The Plasmid-Encoded pGP3 Promotes Chlamydia Evasion of Acidic Barriers in Both Stomach and Vagina

Abstract

Although Chlamydia trachomatis is a human genital tract pathogen, chlamydial organisms have frequently been detected in both vaginal and rectal swab samples of animals and humans. The plasmid-encoded pGP3, a genital tract virulence factor, is essential for Chlamydia muridarum to colonize the mouse gastrointestinal tract. However, intracolon inoculation to bypass the gastric barrier rescued the colonization ability of a pGP3-deficient C. muridarum mutant, suggesting that pGP3 is required for C. muridarum to reach but not to colonize the large intestine. The pGP3-deficient mutant was rapidly cleared in the stomach and was 100-fold more susceptible to gastric killing. In mice genetically deficient in gastrin, a key regulator for gastric acid production, or pharmacologically treated with a proton pump inhibitor, the ability of pGP3-deficient C. muridarum to colonize the gastrointestinal tract was rescued. The pGP3-dependent resistance was further recapitulated in vitro with treatments with HCl, pepsin, or sarkosyl. In the genital tract, deficiency in pGP3 significantly reduced C. muridarum survival in the mouse vagina and increased C. muridarum susceptibility to vaginal killing by ϳ8 times. The pGP3-deficient C. muridarum was more susceptible to lactic acid killing, and the pGP3 deficiency also significantly increased C. trachomatis susceptibility to lactic acid. The above-described observations together suggest that Chlamydia may have acquired the plasmidencoded pGP3 to overcome the gastric barrier during its adaptation to the gastrointestinal tract and the pGP3-dependent resistance may enable chlamydial evasion of the female lower genital tract barrier during sexual transmission.

Distinct Roles of Chromosome- versus Plasmid-Encoded Genital Tract Virulence Factors in Promoting Chlamydia muridarum Colonization in the Gastrointestinal Tract

“…It is worth pointing out that G28.51.1 did initially reach the colon. In contrast, the plasmid mutant CMpGP3S never reached the colon at any time point following oral inoculation, which is consistent with our recent finding that CMpGP3S is extremely susceptible to the clearance by gastric acids (35). These observations together suggest that plasmid genes may mainly promote chlamydial resistance to , designated a chromosomal mutant, or a premature stop codon in plasmid gene pgp3 (CMpGP3S, designated a plasmid mutant) was orally/intragastrically inoculated into female C57BL/6J mice at the indicated doses (IFUs) (n ϭ 5 mice per group).…”

“…No live organisms were ever recovered from the IFN-␥-deficient mice orally inoculated with CMpGP3S. In contrast, in gastrin-deficient mice that are defective in gastric acid secretion without significant alterations in other host defense mechanisms (37), the plasmid mutant CMpGP3S was rescued, as shown previously (35), while the chromosomal mutant G28.51.1 was not, as shown in Fig. 6.…”

“…2). As we have previously shown (35), intracolonic inoculation with CMpGP3S successfully rescued its colonization defect in the GI tract. High levels of live organisms were recovered from the rectal swabs of the inoculated mice throughout the experiment.…”

“…Thus, these genital tract virulence factors are more important for chlamydial growth in mouse GI tracts than genital tracts. We recently found that orally delivered plasmid mutant CMpGP3S was rapidly cleared by gastric acid in the stomach and unable to reach the colon to establish stable colonization (35). In the current study, we found that the chromosomal mutant G28.51.1 was still able to reach the colon although the plasmid mutant CMpGP3S failed to do so in the same experiments, suggesting that lack of GI tract colonization by different mutants may involve distinct mechanisms.…”

“…We did note a delay in liveorganism shedding in these mice (the first positive detection was on day 21), which may reflect the time required for the orally inoculated G28.51.1 organisms to overcome the barriers in the stomach and small intestine. Indeed, as we have shown previously (35), IFN-␥-deficient mice still maintain robust acidic barrier function in the stomach since the gastric acid-susceptible plasmid mutant CMpGP3S was unable to overcome these barriers. No live organisms were ever recovered from the IFN-␥-deficient mice orally inoculated with CMpGP3S.…”