcus Aureus

• Bacteremia
• Endocarditis
• Pneumonia
• Meningitis
• Skin and soft tissue infections
• Food poisoning
• Scalded skin syndrome
• Major bone and joint infections like osteomyelitis and septic arthritis
• Urinary tract infections

Antibiotic Resistance

• Antibiotic resistance is widespread in S. aureus, including Methicillin-Resistant S. aureus (MRSA).
• MRSA is resistant to certain antibiotics, including methicillin.
• First-line treatment for serious invasive infections caused by MRSA includes glycopeptide antibiotics(vancomycin and teicoplanin).

Streptococcus pyogenes

• Gram-positive cocci arranged in chains
• Catalase-negative
• Mode of transmission includes inhalation of respiratory droplets, skin contact with infectious lesions, and contact with contaminated objects, surfaces, or dust.
• Diseases include:
  • Streptococcal pharyngitis and tonsillitis
  • Scarlet fever
  • Skin infections (impetigo)
  • Erysipelas
  • Invasive skin infection
  • Cellulitis
  • Streptococcal Toxic Shock Syndrome (TSS)

Other Gram-positive cocci

• Streptococcus pneumoniae
  • Causes pneumonia, otitis media, sinusitis, and meningitis

Streptococcus viridans

• Dental caries, bacteremia
• Subacute bacterial endocarditis
• Neonatal meningitis (and Neonatal pneumonia) occurs from transmitted during the birth canal.

Clostridium

• Gram-positive bacilli
• Obligate anaerobe
• Clostridium botulinum produces botulinum toxin in food or wounds and causes botulism
• Clostridium perfringens cause a range of symptoms- cellulitis, fasciitis, necrotic enteritis, gas gangrene
• Clostridium tetani causing tetanus
• Clostridium difficile causes antibiotic associated diarrhea

Gram-Negative Bacteria

• Includes diplococci, coccobacilli, bacilli, comma shaped
• Examples: Escherichia coli, Klebsiella pneumoniae, Salmonella, Neisseria, Helicobacter pylori

Escherichia coli

• Gram negative bacilli
• Facultative anaerobe
• Peritrichate flagella
• Ferments lactose
• Common in the human lower intestine
• Some serotypes cause serious forms of gastroenteritis, Uropathogenic E. coli is a major cause of urinary tract infections.
• Can also causes neonatal meningitis.

Klebsiella pneumoniae

• Gram negative bacilli
• Facultative anaerobe
• Non motile
• Diseases caused by K. pneumonia include:
  • Pneumonia
  • Urinary tract infections
  • Sepsis
  • Wound infection
  • Meningitis

Salmonella

• Gram-negative bacilli
• Facultative anaerobes
• Do not ferment lactose
• Most infections are due to ingestion of contaminated food or water
• Typhoidal serotypes (e.g., Typhoid fever) only transfer from human to human

Neisseria

• Gram-negative diplococci
• Oxidase-positive and aerobic
• Important pathogens include N. meningitides and N. gonorrhoeae
• N. gonorrhoeae causes the sexually transmitted genitourinary infection gonorrhoea
• N. meningitides causes meningitis and other forms of meningococcal disease such as meningococcemia

Helicobacter pylori

• Gram-negative spiral (helical) shaped bacilli
• Usually found in the stomach
• Has four to six unipolar flagella for penetrating stomach mucus lining
• May cause no symptoms but can lead to gastritis, ulcers in the stomach or the first part of the small intestine (duodenum)
• Associated with the development of certain stomach cancers.

This quiz covers key concepts related to bacterial infections, focusing on the classification and characteristics of gram-positive and gram-negative bacteria. Special emphasis is placed on Staphylococcus aureus, its modes of transmission, and diseases it can cause. Test your knowledge about the sources and risks associated with these infections.