Detection and molecular characterization of methicillin resistant Staphylococcus aureus from table eggs

Authors: SYED, MUHAMMAD - University Of Haripur; SHAH, SYEDA - University Of Haripur; SHERAFZAL, YASMIN - University Of Haripur; SHAFI-UR-REHMAN, SYED - University Of Haripur; KHAN, MUSHTAQ - University Of Haripur; Barrett, John; Woodley, Tiffanie; JAMIL, BUSHRA - Comsats Institute Of Information Technology; ABBASI, SHAHID - Al-Sayed Hospital; Jackson, Charlene

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2017
Publication Date: 2/1/2018
Citation: Syed, M., Shah, S., Sherafzal, Y., Shafi-Ur-Rehman, S., Khan, M., Barrett, J.B., Woodley, T.A., Jamil, B., Abbasi, S., Jackson, C.R. 2018. Detection and molecular characterization of methicillin resistant Staphylococcus aureus from table eggs. Foodborne Pathogens and Disease. 15(2):86-93.

Interpretive Summary: Staphylococcus aureus is a bacterium that can be commonly found on the skin or in the nasal passages of most humans and animals. It can cause a number of diseases in humans including staphylococcal food poisoning characterized by vomiting and diarrhea. Eggs are usually considered safe and are naturally protected by the egg shell and a semi-permeable membrane; however, bacteria such as S. aureus may enter and contaminate the eggs by crossing both the egg shell and the membrane. In addition, there is increasing interest in the presence of antimicrobial resistance in S. aureus, specifically methicillin-resistant S. aureus (MRSA). In this study, staphylococci were isolated from table eggs in Pakistan and MRSA from the products were characterized. MRSA were recovered from 11% of the eggs and all were multidrug resistant. Using molecular analysis, the MRSA were characteristic of MRSA known to cause human infections. Results from this study showed that MRSA are present in table eggs which may be transmitted to humans. This information is especially useful for consumers and personnel who handle eggs as safe handling and cooking methods should be followed to avoid colonization and infection with MRSA. It is also useful for scientists as they develop prevention and control strategies.

Technical Abstract: Table eggs are nutritionally important food consumed globally. Despite being protected inside the hard shell and a semi-permeable membrane, the egg contents may be contaminated with microbes and thus become a possible carrier of infectious agents to humans. A number of medically significant bacterial species such as Salmonella enterica, Listeria monocytogenes and Yersinia enterocolitica have already been reported from table eggs. More important is the presence of antimicrobial resistant bacterial strains in this food source. The present study was aimed at detection and characterization of Staphylococcus aureus from table eggs collected from different retail shops in Haripur city of Pakistan. Staphylococci were isolated from 300 eggs collected from December, 2015 to May, 2016. Staphylococcus aureus isolates were tested for antimicrobial susceptibility using broth microdilution and characterized using Pulsed-Field Gel Electrophoresis (PFGE), Multi-Locus Sequence Typing (MLST), SCCmec typing and spa typing. The presence of Panton-Valentine Leukocidin (PVL) and antimicrobial resistance genes were detected using PCR. Staphylococci were isolated from 21.3% (64/300) of the table eggs tested. Of those, 59% (38/64) were identified as S. aureus of which 33 (86.8%) were positive for mecA (MRSA, Methicillin-Resistant S. aureus). All MRSA were multidrug resistant (resistant to two or more antimicrobial classes), contained aac-aph, and were pvl+. Using MLST, spa typing, and SCCmec typing, three genotypic patterns were assigned: ST8-t8645-MRSA-IV, associated with USA300; ST772-t657-MRSA-IV and ST772-t8645-MRSA-IV, both characteristic of the Bengal Bay community-associated MRSA clone. Molecular typing by PFGE revealed that the bacterial population was highly homogenous with only two patterns observed. This study is the first report of detection of human-associated, pvl+ MRSA from table eggs. The genetic similarities of MRSA present in the eggs to that of humans may suggest human to poultry transmission of MRSA via contamination.