What Microorganisms Cause Infection in Pregnancy?

Bacteria, fungi, viruses, and protozoa are all microorganisms. They can survive anywhere in the world. Some live in the human body, and people and microorganisms generally co-exist peacefully-often in mutually beneficial ways. But, a microorganism can cause an infection if it invades a part of the body where it is not welcome, multiplies, and adheres to cells.


Bacteria are primitive organisms that differ from plant and animal cells in that they do not possess a separate nucleus. They can be seen with a microscope at high magnification when special stains are used.

The human body is a host to billions of bacteria. Most of the body's normal bacterial flora reside in the skin, mouth, gastrointestinal tract, and lower genital tract (a woman's vagina and cervix). This generally does not cause trouble, and some bacteria actually help protect the body against disease. Meanwhile, the body normally has an intact immune system and other defenses that protect against bacterial colonies growing too numerous or expanding beyond certain areas of the body.


Did You Know?

Some types of bacteria are tougher to kill than others. This is true, for example, of gram-negative bacilli-such as Campylobacter, Salmonella, Shigella, and Vibrio. Unlike other types of bacteria, these have a double-membrane surrounding each cell, which partly explains their added resistance to antibiotics.


But, if bacteria manage to land in a place that is usually sterile, such as the lungs or urinary tract, they can cause illness. Bacteria that are not usually part of the normal flora are more likely to cause disease. Termed pathogenic bacteria, they possess virulence factors that promote disease. Examples include Staphylococcus aureus (the bacterium that causes most wound infections), Group A streptococcus (which causes sore throats), and Streptococcus pneumoniae (which causes pneumonia, meningitis, and ear and sinus infections). In some cases, bacteria that are normally present in some areas of the body can cause infection when they gain access to a sterile space and multiply beyond typical levels-as is the case with chorioamnionitis, an infection of the amniotic fluid and fetal membranes caused by Escherichia coli ( E. coli ) and other bacteria. Some bacteria grow very quickly- E. coli, for example, divides every 20 minutes. Others may take several days to replicate.

Bacteria are generally easy to grow in hospital laboratories, and new methods now allow some bacteria to be identified within minutes or hours. This can help doctors diagnose rapidly and treat some types of bacterial infection. Drugs used to fight bacterial infections are called antibiotics.