<< Chapter < Page Chapter >> Page >

When an infection becomes disseminated throughout the body, we call it a systemic infection . For example, infection by the varicella-zoster virus typically gains entry through a mucous membrane of the upper respiratory system. It then spreads throughout the body, resulting in the classic red skin lesions associated with chickenpox . Since these lesions are not sites of initial infection, they are signs of a systemic infection.

Sometimes a primary infection , the initial infection caused by one pathogen, can lead to a secondary infection by another pathogen. For example, the immune system of a patient with a primary infection by HIV becomes compromised, making the patient more susceptible to secondary diseases like oral thrush and others caused by opportunistic pathogens. Similarly, a primary infection by Influenzavirus damages and decreases the defense mechanisms of the lungs, making patients more susceptible to a secondary pneumonia by a bacterial pathogen like Haemophilus influenzae or Streptococcus pneumoniae . Some secondary infections can even develop as a result of treatment for a primary infection. Antibiotic therapy targeting the primary pathogen can cause collateral damage to the normal microbiota, creating an opening for opportunistic pathogens (see Case in Point: A Secondary Yeast Infection ).

A secondary yeast infection

Anita, a 36-year-old mother of three, goes to an urgent care center complaining of pelvic pressure, frequent and painful urination, abdominal cramps, and occasional blood-tinged urine. Suspecting a urinary tract infection (UTI) , the physician requests a urine sample and sends it to the lab for a urinalysis. Since it will take approximately 24 hours to get the results of the culturing, the physician immediately starts Anita on the antibiotic ciprofloxacin. The next day, the microbiology lab confirms the presence of E. coli in Anita’s urine, which is consistent with the presumptive diagnosis. However, the antimicrobial susceptibility test indicates that ciprofloxacin would not effectively treat Anita’s UTI, so the physician prescribes a different antibiotic.

After taking her antibiotics for 1 week, Anita returns to the clinic complaining that the prescription is not working. Although the painful urination has subsided, she is now experiencing vaginal itching, burning, and discharge. After a brief examination, the physician explains to Anita that the antibiotics were likely successful in killing the E. coli responsible for her UTI; however, in the process, they also wiped out many of the “good” bacteria in Anita’s normal microbiota. The new symptoms that Anita has reported are consistent with a secondary yeast infection by Candida albicans , an opportunistic fungus that normally resides in the vagina but is inhibited by the bacteria that normally reside in the same environment.

To confirm this diagnosis, a microscope slide of a direct vaginal smear is prepared from the discharge to check for the presence of yeast. A sample of the discharge accompanies this slide to the microbiology lab to determine if there has been an increase in the population of yeast causing vaginitis. After the microbiology lab confirms the diagnosis, the physician prescribes an antifungal drug for Anita to use to eliminate her secondary yeast infection.

  • Why was Candida not killed by the antibiotics prescribed for the UTI?
  • List three conditions that could lead to a secondary infection.

Transmission of disease

For a pathogen to persist, it must put itself in a position to be transmitted to a new host, leaving the infected host through a portal of exit ( [link] ). As with portals of entry, many pathogens are adapted to use a particular portal of exit. Similar to portals of entry, the most common portals of exit include the skin and the respiratory, urogenital, and gastrointestinal tracts. Coughing and sneezing can expel pathogens from the respiratory tract. A single sneeze can send thousands of virus particles into the air. Secretions and excretions can transport pathogens out of other portals of exit. Feces, urine, semen, vaginal secretions, tears, sweat, and shed skin cells can all serve as vehicles for a pathogen to leave the body. Pathogens that rely on insect vectors for transmission exit the body in the blood extracted by a biting insect. Similarly, some pathogens exit the body in blood extracted by needles.

Portals of exit: eye (tears), needle,  mammary glands (milk, secretions), placenta (transmission to fetus), vagina (secretions, blood), urethra (urine), broken skin,  broken skin (blood), skin (flakes), nose (secretions), mouth (saliva, sputum), ear (earwax), urethra (urine, semen, secretions), anus (feces).
Pathogens leave the body of an infected host through various portals of exit to infect new hosts.

Key concepts and summary

  • Koch’s postulates are used to determine whether a particular microorganism is a pathogen. Molecular Koch’s postulates are used to determine what genes contribute to a pathogen’s ability to cause disease.
  • Virulence , the degree to which a pathogen can cause disease, can be quantified by calculating either the ID 50 or LD 50 of a pathogen on a given population.
  • Primary pathogens are capable of causing pathological changes associated with disease in a healthy individual, whereas opportunistic pathogens can only cause disease when the individual is compromised by a break in protective barriers or immunosuppression.
  • Infections and disease can be caused by pathogens in the environment or microbes in an individual’s resident microbiota .
  • Infections can be classified as local , focal , or systemic depending on the extent to which the pathogen spreads in the body.
  • A secondary infection can sometimes occur after the host’s defenses or normal microbiota are compromised by a primary infection or antibiotic treatment.
  • Pathogens enter the body through portals of entry and leave through portals of exit . The stages of pathogenesis include exposure , adhesion , invasion , infection , and transmission .

Fill in the blank

A(n) __________ pathogen causes disease only when conditions are favorable for the microorganism because of transfer to an inappropriate body site or weakened immunity in an individual.

opportunistic

Got questions? Get instant answers now!

The concentration of pathogen needed to kill 50% of an infected group of test animals is the __________.

LD 50

Got questions? Get instant answers now!

A(n) __________ infection is a small region of infection from which a pathogen may move to another part of the body to establish a second infection.

focal

Got questions? Get instant answers now!

Cilia, fimbriae, and pili are all examples of structures used by microbes for __________.

adhesion

Got questions? Get instant answers now!

Questions & Answers

microbial genetics mcqs
kajal Reply
hii
Happy
what is the importance of learning microbiology in nursing?
Grace Reply
привет
__
it's about child-care?
__
the way of common children disease? hmm 🤔🤔
__
how do you mean child care?
Grace
Was ist die Wichtigkeit beim Lernen von Mikrtobiologie in der Pflege? Es ist notwendig dass die Schwestern allgemein und auch die Kinderschwestern eine Ausbildung in der Mikrobiologie erfahren. Sie sind in ihrem Beruf gefo
__
you need to know the truth about diseases. the microbes are have immunity to some pharmacy.
__
is base pairing rule states that adenine pair with thymine cytosine pair with guannie what will be the complementry strand to acggt
KooL Reply
tgcca
Tanaya
yes
Swetha
introduction to microbiology
Shweta Reply
Study the life of microorganisms present in the environment their survivals etc..
ayesha
Microscopic organisms, commonly known as microorganisms or microbes, are found all around us and even inside our bodies. The category 'Microbes' includes a massive range of organisms including bacteria, fungi, viruses, algae, archaea and protozoa.
Amre
fermented foods likely benefited ancestors to preserve foods and make other foods like milk, cheese, and bread using microbes.
Zinnia Reply
the evidence that I would support the statement regarding ancient people ideas that disease was transmitted by things they could not see is by the discoveries under a microscope. Many microbiologists have discovered certain diseases caused by microbes.
Zinnia
plz give the information about glyoxylate cycle
kamini Reply
what type of information?
Sapiens
I need medical microbiology mcqs books for Mbbs
Kisota
for pakistani mbbs or other?
Sapiens
what is microbial soup?
Osborn Reply
😃😂funny question isn't it?!!! sorry for inconvenience 😊
ayesha
most bacterial pathogens that cause disease in humans are classified in terms if their preferable ph as
Beesan Reply
what is micro
Kabul Reply
extremely small in size
Swetha
almost invisible to the naked eye
Peter
thanks
Sadiq
uwc
Peter
invisible sized objects
Sivasri
invisible sized object or specimens.which is used to see in only the microscope that specimens or objective called the micro
Sivasri
small organism that can be seen by use of Microbes
Manyang
why do you need to study microorganisms
Sala
what is microbiology?
Green Reply
microbiology is a branch of biology .it deals with the study of microorganisms life cycle , uses, disadvantages,and it impact in any other fields .which is used to view in microscope .
Sivasri
Microbiology is the study of microorganisms, those being unicellular, multicellular, or acellular. Microbiology encompasses numerous sub-disciplines including virology, bacteriology, protistology, mycology, immunology and parasitology. 
Raj
In short , it is the study of micro organisms and types , characteristics.
Kaviya
can you explain the structure of rna in detail
Dhanalakshmi Reply
RNA is of many types....like mRNA,tRNA,rRNA,snRNA,guideRNA..etc .
Swetha
but generally RNA is single stranded
Swetha
It contains adenine guanine cytosine , instead of thymine it contains uracil.
Swetha
ribonucleic acid present in RNA.. where as in DNA it is deoxyribonucleic acid...and ribonucleotide is present in RNA
Swetha
RNA is a blue print of DNA. it has the information from DNA....and we can predict the base panirs in DNA if we have the RNA....copy of that DNA
Swetha
can either have positive or negative polarity
Ernestine
Diatoms need..... With the help of which they can construct their beautiful cell wall
Prathmesh Reply
Microbial growth curve shows a.... Curve.
Shambhuraj Reply
diminishing curve
Oluwapamilerin
It represents the decreasing growth of an organism.
Swetha
what is meant by reverse isolation in tuberculosis treatment?
Swetha Reply
why do we study microbiology
HABIBA Reply
Microbiology is the way of gaining knowledge about those organisms which are surround us but we can't see them with our naked eye,such organisms called microorganisms..We can see them only under microscope.
ayesha
from our birth to death microorganisms are with us in the environment as well as on our body which are called Microflora.
ayesha
Microfloras are non pathogenic
ayesha

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play




Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Microbiology' conversation and receive update notifications?

Ask