A SHORT NOTE ON Gardnerella vaginalis

 A SHORT NOTE ON PASTEURELLA
                                                                                              
Compiled by: Zenisha Acharya          
                    : Samikshya Sharma 
Central Department of Microbiology
Tribhuvan University, Kirtipur

}  Pasteurella are gram negative coccobacilli that inhabits the oral cavity and gastrointestinal tract of many animals and cause various infectious problems, including  septicemia and pneumonia.
}  Currently, there are 22 species of Pasteurella.
}  It causes a wide range of diseases in mammals and birds, including fowl cholera in poultry, atrophic rhinitis in pigs, and bovine hemorrhagic septicemia in cattle and buffalo.
P. aerogenes                   
P. anatis
P. avium
P. bettyae
P. caballi
P. canis
P. dagmatis
P. gallicida
P. gallinarum
 P. granulomatis
P. langaaensis
P. lymphangitidis
P. mairii
P. multocida
P. oralis
P.pneumotropica
P. skyensis
P. stomatis
P. testudinis
P. trehalosi
P. ureae
P. volantium
}  The most common species in human infections are P. multocida and P.canis, and less commonly P.stomatis and P.dagmatis
}  P.multocida is subdivided into four subspecies- P.multocida subsp.multocida, P.multocida subsp.septica , P.multocida subsp.gallicida and P.multocida subsp.tigris.

Classification
}  Kingdom             :Bacteria
}  Phylum               :Proteobacteria
}  Class                    :Gammaproteobacteria
}  Order                  :Pasteurellales
}  Family                 :Pasteurellaceae
}  Genus                 :Pasteurella
}  Species               :multocida
 
Morphological characteristics
}  Pasteurella multocida is an gram negative , nonmotile, penicillin-sensitive , non acid-fast coccobacillus.
}  Measuring about 0.7x0.3-0.6μm, i.e.smaller than Yersinia
}  Capsulated in culture at optimum temperature of 37°C.
}  In smears of blood or tissue stained with methylene blue , Leishman stain,or Giemsa stain exhibits bipolar staining.
}  Repeated subculture or cultures grown under unfavourable conditions tend to be pleomorphic, may be longer and filamentous forms.
}  It is present in the respiratory tract of many species of wild and domestic animals and birds, where it may remain latent or cause a variety of primary and secondary pathogenic conditions including severe and fatal haemorrhagic septicaemia.
}  Humans, especially farmers and other persons living in rural areas, are susceptible to infection through contact with animals.

Cultural characteristics      

                                            
}  Aerobe and facultative anaerobes
}  Optimum temperature : 37°C
}  Grows fairly well on nutrient agar forming circular colonies 0.5-1 mm in diameter in 24 hr.
}  Does not grow on MacConkey agar;
}  Non-haemolytic on blood agar.
}  Grows well on 5% sheep’s blood(the preferred culture medium) in dextrose-starch agar and casein-sucrose-yeast(CSY), chocolate agar, Mueller Hinton agar, or brain heart infusion(BHI) agar.
}  Special media dextrose-starch agar (DSA)  and casein-sucrose-yeast(CSY) medium support an abundant growth.
}  Blood agar and CSY agar with 5% blood (bovine, sheep) are convinient media for routine laboratory culture
}  The colonies may be of three forms, smooth, rough or mucoid.
}  The smooth form contains a type-specific polysaccharide capsular antigen and the organisms are virulent for rabbits.
}  The rough form is developed by organisms that are non-capsulate and avirulent
}  The mucoid form by organism that may or may not contain a polysaccharide capsular antigen and are of intermediate virulence.
}  Media containing vancomycin, clindamycin, gentamicin, neomycin, kanamycin, and/or amikacin, either singly or in combination, have been used to select for Pasteurella , but results are not always consistent.

Biochemical reaction
}  All strains produce acid but no gas from glucose and sucrose.
}  Other sugars are fermented slowly and variably depending on the source of the strain.
}  Most clinical isolates are catalase , oxidase, indole and ornithine decarboxylase positive.

Survival and antibiotic sensitivity
}  Killed quickely by heat at 55°C and by phenol (0.5%) in 15 min.
}  May survive and maintain its virulence in dried or putrified blood for about 3 weeks and in culture or tissue for many months if kept frozen.
}  P.multocida is sensitive to penicillin, tetracycline, erythromycin, cotrimoxazole and sulphonamides.
}  In severe conditions such as osteomyelitis following animal bites, antibiotic therapy should be continued for at least 8 weeks.
Antigenic structure
}  P.multocida isolates are classified based on combination of capsular polysaccharide serotyping, which distinguishes isolates into one of the five capsular serogroups A(hyaluronic acid), B(arabinose,mannose and galactose), D(heparin), E(uncharacterized) or F (chondroitin)
}  serotypes A and D account for most human disease
}  Isolates are also subtyped based on their lipopolysaccharide(LPS), which separates isolates further into 16 serovars.

Mode of transmission

                                        

}  Pasteurella infections are most commonly associated with bites or scratches from cats or dogs.
}  Infections also have been associated with licking by animals of open wounds.
}  Some flies also helps in transmission.

Virulence factors

} Some of the genes encoding putative  virulence factors are present in all of the strains of Pasteurella multocida and these genes include;

1. Genes encoding outer membrane protein (ompA, ompH and ompW)
2. Iron acquisition genes(exb B-exbD-tonB,hgbA and fur),
3. Thiamine metabolism genes( tbpA, thiP, and thiQ)
4. The adhesion/Flp pilus assembly gene cluster (tadZACDEFG).

o   Iron acquisition mechanisms that enable invivo growth
o   Membrane lipopolysacharide(LPS) that confers serum resistance
o   Capsule that prevents phagocytosis and complement mediated opsonization.
o   Surface components that provide adherence properties(ompA; serves as adhesin by binding to an         host extracellular matrix protein;fibronectin and ompH;major outer membrane porin that forms homotrimeric channel and shown some potential as a protective antigen).
o   Extracellular matrix degrading enzymes such as hyaluronidase, neuraminidase, and         protease that facilitate colonization and/or dissemination
o   In some highly virulent strains a dermonecrotic toxin(PMT) that causes atrophic rhinitis and dermonecrosis and modulates the immune response by inhibiting dendritic cells migration.

Pathogenesis
}  Following the bite of dog or cat the organism in saliva may pass directly to the wound which spreads quickly through the soft tissue and proximally along lymphatic vessels causing a local abscess with cellulitis, adenitis and sometimes osteomylitis.
}  Alternatively , the organism may reside as a commensal in the human respiratory tract and nasal sinuses from where it may pass by way of the blood to damaged tissues, e.g. Following operations,where it multiplies.
}  Leukocyte and neutrophil counts are typically high at the infection sit, and inflammation develops very rapidly.
}  In more severe  cases, pasteurellosis can rapidly progress to bacteremia(fulminant sepsis) and other complications.
}  Head injury may lead to meningitis.
}  It may also cause suppurative respiratory infections such as pleurisy, pneumonia,empyema, bronchitis and nasal sinusitis.

Clinical signs and symptoms
}  P.multocida infection typically produces cellulitis and/or abscesses at the site of the bite or scratch, usually 3 to 6 hours after inoculation.
}  Occasionally, the local infection can progress to necrotising fascitis, septic arthritis and osteomyelitis.
}  Respiratory infection, pneumonia and bronchopneumonia also are common, mostly in patients with a pre-existing lung disease
}  Less frequently, a disseminating infection may produce septicaemia, which may lead to septic shock, meningitis, endocarditis, peritonitis, arthritis and other serious consequences.
}  Weber and colleagues in 1984 reported 34 cases of Pasteurella infection and reviewed the literature. Of their reported and reviewed cases totaling  446, nearly 50% were skin and soft tissue. The remaining major sites of infection included:
Ø  bone and joint (13%) (septic arthritis, osteomyelitis, bursitis)
Ø  oral and respiratory tract (14%) (peritonsillar abscess, sinusitis, pharyngitis, epiglottitis, submandibular abscess, tracheobronchitis, pneumonia, empyema)
Ø  cardiovascular (13%) (bacteremia, endocarditis, mycotic aneurysm, purulent pericarditis, infected vascular graft)
Ø  central nervous system (5%) (meningitis, brain abscess, subdural empyema)
Ø  gastrointestinal (4%) (liver abscess,
SBP, appendiceal abscess, peritonitis, gastroenteritis)
SBP, appendiceal abscess, peritonitis, gastroenteritis)
Ø  genitourinary tract (2%) (cystitis, pyelonephritis, infected ileal loop, renal abscess, vaginitis, cervicitis, Bartholin gland abscess, chorioamnionitis, epididymitis)
Ø  eyes (1%) (conjunctivitis, corneal ulcer, endophthalmitis)
Ø  Severe infection are usually seen in children, pregnant women, patients on chronic immunosupressive therapy, and immunocompromised persons.
Ø  Chronic liver disease and cirrhosis entail a special risk of sepsis  and peritonitis by Pasteurella

Hemorrhagic septicaemia
}  Disease caused by certain strains of Pasteurella multocida  frequently in cattle and water buffalo but infequently affects pigs, small ruminants, and other hoof stock.
}  Rapidly fatal
}  Disease is spread through contact with infected animals, contaminated clothing, equipment, and ingestion or inhalation of the bacteria
}  Symptoms :lethargy, reluctant to move nasal discharge, painful/difficult in breathing, excessive salivation, congestion, fever and sudden death
Atrophic Rhinitis in pigs
}  Type D or type A-severe.
}  Presence of Borditella bronchioseptica predisposes
}  Overstocking and poor ventillation
}  Young and any age affect
}  Symptoms:lacrimation, snoozing and epitaxis, snout gradually becomes shortned and wrinkled.

Laboratory diagnosis

}  Specimen

1. Swabs from bite wounds
2. CSF from cases of meningitis
3. Secretions from suppurative respiratory infections

}  Media: Blood agar plates                                                                     
incubated at 37°C for 24 hr
}  Identify organism: By non haemolytic colonies by further cultural and biochemical test

Treatment  and Prevention
}  Pasteurella species are not very susceptible to erythromycin, lincosamides(such as clindamycin), or certain β-lactams(such as dicloxacillin or cephalexin), so these antibiotics are not reccomended as monovalent treatments for animal bites.
}  Instead, a combination of amoxicillin and the β-lactamase inhibitor clavulanic acid(Augmentin), doxycycline plus metronidazole for the patients with penicillin allergies, or clindamycinplus fluoquinolone (ciprofloxacin, or trimethoprim-sulfamethoxazole combination for children or ceftraxone for pregnant women) is the recommended teatment regimen.
Pasteurella pneumotropica
}  It is frequently present in the upper respiratory tract of laboratory animals.
}  It has occasionally been responsible for septicaemia and upper respiratory infections in man and has been isolated from animal bite wounds.
Pasteurella haemolytica
}  It is the cause of various diseases of domestic animals and poultry, including pneumonia of sheep and cattle and septicaemia of lambs.
}  It differs from P.multocida in forming haemolytic colonies on blood agar, in its ability to grow on MacConkey medium and in its greater range if fermentation reactions.
}  The T type ferments trehalose but not arabinose but A-type ferment arabinose but not trehalose.
Pasteurella ureae
}  This organism was isolated from the human respiratory tract.
}  Grow better on blood or serum containing media than on unenriched media;mucoid
}  Non haemolytic and no growth on MacConkey’s medium.
}  Hydrolyse urea strongly
}  Indole and H2S negative
}  Acidifies maltose and mannitol but not xylose.
}  Usually non pathogenic for laboratory animals.
Pasteurella dagmatis
}  It is associated mainly with dog and cat bite  wound infections in humans
Pasteurella canis
}  It is an opportunistic pathogen that can infect both animals and humans.
Pasteurella stomatitis

}  Commensals in dogs and cats, bite- wound contamintion (humans and animals), bronchitis.

 References

https://en.wikipedia.org/wiki/Pasteurella

file:///C:/Users/default.DESKTOP-S673BEP/Documents/medical/Bailey_&_Scott_s_Diagnostic_Microbiology_12th_Edition(1).pdf 

https://microbewiki.kenyon.edu/index.php/Pasteurella