bacteriology Flashcards
General characteristics of S. aureus are
- Gram-positive cocci
- Catalase positive
- Nonmotile
- Aerobic or facultatively anaerobic
- Medium, circular and entire, smooth, convex, and usually white-to-yellow colonies
Transmission of Staphylococcus
- Person-to-person
Persistent carriers
Intermittent carriers
Noncarriers
Capsule
- Slime laver
- Biofilm
Cell wall
- Peptidoglycan
- Protein A
Disrupts smooth muscle and toxic to many cell types
Alpha toxins
Heat labile sphingomyelinase
Beta toxins
Cytotoxic to erythrocytes
Delta toxins
Mav function in association with Panton-Valentine Leuckocidin (PVL)
Gamma toxins
Heat stable enterotoxins in up to
50% of S. aureus strains
Localized skin infections
- Folliculitis
- Furuncles
- Carbuncles
- Impetigo
Infections in those who are immunocompromised
microcccus
- Skin and soft-tissue infections
- Toxic shock syndrome (TSS)
- Food poisoning
- Scalded skin syndrome
S. aureus
*Associated with UTIs in sexually active young women
S. saprophyticus
Panton- Valentine leukocidin (PVL) toxin
S. aureus
community -associated infections
MRSA or CA-MRSA
- Usually infects neonates
- Cause extensive sloughing of epidermis to produce a burn like effect on the patient
Scalded skin syndrome
Systemic effects on the patients; including fever, desquamation, hypotension leading to shock and death
Toxic Shock syndrome
Virulence Factors of Staphylococcus aureus
- Produce and secretes toxins and enzymes
- Leucocidin mediates destructio of phagocytes
- Clumping factor
- Coagulase
- Hyaluronidase
- Potent exotoxins (TSST-1) and enterotoxin
Spectrum of Diseases and infections in Staphylococcus aureus
- Necrosis
- Localized skin infections
- Folliculiis
- Furuncles (Boils)
- Carbuncles
- Impetigo
- Coagulase negative staphylococci
- Less virulent
- Their prevalence as nosocomial infection is ,if not more related to medical procedures and practices
Staphylococcus epidermidis
virulence of epidermidis
- Certain factors facilitate attachment to implanted medical devices
- Production of exopolysaccharide “slime” or biofilm
INFECTIONS of epidermidis
- Ubiquitous (contaminant)
- Difficult to establish clinical significance
- Nosocomial bacterimia
- Involve implantation of medical devices
- Production of slime layer or biofilm that facilitates attachment to implanted medical devices.
S. haemolyticus and S. lugdunensis
- Community acquired UTI in young sexually active females
- Not commonly associated with hospital-acquired infections,
S. saprophyticus
- Virulence factor-UNKNOWN
- Rarely associated with infection
- Low virulence
micrococcus
- May appear as catalase +
- Aerococcus
- Enterococcus
- Rothia (forrmerly Stomatococcus)
Pseudocatalase reaction
Rapid method to differentiate Staphylococcus from Micrococcus.
microdase test
blue to purple blue color
+ - micrococcus
No color change
- staphylococcus
Micrococcus
- Not lysed with lysostaphin
- Susceptible to 0.04U bacitracin
- Resistant to the antibiotic furazolidone
- microdase positive
staphylococcus
- Lysed with lysostaphin
- Resistant to 0.04U bacitracin
- Susceptible to furazolidone
- Microdase-negative
- Facultatively anaerobic
Bound
- Clumping factor
- Rapid slide test
Free
- Extracellular (free) coagulase
- Tube coagulase test
- Clot formation witin 1-4 hours of inoculation
Most laboratories do not identify coagulase negative staphylococci; EXCEPT:
- Isolates from normally sterile sites:
- Blood
- Joint fluid
- CSF
- Isolates from prosthetic devices
- Catheters
- Shunts
- Isolates from UTI that may be S. saprophyticus
- Antibodies to teichoic acid
- Performed in reference laboratories
SERODIAGNOSIS
Antimicrobial susceptibility testing and therapy
Antistaphyococcal therapy
- Penicillinase-resistnt penicillin
- Methicillin
- Nafcillin
- Oxacillin
- most commonly used cell-wall active agent that retains activity
- Alternative drug for resistant strain
VANCOMYCIN
two newer agents available for use agains resistant strains
- Linezolid
- Daptomycin
- Rarely encountered infections in humans
- Therapeutic guidelines and standardized testing methods do not exist.
- Appear to be susceptible to most beta-lactam antimicrobials
micrococcus spp.
Prevention of staphylococcus
- No approved antistaphylococcal vaccines
- Health careworkers identified as intranasal carriers of an epidemic strain of S. aureus. Treated with muciprocin and in some cases, with rifampin.
Some doctors recommended use of antibacterial substances to umbilical cord stump to prevent staphylococcal disease in hospital nurseries such as:
- gentian violet
- Acriflavie
- Chlorhexidine
- Bacitracin
Recommended that all full terms infants be bathed with __________ as soon after birth as possible and daily after discharge
3% hexachlorophene
Normal flora of anterior nares, nasopharynx, perineal area, & skin
S. aureus
Normal flora of skin and mucous membrane
S. epidermidis
Similar to S epidermidis, but in lower number
S. haemolyticus & lugdunensis
Normal flora of the skin and mucosa of GUT
S. saprophyticus
Normal flora of the skin mucosa and oropharnyx
Micrococcus spp.
Traumatic introduction, person person, fomites, air (TPFA)
S. aureus
Implantation of medical devices;
person to person
S. epidermidis
Same with S. epidermidis
S. haemolyticus & lugdunensis
- Introduction of edogenoua flora into sterile urinary tract,
- Community acquired infection
S. saprophyticus
Uncertain
Micrococcus
Colonial on 5% sheep blood agar
S. aereus - beta hemolytic
S. epidermidis - Non hemolytic
S. haemolyticus & lugdunensis - beta hemolytic
S. saprophyticus - yellow to orange colonies
Micrococcus - Non hemolytic (gamma)
