Micro opto Flashcards
What term describes the phenomenon in which a bacterium directs its movement TOWARD a chemical in its environment?
Transposition
Phagocytosis
Chemotaxis
Apoptosis
Chemotaxis
Many bacteria possess flagella, or thread-like appendages, which allow for movement. Certain chemicals attract bacteria (chemoattractants), while others repel them (chemorepellents). Chemotaxis refers to the response of the bacteria to either chemoattractants or chemorepellents. In the absence of either of the aforementioned chemicals, bacteria will move in random patterns. Some bacteria possess genes and proteins which allow for the sensing of concentration gradients in their environment. In the presence of a chemoattractant, bacteria will have longer runs in the appropriate direction.
Apoptosis is defined as programmed cell death.
Phagocytosis refers to the engulfment of a particle (for example, bacteria) by a phagocyte (for example, a macrophage).
Transposition refers to the rare phenomenon in which genes move from one place on the genome to another position.
A patient presents with acutely progressive keratitis. A scraping is performed, and the material is stained with a Gram stain. The causative agent is a bacterial coccus that stains violet on the Gram stain. Which of the following agents could this be?
Staphylococcus
Mycobacterium
Acanthamoeba
Pseudomonas
Staphylococcus
This is a description of a Gram-positive round bacteria. Staphylococcus is the only choice that fits this description. It is also the most common cause of many ocular infections. Staphylococcus aureus and Staphylococcus epidermidis are the most common species. Pseudomonas is a Gram-negative bacterium, and mycobacterium is a Gram-resistant rod that stains best with an acid-fast stain. Acanthamoeba is a protozoan and is not a bacteria.
which of the following mechanisms is NOT employed by viruses as a means of host penetration?
Direct injection of the virus’ DNA into the host
Entry of the virus via fusion with the host cell’s plasma membrane
Endocytosis of the virus into the host cell
Passive diffusion via osmosis into the host cell
Passive diffusion via osmosis into the host cell
Osmosis refers to the net movement of water through a semi-permeable membrane down its respective concentration gradient. There are many ways in which a virus can infect a host cell. A non-enveloped virus can directly inject their DNA into host cells. Viruses with envelopes can fuse the host cell, leading to the incorporation of the envelope into the plasma membrane of the host, which then leaves the DNA free to transfer into the host cell. Viruses may also enter the host cell via endocytosis. After the process of endocytosis is complete, the virus sheds its envelope and releases its DNA into the host cell.
Traveler’s diarrhea, also known as Montezuma’s revenge, is most commonly caused by which organism?
Escherichia
Salmonella
Staphylococcus
Streptococcus
Escherichia
Traveler’s diarrhea (TD) is usually linked to ingestion of contaminated water or food which results in loose stools, abdominal cramping, and nausea. The most frequent cause of TD is enterotoxigenic E. coli. Treatment is not usually required, as most cases are self-limiting; however, it is important to maintain hydration and prevent loss of electrolytes. The best prevention is to avoid questionable sources of food and water.
Which of the following infections is considered parasitic in nature?
Scabies
Tinea
Molluscum contagiosum
Impetigo
Scabies
Scabies is a skin condition that is caused by parasitic mites that burrow under the skin and cause itching, rashes, and blisters. The condition is spread via close contact with infected people or infected linens or towels. Patients typically report that the severity of the itching worsens at night. Scabies is treated via the application of prescribed topical cream or lotion or via oral medication. Although scabies will self-resolve, it is best to seek treatment immediately if the condition is suspected in order to minimize its chances of spreading.
Molluscum contagiosum is a cutaneous viral infection that results in small red or skin-colored bumps. Lesions can be removed, or a topical ointment can be prescribed to decrease healing time. The condition, if left untreated, will self-resolve.
Impetigo is bacterial in nature (caused by staphylococcus) and results in cutaneous blisters of various sizes. The lesions are frequently limited to the arms, legs, and face.
Tinea, also known ringworm, is a fungal infection of the skin. The lesions associated with this condition appear circular with clear centers. Athlete’s foot is a type of ringworm.
Antibiotic resistance that is rapidly spread within a population of bacteria is due to what mechanism?
Transformation
Budding
Binary fission
Conjugation
Conjugation
Conjugation occurs between a donor (possesses a conjugative plasmid) and recipient bacteria. The donor bacterium initiates contact with the recipient via a sex pilus, allowing for cell-to-cell contact and transfer of DNA. The plasmids often contain genes that encode for toxin production, virulence factors, and antibiotic resistance. Genetic transformation is achieved by very few strains of bacteria and may only occur during certain phases of growth; therefore, rapid antibiotic resistance is not feasible. Budding and binary fission are means of reproduction but are not directly responsible for antibacterial resistance. Genes must have been transferred that code for resistance prior to budding and binary fission in order for the progeny to contain genes that allow for drug resistance.
Which organism is associated with the development of toxic shock syndrome
Chlamydia trachomatis
Neisseria gonorrhoeae
Staphylococcus aureus
Toxoplasma gondii
Staphylococcus aureus
Toxic shock syndrome is a potentially lethal infection caused by S. aureus. The infection is caused by the use of super-absorbent tampons which decreases the need for frequent replacement. The environment and the tampon contribute to a great breeding ground for this pathogen.
C. trachomatis is a sexually transmitted disease (STD) characterized by burning sensation during urination, penile or vaginal discharge, and, if left untreated, may cause infertility. People affected with chlamydia may also be completely asymptomatic. Gonorrhea is also an STD. Symptoms include those seen with chlamydia as well as fever, sore throat, increased urinary frequency, and other symptoms. If left untreated, long-term complications of gonorrhea include infertility, long-term joint pain, meningitis, and heart valve infection. People infected with gonorrhea must be reported to the centers for disease control and prevention (CDC).
T. gondii is commonly associated with improper handling of raw meat or cat fecal matter from an animal that has ingested infected meat; however, it rarely leads to illness in healthy individuals. For this reason, it is important that pregnant mothers do not handle feline fecal matter so as not to potentially harm the unborn fetus, as toxoplasmosis can result in blindness if enough retinal damage occurs. Immunocompromised persons may suffer from encephalitis and chorioretinitis, among other problems.
Which of the following is NOT present in the cellular envelope of a Gram-negative bacteria?
Periplasmic spaces
Peptidoglycan
Teichoic acids
Porin proteins
Teichoic acids
Cell walls define the shape of the cell and serve as protection for the bacteria. Gram-negative cells have complex cellular envelopes comprised of only a thin layer of peptidoglycan sandwiched between an outer and inner membrane. The outer membrane contains porin proteins, within its matrix which allow for the passage of molecules (i.e., nutrients) into the cell. The outer membrane also includes lipopolysaccharides, which consist of an O side chain (antigen), a core polysaccharide, and lipid A (endotoxin). In contrast, the composition of a Gram-positive cell wall is relatively simple: it contains a thick layer of peptidoglycan, teichoic, and lipoteichoic acids. Gram-positive cells have only one plasma membrane.
What type of organism is responsible for the development of syphilis infections?
Lentivirus
Actinobacteria
Nematode
Mycobacteria
Parasite
Spirochete
Spirochete
The causative organism of syphilis is a spirochete known as Treponema pallidum. Spirochetes have a unique structure that is responsible for their motility. This distinctive configuration consists of a central protoplasmic cylinder, bound by a plasma membrane, cell wall, and an outer sheath composed of glycosaminoglycans. Between the cell wall and outer sheath are multiple periplasmic flagella. These flagella span the entire length of the cell and are anchored at both ends. It is believed that the flagella rotate and cause the organism to propel forward in a corkscrew-like manner. Spirochetes can easily move through viscous solutions with little impediment, which explains their ability to easily penetrate and invade host tissue.
Gonorrhea, chlamydia, and tuberculosis are all infections caused by bacteria. The causative organism of HIV (human immunodeficiency virus) is a lentivirus; toxoplasmosis is caused by a parasite, and toxocariasis is caused by a nematode.
Which of the following regarding zone of inhibition is TRUE?
Allows one to quantify the number of plaque-forming units (PFU)
The larger the zone of inhibition, the greater the degree of resistance displayed by the organism
Allows for the determination of which type of media promotes the proliferation of a specific bacteria
Denotes the sensitivity of an organism to an antibiotic
Denotes the sensitivity of an organism to an antibiotic
An agar plate is inoculated with an isolated bacterium. Disks that are permeated with different antibiotics are placed in separate places on the agar plate. After the incubation period is over, the amount of bacteria that have grown on the plate is assessed. A clear ring surrounding a disk indicates that the bacteria are sensitive to this particular antibiotic and were unable to grow in its presence. A larger ring indicates a greater sensitivity to the antibiotic. The lack of a clear zone denotes that the bacteria are resistant to the antibiotic; therefore treatment of the bacteria with this particular antibiotic would be ineffective. PFU allows for the functional determination of the number of virus particles capable of cell damage. For this test, host cells are infected with a virus. The combination is plated on agar, and the number of plaques that form are counted. Plaques are localized areas of cell damage or cell lysis. Each plaque is thought to represent a single virion.
Gram stains are used to differentiate between gram-positive and gram-negative bacteria. Why do gram-positive bacteria stain purple with crystal violet?
Gram-positive bacteria cell walls contain teichoic acid
Gram-negative bacterial cell walls contain lipopolysaccharides, which repel crystal violet
The large periplasmic spaces in the cellular wall allow for greater absorption of crystal violet
Due to the presence of high amounts of peptidoglycan contained within the cellular wall
Due to the presence of high amounts of peptidoglycan contained within the cellular wall
Crystal violet binds to peptidoglycan. The greater the percentage of peptidoglycan contained within the cellular wall, the greater the intensity of staining. Gram-positive cell walls are comprised of a larger amount of peptidoglycan (50-90%) than gram-negative cell walls (roughly 10%).
Blood agar is a suitable culture media for most bacterial and fungal samples except Neisseria, Haemophilus, and Moraxella species. If one of these organisms is suspected, which of the following media should be utilized for culturing purposes?
Knop agar
Sabouraud’s agar
Malt extract agar
Chocolate agar
Phenethyl alcohol agar
Chocolate agar
Chocolate agar is a variant of the blood agar plate that contains red blood cells that have been slowly heated to a temperature in which the blood cells are lysed (80 degrees Celsius). The agar is named after the color of the plate, and does not actually contain any form of chocolate. This type of agar is specifically used for growing fastidious organisms such as Neisseria, Haemophilus, and Moraxella species that do not grow well on conventional blood agar plates.
Chocolate agar with the addition of bacitracin becomes selective for Haemophilus, while another variant of chocolate agar, known as Thayer-Martin agar, contains an assortment of different antibiotics that results in selection of Neisseria species.
Sabouraud’s agar and malt extract agar are fungal media. Knop agar is a type of moss media, and phenethyl alcohol agar selects for staphylococcal species while inhibiting Gram-negative bacilli.
In adults, which organism is the most common cause of bacterial conjunctivitis in warmer climates?
Staphylococcus aureus
Streptococcus pneumonia
Neisseria meningiditis
Haemophilus influenza
Haemophilus influenza
Haemophilus influenza is the predominant cause of bacterial conjunctivitis in adults in warmer climates, while Streptococcus pneumonia is the most common cause in adults in cooler climates. Acute conjunctivitis is characterized by mucopurulent discharge that is worse in the morning. It usually begins unilaterally and spreads to the other eye. Under normal circumstances the most common isolate in adults is S. aureus while in children under five years old, the common culprit is H. influenza.
hich organism is responsible for Rocky Mountain spotted fever?
Rickettsia
Mycoplasma
Cryptococcus neoformans
Corynebacterium
Rickettsia
Rickettsia is a Gram-negative obligate intracellular bacterium. Rickettsia is found on ticks, fleas, and lice and can cause many diseases in humans including typhus, Rocky Mountain spotted fever, and rickettsial pox. Rocky Mountain spotted fever is caused by tick bites. Symptoms include chills, fever, rash, headache, nausea, vomiting, muscle pain, and confusion. The prognosis is good with treatment. Rarely, complications can lead to hearing loss, paralysis, brain damage, lung failure, kidney failure, nerve damage, and death. Treatment includes careful removal of the tick along with tetracycline or doxycycline.
Mycoplasma is a genus of bacteria that lack a cell wall and are capable of causing atypical pneumonia. Corynebacterium is associated with diphtheria. Cryptococcus neoformans is a type of fungus that causes cryptococcosis which is an infection that involves the central nervous system and the lungs.
Which 3 of the following are utilized by bacteria as a means of protection from desiccation? (Select 3)
Capsules
Flagellum
Slime layer
Pili
Glycocalyx
Capsules
Slime layer
Glycocalyx
Pili are small hair-like appendages found on some bacteria that play a role in attaching bacteria to each other or to various surfaces.
Flagella are projections of the cell that provide locomotive capabilities as well as occasionally serving to detect temperature or chemical gradients.
Slime layers, capsules, and glycocalyces are generally composed of polysaccharides. The composition and complexity of glycocalyces varies from bacteria to bacteria. The presence of a glycocalyx generally infers an ability of the bacteria to cause infection. A very condensed glycocalyx that is tightly bound to the cell wall is termed a capsule. A loosely-adhering glycocalyx is called a slime layer. Both serve to defend the cell from desiccation as well as to protect it from phagocytosis.
