New congruences on multiple harmonic sums and Bernoulli numbers

Let P-n denote the set of positive integers which are prime to n. Let B-n be the n-th Bernoulli number. For any prime p >= 11 and integer r >= 2, we prove that Sigma(l1+l2+ ... +l6 = pr l1, ... ,l6 is an element of Pp) 1/l(1)l(2)l(3)l(4)l(5)l(6) - 5!/18p(r-1) B-p-3(2) (mod p(r)). This extends a family of curious congruences. We also obtain other interesting congruences involving multiple harmonic sums and Bernoulli numbers.