Short Review on Gardnerella, Serratia, Hafnia and Francisella
1. Gardnerella
1.1 Habitat
Normal Vaginal flora of human. May also colonize distal urethra of males.
1.2 Morphology
Gram variable or gram-negative coccobacilli or pleomorphic rod 1-1.5um in diameter Saline wet mount reveals clue cells which are large squamous epithelial cells with numerous attached small rods Non sporing , non-motile
1.3 Culture
Facultative anaerobes grow best at 35° C to 37° C but growth occurs between 25- 42oC Optimum pH 6-6.5 On Human Tween Blood Bilayer Agar (HBT), Pin point colonies Small, gray, opaque colonies surrounded by diffuse zone of beta haemolysis
1.4 Species
Only one species i.e G. vaginalis
1.5 Mode of Transmission
Infection caused by person’s endogenous strains
1.6 Diseases
I. Bacterial vaginosis
II. Urinary Tract Infections
III. Bacteremia- extremely rare conditions
1.7 Bacterial vaginosis
Most common cause of vaginitis in women of reproductive age group
Caused by G.vaginalis and also by synergistic activity of anaerobic organisms
eg Prevotella spp., Porphyromonas, Peptostreptococci, Mobiluncus spp. Mycoplasmas
1.8 Bacterial vaginosis diagnosis
Diagnosed by the presence of 3 of the following 4 signs (Amsel's criteria):
- Homogenous adherent discharge
- Clue cells
- Vaginal fluid pH>4.5
- Presence of fishy odour when 10% KOH is added to vaginal fluid.
1.9 Urinary Tract Infections
In extremely rare patients (<0.5%)
-Majority of male sexual partners of women with BV have G.vaginalis recoverable from the urethra.
-Genitourinary tract infections in males including prostatitis have been reported.
1.10 Virulence factors
-Cell adhesion factors - Adherence to epithelial cells is associated with outer fimbrial coat whereas to RBCs to fimbriae
-Haemolysin is a 59kDa cytolytic exotoxin that is active on human but not on animal RBCs
1.11 Laboratory Diagnosis
Specimens include:-
*Vaginal swab/discharge- classical BV discharge is thin, homogeneous and grey/yellow in colour.
*Suprapubic bladder aspirates
-Since the presence of Gardnerella in MSU may represent contamination and difficult to diagnose
-Suprapubic bladder aspirates cultured in symptomatic women without conventional uropathogens
*Blood
1.12 Direct microscopy
Saline wet mount reveals clue cells which are large squamous epithelial cells with numerous attached small rods.
1.13 Culture
-CA
-Columbia agar with 5% sheep blood
-Human Tween Blood Bilayer Agar (HBT)
-Since Gardnerella is susceptible to SPS, SPS-free or gelatin-supplemented blood culture media may enhance its recovery from women with Post-partum sepsis
-Incubation at 37oC in candle jar
G.vaginalis is identied by
Catalase- Negative
Alpha glucosidase- Positive
Beta glucosidase- Negative
Starch hydrolysis –Positive
Hippurate hydrolysis- Positive
1.14 Treatment
- Metronidazole
- Clindamycin
2. Serratia
2.1 History
-In 1819, Bartolomeo Bizio, a pharmacist from Padua, Italy, discovered and named S marcescens when he identified the bacterium as the cause of a bloody discoloration in a cornmeal mush called polenta. -Bizio named Serratia in honor of an Italian physicist named Serrati, who invented the steamboat, and Bizio chose marcescens (from the Latin word for decaying) because the bloody pigment was found to deteriorate quickly
2.2 Classification
Member of the family Enterobacteriaceae
14 species of Serratia, eight of which are associated with human infection
S. marcescens is the most common clinical isolate and the most important human pathogen
- Other possible pathogens- S. liquefaciens and S. odorifera
- S. ficaria
- S. fontiola
- S. liquefaciens
- S. marcescens
- S. odorifera
- S. plymuthica
- S. rubidaea
2.3 Structure
Gram negative rods, Non sporing, Motile
2.4 Cultural Characteristics
Facultatively anaerobic
- Capsulated
- On BA, many produce narrow zone of haemolysis within 24-48 hrs
- On Egg yolk medium, most strains produce opacity due to formation of lecithinase C except S. fonticola
- Optimum temp 30-37oC but few fail to grow at all at 37oC
- Many grow at 1-5oC
2.5 Habitat
- Soil, water, plant, animals, insects
- Some strains occur in animal body
2.6 Biochemical tests
-Actively proteolytic
-can be distinguished from other members of the Enterobacteriaceae family by their unique production of three enzymes: DNase, lipase, and gelatinase -Indole negative
-MR negative
-VP positive
-Citrate positive
2.7 Pigment production
-Some strains produce non-diffusible Red pigments e.g. S. marcescens, S. plymuthica, S. rubidaea - The red pigment prodigiosin is soluble in absolute alcohol, acetone, benzol, chloroform and ether but insoluble in water
- The pigment is not a single substance but consists of three red fractions and one blue fraction
- Pigmented strains alarm by
>> Giving rise to red colours in various foods
>> Simulating the appearance of blood in the sputum
>> Producing stains on babies’ napkins
- Derivatives of prodigiosin have recently been found to have immunosuppressive properties and antitumor activity in vivo and are also currently being considered as a candidate treatment for Chagas disease.
2.8 Flavours
- S.odorifera, S.ficaria and some strains of S. rubidaea produce alkyl-methoxypyrazines responsible for potato like odour
- Chitinase - S.marcescens and S.liquefaciens produce proteins with chitinolytic activity that may be used in treatment of chitin containing wastes
- S.marcescens is opportunistic pathogen causing diseases in IC patients
2.9 Virulence factors
-Fimbriae
-Siderophores
-Haemolysin
-DNase production
Antibiotic resistance- mainly in non-pigmented strains since they harbor resistance plasmids
2.10 Clinical manifestations
-RTI
-UTI
-Wound infections
-Arthritis
-Meningitis
-Ocular infections; mainly in contact lens related keratitis
-Endocarditis- rare
3. Hafnia
3.1 General characteristics
Member of Enterobacteriaceae
-Gram negative rods, Non-sporing
-Many strains non-motile at 37oC but all motile at 30oC
-Habitat- found in faeces, soil and water
-Only species- H. alvei
3.2 Biochemical tests
Produce gas from glucose
· Produce acid from arabinose, glycerol, maltose, mannitol, rhamnose, trehalose, xylose
· Citrate Positive
· VP positive at 22oC
3.3 Clinical manifestations
>Diarrhoea
4. Francisella
4.1 General characteristics
Gram-negative coccobacilli
Non sporing , Non motile
Capsulated
Obligate aerobe
Facultative intracellular pathogen that requires cysteine and a source of iron for growth
4.2 Species
F. hispaniensis
F. novicida
F. noatunensis
F. philomiragia
F. piscicida
F. tularensis
Worldwide in distribution
Carried by wild rodents, rabbits and muskrats
Persists in waterways possibly in association with amoebae
Human become infected by F. tularensis by
- Handling the carcasses or skin of infected animals
- Insect vectors primarily deerflies and ticks
- Bitten by carnivores that have themselves eaten infected animals
- Inhalation of infectious aerosols
capsule allows the organsims to avoid immediate destruction by PMNs
Intracellular parasite that can survive in the cells of reticuloendothelial system where it resides after a bacteremic phase.
Specimens include
Scrapping from infected ulcers
Lymph node biopsies
Sputum
Gram staining of specimen-little use
Fluorescent antibody testing –reference lab
PCR
For culture, BSC level 3 is recommended
Since tularemia is one of the most common lab acquired infections, specimens are generally sent to reference lab
F. tularensis is strictly aerobic and requires enriched media containing cysteine
F. tularensis can grow on
- Chocolate agar supplemented with IsovitaleX
- Buffered Charcoal Yeast Extract Agar
Commercial media available are
- Glucose cystine agar
- Cystine Heart agar
Colonies develop within 2-4 days – mucoid
Catalase- weakly positive
Oxidase- Negative
Identification- by serology (agglutination), Fluorescent ab test
Ideally, the isolates should be sent to reference lab for characterization
Streptomycin- drug of choice
Gentamicin- possible alternative
(i)Ulceroglandular
(ii) Glandular
(iii) Oculoglandular
(iv) Oropharangeal
(v) Systemic tularemia
(vi) Pneumonic tularemia
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