I was messaged below:
Hello, could you tell me which antimicrobials are okay to use without killing the good bacteria? I have hydrogen SIBO, methane SIBO, and hydrogen sulfide SIBO. I don’t want to make things worse because I no longer have bifidobacteria, lactobacilli, and Oxalobacter in particular. And I don’t want to take something broad-spectrum.
I was especially wondering about clove and thyme. I also have fungal issues and yeast in my body, possibly related to mold. Could you explain how to tell whether an antimicrobial is harmful to the good bacteria? Thank you
What is defined as good or bad?
The issue is not that simple as “good” or “bad”. Too much of a “good” bacteria is associated with a variety of conditions. Let us look at the research for two commonly believed “good” bacteria:
- Lactobacillus is reported HIGH (from 119 studies) with
- Allergies
- Alzheimer’s disease
- Amyotrophic lateral sclerosis (ALS) Motor Neuron
- Asthma
- Atherosclerosis
- Atrial fibrillation
- Autism
- Carcinoma
- Celiac Disease
- Chronic Obstructive Pulmonary Disease (COPD)
- Cognitive Function
- Colorectal Cancer
- COVID-19
- Crohn’s Disease
- Depression
- Endometriosis
- Fibromyalgia
- Graves’ disease
- Heart Failure
- High Histamine/low DAO
- hypertension (High Blood Pressure
- Hypoxia
- Inflammatory Bowel Disease
- Insomnia
- Irritable Bowel Syndrome
- ischemic stroke
- Juvenile idiopathic arthritis
- Liver Cirrhosis
- Long COVID
- Metabolic Syndrome
- Mood Disorders
- multiple chemical sensitivity [MCS]
- Multiple Sclerosis
- Multiple system atrophy (MSA)
- Neuropathy (all types)
- Nonalcoholic Fatty Liver Disease (nafld) Nonalcoholic
- Obesity
- Osteoporosis
- Parkinson’s Disease
- Polycystic ovary syndrome
- primary biliary cholangitis
- Primary sclerosing cholangitis
- Psoriasis
- rheumatoid arthritis (RA),Spondyloarthritis (SpA)
- Schizophrenia
- Small Intestinal Bacterial Overgrowth (SIBO)
- Stress / posttraumatic stress disorder
- Systemic Lupus Erythematosus
- Type 1 Diabetes
- Type 2 Diabetes
- Ulcerative colitis
- Unhealthy Ageing
- Bifidobacterium is reported HIGH (from 120 studies) with
- ADHD
- Allergic Rhinitis (Hay Fever)
- Allergies
- Alzheimer’s disease
- Amyotrophic lateral sclerosis (ALS) Motor Neuron
- Ankylosing spondylitis
- Anorexia Nervosa
- Asthma
- Atherosclerosis
- Atrial fibrillation
- Autism
- Autoimmune Disease
- Brain Trauma
- Breast Cancer
- Carcinoma
- Cerebral Palsy
- Cognitive Function
- Colorectal Cancer
- COVID-19
- Crohn’s Disease
- Depression
- Endometriosis
- Epilepsy
- Fibromyalgia
- Functional constipation / chronic idiopathic constipation
- Graves’ disease
- Hashimoto’s thyroiditis
- Hyperlipidemia (High Blood Fats)
- hypertension (High Blood Pressure
- Hypoxia
- Inflammatory Bowel Disease
- Irritable Bowel Syndrome
- ischemic stroke
- Juvenile idiopathic arthritis
- Liver Cirrhosis
- Long COVID
- Metabolic Syndrome
- Mood Disorders
- Multiple Sclerosis
- NonCeliac Gluten Sensitivity
- Obesity
- Parkinson’s Disease
- Polycystic ovary syndrome
- Premenstrual dysphoric disorder
- Psoriasis
- rheumatoid arthritis (RA),Spondyloarthritis (SpA)
- Rosacea
- Schizophrenia
- Sleep Apnea
- Stress / posttraumatic stress disorder
- Type 2 Diabetes
- Ulcerative colitis
- Vitiligo
There are a very small number of bacteria deemed absolutely bad.
- Bacillus anthracis.
- Francisella tularensis.
- Clostridium botulinum
From Dangerous Microbes, 2018
The Human Need for Simplicity versus Biological Reality
I am a high functioning autistic spectrum individual. Others in the spectrum include those with photographic memory and complete memory recall. I lack those, but where I excel is my tolerance for complexity and uncertainty.
Across my 50-year career in software development, I’ve noticed that code I find straightforward often overwhelms other developers. One once remarked, “Any JavaScript file over 200 lines is black magic to me,” while reviewing what I considered a simple application. That experience reflects something broader: people naturally seek simplicity, even when reality is irreducibly complex.
In the same way, many approach microbiome science by labeling bacteria as “good” or “bad.” This reduction helps those who feel saturated by excessive detail—but the truth is far more nuanced.
The Evolution of Microbiome Prescription
For more than a decade, my goal with the Microbiome Prescription project has been simple in principle:
- Accept scientific evidence—a microbiome test.
- Compute suggestions aimed at correcting dysbiosis.
- Provide direct links to supporting literature.
(See an example for Depression.)
The biggest challenge lies in determining which bacteria should shift, and in what direction. My early approach relied on lab-provided ranges: if a value was above range, reduce it; if below, increase it. But this method failed. Lab ranges are based on naïve averages and assume normal distributions. After teaching Ph.D.-level statistics, I knew better—bacterial populations follow heavily skewed distributions, not bell curves.
The next phase was to use symptom-annotated samples to mathematically model bacterial associations. When a new sample arrived, the system forecasted likely symptoms. Users checked which symptoms applied, improving both the model and predictive power.

Subsequent tests validated these forecasts: 53 predictions improved, while 19 worsened. It became clear that “gut health” cannot be captured by any single number. The ecosystem is too complex.

“No Protocol Can Serve Two Symptoms”
This phrase is an adaptation of Matthew 6:24: “No man can serve two masters.” When multiple symptoms are modeled independently, the results often conflict—what helps one symptom can worsen another. The earlier data illustrates this problem: 53 improvements, 19 regressions.
Rather than fighting symptoms individually, I began shifting focus toward the overall trajectory of health.
From Symptom Fighting to Health Trekking
A turning point came during an experiment using odds ratios derived from annotated microbiome samples—this time ranking bacteria by percentiles instead of percentages. Different labs report percentages inconsistently; percentiles normalize those variations (as discussed in this review).
Using 1,000 healthy individuals’ shotgun results from PrecisionBiome.EU, I noticed a striking pattern: “Asymptomatic: No Health Issues” consistently ranked as the top prediction.
That insight simplified everything. Instead of juggling countless symptom-specific models (10, 20, or even 200 symptoms), we can statistically track a single target—how far a sample deviates from “asymptomatic.” See definition here.
Now we’re just juggling one ball.
Reality vs. Model
The refined model depends on detailed microbiome tests—at least 16s sequencing, shotgun preferred—and percentile rankings for each bacterium. Unfortunately, most labs don’t provide percentile data. From Biomesight and Ombre, I can derive percentiles accurately from their percentage data. Some others attempt to estimate percentiles by assuming a bell curve—again, incorrect.
Recommendations for Individuals
Before ordering a microbiome test, confirm that it allows downloadable data with:
- Percentile and percentage values.
- Bacteria identified by NCBI Taxon numbers.
Recommended providers: Ombre or Biomesight (for better percentile reliability).
After testing, upload your results to Microbiome Prescription and simply click to start analysis.

Older analytical methods remain available and effective for many users, though progress may plateau for some. See Another ME/CFS Microbiome Update for details.










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