Microbiology I Flashcards
Bacteria
Unicellular organisms
Reproduce by binary fission
Four basic morphological types of bacteria
Cocci (spherical-shaped cells)
Bacilli (rod-shaped cells)
Spirilla (spiral-shaped cells)
Vibrios (comma-shaped cells)
Obligate anaerobes
Require oxygen
Facultative anaerobes
Grow in both aerobic and anaerobic environments
Obligate anaerobes
Cannot grow in the presence of oxygen
Capnophilic
Require 5%-10% CO2 for optimal growth
Microaerophilic
Grow optimally in a reduced level of oxygen
Cell membrane of bacteria
Osmotic barrier
Cell wall of bacteria
Gm pos- thick rigid peptidoglycan layer
Gm neg- Also has an outer lipopolysaccharide (LPS) layer
-Endotoxin (important virulence factor)
Polysaccharide capsule of bacteria
Covers many bacteria and serves to prevent or inhibit phagocytosis (S. pneumoniae)
Endotoxin side effects
Shock Sepsis Fever DIC Leukopenia
Gram stain process
Crystal violet, iodine, decolorizer, safranin O
- Gm pos cells stain purple
- Gm neg cells stain red
Acid-fast stain
Used to detect organisms that do not stain well with other conventional stains due to their high lipid content (Mycobacterium spp)
Nl flora in skin
Micrococcus
Staphylococcus spp
Nl flora in mouth
Streptococcus spp
Anaerobes
Nl flora in nasopharynx
Staph and strep
Nl flora in GI
Mostly anaerobes
Enterobacteriaceae
Nl flora in GU
Vagina is colonized with Lactobacillus
General guidelines for taking microbial specimens
Specimen should be from the infection site and not contaminated by the surrounding area
Whenever possible, the specimen should be collected before antimicrobials are administered
Aseptic technique is required
Throat collection
Tongue depressed, swab between the tonsillar pillars and behind the uvula (cheek, tongue, and teeth should not be touched)
Nasopharynx collection
Flexible wire nasopharyngeal swab inserted into posterior nasopharynx
Sputum collection
1st gargle with water, early morning deep cough specimen preferred
Blood collection
2-3 cultures obtained after skin disinfected with 70% alcohol, followed by iodine
-Iodine must dry and area cannot be palpated again
Urine collection
Midstream clean-catch is preferred
Stool collection
Never taken from toilet nor contaminated with urine
Kirby-Bauer disk diffusion test
Measure diameter of growth inhibition around filter paper disk containing abx
Zone of inhibition
Minimum inhibitory concentration (MIC)
Lowest concentration of antibiotic that inhibits visible growth, as detected by lack of turbidity
- Antibiotic is added to broth in serial twofold dilutions
- Standard inoculum of bacterium is added to each
- The MIC is the concentration of the first well that shows no growth or turbidity
Susceptible results
The organism should respond to the usual doses of the drug
Moderately susceptible
The isolate may be inhibited by concentrations of a drug that are achieved when the maximum parenteral doses are given
Intermediate susceptibility
The results are equivocal or indeterminate
Resistant- susceptibility
The bacterium is not inhibited by achievable concentrations of the drug
Staphylococcus
Catalase-positive, nonmotile, facultative anaerobes in grape-like clusters
Nl inhabitants of the skin and mucous membranes
-Commonly cause human infections
Coagulase test for staphylococcus
Pos- Staphylococcus aureus
Neg- S. epidermidis, S. saprophyticus
S. aureus and skin infections
Boils
Carbuncles
Furuncles
Folliculitis
S. aureus and food poisoning
Enterotoxins A and D
S. aureus and scalded skin syndrome (Ritter’s disease)
Extensive exfoliative dermatitis due to toxin
S. aureus and toxic shock syndrome (TSS)
High fever Rash Hypotension Shock Desquamation of the hands and feet Possible death
S. aureus and osteomyelitis
Often secondary to bacteremia
Antibiotic susceptibility to staphylococcus
Penicillin resistance is high
B-lactamase: an enzyme that inactivates the B-lactam abx
B-lactamase pcns (Methicillin, Oxacillin)
Methicillin-resistant S. aureus (MRSA)
-Nosocomial and community-associated infections
-Tx with bactrim (skin) or vancomycin
Methicillin-resistant S. epidermidis (MRSE)
Steptococcus/enterococcus
Catalase-negative, facultative anaerobes
Hemolysis patterns on sheep blood agar are helpful in identification
Gm-pos cocci, arranged in pairs or chains
S. pneumoniae
Important human pathogen causing sinusitis, otitis media, pneumonia
-Meningitis, bacteremia
-Vaccination
The key virulence factor is an antiphagocytic capsule
Lab findings in S. pneumoniae
Gram pos cocci in pairs
S. pyogenes
AKA group A streptococcus or B-hemolytic group A streptococcus (GABHS)
Streptolysin O- causes hemolysis of RBC
-Antistreptolysin O titer (ASO titer)
Infections of S. pyogenes
Pharyngitis- “Strep throat” or scarlet fever
Skin infections
-Impetigo, necrotizing fasciitis, pyoderma
-Rheumatic fever and glomerulonephritis
Group D streptococci
Strep bovis and Strep equinus
May be nl intestinal flora
May also be etiologic agents of bacterial endocarditis and other infections
Viridans Streptococci
Alpha hemolytic streptococci that do not meet full criteria for S. pneumoniae
Part of nl flora of the oropharynx
May cause subacute bacterial endocarditis
Enterococcus
Genus found in the intestinal tract
- E. faecalis, E. facium, E. avium, E. durans
- Share many similarities as the Group D streptococci
- May cause UTIs
- Vancomycin-resistant Enterococcus (VRE)
- E. faecium> E. faecalis
Listeria monocytogenes
Aerobic Gm pos bacilli
Widespread in the environment
Various infections in neonates and immunosuppressed persons including meningitis
Corynebacterium diphtheriae
Aerobic Gm pos bacilli
Causes diphtheria- inflammation of the throat with a pseudomembrane. Toxin damages major organs. Tx: antitoxin, erythromycin
Neisseria
Gm neg cocci seen in pairs (intracellular diplococci)
Neisseria gonorrhoeae
Venereal disease with burning and d/c from the urethra. May lead to female PID or spread to skin and/or joints
Ophthalmia neonatorum- newborn conjunctival infection
Grows on chocolate agar (but NOT on blood agar) and in selective media like Thayer-Martin media
Neisseria meningitidis
Meningococcal meningitis transmitted by respiratory droplets usually between prolonged close contacts
Onset is abrupt, with HA, stiff neck, fever +/- rash
Specimens
-CSF, blood, and joint fluid
-Nasopharyngeal swabs can be cultured to detect carriers
Morexella catarrhalis
Nl upper respiratory tract flora
Sinusitis, otitis media, community acquired pneumonia
Haemophilus
Gm-neg nonmotile bacilli and coccobacilli
Haemophilus influenzae
Can cause sinusitis, otitis media, epiglottitis, pneumonia, meningitis
Vaccination
Haemophilus ducreyi
Causes chancroid, a sexually transmitted disease with a painful ulcer
Bordetella
Very small gram-neg bacilli
Bordetella pertussis
Causes whooping cough via droplets
Catarrhal stage (cold)- paroxysmal stage (cough)- convalescence stage (healing +/- complications)
Nasopharyngeal swab specimen
Tx: macrolide antibiotic
Enterobacteriaceae
Largest and most medically important family of Gm neg bacilli
- Escherichia
- Klebsiella
- Salmonella
- Shigella
- Yersinia
- Proteus
Escherichia
Nl intestinal flora Opportunistic organism Mcc of UTI Sx -Urgency -Frequency -Dysuria -Hematuria -Pyuria
Klebsiella
Gm-neg rod-shaped bacteria
- Facultative anaerobes
- Found routinely as nl flora in nose, mouth, GI tract
- Pathogen
- -Pneumonia- K. pneumoniae
- -UTI, meningitis, diarrhea
Enterobacter
Gm-neg, rod-shaped bacteria
- Pathogenic and opportunistic infections
- -Respiratory and urinary tract
- Tx
- -Cefepime, aminoglycosides, quinolones
Salmonella
Gm-neg rod-shaped bacteria Pathogenic when acquired by oral route -Usually a self-limiting disease --Diarrhea -Typhoid fever, paratyphoid fever, food poisoning --+/- toxin --Hypovolemic and/or septic shock --Oliguria and azotemia -Tx: Ciprofloxacin (inc. resistance), Azithromycin
Shigella
Natural habitat limited to the intestine of humans and other primates where they produce bacillary dysentery
-Slender gm neg rods
-Facultative anaerobes (ferment glucose)
Infections are almost always limited to the GI tract
Sx and resolution of shigella
Sudden abd pain, fever, watery diarrhea due to exotoxin
Each BM is accompanied by straining and rectal spasms
More than half resolve in 2-5 days but most shed dysentery bacilli for a short period while few remain chronic carriers
Tx: Cipro, Ampicillin, Bactrim, supportive
Serratia
Opportunistic pathogen in hospitalized pt
Pneumonia, bacteremia, endocarditis esp in narcotic addicts and hospitalized pts
S. marcescens is often resistant to aminoglycosides and pcn
Tx: 3rd gen cephalosporin
Yersinia
Gm neg, rod-shaped bacteria Yersinia pestis causes the plague -Rodents are reservoirs --Flea bites spread to lymphatics -May be associated with Crohn's disease -Implicated as one of the causes of worldwide reactive arthritis -Tx: streptomycin and tetracycline
Proteus
Produce infections in humans when bacteria leave the intestinal tract
UTI, bacteremia, pneumonia
Produce urease resulting in alkaline urine
Organism is rapidly motile
Tx: Cephalosporin, aminoglycosides
Campylobacter
Campylobacter jejuni
Ingestion of contaminated food/water (raw chicker)
Causes diarrhea +/- blood
Helicobacter
H. pylori
Gastritis, nausea, abd pain
Increased risk of ulcers and stomach cancer
Vibrionaceae
Vibrio cholerae
Life-threatening diarrhea loss of 20 L/day
Rice water stools
Pseudomonas
Gm-neg rod-shaped bacteria
-Ubiquitous organism that thrives in harsh conditions
Pseudomonas aeruginosa
Ermerging opportunistic infection Cystic fibrosis Hot tub folliculitis Otitis externa ICU pneumonia, sepsis Tx: beta-lactam and aminoglycoside antibiotic
Legionella
Gm-neg rod-shaped bacteria
Sx: pneumonia, hyponatremia
Labs for legionella
Silver stain Charcoal yeast extract agar UV light Immunological assays PCR
Tx for legionella
Quinolones
Macrolides
Gardnerella
Gram-variable bacteria
Causes bacterial vaginosis
-Gardnerella vaginalis
Sx: vaginal d/c, fish-like odor
Labs for gardnerella
Chocolate agar
Wet-mount slide
Clue cells (bacteria adhering to the surface of squamous epithelial cells)
Tx for gardnerella
Metronidazole or clindamycin
Mycoplasma
Bacteria that lack a cell wall around their cell membrane
- Unaffected by many common abx like pcn
- Atypical pneumonia
- -Mycoplasma pneumoniae
- Infertility, vaginal infections
- Tx: macrolide or doxycycline
Chlamydia
Bacteria that replicate inside host cells and are termed intracellular
Located in an inclusion body or vacuole
Pathogen of chlamydia
Chlamydia trachomatis
STI
Genital and eye disease (trachoma)
Reactive arthritis
Lab of chlamydia
Culture
Nucleic acid amplification tests
PCR
Tx of chlamydia
Azithromycin
Doxycycline
Spirochetes
Helical shaped gram-neg bacteria with spiral coils
Treponema pallidum
Spirochete Syphilis Primary- painless chancre Secondary- rash on palms and soles, arthritis Tertiary- cardiac/neuro
Labs for Treponema pallidum
RPR
VDRL
FTA-ABS
Tx for Treponema pallidum
PCN
Borrelia burgdorferi
Lyme disease Spirochete Transmitted by Ixodes tick Stage 1- localized rash Stage 2- heart, bones, nervous system Stage 3- chronic arthritis
Labs for Borrelia burgdorferi
Serology (ELISA)
Tx for Borrelia burgdorferi
Doxycycline x 10-14 days
Mycobacterium leprae
Leprosy- granulomas of nerves, skin, etc.
Mycobacterium tuberculosis
Mostly lung infection- cough, blood-tinged sputum, fever, night sweats, weight loss
Spread by air droplets
Lab for mycobacteria
Acid-fast bacilli
PCR
Tx for mycobacteria
Isoniazid x 9 mos for latent infection
Gram-neg bacilli- anaerobes
Bacteroides fragilis
90% of anaerobic peritoneal infections
Gram-pos spore-forming bacilli- anaerobes
Clostridium- produce endospores Clostridium botulinum- botulism (toxin) Clostridium tetani- tetanus (lockjaw) Clostridium difficile- diarrhea Clostridium perfringens- gas gangrene
Clostridium difficile
Gm-pos spore forming bacilli
Antibiotic-associated diarrhea and pseudomembranous enterocolitis
Lab for Clostridium difficile
Culture
Serology for toxin (ELISA)
Stool antigen
PCR
Tx for Clostridium difficile
Metronidazole
Oral vancomycin
Stool transplantation
Gm-pos nonspore-forming bacilli
Actinomyces israelii
Propionibacterium
Lactobacillis
Actinomyces israelii
Periodontal disease
Propionibacterium
P. acnes is the most common isolate (skin)
Lactobacillis
Nl flora in the mouth, intestinal tract, and vagina
Long chains of Gm pos rods
