Cocci Flashcards
Intro to Cocci
- apherical, about 1 micron diameter, non spore-forming, human-restricted
- they can be cultured readily in the laboratory
- even within one species they can vary a lot, with big differences in virulence
Classification
- Gram stain: Gram positive and gram negative
- Morphology: twos, chains, clumps
- Appearance on blood agar- Alpha, Beta, Gamma hemolytic
- DNA sequencing: Firumicutes/ Proteobacteria
- Nutritional requirements- specific antisera, phage typing, or DNA analysis
Medically Important cocci
Streptococci:
- Group A
- Group B
- Pneumococci
- Viridans streptococci
- Enterococci
Staphylococci:
- S aureus
- S epidermidis
- S saprophyticus
Neisseria:
N meningitides
N gonorrhoeae
Streptococci general
- gram positive cocci which grow in chains
- classified by Lancefield group: method based on carboydrate antigens found in cell wall
- they can be classified by hemolysis on blood agarplates
- all are catalase negative
Group A Streptococci (Streptococcus pyogenes)
-Lab: Beta hemolytic, Sensitive to bacitracin, reacts to Group A antiserum, rapid office test: antibody to carbohydrate antigen
- Virulence factors: Pili and M protein
- streptokinase, streptodornase, hyaluronidase, pyrogenic toxin, erythrogenic toxin
- Reservoir and transmission- pharynx and skin, 10%, dogs?
- Prevention and treatment- penicillin- no serious resistance, erythromycin as alternative
Post-streptococcal conditions
- Skin infection (M49 strain)- recovery, and then pain, blood and protein in urine = post streptococcal nephritis
- Sore throat (M18 strain)- recovery, and then fever, arthritis, endocarditis= rheumatic fever
- Sydenham’s chorea- neurological
- Obsessive Compulsive Disorder?
Group B streptococci
Laboratory properties- Beta hemolytic streptococci- NOT sensitive to bacitracin. Positive on CAMP test
Physiology- main virulence factor is a capsule, which prevents phagocytosis
Reservoir and Transmission- female genital tract in 25% of people. Transmitted to baby, at or before birth
Prevention and treatment- all pregnant women should be screened. Penicillin must be given 18 hours after rupture of membranes if labor has not started, to prevent ascending infection of the uterus and baby
Streptococcus pneumoniae (pneumococci)
Laboratory properties: alpha hemolytic diplococci. No Lancefield Group
Physiology- No toxins. The polysaccharide capsule is both antigen and the virulence factor. It prevents phagocytosis, but stimulates opsonizing antibody
Reservoir and transmission: Throat 5-50% people
Prevention and treatment: polysaccharide capsule is used in a polyvalent vaccine
- penicillin is usually effective but resistance is increasing
- most strains are sensitive to Cephalosporin
Natural resistance: mechanical clearance by mucus/ cilia- inhibition by smoking, virus, allergy, immobility, tumor, depressed cough reflex
Enterococcus fecalis (Streptococcus fecalis, Group D streptococci)
Lab: Non hemolytic (gamma), Bile resistant
Physiology: Normal flora of colon. Causes abdominal absesses, UTI, endocarditis,
Viridans streptococci
-alpha hemolytic. No lancefield group. Optochin/bile resistant
Physiology: Extraceullar polysaccharides. Acids. Sugar metabolizing enzymes
Reservoir and transmission: Mouth (100%) and female genital tract
Prevention and treatment: dental carries detectable at early stages by dental checkups. Penicillin-sensitive but no long term benefit. Bacteremia is manageable by prophylactic antibiotics at the time of dental treatment
Peptostreptococcus
Lab: Non hemolytic. Non Lancefield Group. Obligate anaerobes
Physiology: Found in abscesses which contain a complex mixture of organisms. Not primary pathogens
Reservoir: Normal flora of mouth, respiratory tract, female genital tract, bowel
Staphylococci General
- seen in clumps
- gram positive
- catalase test positive
Staphylococcus aureus
Lab: gold colonies, coagulase positive, beta hemolytic. Susceptible to bacteriophages-different phages affect different strains thus allowing sub-typing
Virulence factors: Protein A (binds immunoglobins), Capsule (inhibits phagocytosis), Coagulase; Toxins: DNAse, Enterotoxin, Exfoliatin, Leukocidin, Toxic Shock Syndrome Toxin
Prevention and treatment:
-No vaccine: Wash hands, cover lesions, reduce carrier state prior to surgery
-multi-drug resistance
Staphylococcus epidermidis
Lab: catalase positive but coagulase negative. Non hemolytic. Normal flora of skin and and mucous membranes of many people
Physiology: attaches to nylon and plastic readily. Therefore can infect IV catheters, IV lines, shunts
Prevention and treatments: change indwelling cath, iv lines on a regular sechedules
-use gold or surgical stainless steel for decorative pierces- not plastic. Antibiotics can not eliminate infections
Staphylococcus saprophyticus
Lab: Coagulase negative. Non hemolytic
Physiology: UTI in women “Honeymoon cystitis”
Several other coagulase negative staphlococci are carried by healthy people. Most do not cause any diseases
