micro sheet # 15 - Eman Almomani (modified)

Streptococci


We will continue with the streptococci and related genera, this group is composed of a heterogonous collection of α-hemolytic and non-hemolytic streptococci the only feature that is common to the α-hemolytic is the greenish color that can develop around these organisms This” greening” is caused by H2O2, which converts hemoglobin into methemoglobin.
These organisms are fastidious (requiring or characterized by excessive care), i.e.: they require blood and co2, they Inhabit oropharynx, gastrointestinal and urogenital tracts.
The most important organisms of this group is that the ones which forms dental caries These streptococci can attach to the proteins covering the tooth enamel, where they then convert sucrose into extracellular polysaccharides (the most important streptococci are S. mutans, S. sanguis. These sticky substances, in which the original bacterial layers along with secondary bacterial colonizers are embedded, form dental plaque. The final metabolites of the numerous plaque bacteria are organic acids that breach the enamel, allowing the different caries bacteria to begin destroying the dentin.
Associated with dental caries the patient can suffer from endocarditis, this is due to the transition of these organisms to the heart from the mouth due to scratching the gingiva during brushing or vigorous chewing (and this transition cant be prevented).

Streptococcus pneumoniae
Pneumococci are Gram-positive, oval to lancet-shaped cocci that usually occur in pairs or short chains. The cells are surrounded by a thick capsule.
When cultured on blood agar, S. pneumoniae develop a-hemolytic colonies with a mucoid (smooth, shiny) appearance.
Mutants without capsules produce colonies with a rough surface, these rough Pneumococci are non pathogenic, the pathogenic Pneumococci are the encapsulated ones.
The capsule can be demonstrated by a reaction which is known as capsular swelling reaction (quellung reaction); were an antibody is added to a drop of suspension of bacteria then under the microscope the reaction of the antigen with the antibody result in an appearance like an empty structure surrounded by a large area of clear zone.
There are 84 cell types that belongs to streptococcus pneumoniae … out of these cell types, few types are responsible for 75% of diseases … we have certain vaccines which are used to kill these organisms… one of which is still in use is the P7 because it can kill 7 types…but now scientists increased it to be able to kill 13 types (P13)…
an important surface component of streptococcous pneumoniae is a carbohydrate in the cell wall called C-substance. This carbohydrate is medically important, but because it reacts with a normal serum protein made by the liver its called C-reactive protein (CRP).
CRP precipitates when it reacts with c-substance of streptococcous pneumoniae in the presence of Ca+2 .
CRP is elevated as much as a 1000-fold in acute inflammation. CRP is not an antibody but rather a beta-globulin. (Plasma contains alpha, beta, and gamma globulins.) Note that CRP is a nonspecific indicator of inflammation and is elevated in response to the presence of many organisms, not just streptococcous pneumoniae. Clinically, CRP in human serum is measured in the laboratory by its reaction with the carbohydrate of streptococcous pneumoniae. The medical importance of CRP is that an elevated CRP appears to be a better predictor of heart attack risk than an elevated cholesterol level.
OTHER than pneumoniae, streptococcous can cause meningitis
Pathogenesis
The most important virulence factor is the capsular polysaccharide, non-capsulated are non- pathogenic.
Pneumococci produce IgA protease that enhances the organism's ability to colonize the mucosa of the upper respiratory tract.
Pneumococcal disease originates from spread of organisms colonizing the nasopharynx and oropharynx to distal loci.
Bacteremia can follow all infections (25-30% after pneumonia and >80% of meningitis).
Patients with sickle cell anemia, Hodgkin's lymphoma, multiple myeloma, HIV infection, and the absence of spleen for any reason, should be vaccinated to protect them from steptococcous pneumoniae. (spleen produces tuftsin (- Its biological activity is related primarily to the immune system function-) which is a tetrapeptide required for phagocytosis of streptococcus pneumonae so that's why these patients should be vaccinated).
Alcoholism is another important risk factor; alcoholic individuals are at more risk in developing steptococcous pneumoniae.
Meningitis due to s.pneumoniae is not different from other meningitis, it is characterized by high fever, sever headache, and local rigidity.
Treatment
Most pneumococci are susceptible to penicillins and erythromycin. In severe pneumococcal infections, penicillin is the drug of choice, whereas in mild pneumococcal infections, oral penicillin can be used. In penicillin-allergic patients, erythromycin or one of its long-acting derivatives, e.g., azithromycin, can be used.


Enterococci
They were classified in 1984 as separate genus, specifically they were included under the category D-antigen group. The group D-streptococci was divided into 2 categories: enterococci and nonenterococci.
Normally they are found in the intestines of humans and other animals.
The growth in 6.5% NaCl characterizes enterococci and that distinguishes it from other streptococci.
The genus consists of 12 species, 2 of which are responsible for more than 95% of infections; Enterococcus fecalis and Enterococcus facium (which is responsible for 8% of infections).
They are the second or the third to cause blood stream infection and the most cause of urinary tract infection.
A major cause of nosocomial infections especially in ICUs being selected by the use of cephalosporins and other antibiotic to which they are resistant.
They are naturally resistant to cephalosporins, penicillinase – resistant penicillins, and monobactams.
The enterococci have assumed an increase significant in the last few decades because of there association with nose problem infections.
They are the 2nd or 3rd cause of blood stream infection and the most important cause of urinary tract infections.
Grame –ve cocci
Neisseria are gram-negative, aerobic cocci that are often arranged in pairs.
The shape of neisseria resembles the shape of the kidney.
The genus Neisseria is one of several in the family Neisseriaceae. A separate genus contains the organism Moraxella, catarrhalis, Kingella and coccobasilla.
From these organisms two are important human pathogens: Neisseria meningitidis and Neisseria gonorrhoeae. N. meningitidis mainly causes meningitis.
The major difference between the Neisseria meningitidis and Neisseria gonorrhoeae is that the first is encapsulated while the second is not, that’s why there is a vaccine for Neisseria meningitidis but there’s no vaccine for Neisseria gonorrhoeae.
these are the main differences between them:



Species
Portal of Entry
Polysaccharide Capsule
Lactamase Production
Available Vaccine
N. meningitidis (meningococcus)

Respiratory tract
+
None
+
N. gonorrhoeae (gonococcus)

Genital tract
ــ
Some
ــ



They both produce oxidase, and most of these species are catalase +ve, so they are capable of dealing with toxic metabolites, they are non-motile and they produce acid because of fermentation.

Neisseria gonorrhoeae,
Are sexually transmitted organisms, pillated, i.e. they have an outer membrane structure with highly branched basal oligosaccharide, they release an outer membrane fragment known as blips which contains lippopolysaccharid(has an indotoxin activity).
Neisseria gonorrhoeae is an obligatory neuron pathogen, they are not present in the normal flora, there infection is silent, i.e. there are no symptoms.
They primarily infect the mucosal surfaces by the attachment of the Pilli and a protein - present on its outer membrane - to the mucosal cells then they are engulfed, they can survive inside the host cell, that’s very important in the diagnosis, (the diagnosis can be demonstrated by making a gram –ve test to the cell if the test was positive that means that this cell is infected).
The deficiency of the complement components (C6–C9) can increase the risk of being infected.
Note : the Dr. said that” the dificiency of the complement components from C5-C9”… but when I looked it up it was C6-C9…SO WHEN HE GIVES US THE SLIDES CHECK IT PLZ…
The complement system is a biochemical cascade that helps, or “complements”, the ability of antibodies to clear pathogens from an organism.

Although Neisseria gonorrhoeae are not encapsulated, it has a capsule-like negative surface charge, so a net negative charge is present around this type of Neisseria gonorrhoeae which by itself prevents fagocytosis.

Additionally Neisseria gonorrhoeae has many iron binding proteins which allows the cell to survive. They compete with most cycles to obtain iron, these include transferrin binding protein 1 & 2, lactoferrin binding protein and hemoglobin binding protein. So they can obtain iron from all components of the body.


Done by: Eman Hashem Al-Momani
Lec: 15, Dr:Azmi

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