Question

1. When placed in a GasPak system, what will happen to the following bacteria after incubation at 37C? a) Bacillus subtilis b) Clostridium sporogenes

2. a) A patient arrives at a clinic with a urinary tract infection caused by E. coli. A urine sample is collected and inoculated onto EMB agar. Describe the expected appearance of the growth on this media.

b) A patient is experiencing all the symptoms of having a urinary tract infection. A urine sample is collected and inoculated onto EMB agar. Nothing grows on the plate. Assuming he indeed has a urinary tract infection, provide a likely explanation for this.

Answer 1

Answer :

1.a) Bacillus subtilis will not grow in anaerobic condition because it is considered as strict aerobe.

b) Clostridium perfringens will grow since it is strict anaerobe.

2. a) E.coli on EMB agar will produce large blue black colonies with green metallic sheen.

b) The likely causative pathogen for urinary tract infection may be Gram positive bacteria such as Staphylococcus or Enterococcus in this case. EMB agar is a selective medium which inhibits the growth of Gram positive bacteria while enhancing the growth of Gram negative bacteria such as E.coli , hence on EMB culture there will be no growth of Gram positive bacteria.

Discussion and explanation:

1.Gas pak system is a set up to build an anaerobic environment. Components of this system are - Polycarbonate jar, lid to tightly pack the jar, pallidium as catalyst, a special pouch with sodium borohyride and sodium bicarbonate which react in the presence of water to form hydrogen and carbon dioxide gases. This produced hydrogen reacts with any available oxygen with help of pallidium as a catalyst producing water. This provides a perfect anaerobic condition within jar which can be detected by methylene blue's white colour.

As Bacillus subtilis is considered to be strictly aerobic, it will not survive in the absence of oxygen (anaerobic condition).

As Clostridium perfringens is strict anaerobe it will survive in gas pak jar, infact this system will be favourable for its growth.

2. EMB agar also known as Eosin Methylene blue agar is a selective and differential medium. Eosin and methylene blue inhibit the growth of Gram positive bacteria allowing the growth of only Gram negative bacteria. Lactose fermenters such as Escherichia coli will produce pigmented colonies due to acidic pH and indicators such as methylene blue and eosin. While nonlactose fermenter such as Shigella will produce non pigmented colonies on EMB agar. E.coli is a lactose fermenter producing large blue black colonies with green metallic sheen.