12/11/2023 0 Comments Gram negative rods blood cultureThey also cause opportunistic diseases in ICU patients who undergo invasive procedures. The non-fermenter, gram-negative bacilli (BNF) have a lower frequency of isolation when compared to Enterobacteriaceae however, they are a relevant group since they cause severe, fatal infections, especially in the hospital environment. Laboratory characterization is an essential component when it comes to microorganisms therefore, it is imperative to expose characteristics of Enterobacteriaceae, which are bacilli, non-sporulated, have variable motility, grow in the presence and absence of oxygen, ferment organisms of glucose, are cytochrome oxidase negative, and can reduce nitrate to nitrite. The general/species that frequently affect humans are Escherichia, Proteus, Enterobacter, Klebsiella, Citrobacter, Yersinia, Shigella, and Salmonella, among others. They account for about 80% of gram-negative isolates with a myriad of disease-causing general/species in humans, including urinary tract infections, pneumonia, diarrhea, meningitis, sepsis, endotoxic shock, and many others. Two large groups, Enterobacteriaceae and the non-fermenters, are responsible for most clinical isolates nevertheless, other clinically concerning gram-negative organisms exist, including but not limited to Neisseria, Haemophilus spp., Helicobacter pylori, and Chlamydia trachomatis.Įnterobacteriaceae are a heterogeneous group widely dispersed in nature. These microorganisms have significant clinical importance in hospitals because they put patients in the intensive care unit (ICU) at high risk and lead to high morbidity and mortality. Of course, always exceptions to these pearls, so await speciation!ĭr.Gram-negative bacteria (GNB) are among the world's most significant public health problems due to their high resistance to antibiotics. Ex: while you await speciation for that aerobic box car shaped GPR, these clues suggest Bacillus, usually a contaminant!įor Gram(–) rods, the pearl is that Pseudomonas is a ‘strict’ aerobe and ought to grow preferentially in the aerobic bottle – thus, a GNR that grows in the anaerobic bottle first is less likely Pseudomonas. For GPRs, preferential growth in the aerobic v anaerobic bottle helps organize the ‘shape’ chart. A great reason to go to micro lab and review the Gram stain!Īpply Q3) to Gram(+) rods & perhaps Gram(–) rods too. Here’s a comparative chart of GPRs to illustrate. There are some uniquely shaped Gram(–) rods too, but rare (think Fusobacterium). Can use Number of positive cx fact to your advantage – before abx, obtain more cx & increase the denominator!Īpply Q2) to Gram(+) rods since their shapes are so distinct. Time to positivity tough to interpret unless extreme (ex. Now, w/ the bugs organized, when you get that call from the micro lab, here are 3 questions to ask yourself/the lab:ġ) Number of positive bottles/cultures and time to positivity?įewer positive cultures & longer time to positivity suggests a contaminant. Remember that clinician adjudication is the ‘gold standard’ for deciding what is a contaminant! The orgs are deliberately ordered this way: Gram(+) orgs are often contaminants, Gram(–) orgs & yeast are not. Gram(+) cocci are grouped by ‘morphology’ since the lab usually tells you this: clusters, pairs, chains, etc. I arrange the potential Gram stain results that one can be called w/ as follows: Gram(+) cocci, Gram(+) rods, Gram(–) rods, Gram(–) cocci, yeast. Description Guide to Interpretation of Positive Blood Cultures
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