staphylococcus aureus : what , why and how it infects and it’s treatment

Staphylococcus are one type of bacterial species (genus to be precise) which have many pathogenic species for animals and humans , pathogenic means which can cause disease. They are mostly found on skin , nose and hospitals also . but they are one type of staphylococcus which is known as staphylococcus aureus. They are the ones who cause wound infection , pharyngitis, meningitis. Commonly staphylococcus species are gram +ve (positive) bacteria which if we examine them in a microscope looks like grape shaped clusters. They are the most common one to cause any diseases in human beings.

Most commonly they infect us in hospital environment so let’s talk about them

So first question is

When staphylococcus were first found and by whom ?

Staphylococcus were first observed in human pyogenic lesions by von recklinghausen in 1871, pasteur (1880) obtained liquid cultures of the coccoi from pus and produced abscess by inoculating them into rabbits. It was sir alexander ogston , a scottish surgeon ,who established conclusively the causative role of coccus in and other lesion

Infect staphylococcus itself means bunch of berries.

What is the classification of Staphylococcus?

Mostly bacterial species were classified by the colony they produced , pigmentation , colours of their colony , enzymes , toxins and many other properties . so in case of staphylococcus it was a enzyme called coagulase , and a sugar called mannitol .

To classify staphylococcus virulence properties , enzyme production and fermentation of sugar was taken into consideration and staphylococcus was classified into two groups

1. S. aureus (AKA S. pyogenes)
   1. Which produces coagulase
   2. Ferments mannitol
   3. And it is pathogenic
2. S. epidermidis
   1. Which does not produce coagulase
   2. Does not ferments mannitol
   3. And it is not pathogenic

How many types of Staphylococcus are there?

They are many other species (32 spices, 15 subspecies ) like s. Epidermidis, s. Haemolyticus and s. Saprophyticus which are pathogenic to humans means they can cause disease.

Where as s. Hominis and s. Capitus are part of commensal flora of the human skin .

What is the morphology of Staphylococcus?

Now we know how many staphylococcus are there and which one of them are the bad guys .

So let’s talk about how bad guys look or in scientific terms morphology of the staphylococcus

So morphology :

1. Spherical coccoi
2. 1 micrometre diameter
3. Grape like structure
4. Non motile
5. Non sporting
6. aerobic/ facultative anaerobic
7. Gram positive
8. 10-42℃
9. 7.4-7.6 ph

Few young strains possess capsules many apparently non capsulated strains have small amount of capsular material

They stain (for non scientific, people we colour them ) readly in aniline dyes. And in influence of penicillin they also change to L forms

What is the Colour of Staphylococcus aureus and their culture characteristic ?

Culture media characteristics :

1. Blood agar – complete hemolysis
2. Nutrient agar – golden yellow
3. Nutrient agar + aerobic condition + 22℃+1% glycerol monoacetate – pigmentation production will increase

Selective media for staphylococcus are :

1. Salt milk agar
2. Manitol salt agar
3. Ludlom’s lithium chloride tellurite media

Reaction of Staphyloccocus on diffrent media are

1. Blood agar – beta hemolytic
2. Mckonkey agar – tiny lactose fermentation

Differential media will be mannitol salt agar because s.aureus only ferments mannitol

What is the role of Staphylococcus?

Now to understand what is their role we need to understand some of their features like

Cell wall associated polymers and proteins and their enzyme to understand their role so

They consists of

Peptidoglycan – which inhibits the chemotoxins and phagocytosis

Teichoic acid – which meditates attachments

Protein A – which inhibits phagocytosis

Capsular polysaccharide – which also inhibits phagocytosis

Staphylococcus have some enzymes also which are

Coagulase – coats bacterial wall with fibrin

Lipase – which hydrolyses lipids

Nuclease – which hydrolyses DNAs

Some of the toxins are :

Toxic shock syndrome toxins – stimulates large amount of interlukins

Leukocidin – lysis of leukocytes

Hemolysin – lysis of RBCs

All these features causes diseases which we will see in next question which is

What are the main diseases / causes of Staphylococcus aureus?

They cause wound infection , meningitis , arthritis , osteomyelitis, septicemia, pharyngitis, sinusitis

Where is Staphylococcus found?

They are mostly found on skin but most common source of s. Aureas infection is hospitals

How is Staphylococcus spread?

They spread via contacts of skin like hand shakes , sharing anything like razors , towels , clothes

Which antibiotic is most effective against Staphylococcus aureus?

S. aureus is very drug resistant staphylococci so to surely treat the infection is to first perform Laboratory diagnosis and then give antibiotics

Common antibiotics used against S. aureus is

• Benzyl penicillin
• Vancomycin
• Bacitracin
• Rifampicin