Gram Positive Bacilli Flashcards
Bacillus anthracis
Clinical Case: A 33 year old woman presents with an ulcerous lesion on the neck. The ulcer has a blackened necrotic eschar surrounded by edema. The woman first noticed the lesion 2 weeks ago as a painful, small red macule that gradually developed into an ulcer and, over the last few days, became painless. On the occupational history, the patient reveals that she works in the imported wool and hides industry.
Structure: bacilli with prominent central or paracentral oval spores; poly d-g-glutamic acid capsule (PGA)
Reservoir: spores from goat, cow, or other herbivores
Transmission: cutaneous, inhalation, ingestion
Toxin: protective antigen (PA) binds cells membrane and mediated entry of edema factor (EF) or lethal factor (LF); edema factor (EF) increases cAMP causing edema and inhibition of PMN; lethal factor (LF) causes cell death
Disease: cutaneous –> tissue hemorrhage and necrosis –> malignant pustules –> classic black eschar; inhalation –> fever, dyspnea, nonproductive cough –> 100% mortality if not treated –> pleural fluid and wide mediastinum; ingestion –> lesions in throat, intestines –> dysentery
Diagnosis: gram positive, protein capsule, aerobic, nonmotile, catalse positive
Treatment: ciprofloxacin, parenteral penicilin G; anti-PA vaccine
Clostridium tetani
Clinical Case: A teenage girl enters the emergency room suffering painful muscle spasms. Throughout her examination, she sustains a facial sneer, a stiff arched back, and clamped palms. Her father is anxious about the fact that she has also experienced difficulty eating, probably due to a stiff jaw. The father affirms that his daughter is usually quite active and boasts how, a week ago, she continued a soccer game even after falling on a nail in the field.
Structure: bacillus with bulging spores (tennis racquet-drumstick)
Reservoir: soil
Transmission: puncture wounds –> stepping on a nail, burn wounds
Toxin: tetanus toxin (tetanospasmin) –> neurotoxin –> spores gain access to tissue (wound), germinate and release toxin –> toxin travels retrogradely on axons of peripheral motor neurons and through blood –> blocks release of inhibitory neurotransmitters, glycine and GABA –> unrestrained excitation of motor neurons –> unopposed muscle spasms and contractions –> spastic paralysis
Disease: generalized tetanus –> spasms of masseter muscle (lockjaw), spasms of facial muscles (risussardonicus), persistent muscle spasms (opisthothonus) –> drooling, sweating, irritability; localized tetanus; cephalic tetanus; neonatal tetanus
At risk: inadequate vaccine-induced immunity, neonates born to unvaccinated mothers
Diagnosis: gram positive with bulging spore (does not stain), motile, obligate anaerobes (fermentation)
Treatment: tetanus immune globulin –> antitoxin, passive immunization; debridgement of wound; metronidazole; DTaP vaccine (tetanus toxoid) –> active immunity –> boosters every 10 years
Clostridium difficile
Clinical case: An old woman comes to the doctor with a fever and loose bowels. Her diarrhea occurs in tremendous volumes, she complains, though she does not remember ever seeing blood. She has an unremarkable past medical history, except for an infection a few weeks earlier that was treated with clindamycin. Signoidoscopy of her colon reveals yellow-white plaques which the doctor predicted after analyzing her stools for toxins.
Structure: bacillus
Reservoir: soil, hospitals –> spores contaminate surfaces
Transmission: ingestion of spores, contaminated hands
Toxins: toxin A (enterotoxin) –> alters fluid secretion –> watery diarrhea; toxin B (cytotoxin) –> cytotoxic to epithelial cells –> pseudomembrane; broad-spectrum antibiotics wipe out normal flora of GI tract while organism survives through spores –> spores germinate following antibiotic treatment (clindamycin is number 1 and cephalosporins are number 2) –> rapid growth leads to disease
Diseases: mild, self-limiting diarrhea ,pseudomembranous colitis
Diagnosis: gram +, strict anaerobe, toxin B is present in stool culture, colonoscopy shows pseudomembranes (yellow-white plaques) present on the mucosa
Treatment: metronidazole or vacomycin, withdrawal of the causative antibiotic
Clostridium botulinum
Clinical case: A woman struggles into the emergency room with a marked paralysis of her upper body. She describes the paralysis as a weakness that began in her neck and spread to her arms. She also complains of blurred double vision and requests water to soothe her dry throat. Though she has no fever, she appears quite dizzy and her eyelids are drooping. The day before, she returned from a camping trip where she insists she maintained good hygiene, limiting her diet to canned foods only.
Structure: bacillus
Reservoir: soil, aquatic sediments
Transmission: ingestion (canned foods), drug users
Toxin: neurotoxin (7 types, A to G) –> coded by a prophage –> heat labile (destroyed at 60 degree C for 10 minutes) –> toxin is absorbed by the gut –> carried by peripheral nerve synapses –> blocks released of acetylcholine at the neuromuscular junction –> flaccid paralysis
Diseases: foodborne botulism –> ingestion of canned foods with spores present –> blurred vision, drooping eyelids, dry mouth, slurred speech; infant botulism (floppy baby syndrome) –> ingestion of spores, honey –> babies are lethargic, feed poorly, poor muscle tone; wound botulism –> wounds/drug users (toxin produced in vivo) –> incubation period is longer with fever present
Diagnosis: gram +, anaerobic, check for toxin in uneaten food and/or stool specimen
Treatment: ventilatory support, metronidazole or penicillin (kills the vegetative cells), antitoxin (A, B, and E toxins) –> binds and neutralizes toxin circulating in blood
Clostridium perfringens
Clinical case: A man enters the emergency rooms claiming to have been stabbed two days earlier. Muscles in his arm hurt, and on palpation small air bubbles are felt below the skin. The wound area exudes a blackish, ill-smelling fluid and generates a crackling sound when touched. The patient has a fever, a low blood pressure, marked tachycardia, and has urinated very little since his injury. The doctors decide to amputate the arm, as well as monitor the patient for shock and renal failure.
Structure: bacillus
Reservoir: soil and human colon
Transmission: foodborne, traumatic implantation
Exotoxin: alpha toxin –> lecithinase degrades lecithin in mammalian cell membranes and damages RBCs, WBCs, platelets, endothelial cells; enterotoxin –> disrupts ion transport (ileun) leading to watery diarrhea
Diseases: cellulitis –> bacteria infects anaerobic environment of necrotic skin wound –> release degradative enzymes –> slow, painless infection and gas production –> forms collection of gas under skin that crackle when touched; gas gangrene –> spores in soil –> introduced via deep muscle laceration –> grows in anaerobic environment –> gangrenous muscle –> black fluid exudate leaking from skin –> shock may follow; food poisoning –> spores in meat/poultry –> survive cooking and germinate –> contaminated food ingested –> bacteria release heat-labile enterotoxin in GI tract –> enterotoxin inhibits glucose transport, damages epithelium –> diarrhea, gastric pain, nausea (no fever or vomiting)
Diagnosis: gram positive, motile, strict anaerobes, culture on blood agar
Treatment: debridement of wounds, clindamycin and penicillin, hyperbaric oxygen to kill anaerobic organism
Clostridium diptheriae
Clinical case: A young immigrant girl goes to the doctor complaining of a sore throat and difficulties in breathing and swallowing. Her voice is unusual and a large gray mucous film is noticed on the oropharynx. The patient exhibits ST-T wave changes on an ECG and a slight paralysis of her tongue. Her blood pressure is low, her lungs edematous, and her neurological examination shows cranial nerve problems. Her physician begins immediate treatment and orders a tellurite potassium culture to confirm.
Structure: bacillus
Reservoir: humans; toxin is carried by a phage
Transmission: respiratory droplets
Disease: local - pseudomembrane, airway obstruction –> bull neck; systemic - myocarditis, polyneuritis
Toxin ADP ribosylates EF-2 and prevents protein synthesis
Diagnosis: gram positive, aerobic/facultative, Chinese letter appearance, non-motile, black colonies on potassium tellurite
Treatment: antitoxin; penicillin and erythromycin; DTaP vaccine (toxoid) –> need boosters every 10 years
Listeria monocytogenes
Clinical case: A mother brings her 2-month old infant to the hospital because he exhibits fever, convulsions, irritability and poor eating. The pediatrician notes a widespread rash and a stiff neck. A spinal tap is ordered which reveals low glucose, increased PMNs, increased protein, and gram positive rods with tumbling motility in cultures. Upon further questioning, the pediatrician discovers that the mother does not breastfeed her baby and gives him fresh cow milk.
Structure: bacilli with flagella to move
Reservoir: animals; associated with milk and milk products
Transmission: poorly pasteurized milk ingestion
Toxin: listeriolysin O
Disease: penetrates GI mucosa and invades phagocytes –> intracellular, spreads through blood –> meningitis; can be transmitted to fetus across placenta or birth canal –> meningitis
At risk: infants younger than 1 month, >60 year, pregnant women, immunocompromised
Diagnosis: gram positive, catalase positive, tumbling and jet motility, heat resistant, grows at 1 degree celcius
Treatment: penicillin with or without gentamicin; not eating uncooked foods/milk
Lactobacillus
Structure: rod-shaped
Reservoir: normal flora in vagina, GI tract
Transmission: -
Disease: dental caries in mouth because of acid production
Diagnosis: converts lactose to lactic acid, gram positive, facultative anaerobes
Maintains vaginal pH at about 4.5 to prevent yeast growth
Propionibacteria
Structure: rod-shaped
Reservoir: pacemakers, shunts, prosthetics
Transmission: contact
Disease: acne vulgaris –> hyperkeratination, sebum production
Diagnosis: synthesize propionic acid, gram positive, anaerobic, commensal
Used in cheese making –> fermentation, carbon dioxide bubbles
Erysipelothrixrhusipathiae
Structure: rod-shaped; d-ala-d-lactate in cell wall
Reservoir: animals
Transmission: fresh water fish or handling raw meat
Disease: bacteremia, sepsis, endocarditis
Diagnosis: gram positive, aerobic and anaerobic; no endotoxin
Treatment: vancomycin resistant
