This research conducted by Abdul Malik and Khalilur Rehman is of much significance because it relates to those bacteria present in food items, that are resistant to antibiotics. Such pathogenic bacteria are transferred into the human body through milk intake, and at times antibiotics that are administered for the treatment of infection do not succeed in destroying the pathogens, causing a threat to the life of the infected person.
The most frequently prescribed drugs for infection are b-lactam based. This is because b-lactamases are the enzymes produced by the pathogens in the body, which are targeted to be destroyed by antibiotics. In this study, bacterial isolates from foods have been examined, showing resistance to antibiotics.
The research initiated with the collection of food samples; 36 food samples, comprising raw and pasteurized milk, fruit juices, and vegetables were collected from a local market. They were sent to the laboratory for initial processing speedily, within three hours of collection. These samples were first homogenized and emulsified by suspending 10ml or 10g, in 90ml normal saline solution. The samples were diluted, and also plated on different selective media for enculturation, followed by colony growths.
Staphylococcus spp. was isolated in accordance with the standard methods prescribed by the American Public Health Association. Samples were placed on Staphylococcus aga, and incubated at 37degrees centigrade for 24 hours. The colonies formed were counted with the colony counter. Some of the suspected colonies were identified for Staphylococci.
An amount of 10ml of samples was added to MacConkey’s broth at 37 degrees centigrade for a span of 48 hours. Those which exhibited acid and gas production were further placed on Escherichia Coli broth and incubated at 44.5±0.2 degrees centigrade for 24 hours, in a shaking water bath. The suspected colonies were identified for Escherichia Coli, and Escherichia Coli B was used as a control.
The minimum inhibitory concentration (MIC) of the E.Coli and Staphylococcus spp. isolates were taken by the plate dilution method. Cultures of each isolate were made, and control experiments with E.Coli B were also being undertaken alongside. The antibiotic solutions were put into sterilized nutrient agar plates. The inoculated plates were kept for incubation at 37 degrees centigrade for 24 hours.
The b-lactamase enzymes were isolated from bacterial strains through spot inoculation on starch agar plates. Positive and negative tests were made for assurance of b-lactamase production by phosphate buffered solutions containing potassium iodide.
The results obtained from these experiments show that the strains obtained were based on cultural, morphological, and biochemical characteristics. All the isolates were differentiated according to the antibiotic susceptibility test. The antibiotics that were chosen for the study included those that were similar to the ones that are commonly used, like amoxyciilin, etc.
This study showed that most of the isolates had multiple resistance to varying antibiotics and drugs. Different numbers of resistance patterns were observed from the Staphylococcal and E.coli isolates from the food items. This resistance was seen against two to seven antibiotics. Also, the MICs of ampicillin and cloxacillin for each isolate were seen. These included the study for b-lactamases.
Those Staphylococcal strains that were highly resistant against ampicillin and coxacillin showed a direct proportionality of their decolorized colonies to the MICs obtained. In the control zones there was no decolorization seen, which indicates that MIC values are also directly related to b-lactamases production. It was a quick method to test for sensitivity against b-lactam antibiotics.
References
M. Khalilur Rahman Khan and Abdul Malik. Antibiotic resistance and detection of b-lactamase in bacterial strains of Staphylococci and Escherichia coli isolated from foodstuffs. World Journal of Microbiology & Biotechnology 17: 863–868, 2001. 2001 Kluwer Academic Publishers. Printed in the Netherlands.