GENUS HAEMOPHILUS GENUS BORDETELLA GENUS BRUCELLA
Fastidious Gram Negative CoccobacilliGenus Haemophilus
General characteristics : Haemophilus spp. normally inhabit the upper RT except H. ducreyi which is not part of normal flora and only found in humans . Gram negative coccobacilli, pleomorphic, non motile, non spore forming facultative anaerobic which grow on enriched media. Require X and V factors for their growth. Among H. influenzae strains , there are two categories , typeable and untypeable . Strains are typed according to capsular characteristics . Encapsulated strains are of 6 groups a, b, c, d, e, and f , Type b is the most commonly encountered in serious human infections. The capsule is composed of a sugar alcohol phosphate ( poly ribitol phosphate, PRP)Morphology
General characteristicsNon typeable strains do not produce capsule and are normal inhabitants of URT Person to person transmission plays a key role in infections caused by type b H. influenzae ( resp. droplets). H. ducreyi is transmitted sexually . Other Haemophilus strains and species are likely arise endogenously as a person own flora gain access to normally sterile sites.
Classification
Species Factors required X V H. influenzae + + H. parainfluenzae - + H. haemolyticus + + H.parahaemolyticus + - H. aphrophilus + - H. paraaphrophilus + - H. segnis + - H. aegyptius + + H. ducreyi + -Pathogenesis of H. influenzae
Haemophilus influenzae infect only human and there is no animal reservoir, it enters the body through the URT.Most infection occurs in children between the age of (6months - 6 years) with a peak between 6 months – 1 yearMost infections are caused by serotype b, known by its resistance to phagocytosis and intracellular killing by neutrophils afforded by the capsule.Pili mediate adherence to human mucosal cells . H. influenzae produces IgA protease enzyme that inactivate human IgA , thus facilitate attachment to the respiratory mucosa. Producec bacteriocin ,hemocins to compete non typeable strains for colonization of nasopharynx .. LPS in cell wall . After establishment in the URT, the organism enters the blood stream and spread to the meninges causing meningitis.
Spectrum of diseases
H. influenzae causes meningitis , pneumonia, empyema, epiglottitis, cellulitis , septic arthritis , endocarditis and osteomylitis . Non typeable strains cause chronic bronchitis , otitis media , sinusitis and conjunctivitis .
Lab Diagnosis
Haemophilus are very susceptible to drying and temp extremes, therefore clinical specimens must be plated immediately . Clinical specimens are nasopharyngeal swabs, pus, CSF, blood & synovial fluid . Direct detection methods: Gram stain : especially for CSF . Antigen detection : particle agglutination. Detection of type b capsule by using specific rabbit antiserum ( capsule swelling test ) .Cultivation
Media used are: Chocolate agar provides the factors hemin ( X- factor ) and NAD (V- factor) . colonies are small, rounded, iridescent and dew like appearance. Most strains will not grow on 5 % sheep blood agar which contain hemin but not NAD . Several bacterial species such as Staph. aureus, Strep. pneumoniae produce NAD, therefore tiny colonies of H. spp. may be seen growing on sheep blood agar very close to bacteria that can produce V- factor(Satellitism )Satellitism
Cont,H. ducreyi needs special medium , Muller- Hinton agar – based chocolate agar supplement with 1 % isovitalex with Vancomycin .Rabbit and horse blood agar are used for detecting hemolysis by hemolysin producing strains .Growth is stimulated by 5- 10 % CO2 , m.o. grow within 24 hrs , may be extended to 72 hrs .
H. parainfluenzae
Can be differentiated from H. influenzae . By : Not require X- factor . Colonies larger, more opaque . Commensal in mouth and throat. Low pathogenicity , considered as opportunistic m.o. causing endocarditis , conjunctivitis, arthritis, soft tissue infection , abscess and brochopulmonary infections, it can cause bacteremia .H. haemolyticus and H. parahaemolyticus
B- hemolysis on horse or rabbit blood agar . They are part of URT . H. aphrophilus : Commensal in mouth and throat . Can cause serious infection such as endocarditis , brain abscess and less frequently meningitis with secondary bacteremia .H. aegyptius
Is the leading cause of purulent bacterial conjunctivitis. One strain causes Brazilian purpuric fever which is a severe infection of high mortality in children characterized by high fever , abdominal pain , vomiting , meningitis ,hemorrhagic skin lesions and vascular collapse .H. ducreyi
Not part of human flora , only found in humans during infections Capsular factor , pili and certain toxins are probably involved in attachment and penetration of host epithelial cells . It causes chancroid , sexually transmitted disease characterized by shallow genital ulceration ( soft chancer) which is usually painful and may be accompanied by inguinal lymphadenopathy . It should be differentiated from other STD e.g Syphlis, herpes simplex.Antimicrobial Therapy
Resistance to ampicillin by production of B- lactamase has become widespread among H. influenzaeResistance to chloramphenicol was 1st recognized in 1977 , the cause is the production of acetytransferase Therapeutic options for treatment of H. influenzae , Haemophilus spp. are macrolides , co-trimoxazole, ciprofloxacin in addition to ceftriaxone and cefotaxime.