Streptococcus pneumoniae

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Streptococcus pneumoniae
Pneumococcus CDC PHIL ID1003.jpg
S. pneumoniae in spinal fluid. FA stain (digitally colored).
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Bacteria
Phylum: Bacillota
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Species:
S. pneumoniae
Binomial name
Streptococcus pneumoniae
(Klein 1884) Chester 1901

Streptococcus pneumoniae, or pneumococcus, is a Gram-positive, spherical bacteria, alpha-hemolytic member of the genus Streptococcus. [1] S. pneumoniae cells are usually found in pairs (diplococci) and do not form spores and are non motile. [2] As a significant human pathogenic bacterium S. pneumoniae was recognized as a major cause of pneumonia in the late 19th century, and is the subject of many humoral immunity studies.[ citation needed ]

Contents

Streptococcus pneumoniae resides asymptomatically in healthy carriers typically colonizing the respiratory tract, sinuses, and nasal cavity. However, in susceptible individuals with weaker immune systems, such as the elderly and young children, the bacterium may become pathogenic and spread to other locations to cause disease. It spreads by direct person-to-person contact via respiratory droplets and by auto inoculation in persons carrying the bacteria in their upper respiratory tracts. [3] It can be a cause of neonatal infections. [4]

Streptococcus pneumoniae is the main cause of community acquired pneumonia and meningitis in children and the elderly, [5] and of sepsis in those infected with HIV. The organism also causes many types of pneumococcal infections other than pneumonia. These invasive pneumococcal diseases include bronchitis, rhinitis, acute sinusitis, otitis media, conjunctivitis, meningitis, sepsis, osteomyelitis, septic arthritis, endocarditis, peritonitis, pericarditis, cellulitis, and brain abscess. [6]

S.pneumoniae growth on blood agar. Streptococcus pneumoniae on agar plates.jpg
S.pneumoniae growth on blood agar.

Streptococcus pneumoniae can be differentiated from the viridans streptococci, some of which are also alpha-hemolytic, using an optochin test, as S. pneumoniae is optochin-sensitive. S. pneumoniae can also be distinguished based on its sensitivity to lysis by bile, the so-called "bile solubility test". The encapsulated, Gram-positive, coccoid bacteria have a distinctive morphology on Gram stain, lancet-shaped diplococci. They have a polysaccharide capsule that acts as a virulence factor for the organism; more than 100 different serotypes are known, and these types differ in virulence, prevalence, and extent of drug resistance.

The capsular polysaccharide (CPS) serves as a critical defense mechanism against the host immune system. It composes the outermost layer of encapsulated strains of S. pneumoniae and is commonly attached to the peptidoglycan of the cell wall. [7] It consists of a viscous substance derived from a high-molecular-weight polymer composed of repeating oligosaccharide units linked by covalent bonds to the cell wall. The virulence and invasiveness of various strains of S. pneumoniae vary according to their serotypes, determined by their chemical composition and the quantity of CPS they produce. Variations among different S. pneumoniae strains significantly influence pathogenesis, determining bacterial survival and likelihood of causing invasive disease. [8] Additionally, the CPS inhibits phagocytosis by preventing granulocytes' access to the cell wall. [9]

History

In 1881, the organism, known later in 1886 as the pneumococcus [10] for its role as a cause of pneumonia, was first isolated simultaneously and independently by the U.S. Army physician George Sternberg [11] and the French chemist Louis Pasteur. [12]

The organism was termed Diplococcus pneumoniae from 1920 [13] because of its characteristic appearance in Gram-stained sputum. It was renamed Streptococcus pneumoniae in 1974 because it was very similar to streptococci. [10] [14]

Streptococcus pneumoniae played a central role in demonstrating that genetic material consists of DNA. In 1928, Frederick Griffith demonstrated transformation of life turning harmless pneumococcus into a lethal form by co-inoculating the live pneumococci into a mouse along with heat-killed virulent pneumococci. [15] In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty demonstrated that the transforming factor in Griffith's experiment was not protein, as was widely believed at the time, but DNA. [16] Avery's work marked the birth of the molecular era of genetics. [17]

Genetics

The genome of S. pneumoniae is a closed, circular DNA structure that contains between 2.0 and 2.1 million base pairs depending on the strain. It has a core set of 1553 genes, plus 154 genes in its virulome, which contribute to virulence and 176 genes that maintain a noninvasive phenotype. Genetic information can vary up to 10% between strains. [18] The pneumococcal genome is known to contain a large and diverse repertoire of antimicrobial peptides, including 11 different lantibiotics. [19]

Transformation

Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the surrounding medium. Transformation is a complex developmental process requiring energy and is dependent on expression of numerous genes. In S. pneumoniae, at least 23 genes are required for transformation. For a bacterium to bind, take up, and recombine exogenous DNA into its chromosome, it must enter a special physiological state called competence. [20] Competence in S. pneumoniae is induced by DNA-damaging agents such as mitomycin C, fluoroquinolone antibiotics (norfloxacin, levofloxacin and moxifloxacin), and topoisomerase inhibitors. [21] Transformation protects S. pneumoniae against the bactericidal effect of mitomycin C. [22] Michod et al. [23] summarized evidence that induction of competence in S. pneumoniae is associated with increased resistance to oxidative stress and increased expression of the RecA protein, a key component of the recombinational repair machinery for removing DNA damage. On the basis of these findings, they suggested that transformation is an adaptation for repairing oxidative DNA damage. S. pneumoniae infection stimulates polymorphonuclear leukocytes (granulocytes) to produce an oxidative burst that is potentially lethal to the bacteria. The ability of S. pneumoniae to repair oxidative DNA damage in its genome caused by this host defense likely contributes to the pathogen's virulence. Consistent with this premise, Li et al. [24] reported that, among different highly transformable S. pneumoniae isolates, nasal colonization fitness and virulence (lung infectivity) depend on an intact competence system.

Infection

Streptococcus pneumoniae is part of the normal upper respiratory tract flora. As with many natural flora, it can become pathogenic under the right conditions, typically when the immune system of the host is suppressed. Invasins, such as pneumolysin, an antiphagocytic capsule, various adhesins, and immunogenic cell wall components are all major virulence factors. After S. pneumoniae colonizes the air sacs of the lungs, the body responds by stimulating the inflammatory response, causing plasma, blood, and white blood cells to fill the alveoli. This condition is called bacterial pneumonia. [25]

S. pneumoniae undergoes spontaneous phase variation, changing between transparent and opaque colony phenotypes. The transparent phenotype has a thinner capsule and expresses large amounts of phosphorylcholine (ChoP) and choline-binding protein A (CbpA), contributing to the bacteria's ability to adhere and colonize in the nasopharynx. [26] The opaque phenotype is characterized by a thicker capsule, resulting in increased resistance to host clearance. [26] It expresses large amounts of capsule and pneumococcal surface protein A (PspA) which help the bacteria survive in the blood. [27] Phase-variation between these two phenotypes allows S. pneumoniae to survive in different human body systems.

Diseases and symptoms

Pneumonia is the most common of the S. pneumoniae diseases which include symptoms such as fever and chills, cough, rapid breathing, difficulty breathing, and chest pain. For the elderly, they may include confusion, low alertness, and the former listed symptoms to a lesser degree.[ citation needed ]

Pneumococcal meningitis is an infection of the tissue covering the brain and spinal cord. Symptoms include stiff neck, fever, headache, confusion, and photophobia.[ citation needed ]

Sepsis is caused by overwhelming response to an infection and leads to tissue damage, organ failure, and even death. The symptoms include confusion, shortness of breath, elevated heart rate, pain or discomfort, over-perspiration, fever, shivering, or feeling cold. [28] [29]

Vaccine

Due to the importance of disease caused by S. pneumoniae, several vaccines have been developed to protect against invasive infection. The World Health Organization recommends routine childhood pneumococcal vaccination; [30] it is incorporated into the childhood immunization schedule in a number of countries including the United Kingdom, [31] the United States, [32] Greece, [33] and South Africa. [34]

Currently, there are two vaccines available for S. pneumoniae: the pneumococcal polysaccharide vaccine (PPV23) and the pneumococcal conjugate vaccine (PCV13). PPV23 functions by utilizing CPS to stimulate the production of type-specific antibodies, initiating processes such as complement activation, opsonization, and phagocytosis to combat bacterial infections. It elicits a humoral immune response targeting the CPS present on the bacterial surface. [35] PPSV23 offers T-cell-independent immunity and requires revaccination 5 years after the first vaccination because of its temporary nature. [36] PCV13 was developed when determining its low efficacy in children and infants. PCV13 elicits a T-cell-dependent response and provides enduring immunity by promoting interaction between B and T cells, leading to an enhanced and prolonged immune response. [36]

Biotechnology

Components from S. pneumoniae have been harnessed for a range of applications in biotechnology. Through engineering of surface molecules from this bacterium, proteins can be irreversibly linked using the sortase enzyme [37] or using the SnoopTag/SnoopCatcher reaction. [38] Various glycoside hydrolases have also been cloned from S. pneumoniae to help analysis of cell glycosylation. [39]

Interaction with Haemophilus influenzae

Historically, Haemophilus influenzae has been a significant cause of infection, and both H. influenzae and S. pneumoniae can be found in the human upper respiratory system. A study of competition in vitro revealed S. pneumoniae overpowered H. influenzae by attacking it with hydrogen peroxide. [40] There is also evidence that S. pneumoniae uses hydrogen peroxide as a virulence factor. [41] However, in a study adding both bacteria to the nasal cavity of a mouse within two weeks, only H. influenzae survives; further analysis showed that neutrophils exposed to dead H. influenzae were more aggressive in attacking S. pneumoniae. [42]

Diagnosis

Optochin sensitivity in a culture of Streptococcus pneumoniae (white disk) S. pneumoniae.jpg
Optochin sensitivity in a culture of Streptococcus pneumoniae (white disk)
Example of a workup algorithm of possible bacterial infection in cases with no specifically requested targets (non-bacteria, mycobacteria etc.), with most common situations and agents seen in a New England community hospital setting. Streptococcus pneumoniae is mentioned at gram stain near top right, and again in the alpha-hemolytic workflow in lower left quadrant. Diagnostic algorithm of possible bacterial infection.png
Example of a workup algorithm of possible bacterial infection in cases with no specifically requested targets (non-bacteria, mycobacteria etc.), with most common situations and agents seen in a New England community hospital setting. Streptococcus pneumoniae is mentioned at gram stain near top right, and again in the alpha-hemolytic workflow in lower left quadrant.

Diagnosis is generally made based on clinical suspicion along with a positive culture from a sample from virtually any place in the body. S. pneumoniae is, in general, optochin sensitive, although optochin resistance has been observed. [43]

The recent advances in next-generation sequencing and comparative genomics have enabled the development of robust and reliable molecular methods for the detection and identification of S. pneumoniae. For instance, the Xisco gene was recently described as a biomarker for PCR-based detection of S. pneumoniae and differentiation from closely related species. [44]

Atromentin and leucomelone possess antibacterial activity, inhibiting the enzyme enoyl-acyl carrier protein reductase, (essential for the biosynthesis of fatty acids) in S. pneumoniae. [45]

Resistance

Resistant pneumococcal strains are called penicillin-resistant pneumococci (PRP), [46] penicillin-resistant Streptococcus pneumoniae (PRSP), [47] Streptococcus pneumoniae penicillin resistant (SPPR) [48] or drug-resistant Strepotococcus pneumoniae (DRSP). In 2015, in the US, there were an estimated 30,000 cases, and in 30% of them the strains were resistant to one or more antibiotics. [49]

See also

Related Research Articles

<i>Streptococcus</i> Genus of bacteria

Streptococcus is a genus of gram-positive or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales, in the phylum Bacillota. Cell division in streptococci occurs along a single axis, thus when growing they tend to form pairs or chains, which may appear bent or twisted. This differs from staphylococci, which divide along multiple axes, thereby generating irregular, grape-like clusters of cells. Most streptococci are oxidase-negative and catalase-negative, and many are facultative anaerobes.

<span class="mw-page-title-main">Pneumonia</span> Inflammation of the alveoli of the lungs

Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity of the condition is variable.

<span class="mw-page-title-main">Group A streptococcal infection</span> Medical condition

Group A streptococcal infections are a number of infections with Streptococcus pyogenes, a group A streptococcus (GAS). S. pyogenes is a species of beta-hemolytic Gram-positive bacteria that is responsible for a wide range of infections that are mostly common and fairly mild. If the bacteria enters the bloodstream, the infection can become severe and life-threatening, and is called an invasive GAS (iGAS).

<i>Staphylococcus aureus</i> Species of gram-positive bacterium

Staphylococcus aureus is a gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often positive for catalase and nitrate reduction and is a facultative anaerobe, meaning that it can grow without oxygen. Although S. aureus usually acts as a commensal of the human microbiota, it can also become an opportunistic pathogen, being a common cause of skin infections including abscesses, respiratory infections such as sinusitis, and food poisoning. Pathogenic strains often promote infections by producing virulence factors such as potent protein toxins, and the expression of a cell-surface protein that binds and inactivates antibodies. S. aureus is one of the leading pathogens for deaths associated with antimicrobial resistance and the emergence of antibiotic-resistant strains, such as methicillin-resistant S. aureus (MRSA). The bacterium is a worldwide problem in clinical medicine. Despite much research and development, no vaccine for S. aureus has been approved.

<span class="mw-page-title-main">Frederick Griffith</span> British bacteriologist

Frederick Griffith (1877–1941) was a British bacteriologist whose focus was the epidemiology and pathology of bacterial pneumonia. In January 1928 he reported what is now known as Griffith's Experiment, the first widely accepted demonstrations of bacterial transformation, whereby a bacterium distinctly changes its form and function.

Atypical pneumonia, also known as walking pneumonia, is any type of pneumonia not caused by one of the pathogens most commonly associated with the disease. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorganisms can cause it. When it develops independently from another disease, it is called primary atypical pneumonia (PAP).

Virulence is a pathogen's or microorganism's ability to cause damage to a host.

<i>Haemophilus influenzae</i> Species of bacterium

Haemophilus influenzae is a Gram-negative, non-motile, coccobacillary, facultatively anaerobic, capnophilic pathogenic bacterium of the family Pasteurellaceae. The bacteria are mesophilic and grow best at temperatures between 35 and 37 °C.

<span class="mw-page-title-main">Bacterial pneumonia</span> Disease of the lungs

Bacterial pneumonia is a type of pneumonia caused by bacterial infection.

<span class="mw-page-title-main">Bacterial capsule</span> Polysaccharide layer that lies outside the cell envelope in many bacteria

The bacterial capsule is a large structure common to many bacteria. It is a polysaccharide layer that lies outside the cell envelope, and is thus deemed part of the outer envelope of a bacterial cell. It is a well-organized layer, not easily washed off, and it can be the cause of various diseases.

<i>Moraxella catarrhalis</i> Species of bacterium

Moraxella catarrhalis is a fastidious, nonmotile, Gram-negative, aerobic, oxidase-positive diplococcus that can cause infections of the respiratory system, middle ear, eye, central nervous system, and joints of humans. It causes the infection of the host cell by sticking to the host cell using trimeric autotransporter adhesins.

Community-acquired pneumonia (CAP) refers to pneumonia contracted by a person outside of the healthcare system. In contrast, hospital-acquired pneumonia (HAP) is seen in patients who have recently visited a hospital or who live in long-term care facilities. CAP is common, affecting people of all ages, and its symptoms occur as a result of oxygen-absorbing areas of the lung (alveoli) filling with fluid. This inhibits lung function, causing dyspnea, fever, chest pains and cough.

Pneumococcal pneumonia is a type of bacterial pneumonia that is caused by Streptococcus pneumoniae (pneumococcus). It is the most common bacterial pneumonia found in adults, the most common type of community-acquired pneumonia, and one of the common types of pneumococcal infection. The estimated number of Americans with pneumococcal pneumonia is 900,000 annually, with almost 400,000 cases hospitalized and fatalities accounting for 5-7% of these cases.

<span class="mw-page-title-main">Pneumococcal vaccine</span> Vaccine to prevent infection by the bacteria Stretococcus pneumoniae

Pneumococcal vaccines are vaccines against the bacterium Streptococcus pneumoniae. Their use can prevent some cases of pneumonia, meningitis, and sepsis. There are two types of pneumococcal vaccines: conjugate vaccines and polysaccharide vaccines. They are given by injection either into a muscle or just under the skin.

<span class="mw-page-title-main">Pathogenic bacteria</span> Disease-causing bacteria

Pathogenic bacteria are bacteria that can cause disease. This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and are often beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. By contrast, several thousand species are part of the gut flora present in the digestive tract.

Pneumococcal infection is an infection caused by the bacterium Streptococcus pneumoniae.

<span class="mw-page-title-main">Pneumolysin</span>

Pneumolysin is a virulence factor of the Gram-positive bacteria Streptococcus pneumoniae.

Streptococcus pseudopneumoniae is a gram-positive coccus that may cause pneumonia in humans. It was first described in 2004. The organism is often mistaken for S. pneumoniae and its clinical importance is as yet uncertain. It seems likely that most cases of S. pseudopneumoniae pneumonia are misdiagnosed as S. pneumoniae.

In biology, a pathogen, in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.

<span class="mw-page-title-main">Competence stimulating peptide</span>

Competence stimulating peptides (CSP) are chemical messengers that assist the initiation of quorum sensing, and exist in many bacterial genera. Bacterial transformation of DNA is driven by CSP-coupled quorum sensing.

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  49. ↑ "Drug Resistance". cdc.gov. Retrieved 17 February 2019.
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