Last updated:
November 12, 2024
Bacillus
- Which gram positive bacilli have vaccines and when are they given
- Clostridium tetani, Corynebacterium diptheriae
- Pentavalent vaccine: 6 weeks, 10 weeks, 14 weeks
- Tetanus Toxoid (TT): pregnant women (1st pregnancy twice 12 weeks, 1 month 2nd – 4th once), women of child bearing age, children at 7-14 years,
- Which of gram positive bacilli organisms do we give immunoglobulins against
- Clostridium tetani: IM human tetanus Immunoglobulin (HTIG)
- Clostridium botulinum: BIG-IV, Bovine (Horse-derived) heptavalent botulism antitoxin
- What are the general characteristics of Bacillus
- 60 species
- Gram positive rods
- Single or in chains
- Saprophytic contaminants or normal flora
- Produce endospores (heat resistance)
- Aerobic or facultatively anerobic
- Ubiquitous in soil, water, vegetation, airborne dust
- Most non-anthracis species are Beta hemolytic, motile and lack the glutamic acid capsule (thus stain negatively with McFadyean’s stain)
- Species: B. anthracis, B. cereus, B.stearothermophilus, B. circulan, B.megaterium. B.sphaericus. B. licheniformis, B.pumilis, B. subtilits
- What diseases are associated with the genus Bacillus
- Anthrax (cutaneous, Gastrointestinal, inhalation)
- Gastroenteritis (emetic and diarrheal types)
- Ocular infections
- Catheter-related sepsis
- Opportunistic infections
- What are the laboratory characteristics of Bacillus
- On Blood Agar (BA):
- Large, spreading, gray-white colonies with irregular margins
- Many are beta hemolytic (differentiates the various species of Bacillus from B.anthracis)
- Most are Catalase positive
- Spores are seen after several days of incubation, but not typically in fresh clinical specimen
- On Blood Agar (BA):
- What is the historical importance of Bacillus anthracis
- First pathogenic bacterium to be seen under microscope
- First bacterium shown to be the cause of a disease (Koch’s postulate)
- First bacterium to be isolated in pure culture and shown to possess spores
- First bacterium used for the preparation of attenuated vaccines by Pasteur
- List the characteristics of Bacillus anthracis
- Gram positive rods: straight or slightly curved
- Edge of colony shows irregular comma-shaped outgrowth on blood agar (Medusa head)
- Bamboo-rod appearance in smears from culture
- Single, in pairs, and in short chains in smears from infected tissue
- Capsulated in tissue: Polypeptide capsule with D-glutamate, plasmid mediated
- Spores forming in vitro: Oval and centrally placed
- Vegetative cells are destroyed by heat at 60*C for 30 min
- Spores are resistant to disinfectant and heat and can survive in soil for years
- Some withstand dry heat at 140C for 1-3 hours and boiling at 100C for 5 – 10 minutes
- Non-motile
- Non-acid fast
- Briefly describe the spores of Bacillus anthracis
- Soil and mammals are reservoirs – spores can remain viable for decades
- Highly refractile: resistant to staining, heat, cold, radiation, desiccation and disinfectants
- Formed in culture or in solid under unfavorable condition – need O2 for sporulation
- Germinate when exposed to nutrient-rich conditions
- Tissue/blood of animals and human host
- Rainfall stimulates spore germination, spread by flies and vultures
- Conditions that facilitate spore formation
- Nitrogen and organic soil content
- environmental pH greater than 6
- Ambient temperature greater than 6*C
- 2% sodium chloride
- Presence of distilled water
- ***inhibited by compounds such as calcium chloride
- Spores are never found in host tissue unless the infected body fluids are exposed to ambient air
- Briefly describe the epidemiology of Bacillus anthracis
- Primarily a disease of herbivorous animals
- Humans are rarely infected
- Transmitted to humans by direct contact with anima products (eg. wool, hair, hide, meat)
- Also via inhalation and ingestion: increased mortality with these portals of entry
- Commonly in wild and domestic animals: Asia, Africa, S and Central America, and parts of Europe
- Still poses a threat
- Importing material contaminated with spores
- Usually an occupational disease: veterinarians, agricultural workers
- Mortality
- Contact with contaminated animal products (hides, wool, hair): 20% – results in 95% of infections
- Ingestion of contaminated food products: 95%
- Inhalation of contaminated dust (Woolsorter’s disease): 95%
- Briefly describe the transmission of Bacillus anthracis
- Sick animal or carcasses shed bacilli through orifies (nose, mouth, faeces)
- Contaminate environment: soil and pastures
- Infectious agent is mostly the spore
- Human and other animals acquire the spore
- Rare in developed countries where routine animal vaccination is done
- Bioterrorism category A
- Sick animal or carcasses shed bacilli through orifies (nose, mouth, faeces)
- List the virulence factors of Bacillus anthracis
- Antiphagocytic capsule: plasmid encoded; contains D-glutamate (thus it is a polypeptide capsule)
- **Anthrax toxin complex (**plasmid encoded)
- A subunit
- Edema factor (EF): Binds to calcium and calmodulin and gains AC activity to increase cAMP and cause edema
- Lethal factor (LF): Zinc metalloprotease that degrades MAPKK leading leading to apoptosis ;also stimulates the release of TNF-a and IL-1 by macrophages
- B subunit
- Protective (Antigen): binds to endothelial receptors and facilitates entry of the A subunit into the host cell
- Edema toxin = PA + EF
- Lethal toxin = PA + LF
- A subunit
- List the diseases caused by Bacillus anthracis
- Cutaneous anthrax: Black eschar
- Inhalation anthrax (Woolsorter’s disease): Hemorrhagic mediastinitis
- Gastrointestinal anthrax: Severe bloody diarrhea
- Describe food poisoning caused by Bacillus cereus
- Transmission: Bacteria grows in heated food that cools down too slowly or is improperly refrigerated, Reheated rice is a common source of infection
- Incubation period: Emetic (30min – 6 hours), Diarrheal (6-15 hours)
- Pathogenesis: Enterotoxin I (preformed cereulide) causes emetic type, Enterotoxin II causes diarrhea
- Clinical feature: Emetic (nausea and vomiting), Diarrheal (watery diarrhea and abdominal pain)
Clostridium
- Concerning Clostridiodes difficile, briefly describe the: reservoir, characteristics, epidemiology, and transmission **
- Reservoir
- Gastrointestinal tract
- Characteristics
- Gram positive rod
- Obligate anaerobe
- Spore forming rod
- Facultative pathogen
- Epidemiology
- Present ubiquitously
- Highly contagious
- Toxigenic or non-toxigenic; toxigenic strains cause Clostridiodes Difficile Infection (CDI)
- Transmission
- Oral route of transmission
- Community acquired CDI: fecal-oral route
- Hospital acquired CDI: via contaminated surfaces and medical equipment
- Oral route of transmission
- Reservoir
- Briefly describe the Virulence factors and pathogenesis of Clostridium difficile
- Toxin A (enterotoxin)
- Active site at N-terminal domain (site of glycosylation)
- Central hydrophobic domain (required for protein conformational change)
- Binding site at C-terminal domain (Binds to the target surface)
- MOA: Binding to brush border of enterocytes → receptor mediated endocytosis → change of conformation → exposure of active domain → glycosylation of target proteins (e.g. Rac, Cdc42, RhoA) → disruption of actin cytoskeletal functioning → increase in epithelial permeability and apoptosis → diarrhea
- Toxin B (cytotoxin)
- Binding site at C-terminal domain (binding to oligosaccharides on cell surface)
- Translocation domain (required for pore formation)
- Cysteine protease-containing domain
- Catalytic domain
- MOA: same as in toxin A, but also causes pore formation within the endosomal membrane via insertion of the translocation domain → release of endosomal content into the cytosol → cytopathic effect
- Toxin A (enterotoxin)
- Briefly describe Clostridiodes difficile infection (CDI)
- Asymptomatic colonization (Non-toxigenic CDI)
- Symptoms develop during antibiotic treatment 2-10 days after initiation
- 25-40% of cases manifest as late as 10 weeks following treatment
- Antibiotic associated diarrhoea (C.difficile associated diarrhoea CDAD)
- Watery-diarrhoes
- ≥ 3 stools per day associated with characteristic odor
- May contain traces of mucus or occult blood
- Hematochezia and melena are both rare
- Cramping abdominal pain, nausea, anorexia
- Fever and dehydration
- Fulminant CDI manifests with abdominal distention and severe hypovolemia (e.g. due to toxic megacolon, paralytic ileus)
- Watery-diarrhoes
- Pseudomembranous colitis
- Colonic inflammation results in fibrin exudates, manifesting as pseudomembranes
- Elevated yellow-white plaques that form pseudomembranes over the colonic mucosa
- List the laboratory features of Clostridiodes difficile
- Specimen: stool
- Stool cytotoxicity neutralization assay (CCNA): detects toxins in stool – distinguishes colonization from active infection
- ELISA: detects toxins A and B
- Latex agglutination test – detects presence of glutamate dehydrogenase, produced by C.difficile
- Stool culture: cannot distinguish colonization (non-toxic strains) from active infection, Robertson-cooked media
- NAATs: detection of C.difficile genes
- How is CDI treated
- D**iscontinue the precipitating antibiotic (**lincosamides are mostly blamed)
- Antibiotic of choice
- Metronidazole
- Oral vancomycin
- Fidaxomicin
- Fecal microbiota transpantation may be indicated in recurrent CDI, severe CDI or fulminant CDI refractory to antibiotic therapy
- Surgical intervention may be necessary for critically ill patients or those with complications necessitating surgery
- Write short notes on 4 different species in the genus clostridium under the following headings: Reservoir, Characteristics, Virulence Factors, Diseases caused
- Clostridium difficile
- Reservoir: Gastrointestinal tract
- Characteristics: Facultative pathogen
- Virulence factors: Toxin A (Enterotoxin), Toxin B (Cytotoxin), Adhesin factor, Hyaluronidase, spore formation
- Diseases: Pseudomembranous colitis, toxic megacolon and antibiotic-associated diarrhea; acute abdomen and fulminant-life threatening colitis (rare), antibiotic associated diarrhea (malaise, anorexia, and mild-moderate diarrhea occasionally with abdominal cramping),
- Lab features: Specimen (stool), Stool cytotoxin test, ELISA (detect toxins), Latex agglutination test (detect glutamate dehydrogenase), Stool cultures not useful due to non-toxigenic strains, NAAT to detect toxin genes
- Treatment: Discontinue precipitating antibiotic, oral metronidazole or vancomycin to suppress growth and toxin production, Fecal microbiota transplant
- Clostridium perfringens
- Reservoir: Soil, skin, gastrointestinal tract
- Characteristics: Club-shaped bacilli, Hemolysis double zone on BA
- Virulence factors: Alpha toxin (Lecithinase), Beta toxin, Epsilon toxin (Permease), Iota toxin, Enterotoxin (Heat-labile), spore formation, aggressins (hyaluronidase, collagenases and proteins that liquefy muscles), bursting factor, neuraminidase
- Disease: Gas gangrene (Clostridial myonecrosis), food poisoning, simple wound contamination, cellulitis, fasciitis, suppurative myositis
- Laboratory diagnosis: Specimen (Sloughs of necrotic tissue, exudate from deep area of wound, blood culture in significant septicaemia), Gram smear: GP bacilli predominant and other bacteria with lack of inflammatory cells, Incubation: anerobic, media RCM (rapid growth at 45*C), then on BA after 4-6 hours (double zone of hemolysis, inner – beta hemolysis theta toxin, outer alpha hemolysis alpha toxin), Biochemical test: ferments glucose, lactose, sucrase and maltose, production of acid and gas (H2S and nitrate to nitrite), MR positive, VP negative, indole negative, Stormy fermentation, Nagler reaction: Lecithinase (a-toxin; phospholipase) hydrolized phospholipids in egg-yolk agar around (Egg agar plate half swabbed with serotype antitoxin and dry)
- Treatment: Wound debridement, penicillin + metronidazole + aminoglycosides or clindamycin + aminoglycosides or broad spectrum antibiotics meropenem or imipenem, Hyperbaric oxygen adjuvant
- Clostridium tetani
- Reservoir: Soil
- Characteristics: Drumstick-shaped, obligate pathogen
- Virulence factors: Exotoxins: Tenospasmin, Tetanolysin
- Disease caused: Tetanus
- Clostridium botulinum
- Reservoir: Soil, intestinal tracts of birds and fish, agricultural products e.g. vegetables
- Characteristics: Club-shaped with flagellum
- Virulence factors: Botulinum toxin
- Diseases: Foodborne botulism, Infant botulism, Wound botulism
- Clostridium difficile
- Briefly describe the pathogenesis of 2 diseases caused by Clostridium spp.
- Tetanus:
- Tetanospasmin reaches CNS via retrograde axonal transport to reach Renshaw cells, Cleaves synaptobrevin (SNARE protein) preventing the release of inhibitory neurotransmitters (GABA and Glycine) from the Renshaw cells
- This causes uninhibited activation of alpha motor neurons causing spastic paralysis (muscle spasm, rigidity) and autonomic instability
- Botulism:
- Botulinum toxin cleaves SNARE proteins, preventing the fusion of transmitter containing vesicles with the presynaptic membrane
- This inhibits acetylcholine release from the presynaptic axon terminals causing Flaccid paralysis
- Pseudomembranous colitis:
- Toxin A (enterotoxin) and Toxin B (cytotoxin) cause actin depolymerization, increased epithelial permeability, apoptosis, diarrhea, and fibrinous exudate that manifests as pseudomembranes
- Gas gangrene (Clostridial myonecrosis):
- Lecithinase (a-toxin) degrades phospholipids causing myonecrosis, inhibition of leukocyte function and gas production
- Tetanus:
- List the General characteristics of Clostridium perfringens
- GP rods with blunt ends
- capsulated
- non motile
- spores- large , oval central
- Nagler reaction- action of its phospholipase on egg yolk medium
- 5 types based on toxin (A-E)
- Briefly describe the epidemiology of Clostridium perfringens
- Type A is commonly found in the GIT of man and animals.
- Type A is also Widely distributed in nature.
- It Causes soft tissue infections, food poisoning, necrotizing enteritis, and septicemia
- Type B-E do not survive in soil but colonize GIT of animals and sometimes, man
- List the biochemical properties of Clostridium perfringens both saccharolytic and proteolytic
- List the virulence factors of Clostridium perfringens
- Spore formation
- Aggressins (Hyaluronidase, collagenase, proteins that liquefy muscles)
- Enterotoxin (food contaminating strains)
- Exotoxins:
- alpha toxin (Lecithinase): lyses all blood cells and endothelia
- beta toxin: causes intestinal stasis, loss of mucosa by necrosis and progression to necrotizing enteritis
- epsilon toxin (permease): activated by trypsin
- iota toxin: produced by type E. necrotic activity
- List the clinical diseases caused by Clostridium perfringens
- Gas gangrene: extensive muscle necrosis, dishwater must odor fluid, crepitations, shock and renal failure. NO INFLAMMATORY CELLS
- Food poisoning: self limited. Caused by enterotoxin produced by type A
- Necrotizing enteritis: Commonly of the jejunum. Caused by beta toxin produced by type C
- Puerperal sepsis
- List the laboratory features of Clostridium perfringens
- Specimen- necrotic tissue, deep wound swabs, blood, faces/cont. food
- Gram smear- GP bacilli with NO inflammatory cells
- Culture – on Robertson’s Cooked Meat agar then BA
- Biochemical tests– ferments lactose
- Nagler reaction
- How is gas gangrene treated
- wound debridement
- high dose antobiotics
- hyperbaric oxygen- controversial
Compare and contrast the paralysis caused by Clostridium botulinum and Clostridium tetani
| Tetanus | Botulism | |
|---|---|---|
| Toxin | Tetanospasmin and tetanolysin | Botulinum toxin |
| MOA | Cleaves SNARE proteins in Renshaw cells to cause unhibited a-motor neuron contraction | Cleaves SNARE proteins in a-motor neurons to inhibit ACh release |
| Type of paralysis | Spastic paralysis | Flaccid paralysis |
| Other features | Trismus, Risus sardonicus, opishtotonus | Floppy baby syndrome, Xerostomia, Mydriasis, Vomiting |
| Treatment | Antibiotics and wound debridement | IV human botulism immune globulin (BIG-IV) |
| Prevention | IM human tetanus immunoglobulin and Tetanus-containing vaccines (DPT, Tdap, DTap, DT) | Boil food twice, avoid exposure |
Compare and contrast food poisoning caused by gram-positive spore forming rods
| Clostridium perfringens | Clostridium botulinum | Bacillus cereus | |
|---|---|---|---|
| Toxin | Heat-labile Enterotoxin (CPE) | Botulinum toxins | Cereulide (Enterotoxin I – emetic; Enterotoxin II – non-emetic) |
| Incubation period | 8-12 hours | 12 – 36 hours | Emetic 30 min – 6 hours; Diarrhea 6 – 15 hours |
| Pathogenesis | Marked hypersecretion | Cleaves SNARE proteins | Stimulates emesis, Hypersecretion |
| Symptoms | Watery diarrhea | Constipation, Nausea, Vomiting | Watery diarrhea, Nausea, Vomiting |
| Treatment | Supportive | Horse-derived heptavalent botulism antitoxin; Boil food twice before canning | Supportive |
- Describe the principles and associated organisms for: Ascoli’s Thermoprecipitation test, Gel liquefaction, Nagler’s reaction,
- Ascoli’s thermoprecipitation test:
- Bacillus anthracis
- Tissue is ground and boiled for 5 minutes, filtered, and the extract layered over anti-anthrax serum in a narrow tube
- A ring of precipitate appears at the junction of the 2 liquids within 5 minutes, indicating a positive test
- Gel liquefaction test
- Bacillus anthracis
- Bacillus anthracis liquefies gelatin along and out of the line of inoculation, forming a treelike pattern
- Nagler’s reaction
- Clostridium perfringens
- AKA Lethicinase
- Performed on egg yolk agar plate. It is half swabbbed with a-toxin antitoxin, and the other half is left dry. The whole plate is streaked with isolated perfringens and incubated for 24-48h.
- The egg yolk on the dry half of plate is hydrolyzed, while the half with a-toxin antitoxin inhibits hydrolysis
- Ascoli’s thermoprecipitation test:
Corynebacterium
- List the characteristics ofCorynebacteria
- Gram positive bacilli with swollen ends
- Associated with leathery pharyngeal membrane (’Korynee’ – club and ‘diptheria’ – leather hide)
- Exhibit pleomorphism
- Non-spore forming
- Non-motile
- Non-spore forming
- Irregular staining due to cell wall structure (are gram positive in general though)
- 46 species of medical importance is Corynebacterium diptheriae
- Others are collectvely called Diptheroids: C.ulcerans, C.pseudotuberculosis, C.jeikeium
- Aerobic and facultative anerobes
- Catalase positive
- Arranged in: Angled pairs or Parrallel rows/ palisade arrangement (a + b together in one field – chinese alphabet)
- Due to incomplete separation of daughter cells during dividion when the organism is grown on inadequate media e.g. Loeffler’s coagulated serum
- Need Biotin to grow
- Due to incomplete separation of daughter cells during dividion when the organism is grown on inadequate media e.g. Loeffler’s coagulated serum
- Historically cultured on Loeffler’s medium
- Culturedd on BA or Cysteine-terullite media – Black/grey colonies after 24 – 48 hours
- Best growth in blood /serum containing medium at 35-37*C with or without CO2 enrichment
- Irregular shaped, club shaped or V-shaped arrangement
- Cytoplasmic (Metachromatic, Volutin or Babes Ernst) granules – stain blue, tend to be polar (Albert, Neisser or Ponder stain) – the granules store metabolites (phosphates) required by Corynebacterium – polyphosphate
- Gram stain easily decolorized especially in older cultures
- Are resistant to drying, susceptible to heat and regular disinfectants
- What are the Corynebacterium biotypes based on effects of toxin, clonal morphology and biochemical reactions
- Gravis (short)
- Severe effects and clinical features
- Large, irregular and gray colonies
- Pleomorphism+
- Intermedius (short to long)
- Small, flat and gray colonies
- Mitis (Long curved bacilli)
- Causes most disease
- Small round convex black colonies
- Pleomorphism ****
- Belfanti
- Used mainly for epidemiological classification of isolates
- Rare
- Cannot produce exotoxin
- Gravis (short)
- Briefly describe Diphtheria
- Acute infectious disease, occurring in epidemics
- Main group affected are children (Source = nasal carrier or patients) – pattern changing due to vaccines
- Largest epidemic was in the USSR
- Transmission: secretions/droplets from URT to URT , rare entry via contact with open sores/clothes, genital tract or eye
- Initial features confined to URT/Oropharynx – go down to the larynx and trachea
- Infection of mucous membrane
- Local invasion and multiplication at the mucosal surface
- Toxic production at the site
- Inflammatory response
- Pharyngitis with pseudomembranes in the throat**:** exudates, EBCs, RBCs, epithelial cells, bacteria, fibrin in the throat
- Bullneck diptheria (Severe lymphadenopathy): involvement of nasal mucosa and soft palate causing the anterior cervical lymph nodes to enlarge
- Diphtheric skin lesions is the cutaneous forms of the disease
- Toxin spread is mediated by tissue destruction via lymphatics and blood vessels (Toxemia)
- Rare bacteremia to cause septicemia
- Effects are due to toxins, C. diphtheria does not penetrate into tissues below the mucus membrane
- Non-toxigenic strains are associated with pharyngitis, cutaneous abscesses
- Uncommon systemic diseases include endocarditis and osteomyelitis
- What are the Complications and other toxic effects of Diphtheria
- Airway obstruction – due to laryngeal involvement
- Organ involvement – via toxemia
- Myocardial damage (cardiotoxic) – Main complication (2/3 of patients)
- Circulatory collapse, heart failure, AV blocks, and dysrhytmias
- Peripheral nerve degeneration (neurotoxic) – Difficulty swallowing and nasal regurgitation of fluids due to paralysis of palatine and ciliary muscles
- Visual disturbance, dysphagia, and paralysis of arms/legs resolve spontaneously
- Damage to adrenal gland, liver, kidney, encephalitis, cerebral infarction, pulmonary embolism
- Most frequent cause of death is airway obstruction or suffocation following aspiration of the pseudomembrane
- Myocardial damage (cardiotoxic) – Main complication (2/3 of patients)
- Briefly describe Cutaneous diphtheria
- Acquired through skin contact with other infected persons
- Colonizes skin → entry into subcutaneous tissue through skin breaks
- Papulae develop first → chronic nonhealing ulcer, sometimes covered with a grayish membrane
- Systemic toxicity is RARE – usually mixed with staphylococcus and streptococci
- Common in tropical areas
- Secondary infection of previous infection or skin abrasion
- Presents as an ulcer surrounded by erythema and covered with membrane
- What is the treatment for Diphtheria
- Specific
- Administration of Diphteria antitoxin
- Hyperimmune horse serum even (on patients with a strong clinical background only)
- IV Penicillin for 14 days OR Erythromycin, azithromycin, or clarithromyin – confirm elimination by nasopharyngeal swab – if positive add 10 days, eradicates organism eliminating toxin source
- Administration of Diphteria antitoxin
- Supportive
- Airway support
- Barrier nursing
- Specific
- How is Diphtheria prevented and controlled
- Detection and treatment of carriers and susceptible contacts: Nose + throat swabs, prophylactic antibiotics (single dose of benzylpenicillin or 7 days of erythromycin) and booster vaccination
- Isolation of infected patients
- Immunization
- DPT schedule: 6, 10 and 14 weeks of age (Pentavalent vaccine)
- One is still able to get infection from non toxigenic strains since diptheria toxoid administration only gives future protection against diptheria causing toxin and not the bacteria
- Most patients fail to develop protective antibodies after a natural infection
- DPT schedule: 6, 10 and 14 weeks of age (Pentavalent vaccine)
Listeria
- Concerning Listeria monocytogenes, list the: Mode of transmission, at risk population and the type of food associated with infection
- Transmission: Ingestion, Contact, Inhalation, Transplacental
- At risk: Pregnant women, Women (Infertility), Elderly, Immunocompromised, Infants
- Association: Delicatessen products
- Describe the Pathogenesis of Listeria monocytogenes
- Enters the cell via Internalins
- Survived via Listeriolysin O and Phospholipase C, which pierce the phagolysosome
- Replicate inside the cytoplasm
- Direct cell-cell spread via Rocktet tail (Express of ActA) – Allows Listeria to spreads without exposure to humoral immunity (antibodies and component)
- Entry into macrophages marks disseminated disease
- List the diseases caused by Listeria monocytogenes and their specific demographic
- Neonatal Listeriosis: Granulomatosis infantiseptica, Meningitis, Meningoencephalitis
- Infection in pregnant women: Spontaneous abortion
- Healthy adults: Mild gastroenteritis ****
- Immunocompromised adults: Meningitis
- Briefly describe the laboratory features of Listeria monocytogenes
- Specimen: CSF, blood and amniotic fluid, Cervical and high vaginal swabs, Neonatal meconium, Placenta, biopsies of granulomas
- Gram stain: GP short coccobacilli often confused with diptheroid, sometimes found in chains
- Tumbling motility at 25C immotile at 37C (differential motility due to temperature dependent flagella expression)
- Culture: conventional non-selective media and selective PALCAM
- BA: small grey, translucent, drop like colonies surrounded by a narrow zone of β-hemolysis
- Clear tryptose agar (Mueller Hinton Agar – MHA): pale blue-green colonies when viewed from side with a beam of white light
- Growth improves at refrigeration temperatures (cold enrichment) – delicatessen (deli) products are usually stored at 4*C
- Biochemical reactions: Ferments fructose and maltose with acid production, Catalase positive, Indole negative, Oxidase negative, Urease negative, Positive CAMP test
- What are the characteristics of Listeria monocytogenes
- Gram positive coccobacilli appearing singly, in pairs or in short chains
- Opportunistic pathogens – immunocompromised and pregnant women
- Non-capsulated
- Non-spore forming
- Aerobic and facultative anaerobe
- Facultative intracellular bacteria
- Capable of growth at broad temp range (1C-45C) and high concentration of salt
- Capable of growth at low pH
- Beta hemolysis on BA
- Catalase positive* – GBS is catalase negative
- Tumbling motility (flagellar) – GBS is not motile
- CAMP positive (Block type CAMP test reaction) – GBS more arrowhead
- How is Listeriosis treated
- Ampicillin
- Cotrimoxazole
- Cephalosporin resistance
- How is Listeriosis prevented
- Thorough cooking of food
- Washing fresh vegetables
- Avoid consumption of unpasteurized daily products
- No vaccines
- Prophylactic antibiotic
Gardnerella
- What are the characteristics of Gardnerella vaginalis
- Gram variable rod
- Facultative anaerobe
- Gram positive cell wall
- Normal vaginal flora – considered a dysbyosis when vaginal Lactobacilli decrease
- Catalase negative
- Name the disease caused by Gardnerella vaginalis and give a short description
- Bacterial Vaginosis
- Abnormal vaginal flora (Low concentration of Lactobacillus acidosis) promotes the proliferation and overgrowth of Gardnerella vaginalis and other anaerobes. There is no vaginal inflammation
- Features: gray or milky vaginal discharge with a fishy odor
- Diagnosis
- Wet preparation of a vaginal mount shows Clue cells
- Positive Whiff test
- Vaginal pH > 4.5
- Bacterial Vaginosis
Erysipelothrix rhusiopathiae
- What are the characteristics of Erysipelothrix rhusiopathiae
- Gram positive
- None-spore forming
- Slender rods
- Hair-like filaments
- Microaerophilic
- No motility – distinguished from listeria
- Catalase negative
- Produce H2S
- Human diseases is zoonotic and occupational (butchers, meat processors, farmers, poultry workers, fish handlers, vets)
- Cutaneous infection: SC inoculation via abrasion or puncture wound while handling contaminated animal products or soil
- Incidence of human disease – unknown, not reportable
- On tonsils of GIT of many wild and domestic animals (mammals, birds, fish)
- High in swine and turkey
- Can survive in soil for months to year
- Resistant to high concentrations of salt, pickling and smoking
- What are the clinical diseases caused by Erysipeloxis
- Erysipeloid
- Not to be confused with streptococcal erysipelas
- Violaceous lesion with raised edge: 2 to 7 days after trauma, on finger or hands
- Spreads peripherally as central discolourization fades
- Painful, pruritic – burning or throbbing sensation
- Suppuration is uncommon (Important distinction from a streptococcal infection)
- Generalized cutaneous disease
- Septicaemia: endocarditis, osteomyelitis, meningitis , arthritis, lymphopharyngitis, lymphadenitis
- Erysipeloid
- Describe the laboratory diagnosis of Erysipeloid
- Sample: Deep aspirate or full-thickness biopsy specimens
- Gram stain: typically negative, presence of thin gram positive rods associated with characteristic lesion and clinical history is diagnostic
- Growth on most conventional lab media in 5% to 10% CO2 (Slow-growth read of 3 to more days)
- Absence of motility and catalase production distinguished from Listeria
- Produces H2S on TSI
- Catalase negative
- Oxidase negative
- Indole negative (Distinguishes it from Enterobacteriaceae)
- Vogues-Proskauer negative (Distinguishes it from Enterobacteriaceae)
- Methyl red negative (Distinguishes it from Enterobacteriaceae)
- Serology not useful
- Produces black colonies on terullite agar like corynebacteria
- convex translucent colonies surrounded by a variable zone of alpha hemolysis
- Positive gram stain with hair-like filament production
- How is Erysipeloid treated, prevented and controlled
- Penicillin
- Cephalosporin, Carbapenems, fluoroquinolones and clindamycin
- Use of gloves and other protective equipment for workers
Cutibacterium
- Describe the sites, group of patients, pathogenesis, clinical features, and treatment ofCutibacterium acnes infection
- Formerly propionibacterium
- Sites found: skin, conjunctiva, external ear, oropharynx, female genital tract
- Common patients: teenagers and yound adults
- Clinical diseases: acne vulgaris, endodontic abscesses, lacrimal canaliculitis
- Pathogenesis: Stimulates local inflammatory reaction: production of Low Molecular Weight peptides in sebacious follicles → neutrophil infiltration → phagocytosis → release of bacterial hydrolytic enzymes
- Culture: Grown on common media (2-5 days for colonies), contaminates blood cultures
- Treatment: acne unreleated to skin cleansing (lesions within sebaceous follicles), managed by topical application of benzoyl peroxide, antibiotics (erythromycin, clindamycin)