What is a bacterial culture and sensitivity test?
A bacterial culture is the activated growth of the sampled bacteria from an infection site of the patient onto a fortified surface in the laboratory. Colonies of cultivated bacteria are exposed to various antibiotics to find the best bactericidal/ bacteriostatic option. This sensitivity test, also referred to as the susceptible test, highlights the growth inhibition status for the micro-organism.

Some tests specify the MIC (minimum inhibitory concentration) levels of the drug so as to optimise the use of the antibiotic.

What is the purpose of such a test and is it a prerequisite in the treatment protocols for different types of infections?
It is an investigative test ordered by the discretion of the physician since the reporting procedures on infection prevention and control are not mandatory in countries without surveillance system oversight.

So, a treating doctor, having taken all factors into consideration including the associated costs for the tests and the potential risks associated with the waiting period (ranging from 24 hours to two weeks for the results, depending on the infection type), will decide on the practicality of ordering a bacterial culture and sensitivity test.

Based on the patient’s presentation (signs and symptoms) from the suspecting invading micro-organism and the clinical evaluation, a decision is made whether to initiate treatment prior to waiting for the results from the culture and sensitivity, which would function as a confirmation to the diagnosis.

For uncomplicated infections with classic characteristics due to those typically known invading pathogens, it may not necessitate a culture and sensitivity test as a routine prerequisite investigation to treatment. However when the physician deduce a complicated or mixed infection with known resistant pathogens, especially if resistant to first line treatment prescribed, then a bacterial culture and sensitivity test is the absolutely required protocol.

What are the established resistant pathogens and in what types of infections they are prevalent?
Globally, the established resistant infections are respiratory infections due to S. pneumonia (55 percent resistant to penicillin in some countries), HIV (resistant to marketed agents), diarrheal diseases due to S. dysenteriae (90 per cent resistant to cotrimoxazole or septrin) and S. typhi (multiple drug resistant), tuberculosis (multiple drug resistant) and malaria due to P. falciparum (resistant to chloroquine in 81 out of 92 countries).

According to the European Antimicrobial Resistance Surveillance System network (29 member countries) and the Center for Disease Control and Prevention National Nosocomial Infection Surveillance System, there have been increasing trends in pseudomonas aeruginosa resistance to three out the five classes of antibiotics to Healthcare-Associated Infections (HAI) or hospital acquired, such as central line-associated bloodstream infection, catheter-associated urinary tract, ventilator associated pneumonia and surgical site infections. These are caused mainly due to multidrug-resistant Gram-negative bacteria (MDR-GNB) where known contributing pathogens are MDR-pseudomonas aeruginosa, MDR-acinetobacter baumanni and enterobacteriacease producing ß-lactamases and carbapenemases. Other isolates under surveillance were escherichia coli and klebsiella pneumonia, where E. coli had as high as 36 percent resistance to third generation cephalosporins. This was reported years prior to COVID-19 when hospital admissions were more controllable, less complicated and less risky.
Interpreting the results from the sensitivity test.

There are three categories to classify the response of the colonies of bacteria to the antibiotics – Sensitive, Intermediate or Resistant. The first option suggests the named antibiotics to which the bacteria under investigation are most responsive (sensitive). It is only if the sensitive antibiotics are not available then consideration of the intermediate options will be made but at higher than normal dosages. The resistant antibiotics should never be prescribed.

In preserving the rational use of antibiotics, fourth generation antibiotics such as vancomycin is considered for use only in life-threatening cases and should only be authorised by a consultant, thereby highly restricting the last arsenal at hand.

In conclusion various measures should be made mandatory so as to minimise the spread of these resistant pathogens that cause such “difficult to treat” infections. We have learnt two of the WHO recommended protocols due to COVID-19 pandemic, which are hand-washing with soap and water, especially when bodily fluids and excretions are visible on the healthcare worker, and routine alcohol sanitisation prior to attending to a patient. Another measure to curb resistance will be to restrict the access and hence use of antibiotics, allowing use only when directed by a doctor, as is done with the anti-retrovirals in the National HIV programme. However, despite these restrictive measures, resistance is still evident since patient compliance may be another contributing factor.

For further pharmacological guidance and physician referral, contact the pharmacist of Medicine Express PHARMACY located at 223 Camp Street, between Lamaha and New Market Streets. If you have any queries, comments or further information on the above topic kindly forward them to medicine.express@gmail.com or send them to 223 Camp Street, N/burg. Tel #225-5142.