Microbiology - NCLEX-PN

A nosocomial infection is an infection that is transmitted from one person to another inside the hospital or other healthcare facility. It is often a result of healthcare workers failing to preform adequate hand hygiene and standard precautions. Those most at risk for infection are those who are immunocompromised (chemotherapy patients), those with breaks in skin integrity (wounds), and those with invasive devices (PICC lines, urinary catheters, invasive monitoring).

C. difficile is an endospore-forming bacteria. While in the endospore (or dormant) stage, C. difficile spores are highly resistant to disinfectants. This renders sterilization procedures less effective in a hospital setting and leads to a higher frequency of infection. While route of transmission and hospital sanitation are important factors in _C. difficile_transmission, it is their endospore formation that gives these bacteria a level of resistance above other fecal-oral species present in a hospital setting.

Antibiotics work exclusively against bacteria. They are not effective against fungal infections, and they are not effective against viruses such as influenza, rotovirus, or rhinovirus (the most frequent cause of the common cold).

The process of asexual reproduction in which a single-celled organism divides into two cells of the same size is called binary fission. This occurs among prokaryotes and is the primary method of reproduction in bacterial species. Mitosis and meiosis are forms of cell division among eukaryotic cells. Conjugation is not a method of bacterial reproduction; rather, it is a method by which joined bacteria may transmit DNA, especially genes on plasmids that confer resistance.

Pili are short, hairlike structures on the surface of some bacteria. Conjugative pili can form a sort of tube between bacterial cells, allowing for the transfer of DNA from one bacteria to another.

Flagella are whip-like structures that allows bacteria to move within a fluid medium. Cilia are hair-like structures found primarily on the surface of mammalian cells, but are also found on bacterial cells, where they aid in attachment. A bacterial capsule is a polysaccharide layer outside the cell envelope that does not take part in bacterial conjugation, and may secrete "slime" which protects the bacteria from the surrounding environment.

Gram negative strains of bacteria possess more lipopolysaccharide than do Gram positive strains. This higher proportion of lipopolysaccharide lies on the exterior of Gram negative bacteria's outer membranes of their cell walls. Gram negative bacteria have significantly less peptidoglycan than do Gram positive strains, which accounts for their observable chromatic differences when using the Gram stain technique. Specifically, the this thin layer of peptidoglycan in Gram negative bacteria fails to retain crystal violet during Gram staining, especially after iodine is added, which acts as a mordant. Subsequent staining with safranin gives Gram negative bacteria a pink or light red color when viewed under a light microscope. Teichoic acid, present in Gram positive bacteria only, functions to increase the rigidity of the cell wall. Murein is another name for peptidoglycan.

Plasmids are found only in prokaryotes. In bacteria, they are transferred either via conjugation, transduction, or transformation. Both prokaryotes and eukaryotes contain ribosomes, however the subunits of eukaryotes are smaller (have a lower sedimentation rate). Both can contain flagella, but they differ in complexity and type of motion. Only eukaryotes contain mitochondria, which is the site of the Krebs cycle, beta-oxidation of fatty acids, and electron transport.

This question involves the concept of generation time, which is the time it takes one colony to double. Therefore, there will be 2 cells in 25 minutes, 4 cells in 50 minutes, 8 cells in 75 minutes, 16 in 100 minutes, 32 cells in 125 minutes, 64 cells in 150 minutes, 128 cells in 175 minutes, and 256 cells in 200 minutes. Note that it is very rare for a single bacterium to be isolated, thus a bacterial colony grows exponentially over a short period of time. Note that 200 minutes represents 8 generation times. The number of bacteria, when starting with a single cell, can be calculated as where is the number of generation (doubling) times. Here, we have .

Students should possess the knowledge that the Clostridium genus produces endospores. This fact makes them extremely virulent. Heating alone will not kill the spores. Only heat, accompanied by pressure, will penetrate spores. This method is obtained either by an autoclave or pressure cooker.

This question requires that the student recognizes that the process illustrated is recombinant DNA (deoxyribonucleic acid) technique. It requires the understanding that the process of producing protein from RNA (ribonucleic acid) is termed translation. Replication is the process by which DNA is synthesized from DNA. Transcription proceeds translation and involves synthesizing RNA transcripts of specific sections of DNA. Transduction is one way bacteria exchange genetic information. Specifically, transduction involves the transfer of bacterial DNA via bacteriophage. Note that this is one way that a group of bacteria can become resistant to antibiotics without ever having been exposed to the antibiotic to which they are resistant.

The question requires the knowledge of pili and that pili are of two types: attachment and conjugation. Conjugation is a way that bacteria become resistant to antibiotics. In this process, a circular piece of deoxyribonucleic acid (DNA) (plasmid) is exchanged through a conjugation pilus. Transformation is genetic alteration caused by direct uptake of naked genetic material from a bacteria's surroundings. A prophage is a bacteriophage that has inserted itself in the genome or plasmid of its host via the lysogenic cycle is latent. Transduction is the movement of genetic material due to bacteriophage that digest host DNA and accidentally package it inside their own capsids. These phage then go on to infect other bacteria, and insert the newly borrowed DNA into the new host cell's genome/plasmids. Translation is the process in which RNA (ribonucleic acid) is converted to protein.

The TB skin test has different thresholds for positive values based on the size of induration. In an HIV-positive individual (low CD4+, immunocompromised), a test is considered positive if it is > 5 mm (not cm). A positive result takes 24 to 48 hours to reveal itself.

The two most common bacterial arrangements are Staph- and Strep-. Staph- is a non-symmetrical arrangement like a cluster of grapes. Strep- indicates a chain of bacteria.

The three most common bacterial shapes are listed below.

Coccus—round or oval

Bacillus—rectangular or rod-shaped

Spirilla (spirochete)—spiral

By breaking down names into arrangement and shape, students can predict or identify the appearance of an organism by its name. In the example Staph indicates arrangement in a chain. Coccus indicates round or oval in shape. Therefore, Staphylococci are round or oval-shaped organisms arranged in a cluster.

Bordetella pertussis is a Gram negative, rod-shaped aerobe. It requires oxygen to function and commonly infects the respiratory tract of young children, causing whooping cough.

Neisseria gonorrhoeae is a Gram negative coccus bacterium that generally presents as a diplococcus (in pairs of cocci).

_Staphyloccocus aureus are Gram positive cocci. Chlamydia trachomatis and Rikettsia prowazekii are both classified as Gram negative rods and Neisseria meningitidis are Gram negative cocci.

All of the bacteria listed are Gram positive except Salmonella, which is a Gram negative facultative rod.

Vibrio cholerae is classified as Gram negative facultative rods. This bacteria is the most well known amongst the Vibrio species as it's the cause of cholera, which produces a toxin that causes very severe diarrhea.

Bacteria or any other microbes that feed on dead matter are termed saprophytes. Thermophilic microbes thrive in heated environments, halophiles such as _Vibrio parahaemolyticu_s prefer salt water, and archaebacteria are a group of bacteria found in high heat, high salt content locations such as sewage treatment plants and are able to tolerate many extreme habitats.