Microbology

Q What is microbiology?

Microbiology is the science of microorganisms, or germs. Microorganisms include parasites, bacteria, and viruses.
What does a microbiology department of a laboratory do?

The microbiology department of a laboratory works to isolate, or find, the microorganism that is causing your infection. An accurate diagnosis of your infection is based upon this information. Medical technologists in the laboratory work closely with your physician, keeping him/her up to date on your cultures. He/she will often base your treatment on this information. For instance, if your infection is caused by a bacterium, you may require antibiotics, which will eradicate, or kill, the germ. However, if your infection is caused by a virus, often times, your physician can only treat your symptoms. There exists no medicine to eradicate most viruses.

Q How does the microbiology lab do this?

Studies are performed on specimens obtained from patients who have an infection. This specimen is "cultured". Specimens which are most often submitted for testing include throat swabs, wound swabs, urine, stool, blood, spinal fluid, sputum, ear swabs, and various types of drainage.

A small portion of the specimen is put on culture plates which are made of the necessary nutrients to support the growth of microorganisms. The "cultures" are then put into an environment which enhances the growth.

For instance, most human pathogens (those germs that infect humans) grow best at body temperature. Therefore, the incubator is heated to this temperature. Some microorganisms will not grow in the presence of oxygen. So, an oxygen-free environment must be provided to "isolate" this germ. (In the intestinal tract, there are many organisms that will not survive when exposed to oxygen. Often, these germs cause infections deep in the body.)

One of the major problems encountered in a bacteriology lab is the separation and identification of infectious microorganisms from those that are normal, or normal flora. Certain areas of the body, such as skin, upper respiratory tract, intestinal tract, female genital area and open wounds, develop an environment of normal microbial flora, or microorganisms. The following represents the major ways of dealing with the problem of normal flora in isolation or interpretation:

1. Cleansing the area with appropriate disinfectant
2. Looking specifically for organisms known to be pathogenic, or infection-causing
3. Bypassing areas of normal flora to reach tissues not normally colonized by microorganisms (by aspiration)

Q How long does it take to get a culture results?

Bacterial cultures usually are incubated for 48-72 hours. They are removed from the incubator and checked for significant bacterial growth at least every 24 hours. If growth is present, the germs are identified and antibiotic testing is performed. You may have a report at 24 hours if the germ grows fast, but it may take several days if the germ is a slow-grower.

If the culture is "negative", this means that your culture did not grow a germ. This could be a result of several situations:

1. Your infection is being caused by a virus, and not a bacterium.
2. Your specimen was not of good quality. (For instance, instead of producing sputum to culture, you submitted saliva. Remember, the germ is deep in your lungs, not in your mouth.)
3. You may already have been taking an antibiotic which, while not eradicating the germ and making you well, inhibited the germ so that it will not grow on culture.

Q How does my doctor know what kind of "antibiotic" to give me?

Determining appropriate treatment for an infectious disease requires both the isolation of the germ and antibiotic studies of the germ.

Infections are usually caused by two different types of microorganisms: viruses and bacteria.

Treatment for Viruses:

There exists no "antibiotic" for viruses that will totally eradicate the organism. However, there are a few "anti-viral" drugs available now that may help reduce the number of infectious organisms. These include acyclovir, amantadine, azidothymidine (AZT), ribavirin, and ganciclovir. While these medications may help the patient, they are very expensive and often toxic. Because of this, they usually are saved for severe viral infections. Your physician usually will be able to give you something to treat your "symptoms". This will make you feel a little more comfortable while the virus runs its course.

HIV is very serious because it is a virus. No drug has been found that will kill the organism. However, there are some promising drugs being studied now. In clinical trials, some have been found to significantly reduce the viral load in some HIV infected people.

Treatment for Bacteria:

Many anti-microbial medications have been discovered or synthesized in research labs which kill many types of bacteria. Different bacteria will be vulnerable, or susceptible, to different drugs. There are very few organisms that are susceptible to all antibiotics. It is very important for your doctor to know what kind of bacteria is causing your infection so he/she can choose a correspondingly effective antibiotic.

For instance, let's say you have Strep throat. Your doctor will give you penicillin or a variation of penicillin, such as amoxicillin. She does this because she knows what the germ is that is causing your infection (Strep), and she knows that the germ is always susceptible to penicillin. It has a predictable susceptibility. It gets more difficult with other infections. Let's say that you have pneumonia. There are many bacteria that can cause pneumonia. Some of those organisms include Streptococcus pneumoniae, Haemophilus influenzae, and Klebsiella pneumoniae. Each of these germs have different antibiotic susceptibility patterns, or in other words, will require different antibiotics to kill them. Therefore, it is important that your physician know which germ is causing your pneumonia. He probably will want to culture your sputum and send it to the microbiology laboratory for isolation and identification of the pathogen (germ). The lab will also do antibiotic studies and will report to your doctor which antibiotic will do the best job of killing the germ. However, initially, he/she will most likely choose to give you a "broad spectrum" antibiotic that will work with all of the above organisms to a certain degree. When he receives the lab report, he may choose to change your antibiotic for one that is more specific.

Q Why should I continue to take my antibiotic, even though I feel better after a couple of days?

It is very important to take all of your antibiotic. Very often if you have been given an appropriate antibiotic, you will feel better very quickly. This is because the drug is inhibiting the growth or spread of the organism. As soon as this happens, you will feel better. However, the organism is still present and still alive.

If you stop taking the medication, the germ will start reproducing again and you will become sick again.

Another reason that you should continue to take all of the medication is to prevent the bacteria from developing a resistance to the drug. Bacteria (and viruses) have a defense mechanism that goes into action when it is exposed to a drug. It is capable of developing a "resistance" to the destructive effect the drug has. If you subject a germ to an antibiotic without killing it, as in the case of taking the antibiotic for a couple of days, you give it a chance to develop a resistance to the drug, and survives with this new resistant characteristic. The more often the germ is exposed to the drug, the more able it will become to "resist' it. You then may transmit to others these "new" germs, capable of resisting the antibiotic that you exposed it to. This has happened quite frequently. For instance, Streptococcus pneumoniae (which causes ear infections and pneumonia) historically has been predictably susceptible to penicillin. Now up to 30% have developed a resistance.

Q What germs cause the most common infections?

Bronchitis:

Chronic bronchitis is present in as many as 15 % of adults at some time. Patients may experience a loss of appetite, fever and chills, production of a purulent sputum, congestion and wheezing.

The germs most often causing this include:

1. Streptococcus pneumoniae: Ceclor is the drug of choice.
2. Haemophilus influenzae: Ceclor is the drug of choice
3. Moraxella catarrhalis: Augmentin, Septra or Bactrim are drugs of choice.

Throat infection (Bacterial):

Acute pharyngitis (sore throat) is an inflammatory syndrome of the pharynx caused by various different organisms, predominately viral. Patients complain of soreness or irritation of the throat also with congestion and headaches. Patients with Strep throat and mononucleosis usually have fever, too.

The germs most often causing pharyngitis include:

I . Streptococcus pyogenes (Group A): Drug of choice is amoxicillin or penicillin.

1. Respiratory syncytial virus: no therapy indicated
2. Influenza virus: no therapy indicated
3. Parainfluenzae virus: no therapy indicated
4. Adenovirus: no therapy indicated
5. Epstein Barr virus (also causes mononucleosis): no therapy indicated

II.  Gastroenteritis:

Patients with bacterial gastroenteritis frequently have lower gastrointestinal symptoms (diarrhea) with or without fever. Bloody diarrhea is also suggestive of a bacterial germ. Patients with non-bacterial gastroenteritis usually have upper gastrointestinal symptoms (vomiting).

The bacteria usually causing gastroenteritis include:

1. Campylobacter jejuni
2. Salmonella
3. E. coli 0157
4. Shigella

Most cases of gastroenteritis don't require antibiotic therapy. They are usually self-limiting. However, severe cases may be treated with one of the following: Ciprofloxacin, Bactrim (Septra), and Cefotaxime or Ceftriaxone.

Urinary Tract Infection:

Bladder infections (cystitis): Patients with lower urinary tract infections usually have frequent and painful urination and suprapubic Oust above the pubic bone) tenderness.

Kidney infections: Patients with upper urinary tract disease usually have a bladder infection with its symptoms, fever and flank (back) pain.

The bacteria usually causing urinary tract infections include:

1. E. colI
2. Klebsiella
3. Proteus
4. Staph saprophyticus

These organisms are most often treated with Bactrim (Septra), or Ciprofloxacin.

Meningitis:

Adults have fever, headache, nausea, vomiting, and nuchal (back of the neck) rigidity.

The bacteria most often causing meningitis in the adult include:

1. Haemophilis influenzae: The drug of choice is a cephalosporin such as Cefotaxime.
2. Neisseria menigitidis: The drug of choice is high dose intravenous penicillin.
3. Streptococcus pneumoniae: The drug of choice is Vancomycin or Cefotaxime, or high doses of Penicillin G if susceptible. Almost 30% are resistant to Penicillin today.

Pediatrics greater than 2 months of age have fever or hypothermia, seizure, sleepiness, irritability, and stiff neck.

The bacteria most often causing meningitis in this age group include:

1. Haemophilus influenzae: The drug of choice is a cephalosporin such as Cefotaxime.
2. Neiserria meningitides: The drug of choice is high dose intravenous penicillin.
3. Streptococcus pneumoniae: The drug of choice is Vancomycin Cefotaxime or high doses of Penicillin G, if susceptible.

Neonatals less than 2 months of age will feed poorly, have fever or hypothermia, seizures, sleepiness, irritability, or other unusual behaviors and a full fontanelle (the "soft spot" at the top of the head).

The bacteria most often causing meningitis in this age group include:

1. E. coli
2. Klebsiella: The drugs of choice include a 2nd or 3rd generation cephalosporin such as Cefotaxime.
3. Listeria monocytogenes: The drugs of choice are Ampicillin and Gentamycin used together.
4. Streptococcus Agalactiae (Group B Strep): The drugs of choice are Ampicillin and Gentamycin used together.

Q How are germs transmitted, or spread, from person to person?

Viruses are transmitted from person to person by the respiratory and fecal-oral routes, by trauma or injection with contaminated objects or needles, by tissue transplants (including blood transfusions), and by insect or animal bites.

Once inside the body, the virus infects cells, frequently in the upper respiratory tract (throat and/or nose). It then spreads throughout the body. This is when symptoms appear. Your infection ends, and you f6el better, when your immune system gears up and does one or two things: (1) produces antibodies to the virus to destroy it (2) your fighter white blood cells attack the virus and destroy it.

Q How do vaccinations work?

The control of many viral diseases has been accomplished by vaccination. This is very important, since anti-viral drugs are sometimes less than desirable, either because they are not very effective or because they are so toxic. Since Jenner developed the first vaccination against smallpox nearly 200 years ago, viral vaccinations have been s4uccessfully used to prevent yellow fever, polio, measles, mumps, rubella (German Measles), hepatitis B, and influenzae (flu). Smallpox was eliminated in 1977 by an effective worldwide vaccination program.

A vaccination against a microorganism, such as the measles virus, will cause your body to design and produce antibodies that are specific for the measles virus.

Then, if and when the measles virus is transmitted to you, the antibodies are already there, waiting to attack the virus as soon as it enters the body. The virus doesn't have time to infect your cells and make you sick.

If the antibodies are not already in your body, waiting to make the attack, the virus has time to spread throughout your body, making you sick until your immune system has time to design and produce the antibodies from scratch. This usually takes a few days. At that time, you get better.

Antibodies are very specific. Antibodies that are produced to fight measles are not able to fight polio viruses. Antibodies to the flu virus are not able to fight the measles virus. This is why you must get different kinds of vaccinations.

Q What are vaccinations?

A vaccination is actually a dose of an "attenuated-live" or an "inactivated-dead" virus. This dose of virus "tricks" your immune system, which sees it as a real, infection-producing enemy! The immune system activates its army of antibody designers, comes up with an effective antibody specific for this virus, and then activates the antibody "factories" in the body and produces the antibodies to attack the virus. this process usually takes several days.

The "virus" that was transmitted to your body, in this case, was not a real enemy. But this is okay. These antibodies will now just wait around until the real enemy arrives. They will then attack and destroy it before it has time to make you sick.

Q What are vaccination "boosters"?

"Booster shots", or doses, are given to reactivate the antibody production in your body. After a long time of inactivity, your body may not be equipped to produce as many of the specific antibodies that will be necessary to fight off a real infection, should you be exposed. This "booster" ensures that your body "remembers" the design of the antibody and acts as a "refresher course" for the "antibody factories".