Hello everybody! This is Jeremy Chu (TG01) attached to bacteriology posting on...
The Miscellaneous Bench
The miscellaneous bench deals with every other specimens besides blood, stool, urine and respiratory specimens. Fluid, tissues and swabs are mainly the samples received. Some examples are heart/liver tissues, peritoneal fluid or peritoneum fluid, wound swabs and high/low vaginal swabs. Detecting bacteria at these sites are important, especially for sterile sites. There should not be any bacteria found at sterile sites such as the heart and liver or patient’s situation could be fatal.
Wound cultures are performed to isolate and identify bacteria infections causing an infection of the wound. This way, doctors can then administer the appropriate antibiotics to kill the causative agent.
Fluid culture is done, similarly to isolate and identify bacteria causing an infection. Peritoneal/Pericardial fluids are sterile fluids and any presence of bacteria is regarded as significant. Gram stain is also performed.
High vaginal swabs are cultured for the purpose of detecting group B streptococci (commonly Streptococcus agalactiae) found in the female reproductive tract. S. agalactiae can cause pneumonia and meningitis commonly in neonates and the elderly.
The different types or media used and its purposes are listed in the table below.
| Media | Purpose | Types of specimens |
| Blood Agar | Enriched media to enhance bacteria growth | Tissues Fluids Fluid swabs Wound swabs Catheter tips/devices Vaginal swabs |
| MacConkey Agar | Selective media to inhibit most gram positive bacteria and differentiates lactose fermenters | |
| Blood Agar (anaerobic) | Enriched media to enhance anaerobic bacteria growth | Tissues Fluids Fluid swabs |
| Cooked Meat broth | Enriched broth for cultivating bacteria | Tissues Fluids Fluid swabs Wound swabs Catheter tips/devices |
| LIM broth | Enriched broth used to grow group B streptococci from vaginal swabs | Vaginal swabs |
Fluid culture agar plates are incubated under CO2 conditions, while its broths in aerobic conditions. Blood, MAC, blood (anaerobic) agars and cooked meat broth are the choice of media.
7 comments:
hi jeremy,
you mentioned high/low vaginal swab, may i ask what are the differences? what exactly does it mean by 'high' and 'low'?
thanks!!
eriko(0700477C)
Hi Jeremy,
in the table u mentioned that MacConkey agar can be used for vaginal swabs, but later on you mentioned only blood and LIM broth.
So can MacConkey agar be used?
Also, what's LIM broth. Could you please tell us a bit more on that?
Yanhong
0703979E
Hi Jeremy,
Can you name some examples of common bacteria that might be found in sterile fluid? Thanks:)
Lok Pui
Hi Eriko,
High vaginal swab (HVS) are swabs from the upper ends of the vagina. Vice versa for low vaginal swab (LVS).
Hi Yanhong,
My apologies for the misunderstanding in the table.
MacConkey is not normally used in routine vaginal swab cultures, though sometimes could be used to differentiate between gram positive and gram negative bacteria if there is a need to. Routinely, blood agar and LIM broth are used.
LIM broth, I've as mentioned in the table, is a selective enrichment broth. It enhances the growth of group B Streptococci. Subcultures from LIM broth onto blood agar plates could be performed if initial culture on blood agar yield no colonies or group B streptococci.
I'm not sure what do you exactly want to know about the broth. Please specify. I am more than willing to help out.
Hi Lok Pui,
Infective peritonitis (inflammation of the peritoneum) caused by gram negative bacilli (e.g. Escherichia coli), anaerobic bacteria (e.g. Bacteroides fragilis), and also Staphylococcus aureus. It can also be due to fungi infections.
Infective arthritis (infection in the joint fluid) caused most commonly by Staphylococcus aureus and Streptococci spp.
Thank you for the questions posted.
Jeremy.
Hey Jeremy,
Why is gram staining performed in fluid cultures but not wound cultures? There's still a need to identify the presence of bacteria in both cultures right?
Felicia
Hi Felicia,
I believe there isn't a need to perform a gram stain for wound cultures. A wound swab is usually collected when there is abscess. Abscess would mean there is an infection, and a gram stain would definitely show presence of organisms, be it normal flora or the causative agent. Gram stain will not identify the particular agent. It is best to perform direct plating immediately so as to isolate the causative agent for the antibiotics susceptibility test.
Regarding fluid culture, gross appearance will not indicate whether there is presence of organisms or not. Thus a gram stain is required.
Jeremy
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