The Laboratory Diagnosis of Food Poisoning

 

Thank you, Sam, for your question and interest.

Sorry I did not write on that because I wanted to make my article on food toxins and food poisoning as brief as possible for general readers, and also for the education of doctors  

Since you are a medical doctor, and wish to know, let me briefly run through the laboratory diagnostic procedures to identify food toxins.

As a doctor yourself, you need to take first, the most important, one, that is, the medical history on what your patient ate, the source of the food, for example, if the food was home cooked, from a food vendor, eaten in a restaurant, or from a canned food, and if from a can if the can was bloated?

Ask your patient(s) a lot of questions about the hygiene of the environment where the food was prepared. Do not just prescribe some antibiotics. That’s not the way to practise medicine. Understanding the root causes, environmental, lifestyle and preventive medicine come first, not just prescribing some medicine. That’s not the way.

In the diagnosis we need to look at the symptoms or signs first presented by the patient before sending samples to the laboratory identification.

I shall explain a little later about organisms responsible if the food can was bloated.

But first, let me deal with how we use various laboratory diagnostic procedures to identify the microorganisms or the chemical toxins responsible for the food poisoning.

First, let me deal with microbial food poisoning. For this part of the investigations, we need to send the food samples, if still available from remnants of the food the patient ate, together with specimens from the patient for microbiological cultures.

The culture techniques involve the isolation and identification of bacteria from food samples or patient specimens (stool, vomit) using selective and differential media.

This examination requires direct observation of pathogens in samples using various staining techniques (e.g., Gram staining, acid-fast staining) seen through a microscope.

What I would normally do myself is, not just use stools and vomit for microbiological cultures, but I would also use molecular methods such as polymerase chain reaction (PCR) for amplification and detection of specific DNA or RNA sequences of pathogens. This can be real-time PCR (qPCR) for quantification of pathogen load in samples.

I will also use the Next-Generation Sequencing (NGS) which would be a more comprehensive analysis of all genetic material in a sample to identify multiple pathogens simultaneously.

Next, available to me if we have an immunological laboratory, I will then use Enzyme-Linked Immunosorbent Assay (ELISA) for the detection of specific antigens or antibodies in patient samples. Immunofluorescence assays use fluorescent-labelled antibodies to detect specific pathogens.

We also have within our analytical means, rapid Immunoassays which are point-of-care tests that provide quick results for specific pathogens or toxins. But this is a less reliable diagnostic test, although fast and easy.

As clinicians, if we suspect chemical poisoning from history taking and clinical presentations, we will use chemical analysis, not send specimens for bacterial cultures.

There are a number of chemical methods for this, such as wet chemical analysis or using a mass spectrometry for identification of bacterial proteins or toxins.  Besides. We also have gas chromatography-mass spectrometry (GC-MS) for detection and identification of chemical toxins and contaminants in food. We use this if we suspect from the symptoms and signs presented by the patients that it was chemical and not microbial food poisoning.

Of course, we are also armed with serological methods such as using agglutination tests for the identification of bacteria based on their ability to clump together when mixed with specific antibodies. This involves Western Blotting for the detection of specific proteins related to pathogens in a sample.

We can also use biochemical methods to identify bacteria based on their metabolic characteristics (e.g., catalase test, oxidase test, fermentation tests).

In food and medical toxicology where I am also familiar when I was working in MIT in this area, other bioassays can also be used for toxin detection.

This involves biological systems (e.g., cell cultures, animal models) to detect the presence of toxins together with chemical assays for known toxins (e.g., aflatoxins, botulinum toxin). We can also use cell culture for the isolation and identification of viruses from patient samples, and for this part of identification and diagnosis, we use the electron microscopy for visualization of virus particles.

Let me emphasize the importance of sample collection and handling because proper sample collection, storage, and transportation are crucial for accurate diagnosis. Samples should be collected as soon as possible after the onset of symptoms and handled according to specific protocols to prevent contamination or degradation.

These methods can be used in combination to provide a comprehensive diagnosis of food poisoning, identifying both the causative agent and any associated toxins.

Let me now go back to this question about food poisoning from a bloated food can as I promised to explain earlier.

A bloated can of food typically indicates spoilage due to the growth of gas-producing microorganisms. The most common microbial organisms involved in this type of spoilage we encounter, mainly from my training and in my working experience, involves the Clostridium species.  These are anaerobic, spore-forming bacteria. They can produce gas as they grow, causing the can to bloat. Clostridium botulinum, in particular, is a dangerous pathogen that can produce botulinum toxin, leading to botulism and rapid death. It is very difficult to manage this infection even with powerful and selective antibiotics.

Having said that, there are also lactic acid bacteria that can also cause a can of food especially milk and milk products to bloat up. Certain species, such as Lactobacillus and Leuconostoc, can ferment sugars into lactic acid and carbon dioxide, resulting in gas production. However, my thinking is, it is less likely to suffer from food poisoning due to lactic acid. After all, yogurt contains lots of lactic acids. The bacteria used for fermenting lactose in milk into lactic acid in yogurt are primarily Lactobacillus bulgaricus and Streptococcus thermophilus. These two species work together in a symbiotic relationship to produce the lactic acid that gives yogurt its tangy flavour and thick texture. They don’t cause food poisoning; in fact, their probiotic actions are most encouraged.

Other bacteria that can cause gas formation are the Enterobacteriaceae.  This family of bacteria includes various genera such as Escherichia, Enterobacter, and Klebsiella. Some of these bacteria can produce gas during the fermentation of carbohydrates. The bacillus species involved are aerobic, spore-forming bacteria. Some species can produce gas and spoil canned foods.

Yeasts and moulds such as Saccharomyces can also produce gas during their growth. They are more likely to be involved in spoilage if the canning process was compromised, allowing oxygen to enter the can.

Gas formation causing canned foods to bloat up is dues to holes and leakages in the seams in the cans. The bloating of a can is a serious sign of spoilage, and such cans should not be consumed as they can pose significant health risks. Proper canning procedures, including adequate heating and sealing, are crucial to prevent the growth of these microorganisms.

I hope my explanation has helped you as a medical doctor to diagnose food poisoning in your patients better and more accurately for their benefit and welfare.  As requested, It is a pleasure for me to use my additional post-graduate training to help you as a medical doctor to diagnose more specifically and very accurately.

Take care Dr Sam

Ju-boo lim