Psychoactive Drugs Induce the SOS Response and Shiga Toxin Production in Escherichia coli

Abstract

Several classes of non-antibiotic drugs, including psychoactive drugs, proton-pump inhibitors (PPIs), non-steroidal anti-inflammatory drugs (NSAIDs), and others, appear to have strong antimicrobial properties. We considered whether psychoactive drugs induce the SOS response in E. coli bacteria and, consequently, induce Shiga toxins in Shiga-toxigenic E. coli (STEC). We measured the induction of an SOS response using a recA-lacZ E. coli reporter strain, as RecA is an early, reliable, and quantifiable marker for activation of the SOS stress response pathway. We also measured the production and release of Shiga toxin 2 (Stx2) from a classic E. coli O157:H7 strain, derived from a food-borne outbreak due to spinach. Some, but not all, serotonin selective reuptake inhibitors (SSRIs) and antipsychotic drugs induced an SOS response. The use of SSRIs is widespread and increasing; thus, the use of these antidepressants could account for some cases of hemolytic-uremic syndrome due to STEC and is not attributable to antibiotic administration. SSRIs could have detrimental effects on the normal intestinal microbiome in humans. In addition, as SSRIs are resistant to environmental breakdown, they could have effects on microbial communities, including aquatic ecosystems, long after they have left the human body.

Keywords: RecA; Shiga-toxigenic E. coli; enterohemorrhagic E. coli; hemolytic-uremic syndrome; hypermutation; phenothiazines; serotonin selective reuptake inhibitors.

Figure 1

Effect of SSRIs on RecA expression and Stx2 release. Panels (A,B): RecA expression was measured using the JLM281 reporter strain and the Miller assay, as described in the Materials and Methods section. Panels (C,D): Stx2 production and release into the supernatant medium was measured at 5 h in response to three SSRIs, using STEC strain Popeye-1.

Figure 2

Effect of antipsychotic drugs on RecA expression and on Stx production. Panels (A–D): RecA expression using the Miller assay. Panel (E): comparison of Stx production triggered by two SSRIs, by the antipsychotic drug trifluoperazine, by zidovudine, and by ciprofloxacin. Stx2 release from Popeye-1 was measured at 5 h.

Figure 3

Structures of several SSRI antidepressant and antipsychotic drugs.

Figure 4

Elongation response of E. coli bacteria to aztreonam, ciprofloxacin, and fluoxetine. Panel (A): E. coli JLM281 was exposed to 0.75 µg/mL aztreonam, beginning 1 h after subculture. Bacteria were collected at 4 h, stained with 0.2% acridine orange in 50% ethanol, then washed, allowed to dry on a glass microscope slide, and photographed at 1000× magnification. Size bar indicates 10 µm. Panel (B): E. coli Popeye-1 was exposed to 12 ng/mL ciprofloxacin, added after a 1 h delay, and was collected at 5 h for acridine orange staining. Panels (C,D): strain Popeye-1 was exposed to either 60 µg/mL fluoxetine (Panel C) or 70 µg/mL fluoxetine (Panel D) and then collected, stained, and photographed. The red arrow in Panel (D) indicates an elongated E. coli bacterial cell. The size bar in Figure 4A applies to the other panels of Figure 4 as well.