fastidious gram negative bacilli

haemophilus general characteristics

gram negative pleomorphic, coccobacilli or rods, non-motile, facultative anaerobic, ferment carbohydrates, generally oxidase and catalase positive, reduce nitrates to nitrites, resides in mucous membranes of humans and animals

haemophilus growth requirements

the name means blood lover, require preformed growth factors that are present in blood, x factor = hemin, v factor - nicotinamide adenine dinucleotide (NAD), species can be distinguished based on x and v requirements, species with the prefix para require only v factor for growth, the production of hemolysis on 5% horse or rabbit blood is a distinguishing characteristics of some species, both x and v factors are found within red blood cells (only x factor is available on 5% sheep blood agar), most clinical labs use chocolate agar since it contains both x and v factors to isolate

satellitism

haemophilus that requires both x and v will grow on SBA only when grown around organisms that produce v factor (s. aureus, S. pneumonia, neisseria spp)

H. influenzae virulence factors

capsule, IgA proteases, outer membrane proteins and LPS lipid A component, adherence by pili

H. influenzae capsules

the most significant role, allows serologic grouping into 6 serotypes, before widespread use of vaccine, there serotype Hib was the most common cause if infection in children, not all strains are encapsulated, encapsulated strains are responsible for invasive disease

infections from encapsulated strains of H. influenzae

septicemia, acute meningitis, epiglottitis, cellulitis, pneumonia

infections caused by non-encapslated strains of H. influenzae

otitis media with effusion (middle ear infections), conjunctivitis, sinusitis, bronchitis, pneumonia in older patients

meningitis caused by H. influenzae

used to be predominantly caused by serotypes b in children between 3 months and 6 years of age, headache, stiff neck and other meningeal symptoms preceded by mild respiratory disease, vaccine has decreased incidence

cellulitis caused by H. influenzae

commonly occurs in the cheek, rapid onset pain and edema

acute epiglottitis caused by H. influenzae

rapid onset acute inflammation and edema, peak incidence in children 2-4 years of age, inflammation obstructs airway

H. aegyptius

difficult to differentiate from H. influenazae, acute contagious conjunctivitis

H. influenza biogroup aegyptius

conjunctivitis primarily in pediatric patients, causes a systemic disease, brazilian purpuric fever (BPF)- recurrent or concurrent conjunctivitis, fever, vomiting, petechiae, purpura, septicemia and shock, mortality rate can reach 70%, more common in warmer climates

H. ducreyi

diagnosis based on clinical symptoms, not part of normal flora, causative agent of chancroid - sexually transmitted disease, incubation period 4-14 days, nonindurated painful lesions with irregular edge usually on genitalia, suppurative enlarged draining inguinal lymph nodes

aggregatibacter aphrophilus

associated with endocarditis usually within one month after dental procedures

haemophilus epidemiology

all except H. ducreyi part of normal flora of upper respiratory tract and mouth. transmission: endogenous, respiratory aerosols, sexual contact (H. ducreyi only)

haemophilus prevention and control

vaccines, prophylactic antibiotics for contact cases of H, flu meningitis

haemophilus direct examination

gram stain clinical specimen, slender gram negative rods and coccobacilli, non-sporogenous, non-motile

haemophilus cultivation

fastidious organisms: organisms suspected of containing haemophilus usually inoculated onto CHOC to ensure the growth of H. influenza

environment: facultative, growth in 5-10% CO2, growth at 35-37 degrees

H. ducreyi grows best at 33 degrees and requires special media such as GC agar, contains vancomycin to reduce the growth of normal flora

culture characteristics of haemophilus

visible colonies in 24 hours, transparent, moist, smooth, convex colonies, a mousy or bleach like odor, encapsulated strains produce larger more mucoid colonies, not visible in broth

X and V factor

presumptive identification, two agar plates: one plate containing X factor (SBA). one mueller hinton plate (neither factor), test organism streaked for confluence, add V producing organism or a V-disc