This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Commonest cause of nosocomial infection 
Select and explain. 
A. Pseudomonas, B. Staphylococci, C. Klebsiella, D. Enterobacteriacea
B: Staphylococci
Answer: B: Staphylococci 
Explanation: Controversial MCQ, no where there is clear cut reference for MC agent of HAI
Initially hospital outbreaks were caused by Gram positive organisms like Streptococcus pyogenes and the methicillin resistant Staphylococcus aureus (MRSA)
Presently Gram negative enteric pathogens (Enterobacteriaceae) including Escherichia coli, Klebsiella and Enterobacter species have emerged as an important cause
Pseudomonas and Acinetobacter species are also common nosocomial pathogens and are extremely resistant to common antibiotics and antiseptics.