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infectious diseases

MRSA - Methacillin-resistant Staphylococcus

Generality

MRSA is a human bacterial infection caused by particular Staphylococcus aureus strains, as they are resistant to some antibiotics such as penicillins and cephalosporins.

Figure: Methicillin-resistant Staphylococcus aureus seen in a scanning optical microscope (artificial coloring).

The disease mainly affects people admitted to hospitals; however, in recent years, it is becoming increasingly widespread even among non-hospitalized people, especially among those who spend a lot of time in close contact with other individuals (prisoners, athletes of sports teams, students, etc.).

The symptoms are extremely variable: MRSA, in fact, can occur not only with boils, abscesses and infectious cellulitis, but also with fever, chills, septicemia, endocarditis and so on.

The therapy depends on the characteristics of the infection and on the results of the culture tests.

What is MRSA?

MRSA is a human bacterial infection caused by particular strains of Staphylococcus aureus, resistant to β-lactam antibiotics such as penicillins (methicillin, dicloxaciline, nafcilina, oxacilina etc.) and cephalosporins .

WHAT HAS BACTERIA RESISTANCE DUE TO ANTIBIOTICS?

The bacteria become resistant to an antibiotic when they accidentally develop a genetic mutation that leads them to survive the bactericidal action of the drug. For example, they can acquire a defense mechanism that they did not previously have.

The great spread of antibiotic-resistant bacteria, occurred in the last decades, is linked to the indiscriminate use of antibiotics: with their abuse, in fact, the susceptible bacteria were exterminated and the resistant were allowed (who were in minor number) to gain dominance within the species.

MEANING OF MRSA

MRSA stands for Methicillin Resistant Staphylococcus Aureus . This acronym (which in the light of the definition given may seem unsuitable) was coined because the first antibiotic, to which some Staphylococcus aureus strains proved to be resistant, was methicillin.

When biologists and doctors noticed that the resistance of these strains was also directed towards other penicillins and cephalosporins, the term MRSA had by now entered the common jargon and was no longer changed.

What are MSSAs?

Non-penicillin and cephalosporin-resistant staphylococci are classified as MSSA, meaning Methicillin-sensitive Staphylococcus Aureus . Also for these, the acronym that identifies them does not fully reflect their characteristics; however, it has now entered common use and has been maintained as such.

STAPHYLOCOCCUS AUREUS

Staphylococcus aureus is a gram-positive bacterium, spherical and asporiginal, which mainly colonizes the nasopharyngeal mucosa, the skin and the cutaneous glands. The infection caused by it can be mild, if limited to the skin (impetigo, abscesses and boils), but it can also be lethal if it passes through the skin and spreads in the blood or heart.

TYPES OF MRSA

The first cases of MRSA have occurred since the early 60s of the last century and, for at least twenty years, they have only concerned hospitalized patients.

In the early 1980s, non-hospitalized individuals also began to become infected. The most affected were people attending extremely crowded places, such as prisons, homeless shelters, student dormitories, gym and sports fields dressing rooms, barracks and schools.

The place of infection, therefore, was taken as a parameter to distinguish two types of MRSA:

  • HA-MRSA, where HA stands for Healthcare-Associated and refers to all cases of MRSA that contracted the infection during a hospital stay.
  • CA-MRSA, where CA stands for Community-Associated and refers to all cases of MRSA that have contracted the infection outside a hospital and, generally, in a crowded place.

Although the number of cases of CA-MRSA is increasing today, HA-MRSA is still the most common type of MRSA.

Causes

The bacterium responsible for MRSA is usually transmitted by direct contact, for example through the hands of an infected or colonized individual (NB: for a colonized individual, a person is meant to spread a pathogen but, despite this, healthy). Other transmission routes are represented by the so-called skin-to-skin contact and everything that has previously been touched by an individual carrying MRSA (for example towels, sheets, clothes, etc.).

MRSA is very resistant and is able to survive on the surface of objects (door handles, sinks, floors, etc.) for long periods of time.

HA-MRSA

MRSA has been, and continues to be, a typical infection in hospitals for at least three reasons:

  • The presence of wounds that represent entry points for the bacterium . Often, hospitalized patients are people with wounds (fortuitous or post-surgery) or catheterized (ie with bladder or intravenous catheters); this means that it is easier for a bacterium like MRSA to penetrate the body and trigger the infection of the same name.
  • The fragility of hospitalized patients . In hospitals, a high percentage of inpatients are elderly or immunosuppressed (ie with reduced immune defenses). Seniority and the lack of immune defenses make people more fragile and vulnerable to infections.
  • The other patients and the number of people circulating every day for a hospital . Hospitals are fairly crowded places (patients, medical staff, relatives, cleaners, etc.); in addition, the high number of sick people facilitates the spread of infectious diseases.

CA-MRSA

CA-MRSA is less common than HA-MRSA, although, over the past few decades, the number of related cases has increased significantly (and will probably continue to rise again).

The favoring factors are numerous; among the most influential are:

  • Attendance or living in crowded places, such as schools, prisons and military bases.
  • The practice of contact sports, like rugby, because the skin-to-skin transmission of the pathogen is easier.
  • The presence of cuts and grazes on the skin, due, for example, to the use of illegal drugs such as heroin.
  • Lack of adequate immune defenses. This can be linked to serious diseases, such as AIDS, systemic lupus erythematosus and tumors, or to organ transplantation.
  • The lack of periodic cleaning of very busy areas, with consequent contamination of all surfaces and all objects present. In this regard, it is recalled that MRSA is a remarkably resistant bacterium.
  • Poor personal hygiene. This explains why MRSA is frequent among the homeless.
  • An indiscriminate use of antibiotics, which promotes the spread of resistant bacterial strains.

Symptoms and Complications

MRSA can manifest itself with different symptoms and signs, depending on whether the responsible bacterium has infected the skin or has penetrated deeper reaching the blood and other internal organs of the body.

MRSA LEATHER LOCALIZED

When MRSA is expressed in the skin it can cause boils, abscesses and phenomena of infectious cellulite.

Pimples and abscesses . A pimple is a cutaneous protuberance, filled with pus, due to a superficial inflammation of the hair follicles; the abscess, on the other hand, is a collection of pus, bacteria, plasma and cellular debris, which can also form in locations other than the skin.

Infectious cellulite . Infectious cellulite is an acute and severe inflammation of the dermis and subcutaneous layers (NB: the dermis is the middle layer of the skin, placed under the epidermis and above the hypodermis). Its onset makes the skin red, warm, soft to the touch, sore and swollen.

According to some estimates, 75% of the forms of CA-MRSA are localized on the skin.

MRSA INVASIVE

Figure: A boil. From the site: prn.org

When the MRSA bacterium manages to overcome the skin (which acts as a protective barrier), and to reach the blood or internal tissues of the body, it can cause unpleasant and sometimes very serious consequences.

In moderate cases, invasive MRSA (this is called MRSA extended to the blood and internal tissues of the body) causes:

  • Fever at 38 ° C
  • Chills
  • Sense of general malaise
  • Confusion
  • Dizziness
  • Muscle pains
  • Sense of pain, swelling and numbness in the affected parts of the body

In more severe cases, invasive MRSA can result in:

  • Septicemia . It is the medical term used to indicate the persistent presence of bacteria in the blood; this condition is different from bacteremia, with which instead there is a transient presence of bacteria in the blood.

    Severe septicemia can degenerate into so-called septic shock, whose main sign is the marked drop in blood pressure (severe hypotension).

  • Infections of the urinary tract (ie ureters, bladder and urethra).
  • Endocarditis . It is an inflammatory process against the membranes that line the internal cavities of the heart and the four heart valves.
  • Pneumonia . It is the inflammation of the lungs.
  • Septic arthritis . It is the inflammation of the joints caused by bacteria.
  • Osteomyelitis . It is an infectious process that affects the bones.
  • Bursitis .

Can abscesses and infectious cellulitis from MRSA give the same symptoms as invasive MRSA?

The answer to this question is: "Yes, when the conditions deteriorate and the bacteria reach the blood". However, with the appropriate care, it is possible to prevent these problems and to control the localized infection on the skin (see the chapter on prevention).

Diagnosis

To find out if a Staphylococcus aureus bacterial infection is in progress, a culture test must be performed on a blood sample ( blood culture ), urine (urine culture ), cells (cell culture ) or sputum. Conceptually, they are all very similar procedures: once the chosen biological sample is taken (for example, blood), it is inoculated into different culture media, each of which is suitable for the growth of a specific bacterium. If a reproduction is observed in the soil suitable for the growth of Staphylococcus aureus, it means that the ongoing bacterial infection is caused precisely by Staphylococcus aureus .

NEXT STEP: ANTIBIOGRAM

The next step after the culture test is the antibiogram, that is the sensitivity test of a microorganism (in this case, Staphylococcus aureus ) to one or more antibiotics. This investigation serves to find out whether Staphylococcus aureus found in the patient:

  • It is resistant or not to penicillins and cephalosporins (so if it is a strain of MRSA).
  • It is sensitive to some particular antibiotic. The antibiotic or antibiotics that have proved effective will then be used during the course of therapy.

Treatment

Treatment for Staphylococcus aureus infections Meticillin-resistant depends on at least three different factors, namely:

  • The site of infection, if limited to the skin or extended to the blood and to some internal tissue of the body.
  • The antibiotic to which the particular MRSA strain was found to be sensitive.
  • The severity of the symptoms in place.

WHAT TO DO WHEN MRSA IS A SKIN LEVEL?

For boils and abscesses, the most indicated treatment is usually the incision of the affected area, followed by pus drainage. Both of these operations are performed, after local anesthesia, with a sterile needle or scalpel.

For infectious cellulite, on the other hand, the cure consists in administering, orally or intravenously, one of the antibiotics that is effective against antibiograms. The duration of treatment, in these cases, is variable and can last from a minimum of 5 days to a maximum of 14 days.

WHAT TO DO WHEN MRSA IS INVASIVE?

In the case of invasive MRSA, hospitalization and an association of several antibiotics are required (an antibiotic alone may not be sufficient). The administration of these drugs is by injection and has a variable duration in relation to the infected organ (it can even reach six weeks).

What does hospitalization involve?

Patients with MRSA are admitted to the isolation ward in order to protect other patients and avoid the spread of infection. They can receive visits from relatives and friends; these, however, must protect themselves with shirts, masks and gloves, and avoid contact with their loved one.

DECOLONIZATION

Decolonization is the process by which bacteria present on a colonized individual are eliminated.

List of the main antibiotics that can be used in case of MRSA:

  • Linezolid

  • Trimethoprim

  • Clindamycin

  • Doxycycline

  • Minocycline

  • Teicoplanina

  • Vancomycin

  • daptomycin

It is carried out by carefully washing the skin (in particular the hands), with detergents (soaps and shampoos), disinfectants and alcohol-based preparations.

To get good results, it is sufficient to perform the entire procedure once a day for 5 consecutive days.

Prevention

To prevent HA-MRSA, it is good that all patients, health staff and those visiting sick relatives adopt certain hygiene measures.

Patients must take care to wash their hands after each use of the bath and at every meal; in addition, they must ensure that the room and the toilet are always properly cleaned.

The medical staff (doctors, nurses and laboratory technicians) must use the indicated garments (ie gown, gloves and, in the case of patients with infectious diseases, masks) and must wash their hands with disinfectant soaps after each contact with the patients (even if minimal).

To prevent CA-MRSA, however, it is good practice:

  • Wash your hands several times a day and take a shower regularly.
  • Keep fingernails short and clean. In nails, in fact, different types of bacteria can lurk and, with a long fingernail, it is easier to scratch or scratch someone else.
  • Do not share products that are used directly in contact with the skin, such as soaps, deodorant sticks, etc.
  • Don't share the towel.
  • Do not share razors, nail files, toothbrushes, hairbrushes and combs.

How to prevent a worsening of MRSA at the skin level?

It is good practice to bandage the involved anatomical area with sterile gauze, at least until you have been examined by the doctor.

Also, if you have touched the area infected with MRSA, you should wash your hands and avoid recycling the gauze used, which should instead be thrown into special waste bins.

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