Microbiology - General Bacteriology, Gram Positive , Mycobacteria Flashcards
What structures are unique to gram-positive organisms?
Lipoteichoic acid (combination of lipids and techoic acid)
What structures are unique to gram-negative organisms?
Endotoxin/LPS (outer membane)
Periplasm
Peptidoglycan
gives rigid support, protects against osmotic pressure
composed of sugar backbone with peptide side chains cross-linked by transpeptidase
Cell wall/cell membrane (gram-positives)
major surface antigen.
Peptidoglycan for support. Lipoteichoic acid induces IL-1 and TNF
Outer membrane (gram negatives)
site of endotoxin (lipopolysaccharide [LPS]); major surface antigen
Plasma membrane
site of oxidative and transport enzymes
-made of phospholipid bilayer
Ribosome
protein synthesis
- made up of 50S and 30S subunits
Periplasm
- unique to gram negatives
- space between cytoplasmic membrane and outer membrane in gram-negative bacteria
- contains many hydrolytic enzymes, including B-lactamases
Capsule
protects against phagocytosis
-composed of polysaccharide (except Bacillus anthracis, which contains D-glutamate)
Pilus/fimbria
mediate adherence of bacteria to cell surface; sex pilus forms attachment between 2 bacteria during conjugation
- made of glycoprotein
Flagellum
- used for motility
- composed of protein
Spore
resistance to dehydration, heat, and chemicals
- keratin-like coat; dipicolinic acid
peptidoglycan
Plasmid
contains a variety of genes for antibiotic resistance, enzymes, and toxins
Glycocalyx
mediates adherence to surfaces, especially foreign surfaces (e.g. indwelling catheters)
- composed of polysaccharide
Pleomorphic bacteria
Ricksettsiae (Giemsa)
Chlamdyiae (Giemsta)
Branching filamentous bacteria
Actinomyces
Nocardia (weakly acid fast)
Bacteria with no cell wall
Mycoplasma (does not gram stain)
Bacteria with unusual cell membranes/walls
Mycoplasma - contains sterols and have no cell wall
Mycobacteria - contain mycolic acid. High lipid content
Bacteria that don’t Gram stain well
“These Rascals May Microscopically Lack Color”
TREPENOMA (too thin) RICKETTSIA (intracellular parasite) MYCOBACTERIA (high lipid content in cell wall detected carbolfuscin) MYCOPLASMA LEGIONELLA CHLAMYDIA
Culture for H. influenza
Chocolate agar with factors V (NAD+) and X (hematin)
Culture: N. gonorrhoeae, N. meningitidis
Thayer Martin (or VPN) media - Vancomycin inhibits gram positive, Polymixin inhibits gram negative organisms except Neisseria, and Nystatin (inhibits fungi)
Culture for B. pertussis
Bordet-Gengou (potato) agar
Culture for C. diptheriae
Tellurite plate, Loeffler’s media
Culture: M. tuberculosis
Lowenstein-Jensen agar
Culture: M. pnuemoniae
Eaton’s agar
Lactose-fermenting enterics culture
Pink colonies on MacConkey’s agar
- fermentation produces acid, turning colony pink.
- E.coli is also grown on EMB as colonies with green metallic sheen
Legionella culture
Charcoal yeast extract agar buffered with cysteine and iron
Fungi culture
Sabouraud’s agar
Obligate aerobes
use an oxygen dependent system to generate ATP
“Nagging Pests Must Breathe”
- Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, and Bacililis
Obligate anaerobes
anaerobes “Can’t Breathe Air”
- Clostridium
- Bacteroides
- Actinomyces
- lack catalase and/or superoxide dismutase and are susceptible to oxidative damage.
- generally foul smelling (short chain fatty acids) are difficult to culture and produce gas in tissue (carbon dioxide and hydrogen gas)
Encapsulated bacteria
- positive Quelling reaction - if encapsulated bug is present, capsule swell when specific anticapsular antisera are added
Name encapsulated bacteria
“SHiNE SKiS
Streptococcus pneumonia H. influenzae type B Neisseria meningitidis Escheria coli Salmonella Klebsiella pneumonia Strep agalactiae (Group B strep)
Obligate intracellular
Rickettsia, Chlamydiae (can't make own ATP) Stay inside (cells), it's Really Cold
Facultative intracellular
"Some Nasty Bugs May Live FaculitiveLY" Salmonella Neisseria Brucella Mycobacterim Listeria Francisella Legionella Yersinia
Catalase-positive organisms
Catalase degrades hydrogen peroxide before it can be converted to microbicidal products by enzyme myeloperoxidase.
Examples: Pseudomonas, Listeria, Aspergillus, Candida, E.coli, S. aureus, Serratia
People susceptible to infection by catalase positive organisms
People with chronic granulomatous disease (NADPH oxidase deficiency) have recurrent infections with these microbes because they degrade the limited hydrogen peroxide
Vaccines
- for those containing polysaccharide capsule antigens, a protein is conjugated to polysaccharide antigen to promote T-cell activation and class switching.
- a polysaccharide antigen can’t be presented to T cells, thus only M antigens would be presented
Transformation
ability to take up naked DNA (i.e. from cell lysis) from environment.
- feature of SHiN (S. pneumoniae H. influenzae Neisseria)
- Any DNA can be used. Adding deoxyribonuclease to medium will degrade naked DNA
Conjugation (F+ x F-)
F+ plasmid contains genes required for sex pilus and conjugation.
Bacteria without this plasmid are termed F-.
Plasmid (dsDNA) is replicated and transfered through pilus from F+ cell.
NO TRANSFER OF CHROMOSOMAL genes
Conjugation (Hfr x F-)
F+ plasmid can be incorporated into bacterial chromosomal DNA, termed high-frequency recombination (Hfr) cell.
Replication of incorporated plasmid DNA may include some flanking chromosomal DNA.
Transfer of plasmid and chromosomal genes
Transposition
Segment of DNA that can “jump” (excision and reintegration) from one location to another, can transfer genes from plasmid to chromosome and vice versa.
When excision occurs, may include some flanking chromosomal DNA, which can be incorporated into plasmid and transferred to another bacterium
Generalized Transduction
“packaging” event. Lytic phage infects bacterium, leading cleavage of bacterial DNA. PArts of bacterial DNA may become packaged into viral capsid. Phage infects anoter baceterium, transferring these genes.
- RECIPIENT ACQUIRES BACTERIAL DNA BUT NO VIRAL DNA
Specialized Transduction
“Excision” event.
Lysogenic phage infects bacterium; viral DNA incorporates into bacterial chromosome.
When phage DNA is excised, flanking bacterial DNA may be excised with it. DNA is packaged into phage viral capsid and can infected another bacterium)
Genes for following toxins encoded in lysogenic stage
Shig-A like toxin Botulinium toxin Cholera toxin Diptheria toxin Erythrogenic toxin of Strep pyogenes
** When times are good, virus leaves bacteria alone but under stress, virus acts up
Gram + positive bacteria, Novobiocin resistant
Staphylococci Saprophyticus
Gram + cocci, novobiocin sensitive
STAPHYLOCOCCI epidermidis
Gram + cocci, Optochin resistant
STREP viridans
Gram + cocci, Optochin sensitive
STREP pneumoniae
Gram + cocci, Bacitracin resistant
Group B strep (Strep agalactiae)
Gram + cocci, Bacitracin sensitive
Group A strep (Strep pyogenes)
Alpha hemolytic bacteria
- form green ring around colonies on blood agar
Beta hemolytic bacteria
- form clear area of hemolysis on blood agar. Including following organisms:
- Staph aureus
- Strep pyogenes
- Strep agalactiae (Group B strep)
- Listeria monocytogenes
Staph aureus
gram + cocci, catalase +, coagulase +
- yellow colonies, Beta hemolytic
- protein A binds Fc portion of IgG to prevent complement fixation and phagocytosis
Infections caused by S. aureus
- inflammatory disease (skin infections, organ ABSCESS, pneumonia)
- Toxic Shock Syndrome (TSST-1)
- Rapid onset food poisoning (enterotoxins within)
- MRSA - resistant to B-lactams b/c of altered penicillin binding proteins
- Acute bacterial endocarditis (common in IV drug users)
- Scalded skin syndrome
S. aureus food poisoning
due to ingesting of PREFORMED toxin
TSST
- associated with S. aureus
- super-antigen that binds to MHC II and T-cell receptor, resulting in polyclonal T-cell actvation
- Presents as fever, rash, desquamation, end organ failure
Staphylococcus epidermidis
gram + cocci, catalase +, coagulase -
Novobiocin sensitive
- produces biofilms on catheters and prosthesis
- component of normal skin flora, contaminates blood cultures
- 10 - 20% UTIs in females
Streptococcus pneumoniae
Gram + diploccoci, Encapsulated
Catalase -, ALPHA hemolytic
IgA protease, Capsule resists phagocytosis
Optichin SENSITIVE
– no virulence without capsule
Toxins: Pneumolysin O - puts pores in pulmonary cells
Infections associated with S. pneumoniae
“MOPS”
Meningitis - (esp. > 60 years old)
Otitis media (in children)
Pneumonia (in adults)
Sinusitis
Pneumococcus
associated with “rusty” sputum, sepsis in sickle cell anemia and splenectomy
Viridins group streptococci
gram + cocci, catalase - alpha hemoltic bile soluble Quelling reaction optichin RESISTANT
- normal flora of oropharynx and cause dental caries and SUBACUTE endocarditis
Subacute Endocarditis
- associated with Strep viridans, Group D Strep
- attacks DAMAGED valves, usually by Group A Strep, by making glycocalyx
Sx of subacute endocarditis
- Janeway lesions
- Osler’s nodes
- Roth’s spots (in retina)
- Splinter hemorrhages under fingernals
ECG shows vegetations on mitral valve - can be shown with dental appointments or rheumatic fever as a child
Strep pyogenes (Group A Strep)
gram + cocci, calatase -
Beta hemolytic
Bacitracin sensitive
Diagnosed by ASO titer
Pyogenic infections associated with S. pyogenes
Pharyngitis, Impetigo, Cellulitis
Toxin-mediated infections associated with S. pyogenes
Scarlet fever, Toxic Shock-Like Syndrome, Necrotizing Fascitis
Virulence factors associated with S. pyogenes
- Streptokinase (converts plasminogen to plasmin) –> fibrinolysis
- M protein - resists phagocytosis
- Hyaluronidase - breaks down connective tissue
- DNAse: digests DNA
Immunogenic infections associated with S. pyogenes
Rheumatic fever, Acute Glomerulonephritis
JONES criteria to diagnose rheumatic fever
J-oints O-bvious signs N-odules (subcutaneous) E-rythema marginatum (targetoid lesions) Syndham's chorea
Scarlet fever
- associated with S. pyogenes
- scarlet rash sparing face
strawberry (scarlet) tongue, scarlet throat
Streptococcus agalactiae (Group B Strep)
gram + positive, Beta hemolytic
Bacitracin resistant
- colonizes vagina, causes pneumonia, meningitis, and sepsis (mainly in babies)
- produces CAMP factors which enlarges hemolysis formed by S. aureus
Treatment of pregnant women positive for Group B Strep
- Screen pregnant women at 33 - 37 weeks
INTRAPARTUM penicillin prophylaxis
Causes of meningitis in babies < 3 months
- Group B Strep
- Listeria monocytogenes
- E. coli
Group D Strep (Enterococci)
Gram +, catalase -
Gamma hemolytic (no hemoylsis)
Can grow in 6.5% NaCl and bile
- Enterococus faecalis and E. faecium are normal colonic flora that are penicllin G resistant
Infections associated with Enterococci (Group D Strep)
** enters bloodstream where mucosal barrier is disrupted (e.g. bedsore) –> can colonize heart valves
UTI
Biliary infections
Subacute endocarditis
Vancomycin Resistant Enteroccoci
important cause of nocosomial infection
Streptoccocus bovis (Group D Streptococci)
colonizes the gut
- can cause bacteremia and subacute endocarditis in colon cancer patients
- Bovis in blood = cancer in colon
Corynebacterium diphtheriae
Gram + rods
- causes diphtheria via exotoxin encoded by B-prophage.
- Potent exotoxin inhibits protein synthesis via ADP-ribosylation of EF-2
Lab diagnosis of C. diptheriae
Based on gram-positive rods with metachromatic (blue and red) granules and Elek’s test for toxin
Toxoid vaccine prevents diptheria
Spores
- some bacteria can form spores at the end of stationary phase when nutrients are limited.
Spores are highly-resistant to head and chemicals. Have dipicolonic acid in their core.
Have no metabolic activity
Must autoclave to kill spores (as is done to surgical equipment) by steaming at 121 C
C. tetani
Gram +, spore-forming, obligate anaerobic bacilli
- produces tetanospasm, an exotin causing tetanus
- Tetanus toxin (and botulinum toxin) are proteases that cleave releasing proteins for neurotransmitters
Tetanospasm toxin
causes tetanic paralysis (blocks glycine and GABA release [inhibitory neurotransmitter]) from Renshaw cells in spinal cord.
Causes spastic paralysis, trismus (lockjaw), and risus sarcondicus
C. botulinum
Gram +, spore-forming, obligating anaerobic bacilli
- produces PREFORMED, heat-labile toxin that inhibits ACh release at NMJ, causing botulism
- diseases is caused by ingestion of preformed toxin.
- babies, ingestion of spores in honey causes disease
C. perfringens
gram +, obligate anaerobe bacilli
produces alpha toxin (“lecthinase” - phospholipase that can cause myonecrosis (gangrene) and hemolysis
C. difficile
gram +, obligate anaerobe bacilli
produces 2 toxins
- Secondary to antibiotic use (clindamycin or ampicillin)
Treatment of C. difficile
Metronidazole or Oral vancomycin
C. difficile toxins
Toxin A, enterotoxin, binds to the brush border of gut.
Toxin B, cytotoxin, destroys the cytoskeletal structures of enterocytes, causing pseudomembranous colitis
Anthrax
caused by Bacillus anthracus, a gram +, spore-forming rod that produces anthrax toxin.
Only bacterium with a polypeptide capsule (contains D-glutamate)
Cutaneous anthrax
contact –> black eschar (painless ulcer) ; can progress to bacterermia
Black skin lesion - black eschar (necrosis) surrounded by edematous ring. Caused by lethal factors and edema factors
Pulmonary anthrax
inhalation of spores –> flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock
Woolsorter’s disease - inhalation of spores from contaminated woool
Bacillus cereus
Gram + rod
causes food poisoning. Survives cooking rice. Keeping rice warm results in germinationof spores and enterotoxin formation
- causes reheated rice syndrome
Types of reheated rice syndrome (Bacillus cereus)
Emetic type - usually seen in rice & pasta (nausea and vomiting within 1-5 hrs) from cerulide (preformed toxin)
Diarrheal type - causes watery, non-bloody diarrhea and GI pain in 8 - 18 hours
Listeria monocytogenes
- Gram + bacilli, non-spore forming
facultative intracellular microbe
-acquired by ingesting unpasteurized milk/cheese and deli meats or by vaginal transmission during birth - form “actin rockets” by which they move from cell to cell. Characteristic tumbling motility
Infections caused of Listeria monocytogenes
Amnionitis, Septicemia, and Spontaneous abortion in pregnant women
Granulomatosis infantiseptica, neonatal meningitis, meningitis in immunocompromised patients; mild gastritis in healthy individuals
Treatment of Listeria monocytogenes
Gastroenteritis usually self-limited
Ampicillin in infants
Immunocompromised patietns
Elderly in empirical treatment of meningitis
Actinomyces
Gram + positive ANAEROBE
- not acid fast
- normal oral flora (say “AAH”)
- causes oral/facial absceses that drain through sinus tracts
- forms “yellow sulfur” granules
Tx: penicillin
Nocardia
Gram + AEROBE
- acid fast
- found in soil
- Causes pulmonary infections in immunocompromised and cutaneous infections after trauma in immunocompetent
Tx: sulfonamides
Primary tuberculosis (infection of non-immune host/usually child)
- infects hilar nodes
- Ghon focus (usually in mid zone of lung)
- deposits in LOWER lobes
Outcomes of primary tuberculosis
- Heals by fibrosis –> tuberculin positive
- Progressive lung disease (HIV, malnutrition)
- Severe bacteremia –> Miliary tuberculosis
- Preallergic lymphatic or hematogenous dissemination –> possible reactivation in adult life
Secondary tuberculosis
- partially immune/ hypersensitized host (usually adult)
- reinfection is cavitary lesion (usually in UPPER lobes)
Extrapumonary tuberculosis
- due to secondary TB
- CNS (parenchymal tuberculoma or meningitis)
- Vertebral body (Pott’s disease)
- Lymphadenitis
- Renal
- GI
Mycobacterium tuberculosis
TB
- often resistant to multiple drugs
- include fever, night sweats, weight loss, and hemoptysis
Cord factor
in virulent strains of Mycobacterium tuberculosis
- inhibits macrophage maturation ad induces release of TNF-alpha (surface glycolipids)
Sulfatides inhibit phagolysosome fusion
M. kansaii
pulmonary TB-like symptoms
M. avium- intracellulare
caues disseminated non TB disease in AIDS
- often resistant to multiple drugs
Prophylactic treatment with azithromyxin
Leprosy (Hansen’s disease)
- caused by Mycobacterium leprae
- poorly Gram stained
- prefers cooler areas of skin (skin and superficial nerves)
- causes chronic disease with hypopigmentation and “stocking” loss sensation
- in US, caused by armadillos
Two forms of Hansen’s disease
LEPROMATOUS - presents diffuselt over skin and is communicable. Characterized by LOW cell mediated immunity with humoral Th2 response
TUBERCULOID - limited to hypoesthetic, hair less skin plaques, charcterized by HIGH cell mediated immuity with large Th1 type response
Treatment of Hansen’s disease
LEPROMATOUS - 6 MONTH course of dapsone and rifampin
TUBERCULOID - dapsone, rifampin, and clofazmine for 2-5 YEARS
Lactose fermenting bacteria
grow pink colonies on MacConkey’s agar
- Citrobacter
- Klebsiella
- E. coli
- Enterobacter
- Serratis
E. coli produces B-galactosidase that breaks down lactose into glucose
Penicillin and gram negative bugs
Gram-negative bacilli are resistant to penicillin G, but may be susceptible to ampicillin and amoxicillin.
- Gram negative outer membrane layer inhinbits entry of penicillin G and vancomycin
Neisseria
Gram - negative diplococci
Fermenst glucose and produces IgA proteinase
N. MeningGoCocci - ferments Maltose and Glucose
N. Gonorrrhoae - ferments Glucose
Sx:
Gram + rod culture
Pseudomembranous pharyngitis (grayish- white membrane) with lymphadenopathy, myocarditis, and arrhythmias
C. diptheriae
Lancefield grouping is based on what?
differences in the C carbohydrate on bacterial cell wall
