Question

A strain of bacteria associated with a bladder infection shows gram-negative rods. What species is most likely to be the causative agent? a. Mycoplasma hominis b. Escherichia coli c. Neisseria gonorrhoeae d. Chlamydia trachomatis

Short answer

Escherichia coli (b) is the most likely causative agent of the bladder infection based on the described characteristics of being gram-negative rods.

Step-by-step solution

Understand the Characteristics

The first step is to understand the described characteristics of the bacteria: It is gram-negative and rod-shaped. This will be the key information to narrow down the options.

Eliminate Nonmatching Options

Analyze each option based on the characteristics of gram-negative rods. Mycoplasma hominis is not a gram-negative rod, Neisseria gonorrhoeae is gram-negative but typically a diplococcus, and Chlamydia trachomatis is not a gram-negative rod. These do not match our criteria.

Identify the Causative Agent

Escherichia coli (E. coli) are known to be gram-negative rods and are a common cause of bladder infections. This matches the characteristics provided in the question.

Key concepts

Escherichia coli

Escherichia coli, commonly abbreviated as E. coli, is a species of bacteria that resides in the intestine of humans and warm-blooded animals. Although most strains are harmless, some variants can cause serious food poisoning and are to blame for other infections, including bladder infections.

E. coli are characterized as gram-negative rods because they do not retain the crystal violet dye used in the Gram staining procedure. Instead, they take up the counterstain, safranin, which results in a pink color under microscopic examination. This gram-negative characteristic relates to their cell wall structure, which is thinner than that of gram-positive bacteria and surrounded by an outer membrane.

The rod shape of E. coli is a key identifying feature—if you were to look through a microscope, you'd see the bacteria as small, rod-like structures. Understanding these characteristics is essential for identifying this bacterium in medical tests and also in the context of the question related to bladder infections.

Bacteria Identification

Identification of bacteria is a pivotal step in diagnosing infections and determining treatment plans. It typically involves a combination of visual observation through microscopy, culture techniques, staining procedures like the Gram stain, and sometimes genetic testing.

The Gram staining method is a traditional and widely used technique to classify bacteria into two groups: gram-positive and gram-negative, based on the properties of their cell walls. Gram-positive bacteria retain the crystal violet stain and therefore appear blue or purple, while gram-negative bacteria, which don't retain the stain and are counterstained with safranin, appear pink.

Shape is another crucial aspect used in bacteria identification. The shapes primarily include cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped). When a bacterium is identified as a gram-negative rod, such as E. coli, experts can further narrow down potential species by considering other factors such as the bacteria's growth conditions, oxygen requirements, and metabolic tests.

Bladder Infection Causative Agent

Bladder infections, also known as urinary tract infections (UTIs), are typically caused by bacteria that enter the urethra and then the bladder, causing inflammation and symptoms like a frequent need to urinate and a burning sensation during urination.

The most common causative agent of bladder infections is E. coli, responsible for approximately 80% of cases. This is because E. coli normally inhabit the intestinal tract, and their proximity to the urethral opening can sometimes lead to transfer and subsequent infection.

Females are generally more susceptible to bladder infections due to their shorter urethra, which allows bacteria easier access to the bladder. Hygiene practices, sexual activity, and certain types of birth control are also factors that can increase the risk of UTIs. Prompt identification and treatment of the causative agent are vital to prevent the spread of the infection to the kidneys, where it can cause more serious issues.