Microbiology: Gram-Positive Bacilli Overview

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Questions and Answers

What effect does the EF (Edema factor) have on macrophages?

It enhances phagocytosis.

It directly kills macrophages.

It causes apoptosis of immune cells.

It causes local edema and interferes with phagocytosis. (correct)

Which factors contribute to the virulence of anthrax in humans?

The presence of an acid capsule and lethal factor. (correct)

Exclusively respiratory transmission.

Only through contaminated water sources.

Sporadic infections from herbivores.

What characteristic distinguishes cutaneous anthrax from other forms?

Results in the formation of black necrotic lesions. (correct)

Leads to systemic infection without local symptoms.

Is transmitted solely through water contamination.

Causes severe respiratory distress.

How was anthrax utilized as a bioterrorism weapon in 2001?

By mailing spore-tainted letters. Signup and view all the answers

In gastrointestinal anthrax, which entry portal is primarily responsible for infection?

Mouth and gastrointestinal tract. Signup and view all the answers

What conditions often predispose herbivores to anthrax infection?

Exposure to contaminated feed and soil. Signup and view all the answers

What distinguishes the eschar in cutaneous anthrax from other skin lesions?

It has a black necrotic appearance. Signup and view all the answers

What was a significant response from institutions following the bioterrorism event involving anthrax?

Implementing or modifying bioterrorism readiness plans. Signup and view all the answers

What is the primary route of bacterial exposure for Nocardia infection, particularly in immunocompromised patients?

Inhalation Signup and view all the answers

Which of the following treatments is NOT effective against Nocardia infections?

Penicillin Signup and view all the answers

Which of the following statements about Bacillus anthracis is FALSE?

It primarily causes gastrointestinal infections. Signup and view all the answers

Which characteristic is true for Bacillus species?

They can grow at temperatures as low as -5 deg C. Signup and view all the answers

In terms of bioterrorism implications, which feature makes Bacillus anthracis a significant pathogen?

It produces highly resistant spores. Signup and view all the answers

What type of anthrax infection is most commonly associated with the inhalation of spores?

Pulmonary anthrax Signup and view all the answers

What is a key differentiator of Clostridia compared to Bacillus?

Clostridia are obligate anaerobes with bulging spores. Signup and view all the answers

What is a characteristic of Bacillus anthracis's capsule?

It is composed of amino acid residues. Signup and view all the answers

Which of the following antibiotics is preferred for post-exposure prophylaxis if the strain is penicillin sensitive?

Doxycycline Signup and view all the answers

What type of food poisoning is associated with the emetic toxin from Bacillus cereus?

Ingestion of reheated rice Signup and view all the answers

Which Bacillus species is commonly used as an autoclave indicator?

Bacillus stearothermophilus Signup and view all the answers

Which symptom is a clinical feature of the diarrheal type of food poisoning caused by Bacillus cereus?

Abdominal cramps Signup and view all the answers

Which statement about Bacillus cereus is true?

It can produce both diarrheal and emetic toxins. Signup and view all the answers

What are the recommended control measures for preventing infections associated with Bacillus spp.?

Burning carcasses and the use of protective clothing Signup and view all the answers

What is the incubation period for food poisoning caused by the emetic toxin of Bacillus cereus?

1 to 6 hours Signup and view all the answers

Which Bacillus species is reported to potentially cause food poisoning bacteremia?

Bacillus pumilus Signup and view all the answers

Which condition is NOT typically caused by Bacillus cereus?

Cutaneous abscesses Signup and view all the answers

Which of the following Bacillus species is primarily a common laboratory contaminant?

Bacillus subtilis Signup and view all the answers

What is the primary mechanism of illness associated with Vibrio cholerae infections?

Production of an enterotoxin causing massive fluid loss Signup and view all the answers

Which risk factor is associated with Vibrio parahaemolyticus infections?

Ingestion of raw or undercooked shellfish Signup and view all the answers

What is the typical symptom profile for a severe Vibrio cholerae infection?

Watery diarrhea with no blood and fever Signup and view all the answers

Which preventative measure is most effective for reducing the risk of Vibrio infections?

Cooking seafood to appropriate temperatures Signup and view all the answers

What complication is associated with Hypersecretion of electrolytes and water in Vibrio cholerae infections?

Hypovolemic shock and metabolic acidosis Signup and view all the answers

What food item is most commonly implicated in Vibrio cholerae infections?

Seafood and contaminated water Signup and view all the answers

What distinguishes the diarrhea caused by non-01/non-0139 Vibrio cholerae strains?

It resembles cholera-like diarrhea but is milder Signup and view all the answers

Which of the following is recommended for preventing infections in water bodies often associated with Vibrio spp.?

Ensuring proper hygiene after accidental trauma Signup and view all the answers

What is a common characteristic of Plesiomonas shigelloides infections?

Associated with ingestion of contaminated water Signup and view all the answers

Which group is Aeromonas spp. primarily responsible for infections in?

Cold-blooded animals like fish and reptiles Signup and view all the answers

Which clinical presentation is most indicative of infections caused by Aeromonas spp.?

Symptoms resembling travelers' diarrhea Signup and view all the answers

Which culture technique is most effective for isolating Aeromonas spp. from samples?

CIN Agar with cefsulodin Signup and view all the answers

What kind of water environments are Plesiomonas shigelloides typically found in?

Freshwater, especially in warmer climates Signup and view all the answers

What laboratory feature allows for the identification of Plesiomonas shigelloides?

Form of straight, gram-negative rods Signup and view all the answers

What is the primary mode of transmission for Plesiomonas shigelloides infections?

Ingestion of contaminated food Signup and view all the answers

What is the risk factor associated with Aeromonas spp. septicemia?

Immunocompromised status Signup and view all the answers

What is the primary mode of transmission for Vibrio vulnificus infections?

Eating raw or undercooked seafood Signup and view all the answers

Which of the following laboratory tests differentiates Vibrio species based on their hemolytic properties?

Blood Agar Plate test Signup and view all the answers

Which symptom is most commonly associated with Vibrio parahaemolyticus infections?

Summer diarrhea Signup and view all the answers

What is a significant risk factor for developing infections caused by Vibrio species?

Exposure to warm coastal waters Signup and view all the answers

What phenomenon is specifically related to the pathogenicity of Vibrio parahaemolyticus?

Kanagawa phenomenon Signup and view all the answers

Which selective agar medium is most appropriate for isolating Vibrio species?

Thiosulfate Citrate Bile Salts Sucrose Agar Signup and view all the answers

Which Vibrio species is primarily known for causing serious infections in individuals with liver disease?

Vibrio vulnificus Signup and view all the answers

How can foodborne outbreaks associated with Vibrio parahaemolyticus be effectively prevented?

Proper cooking of seafood Signup and view all the answers

What is a distinguishing feature of Treponema compared to other spirochetes?

Regular and angular coiling Signup and view all the answers

Which statement accurately describes the role of ticks in the transmission of Lyme disease?

Ticks must attach for at least 24 hours to pass the disease. Signup and view all the answers

Which laboratory method is considered the preferred approach for diagnosing Lyme disease?

Serodiagnosis and antibody detection Signup and view all the answers

What clinical feature is characteristic of the second stage of Lyme disease?

Severe malaise and splenomegaly Signup and view all the answers

What is a common characteristic of Treponema observed under microscopy?

They exhibit a graceful, flexuous movement in liquid. Signup and view all the answers

During which stage of Lyme disease do the symptoms of fever and headache typically first appear?

First stage Signup and view all the answers

Which of the following antibodies develops slowly in response to Lyme disease, specifically targeting proteins such as OSp17 and p39?

IgG antibodies Signup and view all the answers

What temperature range is optimal for incubating cultures of Borrelia burgdorferi?

30-34 degrees C Signup and view all the answers

What is the primary culture media used for isolating Leptospira?

Fletcher’s Signup and view all the answers

Which characteristic is true regarding the structure of Borrelia?

It measures 0.2-0.5 micrometers in diameter. Signup and view all the answers

Which method is considered the gold standard for the serodiagnosis of Leptospira?

Microscopic Slide Agglutination Test Signup and view all the answers

Borrellia species that cause relapsing fever are primarily transmitted by which vector?

Body lice Signup and view all the answers

What is the primary antibody detected in serodiagnosis within one week after the onset of leptospirosis?

IgM Signup and view all the answers

Which virulence factor is specifically mentioned for Borrelia species?

Antigenic variation Signup and view all the answers

Leptospira cultures require which condition to minimize inhibitory effects for successful growth?

Incubation at 30°C in the dark Signup and view all the answers

What method is NOT typically used for the diagnosis of Leptospira?

Widal test Signup and view all the answers

Which characteristic is unique to Leptospira among spirochetes?

Presence of hooked ends Signup and view all the answers

What is the primary mode of reproduction for Borrelia?

Binary fission Signup and view all the answers

Which diagnostic technique is employed to visualize spirochetes that cannot be readily stained?

Dark field microscopy Signup and view all the answers

Which serovar of L. interrogans is most commonly associated with leptospirosis?

L.interrogans serovar Icterohaemorrhagiae Signup and view all the answers

What environmental exposure is primarily linked to the transmission of leptospirosis?

Contact with contaminated water Signup and view all the answers

Which of the following spirochetes is primarily free-living outside of a host?

Leptospira Signup and view all the answers

What structural feature contributes to the corkscrew-like motility of spirochetes?

Endoflagella Signup and view all the answers

Leptospirosis is commonly associated with which of the following professions?

Agricultural workers Signup and view all the answers

Which group of mycobacteria produces pigment only in the presence of light and is classified as a slow grower?

Photochromogens Signup and view all the answers

What type of tuberculosis occurs during a patient's first exposure to the bacteria?

Primary TB Signup and view all the answers

What is a key mechanism of transmission for Mycobacterium tuberculosis?

Direct contact with perspiratory droplets Signup and view all the answers

Which factor significantly contributes to the pathogenicity of Mycobacterium tuberculosis?

Ability to evade host immune responses Signup and view all the answers

Which of the following factors is NOT typically associated with a higher risk of developing tuberculosis?

Age group of 18-25 years Signup and view all the answers

What is the primary pathway through which tuberculosis is transmitted from an infected individual to another person?

Person-to-person contact via airborne droplets Signup and view all the answers

In which type of tuberculosis do latent bacteria become active and the individual begins to exhibit symptoms?

Reactivation tuberculosis Signup and view all the answers

Which of the following factors significantly contributes to the virulence of a strain of tuberculosis?

The amount of bacterial exposure Signup and view all the answers

Which risk factor is NOT associated with the progression from tuberculosis infection to active disease?

Regular exercise Signup and view all the answers

What is the site of infection for tuberculosis once airborne droplets reach the respiratory tract?

The alveoli Signup and view all the answers

Which characteristic differentiates primary tuberculosis from reactivation tuberculosis?

Latent bacteria become active due to a weakened immune response Signup and view all the answers

What is a common presentation of extrapulmonary tuberculosis (EPTB)?

Peripheral lymphadenopathy Signup and view all the answers

In the context of tuberculosis, what does the term 'miliary TB' refer to?

A disseminated form resulting in massive spread throughout the body Signup and view all the answers

Which of the following forms of tuberculosis is most commonly associated with symptoms of cough, fever, and chest pain?

Pleural tuberculosis Signup and view all the answers

What is a common risk factor that may contribute to the development of extrapulmonary tuberculosis?

Immune deficiency Signup and view all the answers

Which of the following statements accurately describes the transmission mechanisms for tuberculosis?

M. tuberculosis can be spread through respiratory droplets. Signup and view all the answers

Which type of tuberculosis is characterized by a non-productive cough and systemic symptoms like weight loss and night sweats?

Pulmonary tuberculosis Signup and view all the answers

What underlying condition is often associated with the predisposition to renal tuberculosis?

Diabetes mellitus Signup and view all the answers

What clinical manifestation indicates advanced tuberculosis infection and potential lung tissue necrosis?

Hemoptysis Signup and view all the answers

Which type of extrapulmonary tuberculosis primarily affects the lymphatic system in children?

Lymphadenitis Signup and view all the answers

Which test is commonly utilized to determine if a person has been exposed to tuberculosis?

Positive PPD Test Signup and view all the answers

Which treatment approach is typically employed for managing tuberculosis disease?

Combination of drugs for at least 6-9 months Signup and view all the answers

In which location can miliary tuberculosis manifest, affecting multiple organ systems?

Spleen, liver, lungs, and bones Signup and view all the answers

Study Notes

Gram-Positive Bacilli

Gram-positive bacilli are a diverse group of organisms found in the environment.
They rarely cause human disease but are used in industry for enzymes and antibiotics.
Some are important food spoilage organisms.

Non-Spore Forming, Non-Branching, Catalase Positive Bacilli

The following organisms are non-acid fast.
Most are part of the normal human flora.
They colonize various parts of the human body.
They are also found in the environment.
Associated with various animals.
- Corynebacteria
- Rothia
- Listeria

Corynebacteria General Characteristics

Usually found in fresh and salt water, soil, and air.
This genus includes many species of aerobic and facultative gram-positive rods.
Closely related to Mycobacteria and Nocardia regarding cell wall composition.
These organisms typically exhibit a meso-diaminopimelic acid (m-DAP) and mycolic acid cell wall.
Lipophilic Corynebacteria are considered fastidious organisms.
They may demonstrate slow growth on standard culture media.

Corynebacterium diphtheriae General Characteristics

Most notable pathogen of Corynebacteria.
Causative agent of diphtheria.
Most common sites of infection: tonsils and pharynx.
Virulence factor: Diphtheria toxin (DT).
Produced by bacteria infected with a lysogenic B-phage, which carries the tox gene.
Diphtheria toxin is heat-stable.
Composed of two fragments: Fragment A (cytotoxicity) - active fragment. Fragment B- binding fragment.
The toxin is not toxic until exposed to trypsin through trypsinization.
This inhibits protein synthesis of cells.
Enhanced considerably when grown in low iron conditions.

Clinical Infections

To cause disease, Corynebacterium diphtheriae must invade and proliferate in local tissues.
Transmitted by droplets, direct contact with cutaneous infections, and fomites.
Characterized by a lesion ranging from a simple pustule to a chronic, non-healing ulcer.
Respiratory diphtheria is pharyngitis with exudative membrane (pseudomembrane).
Pseudomembrane is gray-white and adheres to the mucous membrane.
Spread to nasal mucosa and pharyngeal wall causes neck edema.
Respiratory diphtheria can cause "bull neck" appearance, which involves swelling of lymph nodes.

Treatment

Antitoxin (commercially produced from horses) is the treatment to neutralize the toxin.
Must be administered early, as it only neutralizes circulating toxin.
Has no effect on toxin already fixed or within the cells.
Corynebacterium diphtheriae is susceptible to antimicrobials like penicillin and erythromycin.
Erythromycin is the most effective antimicrobial.

Loeffler's Methylene Blue Staining

Demonstrates the presence of metachromatic granules (Babes-Ernst or Volutin granules).
These granules take on bluish-purple in Loeffler's methylene blue stain.
Often located at the poles of the bacilli (polar bodies).
Composed of Polymetaphosphates and are more strongly gram-positive than other bacterial cells.

Biochemical Tests

Catalase positive (+)
Nitrate reduction (+)
Urease test
Beta hemolysis (variable)
Gelatin hydrolysis (-)
Esculin hydrolysis
Carbohydrate fermentation(glucose (+), maltose (+), sucrose (-))

Cultural Characteristics

Optimal growth at 37°C (15-40°C range), aerobe and facultative anaerobe.
Corynebacterium species usually grow on 5% sheep's blood and chocolate agar.
Media with enrichments (blood, serum, egg) necessary for good growth.
Selective and differential media used if diphtheria is suspected.
Usual media for diphtheria bacillus cultivation: Loeffler serum agar, CTBA, and Modified Tinsdale Agar.
Loeffler's serum agar (or Pai agar) - enriched, rapidly growing colonies that can appear small at first and become large with a distinct yellow tint after incubation.
CTBA (cystine-tellurite blood agar)- selective, differential, used to identify Corynebacterium diphtheriae.
Corynebacteria form black or brownish colonies on CTBA due to reduction of tellurite to tellurium.
Modified Tinsdale Agar - selective, differential.

Listeria General Characteristics

Gram-positive psychrotrophic bacteria found in many environmental sources.
Non-sporulating, catalase positive, indole and oxidase negative, and facultative anaerobic rods.
Show motility at 25°C.
Listeria monocytogenes is the most important species due to pathogenicity in humans and animals.
Capable of surviving within phagocytes.

Listeria Pathogenesis

Hemolysin (Listeriolysin O): major virulence factor, cytotoxic, hemolytic
Internalin (Act A): cell-surface protein that induces phagocytosis.
Phospholipase: L. monocytogenes ingested through contaminated food, producing Listeriolysin (O) and phospholipases.
These allow the organism to escape from WBCs and spread to the bloodstream.
Eventually reaches the central nervous system and placenta.

Listeria Clinical Infections

Listeriosis - infections associated with Listeria monocytogenes.
Common in pregnant women, newborns, and immunocompromised persons, usually during the 3rd trimester.
Signs include spontaneous abortion, stillborn neonates, and newborn death.
CNS infections (meningitis), endocarditis are also possible infections in immunocompromised hosts.
Healthy individuals who ingest large amounts of Listeria monocytogenes can suffer from gastroenteritis.

Listeria Laboratory Diagnosis

Microscopic: gram-positive rod or coccobacilli, singly or in chains, and tumbling motility.
Observation of motility by direct wet mount to identify the organism.
Culture: using blood, CSF, and swabs from lesions.
Listeria from body tissues and fluids (e.g., blood, CSF) can grow.

Listeria Cultural Characteristics

Optimal growth temp: 30-35°C.
Commonly used media include: SBA, chocolate agar, NAP, and Brain-Heart Infusion Agar (BHIB).
Beta-hemolytic, small, color white, smooth, and translucent colonies (1-2 days incubation).
Cold enrichment (4°C several weeks).
CAMP test (positive): "block" pattern.
Rhodococcus equi, New Oxoid Chromogenic Listeria Agar: turquoise colonies with halos.

Listeria Differentiating Characteristics

Pathogenic Listeria species: Listeria monocytogenes and Listeria ivanovii can be distinguished.
Phospholipase: can hydrolyze lecithin from the culture medium, and an opaque zone or halo forms around colonies.
Turquoise colonies with halos indicate Listeria monocytogenes.

Listeria Treatment and Prevention

Penicillin with or without aminoglycosides.
Resistant to tetracyclines.
Prevention: avoid undercooked vegetables, meat, and soft cheeses and unpasteurized dairy products.
Cook foods thoroughly and cook animal products thoroughly.

Erysipelothrix rhusiopathiae General Characteristics

Domestic swines are the major reservoir.
Found in animals (mammals, birds, fish).
Human infections are rare; associated with fish handlers, farmers, and food preparation workers.
Usual route: skin cuts and scratches.
Infections are a result of a puncture wound or skin abrasion.

Erysipelothrix rhusiopathiae Clinical Infections

Erysipeloid: localized skin infection, usually in hands or fingers, resembles streptococcal erysipelas, and is self-limiting (3-4 weeks, low incidence).
Cutaneous infection (generalized, diffuse): rare, associated with endocarditis.
Mortality rate is 38%.
Immunosuppressed patients may develop bacteremia or septicemia.

Erysipelothrix rhusiopathiae Laboratory Diagnosis

Specimens: tissue biopsy and aspirates of skin lesions.
Microscopic: gram-positive, thin, pleomorphic rods (chains), singly (V shape).

Erysipelothrix rhusiopathiae Biochemical Tests

Catalase negative, non-sporulating, non-motile.
H2S positive, urease negative.
Does not hydrolyze urea or esculin, Voges-Proskauer negative, but produce H2S and triple sugar iron agar.
Differentiates from Lactobacillus, Listeria, and Kurthia
Erysipelothrix does not grow at 4°C.
Glucose and lactose fermenter.
E. rhusiopathiae is negative. E. tonsillarum and E. inopinata are positive.

Erysipelothrix rhusiopathiae Culture

Commonly plated on sheep blood agar or chocolate blood agar; patients with sepsis may be inoculated into broth with 1% glucose, incubated in 5% CO2 at 35oC.
SBA or Chocolate agar: non-hemolytic or alpha-hemolytic, pinpoint colonies from systemic infections.

Erysipelothrix rhusiopathiae Treatment and Prevention

Susceptible to sulfonamides, trimethoprim-sulfamethoxazole.
Resistant to penicillin
Treatment options include drainage and surgery.

Lactobacillus General Characteristics

L. acidophilus, L. fermentum, L. vaginalis, L. salivarius, and L. plantarum.
Normally isolated from dairy products.
Also isolated from endocarditis cases.
Reported cases of infections (endocarditis, bacteremia) associated with immunocompromised individuals (HIV) and gastrointestinal diseases.
Important for maintaining proper pH balance in vaginal secretions.

Lactobacillus acidophilus General Characteristics

Widely distributed.
Normal flora in the human mouth, GI tract, and female genital tract (vaginal canal).
Mostly encountered as a contaminant.
Immunocompromised patients may develop bacteremia.
Microscopically: highly pleomorphic bacilli, long chaining rods, and coccobacilli.

Lactobacillus Biochemical Tests

Catalase -, oxidase -, indole -, nitrate -, hydrogen sulfide (-), and glucose, maltose, sucrose (+).
Acidic pH of vaginal secretions inhibits growth of Mobiluncus, Prevotella, Gardnerella vaginalis, and Candida albicans.

Gardnerella vaginalis General Characteristics

First described in 1953.
Normal biota in the human urogenital tract.
Naturally found in the vaginal area.
Also colonizes the distal urethra of males.
Anaerobic gram-positive rod.
Gram-positive with a thinner peptidoglycan layer than typical Gram-positive bacteria.

Gardnerella vaginalis Clinical Infection

Bacterial vaginosis (BV): characterized by an increase in vaginal pH (>4.5).
BV is one of the most common causes of vaginal discharge.
Associated with maternal and fetal morbidity during pregnancy.
Characterized by foul smelling, excessive, and purulent vaginal discharge (malodorous discharge).

Gardnerella vaginalis Laboratory Diagnosis

Specimen: vaginal discharge, isolated from urine (occasional cause of UTI).
Microscopic: short, pleomorphic gram positive rod, staining gram-variable.
Characteristic finding: presence of "clue cells."

Gardnerella vaginalis Cultural Characteristics

Can Grow on 5% sheep blood and chocolate agar.
Does not grow on MacConkey agar.

Gardnerella vaginalis Biochemical Tests

Catalase -, oxidase -, hippurate hydrolysis +.
Other tests include amine test or whiff test for odor, KOH solution as well as special selective, and differential media (HBT, cycloserine, cefoxitin, and fructose agar).
Incubation is at 35 °C, in 5-10% carbon dioxide for 24-48 hrs

Nocardia General Characteristics

Commonly found in soil.
Implicated in human infections, usually in immunocompromised patients.
Gram-positive, often with a beaded appearance, and partially acid-fast or modified acid-fast positive, catalase positive, and strictly aerobic organisms.
Produces branching filaments.
Mycolic acids are shorter chained in cell walls than mycobacteria.
Partially acid-fast (stains with carbolfuchsin).

Nocardia Clinical Infections

Pulmonary Nocardiosis: the most common clinical presentation, caused by inhalation, where it presents as chronic bronchopneumonia.
Can also be acute or relapsing in immunocompromised patients.
Cutaneous: Nocardia brasiliensis associated with primary cutaneous infections resulting from trauma.
Skin infections, skin abscesses, lymphocutaneous infection or sometimes mycetoma.
Mycetoma is a chronic, subcutaneous infection.

Nocardia Laboratory Diagnosis

Specimen: sputum (thick, purulent, and no sulfur granules).
Microscopy: branching filaments, fragmentation.
Culture: may be pigmented, chalky, matte, or velvety; also found in dry, crumbly, and breadcrumb-like appearance.
Nocardia species can grow on standard non-selective media.

Nocardia Treatment and Prevention

Drainage and surgery in some cases.
Antibiotics (sulfonamides, trimethoprim-sulfamethoxazole).
Resistant to penicillin.

Spore-Forming Gram-Positive Bacilli

Bacillus: obligate aerobes; spores are non-bulging.
Clostridia: obligate anaerobes; spores are bulging.

Bacillus General Characteristics

More than 100 species within the genus Bacillus.
It is the largest gram-positive genus.
Found widely in the environment, soil, important medically relevant organisms..
Gram-positive, or gram-variable rods, in singles or pairs.
Spores are not stained; often appear intracellular or extracellular clear oval structures like "empty spaces"
Aerobic or facultative anaerobes
Contains pathogens (Bacillus anthracis).
peritrichous flagella; causing these organisms to be motile
Except for Bacillus anthracis and Bacillus mycoides, which are non-motile organisms.
Growth temperature range: -5°C to 75°C

Bacillus, Bacillus anthracis Clinical Characteristics

Primary virulence factors are two exotoxins (e.g., edema factor, lethal factor).
Edema factor causes edema/swelling, blocks phagocytosis.
Lethal factor: kills macrophages, reducing immune defense of a host.
Capsule is unusual (composed of amino acids rather than polysaccharide). Anti-phagocytic.
Primarily a disease of herbivores.
Endemic in developing countries in Africa, Central, and South America.
Enzootic - the disease typically occurs among animals
Spores are the source of infection spread (animal-to-animal; animal-to-human/environment); these come from contaminated soil, and contaminated animal products or animal carcasses.

Bacillus anthracis Clinical Infections

Cutaneous anthrax: inoculation of endospores through skin breaks, resulting in a central black eschar (black necrotic lesion) surrounded by vesicles and an erythematous ring (malignant pustule)
Pulmonary anthrax (inhalation anthrax):
inhalation of spores.
Respiratory infections resulting from exposure to endospores during handling of animal products.
Flu-like symptoms to severe respiratory distress, dyspnea, cyanosis, pleural effusion, disorientation, and coma which can happen 24 hrs. after exposure.
Gastrointestinal anthrax: ingestion of spores in contaminated meat.
Results in abdominal pain, nausea, vomiting, and bloody diarrhea.

Bacillus anthracis Laboratory Diagnosis

Specimen collection:
- Blood, lung tissue (for pulmonary)
- Fluids under eschar lesions (for cutaneous).
Laboratory Microscopic and Cultural methods

Bacillus anthracis Treatment and Prevention

Antibiotics to treat early-recognized anthrax promptly (e.g., penicillin, ciprofloxacin).
Doxycycline can be used.
General controls: deep burial or burning of animal carcasses; animal products are autoclaved; protective clothing/gloves to handle materials.

Bacillus cereus General Characteristics

Other non-pathogenic Bacillus species
Common soil and airborne contaminant
Virulence: enterotoxins/spores
Clinical infections: common cause of food poisoning (reheated rice or potatoes-diarrheal, emetic).

Bacillus cereus Types of Toxin

Diarrheal toxin (heat-labile):
Food contamination is usually from meat, poultry, vegetables, and dried beans.
Incubation typically is 8-16 hrs.
Emetic toxin (heat-stable):
Food contamination is usually from fried rice.
Incubation typically is 1-6 hrs.

Bacillus cereus Laboratory Diagnosis

Microscopic: Gram-positive sporulating rod.
Culture: SBA, beta-hemolytic, frosted glass appearance, large gray irregular colonies.
Biochemistry test: Catalase positive, motility test (non-motile).
Identify by hemolysis on BAP, lecithinase production, string of pearl test, growth on PEA, and/or gelatin hydrolysis.

Bacillus cereus Treatment and Prevention

Food safety (preventing contamination of food items; proper food preparation/cooking times; and storage) avoidance of reheating.

Clostridium General Characteristics

Saprophytes.
Soil, freshwater, decaying matter, sewage, and other environmental sites.
Gram-positive rods (but wider than vegetative bacteria), non-motile.
Have bulging spores (subterminal position).

Clostridium botulinum General Characteristics

Strictly anaerobic, gram-positive, motile, oval, and subterminal spores.
Widely distributed saprophyte found in soils, vegetables, fruits, mud in lakes, and sea mud.
Causative agent of botulism.
Toxin production (e.g., Types A, B, E).
Spores are heat-resistant.
Improper food preservation/processing methods/heating can lead to toxin-generating organism growth.

Clostridium botulinum Clinical Infections

Infant botulism (baby syndrome): 2-6 months.
Ingesting spores in contaminated food (e.g., honey, food).
Patients do not have the ability to suck and swallow.
Characteristic signs include floppy neck, extreme weakness, and weakened voice.

Clostridium tetani General Characteristics

Strictly anaerobic, gram-positive bacilli.
Terminal, round spores.
Appear as drumsticks.
Widely distributed in soils.
Causative agent for tetanus (acute disease).
Clinical features:
Skeletal muscle spasm, autonomic nervous system disturbance.
Spores/vegetative bacteria produce tetanus toxin (tetanospasmin-neurotoxin).

Clostridium tetani Clinical Infections

Tetanus (lockjaw, trismus): skeletal muscle spasm and autonomic nervous system disturbance due to germination of spores.
Commonly is transmitted via contaminated breaks in skin by spores.

Clostridium perfringens General Characteristics

Commensal in the large intestine.
Gram-positive, non-motile, capsulated bacillus.
Subterminal, bulging spores.
Organism can multiply in tissue.
Produces gas and multiple types of toxins.

Clostridium perfringens Toxins and Clinical Infections

Food poisoning (most common), due to heat-stable enterotoxin.
Incubations typically happen 6 to 15 hrs.
Gastroenteritis (nausea, abdominal cramps, watery diarrhea).
Gas gangrene (rapidly progressing, edematous myonecrosis; associated with contaminated deep wounds/trauma).

Clostridium perfringens Laboratory Diagnosis

Microscopy: boxcar-shaped gram-positive bacilli.
Culture on sheep blood agar with double zone hemolysis (inner zone of complete hemolysis surrounded by a much wider zone of incomplete hemolysis).
The Direct Nagler Test to differentiate Clostridium perfringens.

Clostridium difficile General Characteristics

Gram-positive spore-forming bacillus
A major cause of hospital-acquired infections.
Spores are found widely in nature, particularly in hospitals.
Colonization in the colon of patients with prolonged hospital stays.
Prolonged antimicrobial use disrupts the normal colonic flora.
This increases susceptibility to C. difficile infection.

Clostridium difficile Clinical Infections

Pseudomembranous colitis (colonic disease).
Usually due to toxin-mediated pathogenesis.
Associated with prolonged, and sometimes excessive use of antimicrobial therapies.

Clostridium difficile Laboratory Diagnosis

Cultures on selective (different) media—e.g., CCFA or Cycloserine-Cefoxitin-Fructose Agar or egg yolk agar.
Lecithinase (white zone of opacity), Lipase (iridescent), and Proteolytic E (complete narrow clearing).

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Description

Explore the diverse world of Gram-positive bacilli, including their ecological roles and significance in industry. This quiz covers non-spore forming, non-branching, catalase positive bacilli, specifically focusing on Corynebacteria and their characteristics. Test your knowledge about these important microorganisms and their relation to human health.