Effect of phage on the infectivity of Vibrio cholerae and emergence of genetic variants.
Seasonal epidemics of cholera in Bangladesh are self-limited in nature, presumably due to phage predation of the causative Vibrio cholerae during the late stage of an epidemic, when cholera patients excrete large quantities of phage in their stools. To further understand the mechanisms involved, we studied the effect of phage on the infectivity and survival of V. cholerae shed in stools. The 50% infectious dose of stool vibrios in infant mice was approximately 10-fold higher when the stools contained a phage (1.8 x 10(3) to 5.7 x 10(6) PFU/ml) than when stools did not contain a detectable phage. In competition assays in mice using a reference strain and phage-negative cholera stools, the infectivity of biofilm-like clumped cells was 3.9- to 115.9-fold higher than that of the corresponding planktonic cells. However, the difference in infectivity of these two cell populations in phage-positive stools was significantly less than that in phage-negative stools (P = 0.0006). Coculture of a phage and V. cholerae or dilutions of phage-positive cholera stools in nutrient medium, but not in environmental water, caused rapid emergence of phage-resistant derivatives of the bacteria, and these derivatives lost their O1 antigen. In cholera stools and in intestinal contents of mice prechallenged with a mixture of V. cholerae and phage, the bacteria remained completely phage susceptible, suggesting that the intestinal environment did not favor the emergence of phage-resistant derivatives that lost the O1 antigen. Our results indicate that phages lead to the collapse of epidemics by modulating the required infectious dose of the bacteria. Furthermore, the dominance of phage-resistant variants due to the bactericidal selective mechanism occurs rarely in natural settings, and the emerging variants are thus unable to sustain the ongoing epidemic.
Zahid
M Shamim Hasan
MS
Molecular Genetics Laboratory, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka-1212, Bangladesh.
Udden
S M Nashir
SM
Faruque
A S G
AS
Calderwood
Stephen B
SB
Mekalanos
John J
JJ
Faruque
Shah M
SM
D000818:Animals; D001435:Bacteriophages / Q000235:genetics* / Q000302:isolation & purification; D002771:Cholera / Q000635:transmission*; D005243:Feces / Q000382:microbiology*; D006801:Humans; D051379:Mice; D014734:Vibrio cholerae / Q000235:genetics / Q000472:pathogenicity* / Q000821:virology*
Proc Natl Acad Sci U S A. 2005 Apr 26;102(17):6119-24
15829587
Infect Immun. 2001 Jan;69(1):435-45
11119535
Microbiol Mol Biol Rev. 1998 Dec;62(4):1301-14
9841673
Proc Natl Acad Sci U S A. 2006 Mar 21;103(12):4652-7
16537404
J Infect Dis. 2006 Apr 1;193(7):1029-36
16518766
Nature. 2002 Jun 6;417(6889):642-5
12050664
Int Microbiol. 2004 Dec;7(4):285-9
15666250
Trans R Soc Trop Med Hyg. 1961 Sep;55:440-2
14475439
Proc Natl Acad Sci U S A. 2005 Feb 1;102(5):1702-7
15653771
Clin Microbiol Rev. 1995 Jan;8(1):48-86
7704895
Trop Geogr Med. 1984 Dec;36(4):335-40
6335611
Proc Natl Acad Sci U S A. 2007 Nov 27;104(48):19091-6
18024592
Trends Microbiol. 1997 Apr;5(4):161-5
9141191
Mol Microbiol. 2006 Apr;60(2):417-26
16573690
Proc Natl Acad Sci U S A. 2006 Apr 18;103(16):6350-5
16601099
Nature. 2005 Dec 8;438(7069):863-6
16341015
Mol Microbiol. 1995 Nov;18(4):685-701
8817491
Infect Immun. 2002 Nov;70(11):5990-6
12379674