Outer membrane protein A (OmpA) deficient Salmonella Typhimurium displays enhanced susceptibility towards β-lactam antibiotics: third-generation cephalosporins (ceftazidime) and carbapenems (meropenem)

The invasive non-typhoidal serovar of Salmonella enterica, namely Salmonella Typhimurium ST313, causes bloodstream infection in sub-Saharan Africa. Like other bacterial pathogens, the development of antimicrobial resistance is a severe problem in curing non-typhoidal Salmonella infection. In this work, we have investigated the role of four prominent outer membrane porins of S. Typhimurium, namely OmpA, OmpC, OmpD, and OmpF, in resistance against broad-spectrum β-lactam antibiotics- ceftazidime and meropenem. We found that deleting OmpA from Salmonella makes the bacteria susceptible to β-lactam drugs. The MIC for both the antibiotics reduced significantly for STM ΔompA compared to the wild-type and the ompA complemented strains. Despite the presence of antibiotics, the uninterrupted growth of STM ΔompC, ΔompD, and ΔompF endorsed the dispensability of these three porins in antimicrobial resistance. The β-lactam antibiotics caused massive depolarization in the outer membrane of the bacteria in the absence of OmpA. We have proved that none of the extracellular loops but the complete structure of perfectly folded OmpA is required by the bacteria for developing antimicrobial resistance. Our data revealed that STM ΔompA consumed more antibiotics than the wild-type and the complemented strain, resulting in severe damage of the bacterial outer membrane and subsequent killing of the pathogen by antibiotic-mediated oxidative stress. Upon deleting ompA, the steady decrease in the relative proportion of antibiotic-resistant persisters and the clearance of the STM ΔompA from the liver and spleen of C57BL/6 mice upon treatment with ceftazidime proved the role of OmpA in rendering protection against β-lactam antibiotics.

PATHOLOGY OF EQUINE INFECTION WITH SALMONELLA TYPHIMPRIUM VAR COPENHAGEN

Twelve horses were divided into three equal groups. Group I animals were inoculated orally with (3.7 X1012)CFU of a highly virulent strain of Salmonella typhimurium 3,;a_r cop§_n__hagen. Group 11 animals were inoculated orally with 2 doses of Salmonella and then challenged with a high dose. Group III horses, served as non - infected control. ‘ The main lesions were primarily confined to the digestive tract and were characterized by catarrhal enteritis. Pseudornembrane covered the mucosa of the ileum at the ileo — cecal Valve region. Histopathological examination revealed marked rnononuclear cellular infiltration in the lamina propria and occasionally necrosis and edema in the mucosa and submucosa of the intestine.

BLOOD AND ACID-BASE CHANGES IN CAILVES EICPERIMENTALLY INFECTED WITH SALMONELLA TYPHIMPRIUM

The experimental design of this study was included (12) Friesian calves aged between 3-5 weeks. Calves were divided into two groups. Group I consisted of (8) calves were infected experimentally with 1.5 x 10“ of Salmonella typhimurium and often that treatment with chloramphenicol and electrolytes fluid were takes place. Group II consisted of (4) calves were infected with organisms but without treatment. The clinical findings of the disease were characterized by two forms which includes the septicemic and enteric forms. Haematological changes revealed a variable number of the total and differential leukocytic count, increased PCV, fibnnogen and decreased of the total plasma protein. . The changes in the acid-based balance indicate the development of metabolic acidosis.

ULTRASTRUCTURAL CHANGES OF THE MESENTRIC LYMPH NODES OF CALVES EXPERIMENTALLY INFECTED WITH SALMONELLA TYPHIMURIUM

A systemic study was done on the pathogenesis of experimentally induced Salmonella typhimurium infection in calves. The present investigation was carried out on sixteen normal colostrum fed friesian calves, ranging in age from 3 to 6 weeks. The calves were divided into two equal groups. Group I inoculated orally with (1.5 x 10'') Salmonella typhimurium and group IA served as control. • The early ultrastructural alteration in the mesenteric lymph nodes was the presence of many free Salmonella in localized vacuoles. The interaction between the host cells and phagocytized Salmonella was also observed.

Magnetic Nanoparticles Enhanced Surface Plasmon Resonance Biosensor for Rapid Detection of Salmonella Typhimurium in Romaine Lettuce

Salmonella is one of the major foodborne pathogens responsible for many cases of illnesses, hospitalizations and deaths worldwide. Although different methods are available to timely detect Salmonella in foods, surface plasmon resonance (SPR) has the benefit of real-time detection with a high sensitivity and specificity. The purpose of this study was to develop an SPR method in conjunction with magnetic nanoparticles (MNPs) for the rapid detection of Salmonella Typhimurium. The assay utilizes a pair of well-characterized, flagellin-specific monoclonal antibodies; one is immobilized on the sensor surface and the other is coupled to the MNPs. Samples of romaine lettuce contaminated with Salmonella Typhimurium were washed with deionized water, and bacterial cells were captured on a filter membrane by vacuum filtration. SPR assays were compared in three different formats—direct assay, sequential two-step sandwich assay, and preincubation one-step sandwich assay. The interaction of flagellin and MNPs with the antibody-immobilized sensor surface were analyzed. SPR signals from a sequential two-step sandwich assay and preincubation one-step sandwich assay were 7.5 times and 14.0 times higher than the direct assay. The detection limits of the assay were 4.7 log cfu/mL in the buffer and 5.2 log cfu/g in romaine lettuce samples.

Effects of 405 ± 5-nm LED Illumination on Environmental Stress Tolerance of Salmonella Typhimurium in Sliced Beef

Salmonella Typhimurium is a widely distributed foodborne pathogen and is tolerant of various environmental conditions. It can cause intestinal fever, gastroenteritis and bacteremia. The aim of this research was to explore the effect of illumination with 405 nm light-emitting diodes (LEDs) on the resistance of S. Typhimurium to environmental stress. Beef slices contaminated with S. Typhimurium were illuminated by 405 nm LEDs (18.9 ± 1.4 mW/cm2) for 8 h at 4 °C; controls were incubated in darkness at 7 °C. Then, the illuminated or non-illuminated (control) cells were exposed to thermal stress (50, 55, 60 or 65 °C); oxidative stress (0.01% H2O2 [v/v]); acid stress (simulated gastric fluid [SGF] at pH 2 or 3); or bile salts (1%, 2%, or 3% [w/v]). S. Typhimurium treated by 405 nm LED irradiation showed decreased resistance to thermal stress, osmotic pressure, oxidation, SGF and bile salts. The transcription of eight environmental tolerance-related genes were downregulated by the illumination. Our findings suggest the potential of applying 405 nm LED-illumination technology in the control of pathogens in food processing, production and storage, and in decreasing infection and disease related to S. Typhimurium.

Gram-Negative Bacteria Salmonella typhimurium Boost Leukotriene Synthesis Induced by Chemoattractant fMLP to Stimulate Neutrophil Swarming

Leukotriene synthesis in neutrophils is critical for host survival during infection. In particular, leukotriene B4 (LTB4) is a powerful neutrophil chemoattractant that plays a crucial role in neutrophil swarming. In this work, we demonstrated that preincubation of human neutrophils with Salmonella typhimurium strongly stimulated LTB4 production induced by the bacterial chemoattractant, peptide N-formyl-L-methionyl-L-leucyl-l-phenylalanine (fMLP), while the reverse sequence of additions was ineffective. Preincubation with bacterial lipopolysaccharide or yeast polysaccharide zymosan particles gives weaker effect on fMLP-induced LTB4 production. Activation of 5-lipoxygenase (5-LOX), a key enzyme in leukotrienes biosynthesis, depends on rise of cytosolic concentration of Ca2+ and on translocation of the enzyme to the nuclear membrane. Both processes were stimulated by S. typhimurium. With an increase in the bacteria:neutrophil ratio, the transformation of LTB4 to ω-OH-LTB4 was suppressed, which further supported increased concentration of LTB4. These data indicate that in neutrophils gathered around bacterial clusters, LTB4 production is stimulated and at the same time its transformation is suppressed, which promotes neutrophil swarming and elimination of pathogens simultaneously.

Capsaicin potently blocks Salmonella typhimurium invasion of Vero cells

As at 2021, the center for disease control (CDC) reported that Salmonella causes 1.2 million illness in the United States each year, with a mortality rate approaching 500 deaths per annum. Infants, the elderly, and persons with compromised immunity are the population with higher risk of mortality from this infection. At present there is no commercially available, safe and efficacious vaccine for the control and management of Salmonella typhimurium (S. typhimurium). More so, S. typhimurium has been shown to develop resistance against most antibiotics used for treatment of the infection. Capsaicin, a bioactive compound from Capsicum chinense (C. chinenses) is undoubtedly one of the most widely used spice in the world. This heat producing compound is not only been used as food additive but have been demonstrated to possess unique properties that have pharmacological, physiological, and antimicrobial applications. In this work, the antimicrobial property of pure capsaicin or capsaicin extract against S. typhimurium is tested to determine the compounds effectiveness in S. typhimurium inhibition. Capsaicin extract showed potent inhibition of S. typhimurium growth at concentrations as low as 100 ng/ml, whereas pure capsaicin comparatively showed poorer inhibition of the bacteria. Furthermore, both capsaicin extract and pure capsaicin potently blocked S. typhimurium invasion of an animal cell line in vitro. Taken together, this work revealed that capsaicin might work synergistically with dihydrocapsaicin or the other capsaicinoids to inhibit S. typhimurium growth, whereas individually, capsaicin or dihydrocapsaicin could potently block the bacteria entry and invasion of Vero cells.