Clinical Bacteriology Flashcards
Gram + cocci antibiotic tests: Streptococci
Optochin - Viridans is Resistant; Pneumoniae is Sensitive
OVRPS (overpass)
Bacitracin - Group B strep are resistant; group A strep are Sensitive
B-BRAS
Alpha hemolytic bacteria
Gram + cocci
Partial reduction of hemoglobin causes greenish or brownish color without clearing growth on blood agar
Strep pneumo (catalase -, optochin sensitive)
Viridans strep (catalase -, optochin resistant)
Beta hemolytic bacteria
Gram + cocci
Complete lysis of RBCs –> clear area surrounding colony on blood agar
Staph aureus (catalase & coagulate +)
Strep pyogenes - group A (catalase -, bacitracin sensitive)
Strep agalctiae - Group B (catalase -, bacitracin resistant)
Staphylococcus aureus
Gram + bacteria, beta-hemolytic, catalase +, coagulase +, cocci in clusters
VFs: protein A binds Fc-IgG inhibiting complement activation and phagocytosis
Commonly colonizes in nares
Staphylococcus aureus: Inflammatory disease
Skin infections, organ abscesses, pneumonia (often after influenza virus infection), endocarditis, septic arthritis, and osteomyelitis
Staphylococcus aureus: Toxin mediated disease
Toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), rapid onset food poisoning (enterotoxins)
TSST-1: Superantigen that binds to MHC II and TCR, resulting in polyclonal TC activation
TSS presents as fever, vomiting, rash, desquamation, shock, end-organ failure, increased AST, ALT & bilirubin. Associated with prolonged use of vaginal tampons or nasal packaging
Food poisoning due to ingested preformed toxin –> short incubation period followed by non-bloody diarrhea and emesis (enterotoxin is heat stable)
Staphylococcus aureus: MRSA
Methicillin-resistant S aureus infection - important cause of serious nosocomial and community acquired infections
Resistant to methicillin and nafcillin because of altered penicillin binding protein
Staphylococcus epidermidis
Gram +, catalase +, coagulase -, urease + cocci clusters. Novobiocin sensitive
Found in normal flora of the skin; contaminates blood cultures
Infects prosthetic devices (hip implant, heart valve) and IV catheters by producing adherent bio films
Staphylococcus saprophyticus
Gram +, catalase +, coagulase -, urease + cocci in clusters. Novobiocin resistant
Found in normal flora of female genital tract and perineum
Second most common cause (after E.coli) of uncomplicated UTI in young women
Streptococcus pneumoniae
Gram +, lancet shaped diplococci. Alpha-hemolytic Optochin sensitive (different from S.viridans)
VFs: encapsulated, IgA protease
Most common cause of: meningitis, otitis media (children), pneumonia, sinusitis
Associated with “rusty” sputum, sepsis in pts with sickle cell disease and splenectomy
Streptococcus Viridans group
Gram +, alpha hemolytic cocci. Optochin resistant (different from S.pneumo)
Found in the normal flora of the oropharynx that cause dental caries (strep mutans and strep mitis) and subacute bacterial endocarditis at damaged heart valves (S.sanguinis - makes dextran so which bind to fibrin-platelet aggregates on damaged heart valves).
live in the mouth because they are not afraid of-the-chin (op-to-chin resistant)
Streptococcus pyogenes (Group A)
Gram + cocci, beta hemolytic, bacitracin sensitive, pyrrolidonyl arylamidase (PYR) +
Cause: pyogenic (pharyngitis, cellulitis, impetigo, erysipelas), toxogenic (scarlet fever, toxic shock like syndrome, necrotizing fasciitis), immunologic (rheumatic fever, glomerulonephritis)
Abs to M protein enhance host defenses against S.pyogenes but can give rise to RF
ASO tigers detects recent S.pyogenes infection
S.pyogenes and rheumatic fever
JONES criteria Joints: polyarthritis O: heart, carditis Nodules: subcutaneous Erythema margin atom Sydenham chorea
S.pyogenes and Scarlet Fever
Blanching, sandpaper like body rash, strawberry tongue, and circumoral pallor in the setting of group A strep pharyngitis (erythogenic toxin +)
Streptococcus agalctiae (group B streptococci)
Gram+ cocci, bacitracin resistant, beta-hemolytic (Hippurate test +, PRY -)
Colonizes vagina; causes pneumonia, meningitis and sepsis mainly in babies (screen pregnant women at 35-37 weeks of gestation. Pts with positive culture receive intrapartum penicillin prophylaxis
Produces CAMP factor, which enlarges the are of hemolysis formed by S.aureus
Streptococcus bovis
Gram+ cocci
Colonizes the gut
S.gallalyticus can cause bacterimia and subacute endocarditis (associated with increased risk in pts with CRC) and colon cancer
Bovis in the Blood = Cancer in the Colon
Enterococci
Gram+ cocci, catalase -, PYR+, variable hemolysis
enterococci (E.faecalis and E.faeciium) are normal colonic flora that are penicillin G resistant and cause UTI, biliary tract infections and subacute endocarditis (following GI/GU procedures)
VRE (vancomycin resistant enterococci) are an important cause of nosocomial infection
Enterococci can grow in 6.5% NaCl and bile
Bacillus anthracis
Gram + spore forming rod that produces anthrax toxin
The only bacteria with a polypeptide capsule (contains D-glutamate)
Cutaneous anthrax
Painless papule surrounded by vesicles –> ulcer with black eschar (painless and necrotic) –> uncommonly progresses to bacteremia and cell death
Pulmonary anthrax
Inhalation of spores –> flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis and shock
Also known as woolsorter’s disease
Bacillus cereus
Gram + rod
Causes food poisoning. Spores survive cooking rice, keeping rice warm results in germination of spores and enterotoxin formation (AKA reheated rice syndrome)
Emetic type: usually seen with rice and pasta, nausea and vomiting within 1-5 hours. Caused by cereulide (preformed toxin).
Diarrheal type: water, non-bloody diarrhea and GI pain within 8-18 hours.
Clostridia
Gram + spore forming, obligate anaerobic rods
Two types of exotoxins (C.tetani, C.botulinum)
Clostridium tetani
Produces tetanospasmin (exotoxin) causing tetanus Tetanus toxin (and botulinum toxin) are pro teases that cleave SNARE proteins for neurotransmitters. Blocks the release of inhibitory neurotransmitters, GABA & glycine, from Renshaw cells in the spinal cord Causes spastic paralysis, trismus (lockjaw), risks sardonicus (raised eyebrows with an open grin) Prevent with tetanus vaccine, treat with antitoxin +/- vaccine booster, diazepam and wound debridement
Clostridium botulinum
Produces a heat-labile toxin that inhibits ACh release at the neuromuscular junction, causing botulism
In adults, disease is caused by ingestion of preformed toxin. In babies - the ingestion of spores (e.g. Honey) leading to floppy baby syndrome.
Treat with antitoxin
Clostridium perfringes
Produces alpha toxin (lecithinase, a phospholipase) that can cause myonecrosis (gas gangrene) and hemolysis
PERFringens PERForates a gangrenous leg
Spores can survive in undercooked food; when ingested, bacteria release heat-labile enterotoxin –> food poisoning
Clostridium difficile
Produces two toxins: Toxin A (enterotoxin) that binds to the brush border of the gut. Toxin B (cytotoxin), causes cytoskeleton disruption via actin depolymerization –> diarrhea –> pseudomembranous colitis
Often secondary to antibiotic use, especially clindamycin or ampicillin; associated with PPI use.
Diagnosis: detection of one or both toxins in stool by PCR
Tx: metronidazole, oral vacomycin. For recurrent cases, consider repeating prior regiment, fidaxomicin or fecal microbiota transplant
Corynebacterium diphtheriae
Gram + rod (club shaped), black colonies on cystine-telluride agar
Causes diphtheria via Exotoxin encoded by beta-prophase. Potent Exotoxin inhibits protein synthesis via ADP-ribosylation of EF-2
Symptoms: pseudomembranous pharyngitis, lymphadenopathy, myocarditis, and arrhythmias
Lab diagnosis: gram + rods with Metachromatic (blue and red) granules and + Elek test for toxin
Toxoid vaccine prevents diphtheria
Listeria monocytogenes: characteristics
Gram + facultative intracellular rod
Acquired by ingestion of unpasteurized dairy products and cold deli meats, via trans placenta transmission, or by vaginal transmission during birth
Forms “rocket tails” via actin polymerization that allow intracellular movement and cell to cell spread across cell membranes, thereby avoiding AV
Characteristic tumbling motility in broth
Listeria monocytogenes: Disease
Can cause ammionitis, septicemia, spontaneous abortion in pregnant women
Granuloumatosis infantiseptica, neonatal meningitis
Meningitis in immunocompromised pts
Mild self-limited gastroenteritis in healthy individuals
Tx: ampicillin in infants, immunocompromised and elderly as empirical treatment of meningitis
Nocardia
Gram +, form long branching filaments resembling fungi
Aerobe
Acid fast (weak)
Found in soil
Causes pulmonary infections in immunocompromised (can mimic TB but with - PPD); cutaneous infections after trauma in immunocompetent
Treat with sulfonamides (TMP-SMX)
Actinomyces
Gram +, form long branching filaments resembling fungi
Anaerobe
Not acid fast
Normal oral, reproductive and GI flora
Causes oral/facial abscesses that drain through sinus tracts, forms yellow “sulfur granules” can also cause PID with IUDs
Treat with penicillin
Mycobacteria
Mycobacterium tuberculosis (TB, often resistant to multiple drugs)
-TB symptoms: fever, night sweats, weight loss, cough (non-productive or productive), hemoptysis
-Cord factor creates a “serpentine cord” appearance in virulent M.tb strains; inhibits MP maturation and induces release of TNF-alpha. Sulfatides (surface glycolipids) inhibit pahgolysosomal fusion
M.avium-intracellular even (causes disseminated, non-TB disease in AIDS; often resistant to multiple drugs) Prophylaxis with Azithromycin when CD4+ count
Leprosy (Hansen disease)
Caused by mycobacterium leprae (acid fast bacillus that likes cool temperatures) - infecting skin and superficial nerves (glove and stocking loss of sensation
Cannot be grown in vitro.
Reservoir in USA: armadillos
Treatment: dapsone and rifampin for tuberculoid form, clofazimine is added for lepromatous form
Hansen disease: Lepromatous
Presents diffuse lay over the skin with leonin facies, and is communicable. Characterized by low cell-mediated immunity with a humoral Th2 response
Lepromatous form can be Lethal
Hansen disease: Tuberculoid
Limited to a few heypesthetic, hairless skin plaques; characterized by high cell-mediated immunity with a largely Th1-type immune response
Lactose fermenting enteric bacteria
Fermentation of lactose –> pink colonies on MacConkey agar
E.g. Klebsiella, E.coli, Enterobacter and Serratia (weak fermenter)
E.coli produces beta-galactosidase which breaks down lactose into glucose and galactose
-EMB agar - lactose fermenters grow as purple/black colonies. E.coli grows with a green sheen
Neisseria
Gram - diplococci
Metabolize glucose and produce IgA protease so
N.gonorrhoeae is often intracellular (within neutrophils)
MeningiGococci ferment Maltose and Glucose, while Gonococci ferment just Glucose
N.gonoccoci
No polysaccharide capsule
No maltose metabolized
No vaccine due to antigenic variation of pilus proteins
Sexually or perinatally transmitted
Causes gonorrhea, septic arthritis, neonatal conjunctivitis, pelvic inflammatory disease (PID), and Fitz-Hugh-Curtis syndrome
Prevention: Condoms decrease sexual transmission, erythromycin eye ointment prevents neonatal blindness
Treatment: ceftriaxone + azythromycin OR doxycycline for possible chlamydial coinfection
N.meningococci
Polysaccharide capsule
Maltose fermentation
Vaccine (type B vaccine not widely available)
Transmitted via respiratory and oral secretions
Causes meningococcemia with petechiae hemorrhages and gangrene of toes, meningitis, Waterhouse-Friderichsen syndrome (adrenal insufficiency, fever, DIC, shock)
Prevention: rifampin, ciprofloxacin, or ceftriaxone prophylaxis in close contacts
Treatment: ceftriaxone or penicillin G
Haemophilius influenzae
Small gram - (coccobacillary) rod, produces IgA protease. Culture on chocolate agar (factors V - NAD+ - and X - hematin) for growth (can be grown with S.aureus which provides factor V through hemolysis of RBCs)
Aerosol transmission
Nontypeable strains are the most common cause of mucosal infections (otitis media, conjunctivitis, bronchitis) as well as invasive infections since the vaccine for capsular type b was introduced
Causes Epiglotitis (endoscopic “cherry red” or “thumbprint sign” on XR), meningitis, Otitis media, Pneumonia
Treatment: amoxicillin +/- clavulante for mucosal infections; ceftriaxone for meningitis, rifampin prophylaxis for close contacts