Lactose-fermenting, multiple drug-resistant Salmonella typhi strains isolated from a patient with postoperative typhoid fever

Fosfomycin for the treatment of multidrug-resistant, including extended-spectrum beta-lactamase producing, Enterobacteriaceae infections: a systematic review

Rising rates of resistance to antimicrobial drugs among Enterobacteriaceae limit the choice of reliably active forms of these drugs. We evaluated the evidence on fosfomycin as a treatment option for infections caused by members of the family Enterobacteriaceae with advanced resistance to antimicrobial drugs, including producers of extended-spectrum beta-lactamase (ESBL). We systematically reviewed studies evaluating the antimicrobial activity, or the clinical effectiveness of fosfomycin. 17 antimicrobial-susceptibility studies were found and included in our Review, accounting for 5057 clinical isolates of Enterobacteriaceae with advanced resistance to antimicrobial drugs (4448 were producers of ESBL); 11 of the 17 studies reported that at least 90% of the isolates were susceptible to fosfomycin. Using a provisional minimum inhibitory concentration susceptibility breakpoint of 64 mg/L or less, 1604 (96.8%) of 1657 Escherichia coli isolates producing ESBL were susceptible to fosfomycin. Similarly, 608 (81.3%) of 748 Klebsiella pneumoniae isolates producing ESBL were susceptible to fosfomycin. In two clinical studies, oral treatment with fosfomycin-trometamol was clinically effective against complicated or uncomplicated lower urinary tract infections caused by ESBL-producing E coli in, cumulatively, 75 (93.8%) of the 80 patients evaluated. Initial clinical data support the use of fosfomycin for the treatment of urinary tract infections caused by these pathogens, although further research is needed.

lac repressor is an antivirulence factor of Salmonella enterica: its role in the evolution of virulence in Salmonella

The genus Salmonella includes many pathogens of great medical and veterinary importance. Bacteria belonging to this genus are very closely related to those belonging to the genus Escherichia. lacZYA operon and lacI are present in Escherichia coli, but not in Salmonella enterica. It has been proposed that Salmonella has lost lacZYA operon and lacI during evolution. In this study, we have investigated the physiological and evolutionary significance of the absence of lacI in Salmonella enterica. Using murine model of typhoid fever, we show that the expression of LacI causes a remarkable reduction in the virulence of Salmonella enterica. LacI also suppresses the ability of Salmonella enterica to proliferate inside murine macrophages. Microarray analysis revealed that LacI interferes with the expression of virulence genes of Salmonella pathogenicity island 2. This effect was confirmed by RT-PCR and Western blot analysis. Interestingly, we found that SBG0326 of Salmonella bongori is homologous to lacI of Escherichia coli. Salmonella bongori is the only other species of the genus Salmonella and it lacks the virulence genes of Salmonella pathogenicity island 2. Overall, our results demonstrate that LacI is an antivirulence factor of Salmonella enterica and suggest that absence of lacI has facilitated the acquisition of virulence genes of Salmonella pathogenicity island 2 in Salmonella enterica making it a successful systemic pathogen.

Note: comparison of media for the isolation of lactose-positive Salmonella

We studied the capacity of 10 selective media (Rambach agar, RB; salmonella-shigella agar, SS; SM-ID medium, SM; Hektoen enteric agar, HE; modified semisolid Rappaport-Vassiliadis agar, MSRV; bismuth sulphite agar, BS; MacConkey agar, MC; brilliant green agar, BG; novobiocin-brilliant green-glucose agar, NBG; and novobiocin-brilliant green-glycerol-lactose agar, NBGL), and the C8-esterase test (MUCAP test, Biolife, Italy) to detect the growth of 14 strains of lactose-positive Salmonella (12 Salm. virchow and two Salm. montevideo) and 16 Salm. arizonae. Suspensions of pure strain were plated on the aforementioned media and on Mueller-Hinton, used as a control, with inocula of 3 x 10(2) cfu ml-1. The performance of BS was excellent, determining the 30 strains as typical Salmonella colonies (H2S+). On NBG, 27 strains were detected. On MSRV, only some strains grew and only one produced swarming. On the other media, the two Salm. montevideo and the 12 Salm. virchow strains produced coliform colonies. Some of these latter were inhibited on BG and NBGL. The 16 Salm. arizonae strains produced typical colonies on all the media, except on RB, SM and MSRV. On NBGL, two strains did not produce H2S. The C8-esterase test was only successful with Salm. montevideo and Salm. virchow on NBG and RB (with a few exceptions on the latter). However, with Salm. arizonae the test was positive on SS, MC, HE, BG and NBG. In summary, BS was the best medium of those used (all the 30 strains were isolated), followed by NBG (27 isolates).

Systemic infections in three infants due to a lactose-fermenting strain of Salmonella virchow

Three previously healthy children developed gastroenteritis which led within a few days to systemic infections, two cases of bacteremia and one of meningitis. A lactose-fermenting Salmonella virchow strain was isolated from cerebrospinal fluid and blood cultures. In one case, this strain was also isolated from stool cultures. All the children had been fed the same milk formula. There was no other relationship between them. The batch of dried-milk formula was confirmed as the source of the infection by isolation of an identical lactose-fermenting Salmonella virchow strain by the Centro Nacional de Alimentación.

Fluoroquinolones in the treatment of typhoid fever and the carrier state

Typhoid fever remains an important public health problem throughout the world with a higher morbidity and mortality rate in the developing countries. Early establishment of the diagnosis and prompt initiation of treatment with chloramphenicol, ampicillin or trimethoprim-sulfamethoxazole is not necessarily followed by complete resolution of the infection. Between 1% and 6% of patients with typhoid fever become chronic biliary carriers of Salmonella typhi. These carriers are potential factors in the continued transmission of the disease. The increasing emergence worldwide of strains showing multiple resistance to the agents traditionally used in therapy has encouraged investigators to seek alternatives such as third generation cephalosporins and recently the new 4-quinolones, which have greater activity against Salmonella typhi including multi-resistant strains. The fluoroquinolones seem to be the treatment of choice in those regions where resistant strains of Salmonella typhi are prevalent.

In vivo selection for transmissible drug resistance in Salmonella typhi during antimicrobial therapy

We report the recovery of Salmonella typhi that acquired resistance to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, and gentamicin subsequent to multiple antibiotic therapy. Escherichia coli and Klebsiella pneumoniae isolates which were recovered from the same stool sample displayed identical resistance patterns. Agarose gel electrophoresis revealed that S. typhi and laboratory-derived transconjugants contained a high-molecular-weight plasmid present in the resistant intestinal bacteria.

Bacteremia caused by a lactose-fermenting, multiply resistant Salmonella typhi strain in a patient recovering from typhoid fever

A female patient suffered a typical attack of typhoid fever due to a lactose-negative, fully susceptible Salmonella typhi strain. During convalescence she became febrile, and a lactose-fermenting S. typhi strain resistant to ampicillin, chloramphenicol, tetracycline, and trimethoprim was isolated from blood culture. This isolated was shown to harbor a plasmid which cotransferred lactose fermentation and antibiotic resistance.

Molecular characterization of a conjugative R-lac plasmid in Salmonella typhi isolated from a patient with typhoid fever

In a strain of Salmonella typhi isolated from a patient with post-operative typhoid fever, a 217-Kb conjugative plasmid has been detected which codes for lactose fermentation and drug resistance to sulphonamides (SA), chloramphenicol (CP), ampicillin (AP), kanamycin (KM) and trimethoprim (TP). The physical and genetic map was constructed. The lac region containing the lacI gene, the regulatory region and the lacZ and lacY genes was shown to be structurally identical to that of Escherichia coli K12. A transposon carrying genes for resistance to CP and AP, as well as four copies of IS1-like elements, were detected and localized on the plasmid. Their role in the emergence of such a large plasmid is discussed.