Need help assisting with my Microbiology paper on staphylococcus aureus

Staphylococcus aureus Lab Report

Daphne Sandoval

Microbiology 233

Dr. Ryan Manow

July 23, 2020

Introduction:

Staphylococcus aureus is a Gram-positive spherical bacterium, clustered, similar

to grapes. This type of bacteria is commonly found in the nostrils, skin, armpits, nose,

and other areas. Roughly up to 30% of the human population is colonized with

Staphylococcus aureus in their nose (Sakr, Adèle, et al, 2018). In 1880, a Scottish

surgeon, Alexander Ogston first discovered the cause of pus from a surgical abscess.

Ogston made a stained smear of pus from one of his patients' abscess and examined it

under the microscope. (Orenstein, 2013) Ogston named the bacteria “staphylococci” for

resembling a “bunch of grapes”. Additionally, in 1884, German physician Anton J.

Rosenbach isolated two strains of staphylococci. He is credited for identifying the

differences between Staphylococcus aureus and Staphylococcus albus (S. epidermidis)

based on the color of their colonies. He named Staphylococcus aureus after the Latin

word “aurum” for its golden color. (Orenstein, 2013)

S. aureus can cause many different types of infections that range from mild to life

threatening. Skin infections such as abscesses, furuncles (boils) and cellulitis are the

most common infections. Although most infections caused by S. aureus aren’t critical,

some infections can cause serious infections such as bacteremia (bloodstream

infection), endocarditis (infection in the inner lining of the heart chambers and heart

valves), pneumonia, osteomyelitis and joint infections. (Bush, 2019) Although anyone

can develop a S. aureus infection, people who have chronic conditions such as

diabetes, cancer, chronic lung disorders, chronic skin disorders and injection of illegal

drugs are at a greater risk of getting a S. aureus infection. (Staphylococcus aureus in

Healthcare Settings, 2011) In addition to this, patients who have weakened immune

systems or have undergone procedures have a greater risk of getting S. aureus

infections. (Staphylococcus aureus in Healthcare Settings, 2011) In healthcare facilities,

patients in intensive care units, patients with medical devices in the body like IV’s,

people in dialysis, and people who often visit nursing homes are also at an increased

risk. (Staphylococcus aureus in Healthcare Settings, 2011)

MSSA (methicillin-sensitive Staphylococcus aureus) and MRSA

(methicillin-resistant Staphylococcus aureus) are two types of S. aureus bacteria that

are commonly found in the skin and nose. Even though both bacterias have similar

symptoms, each bacteria are spread and treated differently. MSSA is an infection that

can be treated with certain antibiotics like methicillin. This bacteria spreads easily

through skin-to-skin contact etc. and self-infection is common. It is revealed that 80% of

S. aureus infections are caused by self-infection involving the nose as a source (MSSA

vs. MRSA: What Is the Difference, 2020) MSSA is also known to be an opportunistic

pathogen because it can cause a serious infection if it comes in contact with an open

wound. (MSSA vs. MRSA: What Is the Difference, 2020) When a healthy person gets a

minor skin infection, they usually don’t need antibiotics. (What Is MSSA, 2020) The best

treatment would be to let the wound heal by itself by keeping the area dry and covered.

Yet, someone with a serious infection can be treated with antibiotics like penicillin,

methicillin, or cefazolin. (What Is MSSA, 2020) MRSA is an infection that is resistant to

the effects of methicillin treatment. MRSA is resistant to the antibiotic due to its mecA

gene. The mecA gene codes for the penicillin-binding protein (PBP2a) that allows it to

be resistant to antibiotics. MRSA infections are treated differently. Severe MRSA

infections are treated with antibiotics through an IV for a long period of time depending

on its severity. (Felson, 2019) In addition, other MRSA infections like a skin boil are

treated with oral antibiotics. (Felson,2019) Sometimes a doctor can perform an incision

and drainage. Moreover, hospital patients are at a greater risk of getting MRSA

infections while people in nursing homes have an increased risk of getting MSSA

infections. This is the reason why it is important to practice proper handwashing to

prevent these infections.

Materials:

● Sterile cotton swab (3) - used for swabbing nostrils, ears, and tonsils.

Mannitol salt agar (MSA) plate contains:

● Sodium chloride

● Mannitol sugar

● Phenol red

Methods:

In order to determine if students in my class were carriers of S. aureus, we

gently swabbed our ears, nostrils, and tonsils to pick up bacteria from those

environments. Then we culturized the bacteria onto the mannitol salt agar (MSA) plate.

The plates were left to incubate for about 2 days (48 hours) at a body temperature of

98.6 degrees Fahrenheit.

The mannitol salt agar (MSA) plate is a selective and differential medium for

Staphylococcus aureus and other Staphylococcus bacteria. The MSA plates contain

sodium chloride that is used to kill other bacteria while it encourages S. aureus to grow

in its high salt environment. S. aureus is able to grow well since it lives in environments

with high salt concentrations. Next , we have the mannitol sugar. This sugar is used as

a food source for the bacteria on the plates. This is essential for the bacteria to grow. S.

aureus has the ability to ferment the sugar. Unlike Staphylococcus epidermidis, it

doesn't ferment the mannitol. Since S. aureus was able to ferment the mannitol, it

produced an acid. The phenol red is a pH indicator that detects an acid (this shows that

the bacteria was able to ferment the mannitol). S. aureus was able to grow and was

capable of fermenting the mannitol, causing its acidity to decrease. The pH indicator

detected the low pH due to the acid production. (Tankeshwar, Acharya, et al. 2020) This

led to the change of color of the medium from phenol red to yellow. The yellow color

shows the growth and identification of the presence of S. aureus (Thakur, P., Nayyar,

C., Tak, V., & Saigal, K. , 2017)

Results:

According to the results, it was clear that Staphylococcus aureus is the one in the yellow

zone (right). I know this because S. aureus fermented the mannitol that caused an acid

production. Because of the acid production, it caused the color of the pH indicator to

change from a phenol red to a yellow. Also, Staphylococcus aureus is the only bacteria

that can form small colonies. Staphylococcus epidermidis (left) did produce small

colonies but the medium had no color change. Since S. epidermidis didn’t ferment

mannitol, the medium remained a pink-ish color with colorless colonies.

This is the class data of students from 2017-2020 who were S. aureus carriers

This bar graph shows that 233 students were colonized by S. aureus in the nostrils. 332

students had the presence of S. aureus in their ears and only 88 students had S. aureus

present in their tonsils/throat . Overall, 411 students were colonized by S.

aureus. This shows that the majority of the students are carriers of S. aureus.

This pie chart shows the percentage of how many students tested positive for S. aureus

carriage in different areas of the body. 8.3% tested positive in the tonsils/throat; 31.2%

in the ears; 21.9% in the nostrils; 38.6% were colonized by S. aureus.

Discussion:

The results from the S. aureus carriage surprised me. Among the students,

38.6% were carriers of S. aureus yet it is believed that approximately 30% of the human

population is colonized with S. aureus (Tong, Steven Y. C., et al, 2015) The fact that

anyone can be colonized with S. aureus makes me believe that I do have it. However,

I’m not sure if I’ve been affected by it before. I know that when I was younger, I used to

have mild bacne. I’ve never had issues with severe acne so I used to think it was

unusual for me to have bacne. It’s interesting to think about it now because it could’ve

just been the S. aureus from my scalp that caused it. Today, I know that my brother also

suffers from bacne and I have a friend who has severe cystic acne all over his face.

S. aureus can be easily transmitted through skin to skin contact or by sharing

objects. People who are immunocompromised are susceptible to catching an S. aureus

infection especially in healthcare settings. Lastly, S. aureus can colonize if there’s skin

damage or mucosal damage (Sakr, Adèle, et al., 2018) Colonization of S. aureus on the

nose has been shown to be an important factor for causing infections especially in

patients in intensive care unit (ICU) and those who have had surgery (Sakr, Adèle, et

al., 2018) Depending on the infection, a medication, antibiotics, or intravenous (IV) may

be prescribed. S. aureus infections are usually treated with antibiotics especially if it's a

MSSA infection. For instance, Topical Antibiotic Ointment is an antibiotic ointment that

can be applied to help cure a minor wound infection. However, if a person has a severe

wound, antibiotics are required to treat it. According to Mayo Clinic, S. aureus infections

are treated with commonly prescribed antibiotics: nafcillin or oxacillin, vancomycin,

daptomycin, telavancin or linezolid. (Staph Infections, 2020) Additionally, MRSA

infections are treated with oral antibiotics or intravenously with vancomycin and other

antibiotics (Staph Infections, 2020)

In summary, Staphylococcus aureus is a Gram-positive, spherical (coccal)

bacterium that is commonly found in the nose, skin, and other areas. Although S.

aureus causes acute infections (boils, cellulitis), sometimes some infections can be life-

threatening such as bloodstream infections, endocarditis, and joint/bone infections.

There are two types of staphylococcus bacteria; MRSA is the bacteria that are

resistant to certain antibiotics (methicillin) that are used to treat S. aureus infections

whereas MSSA is not resistant to certain antibiotics. Both Staphylococcus bacteria have

similar symptoms but are treated and spread differently. In the MSA plate, S. aureus

ate the mannitol from the medium. It led to a change in color from phenol red to yellow

due to its acid production. As a result, S. aureus formed white colonies in the

yellow zone; S. Epidermidis had no change in color (light pink) and formed

colorless colonies. S. aureus infections are treated depending on the severity of

the infection. Those with minor wounds can successfully cure it with over- the- counter

medications such as Triple Antibiotic Ointment. However, severe wounds are treated

with antibiotics (vancomycin etc.) either with oral antibiotics or intravenously (IV).

References:

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www.merckmanuals.com/home/infections/bacterial-infections-gram-positive-bacteria/sta

phylococcus-aureus-infections.

Felson, Sabrina. MRSA Diagnosis and Treatment: Antibiotics, Drainage, and More. 14

May 2019,

https://www.webmd.com/skin-problems-and-treatments/understanding-mrsa-detection-tr

eatment

MSSA vs. MRSA: What Is the Difference?: Nozin. 2 July 2020, www.nozin.com/mssa-

vs-mrsa-what-is-the-difference/.

Orenstein A. The Discovery and Naming of Staphylococcus aureus [cited 2013 Jul 10].

http://www.antimicrobe.org/h04c.files/history/S-aureus.pdf

Sakr, Adèle, et al. Staphylococcus Aureus Nasal Colonization: An Update on

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Tankeshwar, Acharya, et al. Carbohydrate Fermentation Test: Uses, Principle,

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test-uses-principle-procedure-results/.

Thakur, P.,Nayyar,C.,Tak, V., Saigal,K. Mannitol-Fermenting and Tube

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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5015504/?report=classic

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What Is MSSA? 21, July 2020, www.nozin.com/what-is-mssa/.