Morganella marganaii
Classification
Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacteriales; Enterobacteriaceae; Proteeae; Morganella [1]
Species
Morganella morganaii
Subspecies
i. M. m. morganaii Biogroups A, B, C, D ii. M. m. sibonii Biogroups E, F, G [2]
Description and significance
Morganella morganii is a Gram-negative, anaerobic rod of the family Enterobacteriaceae commonly found in water, soil, and the intestinal tracts of mammals [3]. The bacteria was first identified by H. de R. Morgan in 1906 as Morgan’s bacillus [4]. Then in 1946, Morgan’s bacillus was assigned to the established genus Morganella, thus named Morganella morganii [5]. Generally, M. morganii has low pathogenicity but there is emerging evidence that M. morganii is an opportunistic pathogen responsible for urinary tract infections (UTI), wound infections, and diarrhea [6]. Most patients, however, recover from the infections with appropriate antibiotic therapy. However, it is resistant to β-lactam antibiotics and can form biofilms. M. morganii also causes the greatest amount of histamine accumulation of any bacteria in food products, such as fish, wine, cheese, and fermented sausage [7,8]. When contaminated products are consumed, histamine poisoning, also known as scrombroid poisoning, may occur and even lead to death [9].
Genome structure
i.M. morganii has a complete genome sequence (3,826,919-bp) with a G+C content of 51.15% as well as 3,565 protein-coding sequences [3]. Genes encoding for drug resistance such as Ampicillin resistance (ampC-ampR), Metallo-β-lactamases (MBL), Tellurite resistance operon, and Tetracycline resistance were identified in M. morganii’s genome [3]. M. morganii’s genome contains the genes include blaCTX-M (beta-lactamase cefotaxime hydrolyzing capabilities), blaSHV (beta-lactamase sulfhydryl variable), blaTEM (beta-lactamase temoneira), and blaOXA (beta-lactamase oxacillin hydrolyzing capabilities) which encode extended-spectrum beta-lactamases [10,11]. The production of ESBL makes the microbe resistant to beta-lactam antibiotics, such as penicillins and cephalosporins. ESBL open the beta lactam ring of the aforementioned antibiotics and thus inactivates beta-lactam antibiotics [10].
ii.The 16S rRNA sequence of the genus Morganella has 1,503 bp and shows 95% similarity to 16S rRNA sequence of some enteric bacteria, specifically all species in Enterobacter, Klebsiella, Citrobacter, Proteus, Providencia as well as the species Hafnia alvei [12].
Cell structure and metabolic processes
i. Morganella morganii are Gram-negative, straight rod-shaped bacteria with a diameter of 0.6 0.7 um and a length of 1.0-1.7 um [13]. Most M. morganii exhibit motility using peritrichroic flagella, or hair-like projections distributed all over the cell body [14]. M. morganii biogroup B is the exception: it is nonmotile with no visible flagella [14]. The flagella also enable the bacteria to adhere to surfaces and one another to create biofilms [3]. M. morganaii does have swarming behavior [15]. M. morganii does not produce spores [16]. When cultured on an agar plate at 35°C, grayish, opaque colonies of 1 to 2 mm in diameter form [14].
ii.The genus Morganella is a group of Enterobacteriaceae that does not ferment lactose or sucrose [1]. M. morganii metabolizes levulose and maltose and slowly metabolizing galactose, glucose, glycerol [13]. M. morganii is indole-positive and urease positive, indicating breakdown tryptophan and urease, respectively [13]. The microbe does not break down cysteine [13]. M. morganii is a facultative anaerobe and oxidase negative [15]. M. morganaii is divided into two subspecies, M.m. morganaii and M.m sibonii, because the former cannot ferment trehalose while the latter can. The two subspecies are further divided into biogroups based on three tests: ornithine decarboxylase (ODC), lysine decarboxylase (LDC), and susceptibility to tetracycline. M.m.morganii contains four biogroups (A, B, C, and D) and M.m. Sibonii contains three biogroups (E, F, and G). Biogroup A is ODC+/LDC-, Biogroup B ODC+/LDC+, Biogroup C is ODC-/LDC-, Biogroup D is ODC-/LDC+, Biogroup E is ODC+/LDC+, Biogroup F is ODC-/LDC variable, and Biogroup G ODC+/LDC-[14]. Biogroup C was the only one found to be nonsusceptible to tetracycline [2]. M. morganii produces extended-spectrum beta-lactamases which contributes to the microbe’s resistance to beta-lactam antibiotics [10]. M. morganii grows optimally at 22°C [14].
Ecology
i. Morganella morganii is found in water, soil, intestinal tracts of humans, mammals, and reptiles as normal flora [17]. The microbe has been isolated from samples of urine, gallbladder, stool, sputum and other respiratory samples in humans without infection [3].Under usual conditions, M. morganii is typically a benign bacteria in the human body; however, it has been associated with urinary tract infection and postoperative infections [18]. Infections are commonly contracted in a hospital, especially in immunosuppressed individuals [12]. M. morganaii is also found in post-mortem, non-frozen fish [19]. When M. morganii is present on food products and post-mortem fish, it synthesizes histidine decarboxylase to convert histidine to histamine [19]. The accumulation and consumption of histamine by humans causes a rash, nausea, diarrhea, flushing, sweating, headache, and sometimes death [20]. Freezing the fish at a temperature at or below 0°C completely inhibits histamine production by M. morganii [21].
Pathology
Morganella morganii has components of a pathogenicity system including adhesion and secretion. M. morganii adheres to hosts using its type IV pili and the dissembling of the pili results in a twitching motility which pulls it towards the host [3]. The microbe uses a type III secretion system needle complex to inject proteins directly into host cells [3].
Current Research
a. Molecular Investigation of extended-spectrum beta-lactamase genes and potential drug resistance in clinical isolates of Morganella morganii Morganella morganii isolates have been exposed to various types of antibiotics for the purpose of testing their drug susceptibility. These antibiotics included piperacillin-tazobactam, piperacillin, ticarcillin, ticarcillin-clavulanic acid, ceftazidime, cefepime, aztreonam, meropenem, imipenem, isepamicin, tobramycin, amikacin, gentamicin, pefloxacin, ciprofloxacin, trimethoprim sulfamethoxazole, minocycline, colistin and rifampicin. M. morganii were considered multidrug resistant because they are resistant to at least three types of antibiotics; piperacillin, piperacillin-tazobactam, and aztreonam [10]. Isolates exposed to these multiple antibiotics have evolved the ability to produce extended-spectrum beta-lactamase (ESBL). This new mutation increased isolates’ resistance to even stronger antibiotics such as ceftriaxone, ceftazidime, and cefotaxime, which were the third- and fourth- generation of cephalosporins [10]. A similar study identified M. morganii isolates showing resistance to first-generation antibiotics cephalosporins, ampicillin-clavulnate, gentamicin, piperacillin-tazobactam, and ciprofloxacin [22]. All isolates tested harbor the ability to generate ESLB. Four genes (CTX-M, SHV, TEM, and OXA) are responsible for ESBL production [10].
b. Characterization of a novel Morganella morganii bacteriophage FSP1 isolated from river water The bacteriophage FSP1, found in river in Hakodate, Hokkaido, Japan may become the next therapeutic drug for Morganella morganii infections. After 6 hours of incubation at 37 °C only FSP1 formed plaques on M. morganii species, which indicates that this bacteriophage was an exclusive antimicrobial agent for M. morganii [23]. When the MOI (average number of virus particles infecting a cell) is 1, the total M. morganii cell count decreased from 7.2 to 3.7 log CFU/ml; when MOI is 10, the cell count is zero. However, the M. morganii started to regrow 2 hours to 5 hours after the observation [23]. In order to prevent phage resistance from happening, one way was to apply phage cocktail to repress the development of resistance. Because of the increasing incidence of M. morganii hospital infections, the threat to our fish food supply, and the antibiotic-resistant nature of M. morganii a substitute for antibiotics against bacteria growth would be highly useful.
