Contents

 

Interpretation of Micro Reports

 

Cut-off values (rare/few/moderate/etc) depend on a number of factors including: source of the culture, Gram stain results, organism, likelihood that the culture was contaminated based on the organisms that are isolated, number of organisms that grow, patient gender, patient age, and type of patient (OB, CF, Immunocompromised, etc).  Of note, when a report says, “rare gram-negative rod”, it does not mean rare as in unusual, it means rare as in very few.

 

Contaminant vs. pathogen

Blood – normally sterile

Pathogens – any organism isolated

 

Likely Contaminants

coagulase-negative staphylococci

alpha-hemolytic streptococci

Bacillus spp.

Corynebacterium spp. (except jeikeium)

Propionibacterium acnes

NOTE: must take into consideration how many cultures were drawn versus how many are positive and what the organism is

                       

Tissue and Body Fluids – should be sterile

Pathogens – any organism isolated; use judgment to evaluate the possibility of normal flora being present in relation to the source of the specimen

 

Normal Flora

Eye/Ear

coagulase-negative staphylococci

non-hemolytic streptococci

alpha-hemolytic streptococci

diptheroids

Skin

coagulase-negative staphylococci

Propionibacterium acnes

diptheroids

alpha-hemolytic streptococci

Bacillus spp.

                       

Genital

Pathogens

Neisseria gonorrhoeae

beta-hemolytic streptococci

Listeria spp.

Gardnerella vaginalis

predominant numbers of S. aureus

predominant numbers of yeast

 

Normal flora

                        Staphylococcus spp.

                        Lactobacillus spp.

                        Diptheroids

                        Enterococcus spp.

                        Streptococcus spp.

                        Gram-negative rods

                        anaerobes

                        yeast

                 Urine – should be sterile

Pathogens

Enterobacteriaceae

Enterococcus spp.

Pseudomonas spp. and other non-fermenters

group B streptococcus (Streptococcus agalactiae)

S. aureus and S.saprophyticus

yeast

 

Likely Contaminants

Diptheroids

coagulase-negative staphylococci

alpha-hemolytic streptococci

Lactobacillus spp.

Gram-negative rods

Bacillus spp.

NOTE: significance of organism is determined by colony count

                       

Gastrointestinal tract

Pathogens

                        Salmonella

                        Shigella

                        Campylobacter

                        E. coli 0157:H7

                        Aeromonas/Plesiomonas

                        Yersinia enterocolitica

                        Vibrio spp.

                        Clostridium difficile (toxin)

                        S. aureus (in the context of enterotoxin food poisoning)

                        Helicobacter pylori (antigen)

 

Normal Flora

                        Enterobacteriaceae

                        Staphylococcus spp.

                        Streptococcus spp.

                        Enterococcus spp.

                        Pseudomonas spp.

                        anaerobes

                        yeast

 

Respiratory tract

Pathogens

                        group A streptococci (Streptococcus pyogenes)

                        Streptococcus pneumoniae

                        Predominant S. aureus

                        H. influenzae

                        Neisseria meningitidis/gonorrhoeae

                        Predominant Enterobacteriaceae

                        Predominant Pseudomonas spp. and other non-fermenters

                        Corynebacterium diptheriae

                        Bordatella pertussis

                        Legionella

                        Mycobacterium

                        Nocardia

                        Predominant Moraxella catarrhalis

                        Predominant yeast

                       

Normal Flora

                        Staphylococcus spp.

                        alpha-hemolytic streptococci

                        Gram-negative rods

                        beta-hemolytic streptococci other than group A

                        Neisseria spp.

                        Enterococcus spp.

                        Corynebacterium spp.

                        Bacillus spp.

                        yeast

                        anaerobes

                        Haemophilus spp.

                        Micrococcus spp.

                        Stomatococcus spp.

 

NOTE: amount of organism present, source of culture, and patient age may determine significance as a pathogen