Culture, gram stain and sensitivity

When would you want to store specimen at 4C rather than RT

When there are a lot of normal flora you want to kill store at low temp → Urine

Blood culture contaminants

Coag-neg staph (saprophyticus, epidermidis, propionibacterium acnes, corynebaterium spp, bacillus spp (non anthrasis)

What is the standard order for blood culture

Two sets (1 aerobic bottle + 1 anaerobic bottle per set) from two different anatomical sites

Steps of blood culture collection

Hand hygiene→ Skin antisepsis → Skin disinfection (central to peripheral) → Collect before Abx or at fever onset → Collect → Use alcohol to clean bottle → Inoculate → transport

What is the recommended timing of blood cultures collection

Non urgent: two samples 15-30 minutes apart

Urgent: two samples from two sites right away

What is blood agar

Can view both gram negative and gram positive bacteria hemolysis pattern

Alpha hemolytic bacteria

Strep viridans, s pneumoniae

Beta hemolytic bacteria

S pyogenes, S agalactiae

Gamma hemolysis bacteria

Non enterococcus, enterococci

What is MacConkey agar

For gram neg only

What is blood agar

H influenzae and N gonorrheae positive

Cause of meningitis in Px population

Neonate → E coli

Infant → S agalactiae

Children < 10 → H influenza

Adult and Children >10 → S. pneumoniae

CNS specimen prep

Centrifuge if there is a lot of clear fluid, don’t centrifuge if there is turbid or small volume of fluid

What is wet smear used for

If you suspect cryptococcus neoformans (india ink) or amebic meningoencephalitis (direct wet mount)

What is thioglycollate (FTM) broth

Tells us if the organism if aerobe or anaerobe based on where it grows on tube (bottom = anaerobe, top = aerobe)

Septic arthritis specimen and lab

Synovial fluid specimen → Use direct wet smear

Direct wet smear for pleura and peritoneal fluids used for what

Look for fungal element (optional)

What would direct wet smear show for gout and pseudogout

Gout → Monosodium urate (needle shaped)

Pseudogout → Calcium pyrophosphate (rhomboid shaped)

To culture salmonella and shigella in stool culture what medium is used

GN broth, XLD, MAC

To culture vibrio spp in stool culture what medium is used

APW, TCBS

To culture yersinia in stool culture what medium is used

Yersinia selective agar

To culture campylobacter in stool culture what medium is used

Campylobacter selective medium, BA base no 2

Stool culture commonly test for what organism

Salmonella, Shigella, Vibrio, Aeromonas, Plesiomonas

URT specimen

Throat swab, nasopharyngeal swab, sinus aspirate, tracheal suction, nasopharyngeal suction

LRT specimen

Sputum, lung biopsy, lung aspirate, tracheal suction, bronchial wash

Lab test for genital culture

Epithelial cell, WBC, test gonorrhea, clue cell = g. vaginalis

Special agar for genital culture

Modified Thayer Martin → N. gonorrhoeae, SDA for candida albicans

When you collect wound culture, what should be careful of

Collect the pus or fluid deeper inside the wound, DO NOT collect superficially → Will contaminate with skin flora