A patient presents to your clinic with this painless lesion on his penis. What is the most likely diagnosis?
What medication should be given for prophylaxis after a close contact is infected with the organism shown?
A 25-year-old woman presents with vaginal discharge that looks like this on microscopy. What is your diagnosis and treatment plan?
Gardnerella vaginalis infection; treatment with metronidazole
What type of organisms stain purple/blue with Gram staining?
Gram-positive organisms are commonly classified into which two shapes?
Cocci or rods (bacilli)
Name four gram-positive rods.
Clostridium, Listeria, Bacillus, and Corynebacterium
Name one gram-positive anaerobic rod.
Staphylococcus and Streptococcus are differentiated by which enzyme?
Catalase; Staphylococcus is catalase positive, and Streptococcus is catalase negative
Which gram-positive cocci are found in clusters?
Which gram-positive cocci are found in chains?
What differentiates Staphylococcus aureus from and other staph species?
Other staph species are coagulase negative
Name two coagulase-negative Staphylococcus species.
Staphylococcus saprophyticus and Staphylococcus epidermidis
Which Staphylococcus species is novobiocin sensitive?
Which Staphylococcus species is novobiocin resistant?
If agar shows clear hemolysis, which Streptococcus species could be present?
Streptococcus pyogenes or Streptococcus agalactiae
What type of hemolysis do both group A and group B streptococci have in common?
Streptococcus pyogenes is a type of group _____ Streptococcus, whereas Streptococcus agalactiae is a type of group _____ Streptococcus.
How are -hemolytic streptococci differentiated from each other?
By their bacitracin sensitivity (Streptococcus pyogenes is sensitive, Streptococcus agalactiae is resistant)
Name two streptococci that are -hemolytic.
Enterococcus and Peptostreptococcus (anaerobic)
True or False: Enterococcus faecalis is a -hemolytic, gram-positive, catalase-negative cocci.
Which -hemolytic streptococcal species is bacitracin resistant?
Group B Streptococcus (Streptococcus agalactiae)
Which -hemolytic streptococcal species is bacitracin sensitive?
Group A Streptococcus (Streptococcus pyogenes)
Staphylococcus saprophyticus is novobiocin _____ (resistant, sensitive); staphylococcus epidermidis is novobiocin _____ (resistant, sensitive).
Resistant; sensitive (remember: On the staph retreat there was NO StRES; Novobiocin: Saprophyticus Resistant, Epidermidis Sensitive)
Group A streptococci are bacitracin _____ (resistant, sensitive); group B streptococci are bacitracin _____ (resistant, sensitive).
Sensitive; resistant (remember: Bacitracin: group B are Resistant, whereas group A are Sensitive (B-BRAS)
Streptococcus viridans is optochin _____ (resistant, sensitive); streptococcus pneumoniae is optochin _____ (resistant, sensitive).
Resistant; sensitive (remember, Optochin: Viridans Resistant and Pneumonia Sensitive; OVRPS- overpass)
What bacterial enzyme degrades hydrogen peroxide?
What antimicrobial product produced by polymorphonuclear lymphocytes is a substrate for myeloperoxidase?
Which gram-positive cocci are catalase positive?
What differentiates Staphylococcus aureus from Staphylococcus epidermidis and Staphylococcus saprophyticus?
Coagulase (Staphylococcus aureus is coagulase positive)
Why do people with chronic granulomatous disease (nicotinamide adenine dinucleotide phosphate oxidase deficiency) get recurrent infections by catalase-producing organisms?
Bacterial catalase easily degrades the little hydrogen peroxide produced, compromising the ability of neutrophils to kill bacteria
What is the function of Protein A, a Staphylococcus aureus virulence factor?
Binding to fragment crystallizable region-immunoglobulin G, to inhibit complement fixation and phagocytosis
Name five types of infections caused by Staphylococcus aureus.
Skin infections, organ abscesses, pneumonia, acute bacterial endocarditis, and osteomyelitis
Staphylococcus aureus can cause which toxin-mediated conditions?
Toxic shock syndrome (toxic shock syndrome toxin 1), scalded skin syndrome (exfoliative toxin), and rapid-onset food poisoning (enterotoxins)
Which organism produces toxic shock syndrome toxin 1?
What is the pathophysiology of toxic shock syndrome?
Toxic shock syndrome toxin 1 acts as a superantigen and causes widespread release of cytokines from T cells
Staphylococcus aureus can cause rapid-onset food poisoning as a result of what product?
Methicillin-resistant Staphylococcus aureus is resistant to methicillin because of its altered structure of what protein?
What bacterium found in normal skin flora commonly contaminates blood cultures and infects prosthetic devices and catheters?
How does Staphylococcus epidermis infect prosthetic devices and intravenous catheters?
By producing adherent biofilms
What four common infections does Staphylococcus pneumoniae cause?
Meningitis, Otitis media, Pneumonia, and Sinusitis (remember: MOPS are Most OPtochin Sensitive)
What is distinct about the pneumonia caused by pneumococcus?
Streptococcus pneumoniae sepsis occurs at a higher rate in what two patient populations?
Sickle cell anemia and asplenic patients
Name two ways Streptococcus pneumoniae evades the immune system.
Immunoglobulin A protease, encapsulation
What three pyogenic infections does Streptococcus pyogenes cause?
Pharyngitis, cellulitis, and impetigo
What two toxigenic diseases does Streptococcus pyogenes cause?
Scarlet fever and toxic shock syndrome
What two immunologic conditions does Streptococcus pyogenes cause?
Rheumatic fever and glomerulonephritis (remember: PHaryngitis gives you rheumatic "PHever" and glomerulonePHitis)
Streptococcus pyogenes is associated with what three major classes of disease?
Infectious, immunogenic, and toxigenic
Human antibodies to Streptococcus M protein enhance host defenses but increase the risk for which complication of streptococcal infection?
Rheumatic heart disease
What blood test would detect a recent Streptococcus pyogenes infection?
An antistreptolysin O titer
Rheumatic fever is associated with what five symptoms?
Subcutaneous nodules, Polyarthritis, Erythema marginatum, Chorea, and Carditis (remember, there is no "RHEUM" for SPECCulation)
Streptococcus agalactiae are bacitracin _____ (sensitive/resistant) and _____(//) -hemolytic.
In what population does group B Streptococcus (Streptococcus agalactiae) cause pneumonia, meningitis, and sepsis?
Babies (remember: B for Babies)
What two infections do enterococci cause?
Urinary tract infection and subacute bacterial endocarditis
How can group D enterococci be differentiated from nonenterococcal group D streptococci by lab testing?
Enterococci can grow in 6.5% sodium chloride, other group D streptococci cannot
Lancefield grouping is based on differences in what components of the bacteria?
C carbohydrate on the bacterial cell wall
True or False? Penicillin G is effective treatment against enterococci.
False; enterococci are resistant to penicillin G
Enterococci resistant to which antibiotic are an important source of nosocomial infection?
What two infections does Streptococcus bovis cause in colon cancer patients?
Bacteremia and subacute endocarditis
A young patient presents with pseudomembranous pharyngitis; what medium could be used to culture the most likely etiologic agent?
Corynebacterium diphtheriae grows on tellurite agar (coryne = club shaped)
The symptoms of diphtheria are caused by what kind of toxin?
Exotoxin (encoded on the -prophage)
How does diphtheria toxin inhibit protein synthesis?
By the adenosine diphosphate ribosylation of elongation factor 2
What disease is caused by Corynebacterium diphtheriae?
Diphtheria; characterized by pseudomembranous pharyngitis (grayish-white membrane) with lymphadenopathy
How is a laboratory diagnosis of diphtheria made based on microscopic appearance?
The presence of gram-positive rods with metachromatic granules (blue and red in color)
How can diphtheria be prevented?
Toxoid vaccine; usually administered in combination with tetanus vaccine
What type of bacteria form spores?
What advantages do bacteria gain by taking the form of a spore?
They become highly resistant to destruction by heat and chemicals and require no metabolic activity in nutrient-poor settings
Why is it important to autoclave surgical equipment?
To kill bacterial spores
What five soil-dwelling, gram-positive rods are spore formers?
Bacillus anthracis, Bacillus cereus, Clostridium perfringens, Clostridium botulinum, and Clostridium tetani
Which bacteria are gram-positive, spore-forming, obligate anaerobic bacilli?
Name four clostridia species that produce exotoxins.
Clostridium tetani, Clostridium botulism, Clostridium perfringens and Clostridium difficile
What kind of toxin produced by Clostridium tetani causes symptoms of tetanus?
An exotoxin called tetanospasmin
Describe the pathogenesis of the symptoms caused by Clostridium tetani?
Clostridium tetani toxins block glycine (an inhibitory neurotransmitter) release from Renshaw cells in the spinal cord, leading to spastic paralysis, lockjaw (trismus), and risus sardonicus (remember: TETanus is TETanic paralysis)
Which gram-positive bacilli are responsible for the flaccid paralysis caused by exposure to improperly canned foods?
Clostridium botulinum (remember: BOTulinum is from bad BOTtles of food)
What are the characteristics of the toxin produced by Clostridium botulinum?
Preformed, heat-labile toxin
What is the predominant symptom of botulism?
How does the toxin produced by Clostridium botulinum cause flaccid paralysis?
It inhibits acetylcholine release
How does the pathogenesis of botulism differ between adults and babies?
Adults consume preformed toxin whereas babies consume spores in honey (floppy baby syndrome)
Which exotoxin-producing, gram-positive bacillus is responsible for gas gangrene?
Clostridium perfringens (remember: PERFringens PERForates a gangrenous leg)
What is the effect of the toxin produced by Clostridium perfringens?
Toxin (lecithinase) causes myonecrosis, gas gangrene, and hemolysis
Which gram-positive bacillus is responsible for pseudomembranous colitis?
Clostridium difficile (remember: DIfficile causes DIarrhea)
Pseudomembranous colitis often follows a course of which antibiotics?
Clindamycin or ampicillin
What kind of toxin is produced by Clostridium difficile?
A cytotoxin, which is an exotoxin that kills enterocytes and causes pseudomembranous colitis
What is the treatment of choice for pseudomembranous colitis caused by Clostridium difficile?
What gram-positive, spore-forming rod that produces a toxin causes a respiratory illness that is associated with black skin lesions and exposure to animal hides and fur?
Bacillus anthracis toxin causes what kind of skin lesion?
Black skin lesions (painless eschars, necrosis) surrounded by edematous ring
The skin changes of cutaneous anthrax are caused by which two toxins?
Lethal factor and edema factor cause a black eschar with surrounding edema at the site of inoculation
The inhalation of Bacillus anthracis spores leads to which symptoms?
Flu-like symptoms that rapidly progress to fever, mediastinitis, pulmonary hemorrhage, and shock
What are the two modes of anthrax inoculation?
Cutaneous and pulmonary
What is Woolsorters disease?
Pulmonary infection of Bacillus anthracis due to inhalation of spores from contaminated wool
How is the capsule produced by Bacillus anthracis unique?
It is the only bacterium to have a polypeptide capsule (contains D-glutamate)
What diseases does Listeria monocytogenes cause in pregnant women?
Amnionitis, septicemia, and spontaneous abortions
How does the disease caused by Listeria monocytogenes differ among adults, neonates, and immunocompromised individuals?
In healthy individuals it causes a mild gastroenteritis but can cause meningitis in neonates and immunocompromised patients
How is Listeria monocytogenes acquired?
By ingestion of unpasteurized milk, cheese, or deli meats or by vaginal transmission during birth
How does Listeria monocytogenes move from cell to cell?
Listeria is an intracellular organism that induces "actin rockets" to move into new cells
Listeria monocytogenes has what identifying characteristic on microscopy?
What distinguishes Listeria monocytogenes from all other gram-positive bacteria?
It is the only gram-positive bacterium to have an endotoxin
Which two bacteria are gram-positive rods that form long-branching filaments that resemble fungi?
Actinomyces israelii and Nocardia asteroides
Which is an anaerobe: Actinomyces israelii or Nocardia asteroides?
Which is a weakly acid-fast aerobe in soil: Actinomyces israelii or Nocardia asteroides?
Describe the lesions caused by Actinomyces israelii.
Oral/facial abscesses that may drain through sinus tracts
True or False? Actinomyces are part of the normal oral flora.
What type of disease does Nocardia asteroides cause in immunocompromised individuals?
How are infections with Actinomyces israelii and Nocardia asteroides treated?
SNAP: Sulfa for Nocardia; for Actinomyces, use Penicillin
What is a characteristic finding in the draining sinuses caused by Actinomyces israelii infection?
Yellow "sulfur granules"
What two mycobacteria species are often resistant to multiple drugs?
Mycobacterium tuberculosis and Mycobacterium avium-intracellulare
What symptoms are caused by Mycobacterium kansasii?
Pulmonary tuberculosis-like symptoms
Infection with Mycobacterium avium-intracellulare is symptomatic in which patient group?
Patients with AIDS
What are the symptoms of tuberculosis?
Fever, night sweats, weight loss, and hemoptysis
Describe the leonine facies of leprosy caused by Mycobacterium leprae.
Loss of eyebrows, nasal collapse, and lumpy earlobe
What is another name for leprosy?
The organism that causes leprosy has what animal reservoir in the United States?
Because Mycobacterium leprae likes cool temperatures, it tends to infect what areas of the body?
The skin and the superficial nerves
What is the treatment of choice for leprosy?
Long-term oral dapsone
What toxicity is associated with long-term oral dapsone treatment?
Hemolysis and methemoglobinemia
What are two alternative treatment options for leprosy?
Rifampin and the combination of clofazimine and dapsone
What are the two forms of Hansens disease?
Lepromatous and tuberculoid
Which of the two forms of leprosy indicates failed cell-mediated immunity and has a worse prognosis?
Lepromatous = Lethal
Which of the two forms of leprosy is self-limited?
True or False? Mycobacterium leprae can be grown in vitro.
How can the skin lesions of lepromatous and tuberculoid leprosy be differentiated?
Lepromatous skin lesions present diffusely over the skin and are communicable (failed cell-mediated immunity) whereas tuberculoid skin lesions are limited to a few hypoesthetic nodules
Gram-negative organisms can be classified into what three shapes?
Cocci, coccoid rods, and rods
Name four organisms that are gram-negative, coccoid rods.
Haemophilus influenzae, Bordetella pertussis, Pasteurella, and Brucella
What is a common source of Pasteurella infections?
Name two gram-negative cocci.
Neisseria meningitidis and Neisseria gonorrhoeae
How are the two gram-negative cocci differentiated from each other?
By maltose fermentation (Neisseria meningitidis is a maltose fermenter; Neisseria gonorrhoeae is not)
Gram-negative rods are differentiated by the fermentation of what substance?
Name three fast lactose-fermenting, gram-negative rods.
Klebsiella, Escherichia coli, and Enterobacter
Name two slow lactose-fermenting, gram-negative rods.
Citrobacter and Serratia
Among nonlactose fermenters, the presence of what substance can be used to differentiate Pseudomonas from Shigella, Salmonella, and Proteus?
Oxidase (Pseudomonas is oxidase positive, Shigella, Salmonella, and Proteus are oxidase negative)
What type of bacteria grows pink colonies on MacConkeys agar?
Lactose-fermenting enteric bacteria
Name five bacteria that grow pink colonies on MacConkeys agar.
Citrobacter, Klebsiella, Escherichia coli, Enterobacter, and Serratia (remember: test with MacConKEES)
True or False? Gram-negative organisms are resistant to penicillin and all of its derivatives.
False; some gram-negative organisms are susceptible to penicillin derivatives such as ampicillin
What part of gram-negative organisms inhibits the entry of penicillin G and vancomycin?
The outer membrane
Neisseria meningitides _____ (does/does not) have a polysaccharide capsule; Neisseria gonorrhea _____ (does/does not) have a polysaccharide capsule.
Does; does not
Neisseria meningitides _____ (does/does not) have a vaccine; Neisseria gonorrhea _____ (does/does not) have a vaccine.
Does; does not
Neisseria meningitides _____ (does/does not) ferment lactose; Neisseria gonorrhea_____ (does/does not) ferment lactose.
Does; does not
What five types of infection can Neisseria gonorrhea cause?
Gonorrhea, pelvic inflammatory disease, septic arthritis, Fitz-Hugh-Curtis syndrome, and neonatal conjunctivitis
What three clinical syndromes can Neisseria meningitides cause?
Septicemia, meningitis, and Waterhouse-Friderichsen syndrome
How is Neisseria gonorrhoeae transmitted?
How is Neisseria meningitidis transmitted?
Respiratory and oral secretions
Why can a vaccine to Neisseria gonorrhea not be created?
Rapid antigenic variation
Name four diseases that can be caused by Haemophilus influenzae.
Epiglottitis, Meningitis, Otitis media. and Pneumonia (remember: HaEMOPhilus)
What is the method of transmission of Haemophilus influenzae?
Which type of Haemophilus influenzae causes the most invasive disease?
Capsular type B
Escherichia coli, Salmonella, Shigella, Klebsiella, Enterobacter, Serratia, and Proteus belong to which bacterial family?
All species in the enterobacteriaceae have what type of antigen?
Somatic (O) antigen, which is the endotoxin polysaccharide
All enterobacteriaceae species ferment _____ and are oxidase _____.
What is the somatic (O) antigen?
The polysaccharide of endotoxin
What does the capsular (K) antigen tell you about the enterobacteriaceae species?
Certain K antigens are correlated with more virulent species
Motile enterobacteriaceae species have what type of antigen?
Flagellar (H) antigen
Aside from diarrhea/dysentery, what diseases does Escherichia coli commonly cause?
Cystitis, pyelonephritis, pneumonia, neonatal meningitis, and septic shock
What three types of Escherichia coli do not invade the intestinal mucosa?
Enterohemorrhagic, enterotoxigenic, enteropathogenic; only enteroinvasive Escherichia coli invades the mucosa
Which Escherichia coli species produces shiga-like toxin?
Enteroinvasive and enterohemorrhagic Escherichia coli
What differentiates the disease caused by enteroinvasive Escherichia coli and enterohemorrhagic Escherichia coli?
Both cause dysentery, but with enteroinvasive, both the toxin and the microbe cause necrosis and inflammation; with enterohemorrhagic, only the toxin does
Which toxins mediate the diarrhea caused by enterotoxigenic Escherichia coli?
Labile toxin/stable toxin
What disease is caused by enterotoxigenic Escherichia coli?
How does enteropathogenic Escherichia coli cause diarrhea?
It adheres to the apical surface, flattens villi, decreasing absorption (this is NOT toxin mediated)
What population tends to get diarrhea following enteropathogenic Escherichia coli infection?
What potentially fatal systemic complication can be caused by enterohemorrhagic Escherichia coli infection?
Hemolytic uremic syndrome
A seven-year-old child has a burger at a barbeque and subsequently develops diarrhea. He then ceases urinating, becomes lethargic, and is found to have low red blood cell and platelet counts. What is your diagnosis?
Hemolytic uremic syndrome secondary to infection with enterohemorrhagic Escherichia coli
What is the pathophysiology of hemolytic uremic syndrome?
Endothelial swelling and narrowing leads to mechanical hemolysis (anemia) and reduced renal blood flow (acute renal failure), with damaged endothelium consuming platelets (thrombocytopenia)
What bacteria classically causes "red currant jelly" sputum in a patient with pneumonia?
An alcoholic man is admitted to the hospital with fever, dyspnea and is coughing up gelatinous red sputum. Chest x-ray is consistent with an abscess. What infection do you suspect?
Klebsiella (remember the "4 As": Abscess, Alcoholic, Aspiration, and diAbetics)
Klebsiella is a cause of what other nosocomial infection in addition to pneumonia?
Urinary tract infection
What do Salmonella and Shigella have in common?
They are both nonlactose-fermenting bacteria that invade the intestinal mucosa causing bloody diarrhea
Which of the following is motile and can disseminate hematogenously: Salmonella or Shigella?
How does Shigella propel itself within the cell?
By actin polymerization
Which antibiotics should be used to treat salmonellosis?
Salmonellosis should not be treated with antibiotics; doing so can prolong symptoms
Which leukocyte response is seen in salmonellosis?
Which is more virulent: Salmonella or Shigella?
Shigella (101 Shigella organisms vs 105 Salmonella organisms)
Which has an animal reservoir: Salmonella or Shigella?
Salmonella (except Salmonella typhi, which is only found in humans); Salmonella is often acquired from reptiles and poultry
What are the modes of transmission of Shigella?
The "4 Fs": Food, Fingers, Feces, and Flies
A woman presents to the clinic with fever, diarrhea, headache, and rose spots on her abdomen. What is the likely diagnosis?
The woman has typhoid fever caused by Salmonella typhi
Chronic carriers of Salmonella harbor the bacteria where in their bodies?
What mode of propulsion do Salmonella use to disseminate?
What are the usual modes of transmission of Yersinia enterocolitica?
Pet feces (eg, puppies) and contaminated milk or pork
Yersinia enterocolitica outbreaks are common in what setting?
Yersinia enterocolitica infections can mimic what other diseases, particularly in teenagers?
Crohns disease or appendicitis
Heliobacter pylori causes what two pathologies in the gastrointestinal tract?
Duodenal ulcers and gastritis
Heliobacter pylori is a urease _____ (positive/negative), gram _____ (positive/negative) _____ (rod/cocci).
Urease-positive, gram-negative rod
What enzyme in Helicobacter pylori helps to create an alkaline environment?
Heliobacter pylori is a risk factor for what two cancers?
Gastric adenocarcinoma and lymphoma
A patient with a chronic ulcer is found to have a positive urease breath test. How would you treat the patient?
Triple therapy: (1) Bismuth, metronidazole, and either tetracycline or amoxicillin; or (2) (more costly) metronidazole, omeprazole, and clarithromycin
What are the three spirochete species that most commonly affect humans?
Borrelia (Big size), Leptospira, and Treponema (remember: BLT)
What is the only spirochete that can be visualized by light microscopy with aniline dyes (ie, Wrights or Giemsa staining)?
Borrelia (remember: Big size)
Which spirochete species is visualized by dark-field microscopy?
Treponema, which causes syphilis
A farmer in the tropics with contaminated water sources presents with fever, headache, abdominal pain, photophobia, and conjunctivitis. What infection do you suspect?
Leptospirosis is most prevalent in which geographical locations?
What is Weils disease?
Severe leptospirosis, which presents with severe jaundice, azotemia, fever, hemorrhage, and anemia
What is another name for Weils disease?
Where is Leptospira interrogans commonly found in the environment?
In water contaminated with animal urine
What is the cause of azotemia and jaundice in patients with Weils disease?
Renal and liver failure
The organism that causes Lyme disease is transmitted by what vector?
The Ixodes tick
What bacteria causes Lyme disease?
The classic symptom of Lyme disease, erythema chronicum migrans, has what appearance?
An expanding "bulls eye" red rash with central clearing
What organs are affected in patients with Lyme disease?
The skin, the joints, the central nervous system, and the heart
Which mammals are required for the life cycle of the Ixodes tick?
Deer and mice
What are the treatments of choice for Lyme disease?
Doxycycline and ceftriaxone
In what region of the United States is Lyme disease common?
The northeastern United States
What are the three stages of Lyme disease and their associated symptoms?
Stage 1: erythema chronicum migrans and flu-like symptoms;
stage 2: neurologic and cardiac manifestations;
stage 3: autoimmune migratory polyarthritis