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4 “Bug” Case Studies

“Life of a Blood Culture” Slide Show

Questions welcomed!

Case #1 UTI BUG

Ambulatory 26 year old female with 101° temperature and painful urination

Physician orders a urine culture with gram stain

Gram Stain Results

Gram stain morphology shows many gram-positive cocci in pairs and chains

Urine Culture Setup

Urine plated to agar plates

1/1000 ml inoculating loop used

One big drop of urine is enough for a culture!

Urine Culture Results

Culture grows >100,000 colonies of bacteria on a blood agar plate

Patient’s UTI caused by a strep-like organism called Enterococcus

Identifying Enterococcus

Produces an enzyme called PYRase

Detectable in a two minute test

Normal sites for Enterococcus

Upper respiratory tract Gastrointestinal tract Genitourinary tract

Enterococcus Infections

UTI’s Nosocomial UTI’s Wound infections

Emerging Resistance

Emerging strains showing resistance to Vancomycin

Resistant strains called Vancomycin Resistant Enterococcus or VRE

Bone marrow transplant and other immunocompromised patients at risk

Identifying VRE

Identify VRE as an Enterococcus faecalis or faecium using biochemical tests interpreted by an automated instrument

Phoenix Automated Instrument

Performs both biochemical tests and susceptibilities

100 organisms can be tested at a time

VRE on the rise

Enterococcus showing resistance to Vancomycin E-strip

VRE strains account for 6% of all Enterococcus

Patients placed in isolation

Reported to RN and Infection Control

Case #2 Wound Bug

65 year old male with 101° temperature after hip replacement surgery

Develops redness, tenderness and drainage at incision site

Physician orders a culture and gram stain on incision site

Incision site Gram Stain

Gram stain shows few gram-positive cocci in clusters with few wbc’s

Bacterial culture results

Staph aureus isolated on culture

White colonies on blood agar

Identifying Staph aureus

Latex agglutination test can identify an organism as Staph aureus in 10 seconds

Staph aureus infections

Skin infections Scalded Skin Syndrome Toxic Shock Syndrome Osteomyelitis Food poisoning

Staph aureus reservoirs

Carried in nose of 20-40% of adults Higher % in hospital personnel Transferred from nose to skin Passed to others by direct contact or droplets Primary way nosocomial infections occur

Staph aureus treatment

Penicillin discovered in 1920 – worked great on Staph!

More difficult to treat the last 50 years Some SA now showing resistant to methicillin,

a commonly used drug

Identifying MRSA

Strains resistant to methicillin are called MRSA

Extraction test can identify SA as an MRSA strain in 15 minutes

Lots of MRSA

Up to 50% of SA isolated are MRSA strains Carriage rate for MRSA higher in hospitals MRSA often found on health club gym

equipment Pets can get MRSA from their owners

Wash Your Hands

Good handwashing essential!

Careful wound dressing technique

Patients with MRSA placed in isolation

Reported to RN and Infection Control

Case #3 GI BUG

38 year-old HIV positive male Several previous hospital admissions Taking AZT & Bactrim antibiotic therapy 3 day history of severe diarrhea with 10 pound

weight loss and profound dehydration

Lab Results Stat

Leukotest = negative (test for fecal wbc’s) Occult blood exam = negative Both tests usually positive with diarrhea

caused by Salmonella or Shigella Negative Leukotest and Occult blood =

noninflammatory diarrhea

Lab Results not Stat

Ova & Parasite exam negative Stool culture negative for enteric pathogens Campylobacter EIA assay negative Shiga Toxin EIA assay negative

Other Findings

No recent travel history Patient has not recently eaten shellfish

Clues from Patient History

Severe diarrhea consistent with enterotoxigenic E.coli or Vibrio cholerae

Endemic in limited regions Raw or undercooked shellfish may contain

Vibrio cholerae Patient had not consumed shellfish

Suppressive Antibiotic Therapy

Normal gut flora protects the bowel from invasive pathogens

Antibiotics destroy large part normal flora Allows overgrowth of organisms usually

suppressed

Responsible Bug

Clostridium difficile frequently causes antibiotic-associated diarrhea

Disrupted normal flora allows C. difficile to multiply

Produces two different exotoxins

Patient’s Diagnosis

Patient suffering from Clostridium difficile colitis “Pseudomembranous colitis”

More about Clostridium difficile

C. difficile is an anaerobe

Gram-positive rods on Gram Stain

Diagnosing C. difficile colitis

Detect exotoxins in stool using EIA assay

Performed twice daily in Microbiology

Takes about 3 hours Pea-size amount of stool

needed for testing Positive results called to

patient’s RN

Important to Establish Cause of Diarrhea

Many causes of diarrhea in AIDS patients untreatable

C. difficile treatable with oral antibiotics Patient placed in isolation to avoid hospital

outbreaks

Life of a BLOOD CULTURE Slide Show

Drawn in yellow-top SPS tubes

Full size & pedi-tube

Life of a BLOOD CULTURE

4 Kinds of Blood Culture Bottles

Aerobic Anaerobic Pediatric ARD

(Antimicrobial Removal Device)

Life of a BLOOD CULTURE

Chlorhexidine preps or swabs disinfect venipuncture site

Scrub arm for 30 seconds, not to exceed a 2 inch square surface

Let arm air dry

Life of a BLOOD CULTURE

Use of Chlorhexidine preps has decreased blood culture contamination rate by 50%

Blood culture considered “contaminated” if common skin flora grows from one or both bottles in a set

Life of a BLOOD CULTURE

Clean SPS tubes with alcohol and let air dry

Draw 2 SPS tubes for each set of cultures

10 ml in each tube One tube –> aerobic One tube –> anaerobic Record collection site on label

(peripheral, art line, etc.)

Life of a BLOOD CULTURE

Recommended draw times: Two sets drawn at least 30 minutes apart in a

24 hour period Bacterial recovery rate increases by 57% when

2 sets are drawn

Life of a BLOOD CULTURE

Bottles placed in an automated Bactec instrument

Incubate for 5 days Monitored every 15

minutes for bacterial growth

Life of a BLOOD CULTURE

Loud alarm sounds when growth is detected!

Positive blood culture considered a STAT

Subcultured to agar plates

Plates incubate for 18 hours

Life of a BLOOD CULTURE

Gram stain slide made from “positive” bottle

Life of a BLOOD CULTURE

Gram Stain takes about two minutes

Look for bacteria on slide under the microscope

Gram stain results called to patient’s RN

Case #4 BLOOD BUG

37 year old man with sickle cell disease and numerous hospitalizations

Porta-cath placed in right subclavian vein Patient admitted to ED two weeks after porta-

cath placement

Emergency Department findings

Patient has right arm discomfort and swelling Physician orders two sets of blood cultures One drawn through porta-cath One drawn through peripheral vein

Blood culture results

Both sets of blood cultures show gram positive cocci in clusters on smear

Both cultures grow the same organism

Responsible Bug

Two positive blood cultures + porta-cath = probable line-related sepsis

Most common bug causing line-related infection is Coagulase Negative Staph or CNS

CNS important cause of nosocomial bacteremia

Foreign body devices act as source

Identifying CNS

Grow as white colonies on blood agar plate

Nonreactive in rapid latex tests

Sources of CNS

Normal inhabitants of skin, mucous membranes and nares

About 20 species of CNS Most common is Staph epidermidis

Slime Producers

CNS secrete a virulence factor called slime Makes them “sticky” Stick to plastic surfaces like catheter tips Slime-producing strains more difficult to treat

with antibiotics Indwelling catheters place patient at risk for

infection

Diagnosing Line-Related Sepsis

Draw 2 sets of blood cultures from a patient with fever or signs of infection at the IV site

One set from catheter line One set from peripheral site

Two sites important

CNS on skin can be a blood culture “contaminant” if blood not collected properly

Single positive blood culture with CNS may be skin contamination and not true infection

Two sites important

Negative peripheral culture and positive line culture with CNS may just show local infection of the catheter site

Two Blood cultures with CNS from two different sites more likely represents true infection

Confirming line-related sepsis

Confirm by performing a catheter tip culture Catheter is removed and sent to Micro Lab

Culturing the Catheter tip

Catheter tip cut to 50mm Roll on surface of blood

agar plate

Interpreting Catheter tip cultures

Culture “positive” if 15 colonies grow from a 50 mm tip

CNS growing on plate

Diagnosis confirmed

If Catheter tip culture has CNS and blood cultures from both the line and peripheral draws have CNS

Patient has a confirmed line-related sepsis

Microbiology Art

Thank you! Please call Microbiology

with any questions: 2-2422 2-2435