Neisseria

Question 1

Genus Neisseria

Answer 1

they are little gram-negative
cocci arranged in pairs with a typical coffee bean shape. We can often find them free in clinical samples, but they can also be found in the cytoplasm of macrophages: they can multiply inside these cells. General features of this bacteria are the following: they are aerobic, they do not form spores, and are nonmotile; they are oxidase and catalase positive, and they can produce acid
from oxidation of carbohydrates, but not from fermentation

Question 2

There are two human pathogenic species of Neisseria

Answer 2

Neisseria meningitidis
(meningococcus), which causes meningitis and sepsis, and Neisseria gonorrhoeae
(gonococcus), that causes gonorrhea. Other Gram-negative cocci are non-pathogenic commensal inhabitants and are found mostly in the mucosa of the upper respiratory tract.

Question 3

Differences between the meningococcus and gonococcus?

Answer 3

1) Gonococci are more fastidious, because meningococci can grow in routine blood agar, while gonococci grow more slowly, and in enriched media, such as chocolate blood agar, and its growth is much more enhanced in the moist atmosphere with 5% CO2.
2) Meningococci has a polysaccharide capsule external to the cell wall, and this is its main virulence factor, while gonococcus’ main virulence factor is given by Pili, which have a specific adhesion to the cells of the urogenital mucosae.

However, both bacteria are able to survive and multiply within phagocytic cells.

Question 3

Pathogenesis

Answer 3

Pathogenesis is similar in the first cases of infection for both bacteria, because they present several outer membrane proteins and fimbriae that allow for the attachment to the target cells; then, they are endocytosed in vacuoles. In the cells, they can multiply in the cytoplasm, and both
can escape the cells and enter the submucosa. Here, gonococcus is phagocytosed and remains localized, while the meningococcal capsule allows the meningococcus to escape phagocytosis and enter the bloodstream. In this case, it can either reach the target site (CNS, meninges) or cause
sepsis.

Question 4

NEISSERIA MENINGITIDIS

Answer 4

To be more specific, meningococcus pathogenicity is given by pili, (as mentioned before) and receptor-specific colonization of non-ciliated cells of nasopharynx. The other essential virulent factor that was previously mentioned is the antiphagocytic polysaccharide capsule, which allows the meningococcus to systemic spread in the absence of specific immunity. The polysaccharides that constitute this capsule can be subdivided into various antigenic groups: thanks to this subdivision, 13 serogroups have been discovered, and 5 of them (A, B, C, Y, W135) cause 90% of ALL infections.

Unlike the other Gram-negative bacteria, which all contain LPS (lipopolysaccharides) as a virulence factor, meningococci contain LOS, (lipooligosaccharides) which still maintains the endotoxic activity: this means that LOS mediates toxic effects [including diffuse vascular damage, thrombosis and disseminated intravascular coagulation (DIC)]. Another important feature is the presence of binding serum factor H proteins which, along with the polysaccharide capsule, allow for resistance to complement-mediated bactericidal activity.

Question 5

Serogroups:

Answer 5

The serogroups are distributed worldwide, however not equally: the incidence of invasive meningococcal infection varies depending on age, geographic area, and serogroup.
In Europe, the main serogroups involved in diseases are B and C groups, while serogroup A strains are found in Russia and in the ‘’meningitis belt’’ in Africa: this serogroup causes large epidemics and it tends to emerge every 10-15 years, resulting in many deaths.

Question 6

the most affected people from meningococci are __________________

Answer 6

infants (<1), and also young people between 15 and 24 are most likely to be affected

Question 7

Humans are the only natural hosts.

Answer 7

Meningococcus commonly colonizes the nasopharyngeal mucosa of 3% to 25% of healthy individuals; the highest carriage rates are in school-age children, young adults, and lower socio-economic conditions. Transmission is more frequent in crowded environments: person-person transmission occurs by aerosolization of respiratory tract secretions, especially when in contact with infectious people (family members, daycare centers, military barracks, prisons, and other institutional settings).
Meningococcus can either exist as a harmless member of the resident microbiota or produce acute disease. For most individuals, the carrier state is an immunizing process associated with the acquisition of protective antibodies. For some individuals, the process of spread from the nasopharynx to produce bacteremia, and endotoxemia takes place too quickly for
immunity to develop

Question 7

Antimicrobial susceptibility of meningococci

Answer 7

Meningococci were almost uniformly susceptible to penicillin until a few decades ago. Penicillin resistance mediated by both β-lactamase and altered penicillin-binding proteins is now over
10%. Third-generation cephalosporins are now the treatments of choice for acute meningitis (moxifloxacin and chloramphenicol are alternatives for those with β-lactam hypersensitivity)
Rifampicin, ceftriaxone, ciprofloxacin and azithromycin are used for chemoprophylaxis of
close contacts of cases

Question 8

Diseases associated with Neisseria meningitidis:

Answer 8

The diseases associated are mainly the following: acute purulent meningitis (with fever, headache, seizures, and mental signs secondary to inflammation and increased intracranial pressure), sepsis with or without meningitis and meningoencephalitis. More rare disease
caused by this bacterium are pneumonia, arthritis, and urethritis. A prominent feature of meningococcal meningitis is the appearance of scattered skin petechiae,
which may evolve into ecchymoses or a diffuse petechial rash. These cutaneous manifestations are signs of the disseminated intravascular coagulation (DIC) syndrome, which is part of the
endotoxic shock brought on by meningococcal bacteremia (meningococcaemia). Meningococcaemia may occur without meningitis and may progress to fulminant DIC and shock
with bilateral hemorrhagic destruction of the adrenal glands (Waterhouse Friedrichsen syndrome). However, some patients have only low-grade fever, arthritis, and skin lesions that
develop slowly over a period of days to weeks

Question 9

Prevention of Meningocci

Answer 9

Prevention is given by vaccines obtained by purified group-specific polysaccharides for groups A, C, Y, and W, and they are available for people who are over 2 years old. For infants, vaccines are made of the same purified polysaccharides, but conjugated with diphtheria toxoid, because these
are antigenic molecules, but they are T-independent; so, in infants, they do not induce a protective response. An exception is for group B meningococcus because group B polysaccharides are constituted by sialic acid polymers, which are like neural adhesion molecules, hence it is recognized as self, and specific antibodies are not produced. Thus, it would be counterproductive to induce a vaccine response, since it would be an autoimmune response. The vaccine against group B meningococcus was produced recently, and it is composed of our antigenic component of meningococcus. It contains serum factor H surface binding proteins (FHbp), Neisseria adhesin A (NadA), Neisseria Heparin-Binding Ag (NHBA), and PorA proteins as immunogens. These vaccines are recommended for immunization to infants: in Italy, they are recommended in the first year of life, and also to young adults, particularly if the person has not
been vaccinated before and any of the predisposing conditions are present

Question 10

NEISSERIA GONORRHOAE

Answer 10

These bacteria lack a proper capsule, as previously explained: they are fastidious, capnophilic and susceptible to cool temperatures, drying, and fatty acids. They are found only in humans with strikingly different epidemiological (and clinical) presentations for females and males; the transmission mainly happens by sexual contact. A typical feature of gonococcus is its ability to undergo antigenic variation: the major gonococcal structures known to undergo antigenic variation are pili, Opa proteins, and LOS. This means that there is a lack of protective immunity and therefore reinfection, partly due to the antigenic diversity of strains, is possible.
Virulence factors found in this bacterium are the Antiphagocytic capsule-like negative surface charge, pili (only fimbriated cells are virulent), and the following outer membrane proteins:
-Por (porin protein), which prevents phagolysosome fusion following phagocytosis and thereby promotes intracellular survival.
-Opa (opacity protein), which mediates firm attachment to epithelial cells and
subsequent invasion into cells.
-Rmp (reduction-modifiable protein), which protects other surface antigens from
bactericidal antibodies (Por protein, LOS).
-Tbp 1 and Tbp 2 (transferrin-binding proteins), Lbp (lactoferrin binding protein), and Hbp (hemoglobin-binding protein) for iron acquisition.
-Lipooligosaccharide (LOS), which has endotoxin activity.
- IgA1 protease.

Question 11

Diseases associated with Neisseria gonorrhoeae.

Answer 11

Most cases in women are asymptomatic. Local extension up the fallopian tubes causes salpingitis, but the disease is rarely invasive.

Most men have acute urethritis, and only a small percentage have local extension to the epididymis. A very small part of either spectrum results in bacteremia or disseminated gonococcal infection.

Question 12

Clinical presentation of Gonorrhoea

Answer 12

In men, the main diseases are Urethritis and epididymitis.
Most infections among men are acute and symptomatic with purulent discharge and dysuria after 2-5-day incubation period.
Male host seeks treatment early preventing serious sequelae, but not soon enough to prevent transmission to other sex partners.
In women, the main diseases are Cervicitis and Vaginitis.
Symptoms include increased vaginal discharge, urinary frequency, dysuria, abdominal pain, and menstrual abnormalities, but women are often asymptomatic or have atypical indications, so infections are often untreated until complications develop.
Pelvic Inflammatory Disease (PID) (10-20%) caused by spread of microorganisms along the fallopian tubes to produce salpingitis and into the pelvic cavity.
They may also be asymptomatic, but difficult diagnosis accounts for many false negatives; the findings include fever, lower abdominal pain (usually bilateral), adnexal tenderness, and leucocytosis with or without signs of local infection.
These diseases can cause scarring of fallopian tubes leading to infertility or ectopic pregnancy. Disseminated Gonococcal Infection (DGI) emerges as a result of gonococcal bacteraemia; often skin lesions are present (petechiae, pustules on extremities).
Arthralgias (pain in joints); tenosynovitis; septic arthritis. Occasional complications: Hepatitis; Rarely endocarditis or meningitis

Question 13

Gonorrhoea: differences in presentation (females)

Answer 13

1) 50% risk of infection after a single exposure
2) Asymptomatic infections are frequently not diagnosed
3) The major reservoir is asymptomatic carriage in females
4) Genital infection’s primary site is the cervix (cervicitis), but the vagina, urethra, and rectum can be colonized
5) Ascending infections in 10-20% including
salpingitis, tube-ovarian abscesses, pelvic
inflammatory disease (PID); chronic infections can lead to sterility
6) Disseminated infections are more common, including septicemia, infection of the skin and joints (1-3%)
7) Can infect infant at delivery (conjunctivitis, ophthalmia neonatorum)

Question 14

Gonorrhoea: differences in presentation (males)

Answer 14

1) 20% risk of infection after a single exposure
2) Most initially symptomatic (95% acute)
3) The major reservoir is asymptomatic carriage in females
4) Genital infection is generally restricted to the urethra (urethritis) with purulent discharge and dysuria
5) Rare complications may include epididymitis, prostatitis, and periurethral abscesses
6) Disseminated infections are very rare
7) More common in homosexual/bisexual men than in the heterosexual population

Question 15

Antimicrobial susceptibility of Gonococcus?

Answer 15

While a few years ago gonococcus was always susceptible to penicillin, over the last 20 years gonococcus acquired two types of antimicrobial resistance:
1) Plasmid-encoded beta-lactamase production
2) Chromosomally mediated changes in cellular permeability with inhibition of entry of penicillin, tetracycline, erythromycin, aminoglycosides

Question 16

Brucellosis

Answer 16

Humans such as farmers, slaughterhouse workers, and veterinarians become infected directly by occupational contact or indirectly by consumption of contaminated animal products such as unpasteurized milk and dairy products.
In people Brucella evade toll-like receptors (TLRs) and innate immunity, survive in
macrophages by inhibiting myeloperoxidase and lysosome fusion, and producing a chronic illness characterized by malaise, chills, fever (39.4°C to 40°C), night sweats, and weight loss lasting weeks to months or even 1-2 years.
The infection is localized in reticuloendothelial organs, so there are few physical findings unless the liver or spleen becomes enlarged (<25% of patients).
The disease has been called undulant because of the cycling pattern of nocturnal fevers.
From a histological point of view, the infection progresses with the formation of small granulomas in the reticuloendothelial sites of bacterial multiplication and with the release of bacteria back into the systemic circulation.
The bacteremic episodes are largely responsible for the recurrent chills and fever of the clinical illness

Question 16

prevention of Gonococcus?

Answer 16

Therapy for uncomplicated infections includes ceftriaxone, cefixime, or fluoroquinolone, combined with doxycycline or azithromycin for dual infections with Chlamydia.
Chemoprophylaxis of newborns against ophthalmia neonatorum is carried out with 1% silver nitrate, 1% tetracycline, or 0.5% erythromycin eye ointments.
Treatment of newborns with ophthalmia neonatorum uses ceftriaxone.
Measures to limit the epidemic include education, aggressive detection, and follow-up screening of sexual partners, use of condoms or spermicides

Question 17

SMALL GRAM-NEGATIVE RODS
GENUS BRUCELLA

Answer 17

Genus brucella comprises small, coccobacillary, Gram-negative bacteria: they are nonmotile and don’t form spores; they can produce catalase, oxidase, and urease, but do not ferment carbohydrates. They have a typical Gram-negative structure, and the outer membrane contains proteins.
Growth of these bacteria is relatively slow, requiring at least 2 to 3 days of aerobic incubation in enriched broth or on blood agar.
All Brucella spp. are facultative intracellular parasites of epithelial cells and professional
phagocytes, meaning that not all the species are human pathogens.
Three species/variants of Brucella, that cause genitourinary tract disease in animals (infection of mammary glands, uterus, placenta, seminal vesicles, and epididymis), can infect humans: B. abortus (cattle), B. melitensis (sheep and goats), and B. suis (pigs). In animals, Brucella spp. is an important cause of abortion, sterility, and decreased milk production. Spreading among animals occurs by direct contact with infected tissues and ingestion of contaminated food

Question 18

Antimicrobial susceptibility of Brucella?

Answer 18

Doxycycline in combination with rifampicin or gentamicin is the primary treatment for
brucellosis.
The therapeutic response is not rapid; 2 to 7 days may pass before patients become afebrile. Up
to 10% of patients have relapses in the first 3 months after therapy.
Prevention is primarily by measures that minimize occupational exposure and by the
pasteurization of dairy products. Control of brucellosis in animals involves a combination of
immunization with an attenuated strain of B. abortus and eradication of infected stock.

Question 19

is there a vaccine for Brucella?

Answer 19

NO

Question 19

GENUS HAEMOPHILUS

Answer 19

These bacteria are small, coccobacillary, Gram-negative rods exclusively found in humans. The most important species is the Haemophilus influenzae, which is found in two variants, and these are the most relevant because they cause the most severe diseases. The most important virulence factor is the presence of a polysaccharide capsule.
The species that do not have a polysaccharide capsule cause minor diseases. Some species known as H. parainfluenzae, do not have the capsule, and they have the same biology as that of
the non-encapsulated strains of H. influenzae.
Other species can be involved in human diseases, and some examples are H. ducreyi and H. aegyptius.
A common feature of all species is the fact that they are all fastidious organisms: Haemophilus species require exogenous hematin (X factor) and/or nicotinamide adenine dinucleotide (NAD, V factor) for growth. These growth factors, present in erythrocytes, are available if the
red blood cells are lysed by gentle heat (chocolate agar) or added separately as a
supplement

Question 20

HAEMOPHILUS INFLUENZAE

Answer 20

It is also called Pfeiffer’s bacillus.
Long thread-like and pleomorphic forms may be seen in cerebrospinal fluid or following culture. H. influenzae occurs in capsulate and non-capsulate forms.
The most present form is the encapsulated H. influenzae, which can be classified into six serotypes: a, b, c, d, e, and f; however, only the b serotype is highly virulent, it comprises a polymer of ribose, ribitol, and phosphate, called polyribitol phosphate (PRP).
Non-capsulated (Non-typable) H. influenzae are less pathogenic.
Capsular polysaccharide has antiphagocytic activity.
Other virulence factors are:
- Pili, which mediates adherence.
- Membrane lipooligosaccharide, which may be responsible for bacterial attachment
- invasiveness, and paralysis of the ciliated respiratory epithelium.
- Outer membrane protein, which contributes to adhesion and invasion of host tissue.
- IgA protease.

Question 21

HAEMOPHILUS DUCREYI

Answer 21

They are short, ovoid, Gram-negative bacilli: they are involved in STDs, and cause genital ulceration.
H. ducreyi causes what is known as chancroid, or soft sore.
The ulcers are painful, and shallow and tend to be ragged with marked swelling and tenderness and bleed easily.
Often there is also painful swelling of inguinal lymph nodes, and abscesses may form. Chancroid increases the
risk of infection with HIV and facilitates transmission of the virus.

Question 21

HEMOPHILUS AEGYPTIUS

Answer 21

Also known as ‘’Kock-Weeks bacillus’, these bacteria closely resemble other H. influenzae.
It also requires factors X and V for isolation, but it grows more slowly.
H. aegyptius causes acute and highly infectious conjunctivitis often referred to as ‘pink eye’.
A specific strain (BFP clone) causes Brazilian purpuric fever, a life-threatening pediatric infection that is preceded by conjunctivitis; the symptoms include high fever, nausea, vomiting, severe abdominal pain, septic shock, purpuric skin lesions affecting mainly the face and
extremities, cyanosis, rapid necrosis of soft tissue, and ultimately death.
The bacterium can be isolated from eye discharge in acute conjunctivitis and from blood culture in Brazilian purpuric fever.

Question 22

GENUS BORDETELLA

Answer 22

These are minute, strictly aerobic, non-motile, Gram-negative coccobacillus, and they are non-spore
forming. They are fastidious organisms since they require blood-supplemented medium to grow.
Species of this bacterium that are of clinical significance include B. pertussis, B. parapertussis, and B. bronchiseptica.
The most important bacterium among these three is Bordetella pertussis, which causes pertussis, also known as whooping cough; it is a strictly human pathogen and is characterized by high infectivity. This bacterium is fragile and is not commonly colonizer of our mucosal membrane;
asymptomatic carriers are rare.
Bordetella parapertussis causes a similar milder disease.
Bordetella bronchiseptica causes diseases in animals and occasionally causes respiratory
diseases and bacteremia in humans, primarily in immunocompromised hosts.

Question 22

Whooping cough pathogenesis

Answer 22

The first step of pathogenesis is the pili-mediated attachment to the epithelial cells; then, bacteria produce toxins that act on the epithelial mucosal
cells, and in particular tracheal cytotoxins can lead to the destruction of ciliated epithelial cells. After infection with this bacterium, mucosal membranes of the upper respiratory tract lack ciliated cells.

Question 22

Diseases associated with Bordetella spp.

Answer 22

Whooping cough is caused by invasion of these toxins: toxins from the organisms cause the secretion of mucus which leads to irritation and the spasms of coughing associated with the disease.
A typical feature of this disease is the presence of a marked leucocytosis and an absolute lymphocytosis.
Complications of infection include lung damage with emphysema, secondary infections leading to bronchopneumonia, bronchiectasis, convulsions and occasionally brain damage.
After an incubation period of about 2 weeks, the “catarrhal stage” develops, with mild coughing and sneezing. During this stage, large numbers of organisms are sprayed in droplets and the
the patient is highly infectious but not very ill.
Following the “paroxysmal” stage, the cough develops its explosive character and the characteristic “whoop” upon inhalation. This leads to rapid exhaustion and may be associated with vomiting, cyanosis, and convulsions.
The “whoop” and major complications occur predominantly in infants; paroxysmal coughing predominates in older children and adults.
After 3-4 weeks the disease enters the convalescent stage, frequency and severity of the coughing gradually decrease, but secondary complications can occur.
The microorganism is susceptible to erythromycin, tetracycline, chloramphenicol. Active
immunization of all infants and during pregnancy is highly recommended so that antibodies can be transmitted to the foetus. The vaccine is not that effective, and that’s because immunization tends
to decline over time; so, research is still involved in trying to improve this vaccine. The currently used one is an acellular vaccine that has substituted the previous vaccine which was constituted
by microorganisms; this is because the older vaccine had several side effects

Question 23

GENUS LEGIONELLA

Answer 23

These bacteria are Gram-negative rods, most are motile thanks to flagella.
There are many species of this genus (>50), however only about 19 species are pathogenic.
The most important species is the Legionella pneumophila, which accounts for >80% of clinical
cases, and in most cases the serotype involved is serotype 1.
L. pneumophila is acquired by inhalation and multiplies within pulmonary alveolar
macrophages.
In nature, Legionella species are ubiquitous in freshwater lakes, streams, and subterrestrial
groundwater sediments and exist as parasites of protozoa including numerous species of
amoebas, which appear to be the environmental reservoir.
Another common feature is biofilm formation and dormancy, which facilitates survival in the pipes
of large buildings.
Common sources of infection are cooling towers, potable water, aerators, shower heads,
misters, humidifiers, ornamental waterfalls, ponds, and fountains.
Legionellae survive in low temperatures and grow well between 20 °C and 45 °C