C1 Gram-Positive Cocci

What are the characteristics of Staphylococcus?

• Gram-positive cocci

• Forms “grape-like” clusters

• Facultative anaerobe

• Catalase positive

What is hemolysis? What are alpha, beta, and gamma-hemolytic strains?

Hemolysis is the destruction or rupture of red blood cells, causing them to release hemoglobin into the surrounding plasma

What is alpha hemolysis?

The partial breakdown which causes a greenish or brownish discoloration in the media surrounding the bacterial colony on the blood agar

What is beta hemolysis?

The complete destruction of red blood cells by bacterial enzymes on blood, resulting in a clear, transparent zone around colonies

What is gamma hemolysis?

The absence of red blood cell lysis, or non-hemolytic behavior, when bacteria are grown on blood agar plates. It appears as an unchanged, red, opaque medium around bacterial colonies.

What is an exotoxin?

Highly potent, protein-based toxin secreted by living bacteria into their environment

What is a superantigen?

Potent toxins produced by bacteria and viruses that cause excessive, non-specific immune system activation

How do Staphylococcus aureus infections begin?

• When the bacteria, commonly found on human skin or in the nose, enter the body through localized cutaneous infection (folliculitis, boils, infected hair follicles, sweat glands) and contamination of surgical wounds

• Nonsocomial (hospital-acquired) infections as it can transferred by skin-to-skin contact, or contact with an infected person’s belongings

Define bacteremia and septic shock.

• Bacteremia: The presence of bacteria in the bloodstream caused by bacteria entering the blood through infections

• Septic shock: Life-threatening stage of sepsis caused by severe infections that trigger extreme, body-wide inflammation

What is toxic shock syndrome? What causes it?

• Rare, life-threatening complication arising from certain bacterial infections, which causes rapid onset fever, rash, scalded skin syndrome, vomiting, diarrhea, low blood pressure, and organ failure.

• It is associated with high-absorbency tampon use and can affect anyone through skin wounds, surgery, or infections.

Describe the chain of events in Staphyloccus food poisoning and its hallmark effect.

S. aureus is quite halophilic, thus it grows at many temperature

If it gets into food that’s left out, it will grow and produce exotoxins in the food

When we eat it, the bacteria are killed, but the exotoxins poision

Hallmarks of S. aureus food poisoning:

• Rapid onset: A few hours after eating

• Rapid recovery: Fully recovered within 1 to 2 days

How is S. aureus infection treated?

Antibiotics are effective, however, there are a limited set of antibiotics available

What does MRSA stand for and why is it of medical concern?

MRSA = Methicillin Resistant Staphloccocus aureus

Methicillin has been the antibiotic choice of years against Staphloccocus aureus, however MRSA it is resistant to common antibiotics, making infections challenging to treat

What is the best defense against Staphylococcus aureus infections?

• Keep the infection from happening in the first place!

• Clean cuts carefully with soap and water

• Proper aseptic and antiseptic techniques in the hospital

• Proper hand washing techniques

What are characteristics of Streptococcus?

• Gram-positive cocci

• Forms chains of cells

• Facultative anaerobe

• Catalase negative

• Group A and Group B= Beta hemolytic

• S. pneumoniae and S. mutans = Alpha hemolytic

What are Lancefield groups?

Rebecca Lancefield groups (A, B, C, D, E, etc.) are a classification system for Strepococcus bacteria based on serotypes

What is Group A Streptococcus (Streptococcus pyogenes)? Describe strep throat, scarlet fever, and impetigo.

• Strep throat: Non-invasive infection of the throat—pharyngitis

  • Extremely sore throat, fever, white spots on the throat

• Scarlet fever: Non-invasive infection of the throat

  • Similar symptoms to strep throat, but causes a red rash on the body

• Impetigo: Local skin infection

  • Pustules that crust over and rupture

Describe necrotizing fasciitis. What finally kills people with this disease?

• Caused by Group A Streptococcus (Streptococcus pyogenes)

• Invasive infections may develop into necrotizing fasciitis, which is a “flesh eating bacteria”

• Produce enzymes that rapidly break down flesh

• Exotoxin A (a superantigen) makes the problem worse by triggering a massive inflammatory response

  • Toxic shock syndrome

What is rheumatic fever? What is its connection to antibiotic treatment of strep throat?

• Disease that develops long after a Group A Strep infection

• Autoimmune disease

• Portions of bacterial cell wall (the M protein) are highly antigenic (cause many antibodies to be made)

• Overactive immune system attacks joints (reactive arthritis)

• 50% of patients develop heart problems due to the immune system attacking the M protein at the heart

• Rapid treatment of strep throat is important to keep the infection from getting large enough to trigger rheumatic fever

• Streptococcus pyrogenes is still generally sensitive to penicillin

What is the most common problem with Group B Streptococcus? How is it prevented?

• Common part of vaginal flora, causing no disease

• Can infect infants during birth

  • Significant cause of newborn meningitis

  • Contagious from mother to infant

• Treatment with antibiotics before/during birth will prevent transmission

• Does not cause rheumatic fever after an infection

Define pneumonia. Why is Streptococcus pneumoniae called the pneumococcus?

• Generally defined as an infection of the lungs that causes the alveoli to fill with fluid

• Streptococcus pneumoniae is the leading cause of pneumonia (~500,000 cases/per)

  • Also known as “typical” pneumonia

Why are the symptoms of pneumonia? What generally causes it?

• Symptoms/Diagnosis:

  • Difficulty breathing

  • Fever

  • Chest pain

  • Positive chest X-ray

• Can have a variety of causes

  • Bacteria (most common)

  • Fungi

  • Viruses

Is streptococcus pneumonia generally contagious? Why or why not?

• Large percentage of the population are carriers (no symptoms)

• Only a problem for vulnerable individuals

How is it streptococcal pneumonia treated? Why an expectorant important?

Antibiotics and an expectorant, which loosens mucus in the lungs

What is meningitis? What are the symptoms?

• Rarely, Streptococcus pneumoniae can migrate from lungs to blood (bacteremia) and from blood to the brain (bacterial meningitis)

• Fever, headache, sore neck

• Progresses to nausea, vomiting, convulsions, coma

Why some heart patients take antibiotics before getting their cleaned?

• Streptococcus mutans, like Streptococcus pneumoniae, is alpha-hemolytic and has no Lancefield group

• Cause of dental caries (cavities)

• If introduced into the blood, it can cause endocarditis (heart infection), particularly if the heart has an artificial valve

What are the characteristics of Enterococcus?

• Gram-positive cocci

• Forms chains of cells

• Facultative anaerobe

• Catalase negative

• Gamma hemolytic

Define UTI. What makes Enterococcus UTIs unusual?

• Urinary Tract Infection (UTIs)

• Enterococcus UTIs

  • One of the only Gram-positive cocci that will cause them

  • Many Enterococcus strains are antibiotic resistant

    • Most are resistant to penicillin

    • Vancomycin Resistant Enterococcus (VRE)

What symptoms are associated with UTIs? Is treatment important? Why?

• Painful urination

• Constant sensation of need to urinate

• Blood in urine

• Slight risk of contagion through sexual contact

• Left untreated, which can lead to infection of the kidneys

What fraction of UTIs are nosocomial? What does nosocomial mean?

• About 7 million UTI cases/year

• About 900,000 are nosocomial, usually from catheters

  • Healthcare-associated infections are diseases acquired in hospital or care settings that were not present upon admission

• Most (due to location) are by enteric (intestinal) bacteria

Why are Enterococcus infections a problem?

• Opportunistic infections of Enterococcus are rare

  • Almost all are nosocomial

  • Problematic due to high antibiotic resistance

What are the characteristics of Lactococcus?

• Gram-positive cocci

• Forms pairs of short chains

• Facultative anaerobes

• Mostly use fermentation

• Not human pathogens

What does Lactococcus do to cause milk to curdle and thus make cheese?

• Metabolizes lactose (milk sugar) into lactic acid

• This acid lowers the milk’s pH, causing casein proteins to denature and coagulate, forming solid curds

What does Lactococcus do to make milk and cheese inhospitable to other bacteria?

• Lactococcus ferments lactose into lactic acid, which lowers pH

  • Causes curdling (coagulation of milk proteins)

  • Ruins the environment for other bacteria

• Many strains produce Nisin

  • Antibiotic

  • Most effective against Gram-positive bacteria