Any organism isolated from properly collected and normally sterile specimens (urine and blood immediately come to mind) is usually significant. “Throat” or “vaginal” cultures almost always have populations of several types of “normal flora” which must be separated from smaller, less obvious, or slower growing true pathogens that are alien to that location but which may be perfectly explainable — for instance, in an improperly collected specimen. In addition, the so-called normal flora by themselves can be significant in inappropriate quantities.
As a general rule, laboratorians no longer collect these “regional” specimens, so we must rely on incomplete or misleading information from the clinicians in order to determine the significance of what we find. Too often, when trying to explain this to an overworked and, perhaps, overwhelmed clinician, we are told, “Just tell me anything that grew out, and I will determine its significance.” After the fourth or fifth page of written reports, some of them might finally get the idea that a little appropriate clinical information provided on the front end could save a lot of trouble on the back end — we can only hope.
—Chuck Millstein, MBA, MT(ASCP), CLDir(NCA),
retired (and loving it)
I say yes: The routine vaginal/cervical culture has outlived its usefulness
Apart from throat cultures, I think genital cultures rank right up there with inconsistent reporting practices. When a genital-culture battery is offered on the requisition menu, it is easy for the provider to put a little check mark in the box and call it good. Now what? You have the age of the patient, the source (usually wrong — vagina and cervix are not synonyms), and maybe a vague reference to symptoms (e.g., discharge or vaginal itching).
So, you have a stack of non-selective, semi-selective, and selective media to wade through. And it is up to the lab tech to figure out what is significant and what is normal for each individual patient specimen. Caution: You are entering a minefield of potential reporting errors (misleading information). Let us look at the media commonly used :
– SBA (sheep blood agar) recovers almost everything except Haemophilus spp and some other fastidious organisms. Gram negatives will overgrow, and Gardnerella vaginalis is inhibited.
– CNA (colistin/nalidixic acid) inhibits the growth of most Gram negatives (exceptions: Providencia and Proteus). G vaginalis and yeast love this media.
– MTM (modified Thayer-Martin) — Why use this media when, for all intents and purposes, probe technology has replaced culture for Neisseria gonorrhoeae. Remember, we are discussing only vaginal/cervical specimens.
– Choc (chocolate agar) — Why use this agar? Haemophilus spp is rare and its significance questionable. Remember, you cannot use the vaginal/cervical specimen to represent upper genital-tract infections (i.e., uterus, fallopian, ovary).
– Lim Broth or Todd-Hewitt — Why include this broth in a routine vaginal/cervical culture? This should only be used for a specifically requested screen for Streptococcus agalactiae colonization during pregnancy. Other than that, indiscriminate reporting of this normal flora will mislead the provider.
– V-Agar — Why use a selective media for G vaginalis? It just encourages over-reporting of this organism. Besides, G vaginalis grows very nicely on CNA.
– MAC (MacConkey Agar) — Why include this agar when enterics are part of the normal vaginal mucosa (e.g., age and estrogen levels)? An exception may be Shigella spp in prepuberty, which I have never seen in all my years as a microbiology specialist. Regardless, it will show up on the SBA.
Gram stain: the Number One most important component of the vaginal/cervical culture workup. I cannot stress this enough. There should never be a debate as to whether the Gram stain should or should not be a part of the culture battery. Without it, you are blind to the significance of anything growing on the culture. Call up and review the direct Gram-stain results of the specimen before attempting to decipher the culture. Go back and read the slide first-hand if you are unsure of someone else’s report. Wash off the oil and re-stain the slide to your own satisfaction, if necessary. Bacterial vaginosis should be identified by the Gram stain and not by culture. Additionally, predominance of microorganisms should be determined by Gram stain and not by culture; organism viability may shift during transport.
My general consensus:
- Limit the routine genital culture to prepubertal patients only. All other cultures should be “organism-specific.”
- Educate providers on proper ordering practices.
- Use the Gram stain (not the wet prep) to identify bacterial vaginosis. (Also, add a comment: “Many small mixed bacteria consistent with bacterial vaginosis. No lactobacillus rods seen. No or few white blood cells seen.”
- Provide ample information for techs regarding pathogen versus normal flora
- Always include a Gram stain with the culture battery. If reimbursement is an issue, make it part of the workup, regardless.
- Remember, there will always be exceptions that prove the rule.
&endash;By Colleen K. Gannon, MT(AMT) HEW,
the “Nancy Grace” for labs