In msberends/AMR: Antimicrobial Resistance Data Analysis

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This page was entirely written by our AMR for R Assistant, a ChatGPT manually-trained model able to answer any question about the AMR package.

Antimicrobial resistance (AMR) is a global health crisis, and understanding resistance patterns is crucial for managing effective treatments. The AMR R package provides robust tools for analysing AMR data, including convenient antibiotic selector functions like aminoglycosides() and betalactams(). In this post, we will explore how to use the tidymodels framework to predict resistance patterns in the example_isolates dataset.

By leveraging the power of tidymodels and the AMR package, we’ll build a reproducible machine learning workflow to predict the Gramstain of the microorganism to two important antibiotic classes: aminoglycosides and beta-lactams.

Objective

Our goal is to build a predictive model using the tidymodels framework to determine the Gramstain of the microorganism based on microbial data. We will:

1. Preprocess data using the selector functions aminoglycosides() and betalactams().
2. Define a logistic regression model for prediction.
3. Use a structured tidymodels workflow to preprocess, train, and evaluate the model.

Data Preparation

We begin by loading the required libraries and preparing the example_isolates dataset from the AMR package.

# Load required libraries
library(AMR)          # For AMR data analysis
library(tidymodels)   # For machine learning workflows, and data manipulation (dplyr, tidyr, ...)

# Select relevant columns for prediction
data <- example_isolates %>%
  # select AB results dynamically
  select(mo, aminoglycosides(), betalactams()) %>%
  # replace NAs with NI (not-interpretable)
   mutate(across(where(is.sir),
                 ~replace_na(.x, "NI")),
          # make factors of SIR columns
          across(where(is.sir),
                 as.integer),
          # get Gramstain of microorganisms
          mo = as.factor(mo_gramstain(mo))) %>%
  # drop NAs - the ones without a Gramstain (fungi, etc.)
  drop_na()

Explanation:

• aminoglycosides() and betalactams() dynamically select columns for antibiotics in these classes.
• drop_na() ensures the model receives complete cases for training.

Defining the Workflow

We now define the tidymodels workflow, which consists of three steps: preprocessing, model specification, and fitting.

1. Preprocessing with a Recipe

We create a recipe to preprocess the data for modelling.

# Define the recipe for data preprocessing
resistance_recipe <- recipe(mo ~ ., data = data) %>%
  step_corr(c(aminoglycosides(), betalactams()), threshold = 0.9)
resistance_recipe

For a recipe that includes at least one preprocessing operation, like we have with step_corr(), the necessary parameters can be estimated from a training set using prep():

prep(resistance_recipe)

Explanation:

• recipe(mo ~ ., data = data) will take the mo column as outcome and all other columns as predictors.
• step_corr() removes predictors (i.e., antibiotic columns) that have a higher correlation than 90%.

Notice how the recipe contains just the antibiotic selector functions - no need to define the columns specifically. In the preparation (retrieved with prep()) we can see that the columns or variables r paste0("'", suppressMessages(prep(resistance_recipe))$steps[[1]]$removals, "'", collapse = " and ") were removed as they correlate too much with existing, other variables.

2. Specifying the Model

We define a logistic regression model since resistance prediction is a binary classification task.

# Specify a logistic regression model
logistic_model <- logistic_reg() %>%
  set_engine("glm") # Use the Generalized Linear Model engine
logistic_model

Explanation:

• logistic_reg() sets up a logistic regression model.
• set_engine("glm") specifies the use of R's built-in GLM engine.

3. Building the Workflow

We bundle the recipe and model together into a workflow, which organizes the entire modeling process.

# Combine the recipe and model into a workflow
resistance_workflow <- workflow() %>%
  add_recipe(resistance_recipe) %>% # Add the preprocessing recipe
  add_model(logistic_model) # Add the logistic regression model
resistance_workflow

Training and Evaluating the Model

To train the model, we split the data into training and testing sets. Then, we fit the workflow on the training set and evaluate its performance.

# Split data into training and testing sets
set.seed(123) # For reproducibility
data_split <- initial_split(data, prop = 0.8) # 80% training, 20% testing
training_data <- training(data_split) # Training set
testing_data <- testing(data_split)   # Testing set

# Fit the workflow to the training data
fitted_workflow <- resistance_workflow %>%
  fit(training_data) # Train the model

Explanation:

• initial_split() splits the data into training and testing sets.
• fit() trains the workflow on the training set.

Notice how in fit(), the antibiotic selector functions are internally called again. For training, these functions are called since they are stored in the recipe.

Next, we evaluate the model on the testing data.

# Make predictions on the testing set
predictions <- fitted_workflow %>%
  predict(testing_data)                # Generate predictions
probabilities <- fitted_workflow %>%
  predict(testing_data, type = "prob") # Generate probabilities

predictions <- predictions %>%
  bind_cols(probabilities) %>%
  bind_cols(testing_data) # Combine with true labels

predictions

# Evaluate model performance
metrics <- predictions %>%
  metrics(truth = mo, estimate = .pred_class) # Calculate performance metrics

metrics

Explanation:

• predict() generates predictions on the testing set.
• metrics() computes evaluation metrics like accuracy and kappa.

It appears we can predict the Gram based on AMR results with a r round(metrics$.estimate[1], 3) * 100% accuracy based on AMR results of aminoglycosides and beta-lactam antibiotics. The ROC curve looks like this:

predictions %>%
  roc_curve(mo, `.pred_Gram-negative`) %>%
  autoplot()

Conclusion

In this post, we demonstrated how to build a machine learning pipeline with the tidymodels framework and the AMR package. By combining selector functions like aminoglycosides() and betalactams() with tidymodels, we efficiently prepared data, trained a model, and evaluated its performance.

This workflow is extensible to other antibiotic classes and resistance patterns, empowering users to analyse AMR data systematically and reproducibly.

msberends/AMR documentation built on March 5, 2025, 2:28 p.m.