باکتریها زندگی را دوست دارند

            Swarming is the fastest known mode of surface translocation, allowing rapid colonization of nutrient-rich environments and host tissues. This complex multicellular behavior requires integration of chemical and physical signals, leading to physiological and morphological differentiation of the bacteria into swarmer cells (Verstraeten et al., 2008). Two model systems for swarming are studied in our group: the opportunistic pathogen Pseudomonas aeruginosa and the nitrogen-fixing bean symbiont Rhizobium etli (Figure 1).
                                                                        
Previously, we have identified genetic determinants affecting swarming in R. etli by screening a transposon mutant library (Braeken et al., 2008). In addition, we have shown that specific R. etli quorum sensing molecules serve a dual role during swarming by acting as signaling molecules as well as biosurfactants (Daniels et al., 2006). These results inspired us to initiate a research program focused on the interaction between biological and physico-chemical processes leading to swarming migration and pattern formation in P. aeruginosa and R. etli.

Physicochemical aspects of bacterial swarming
Despite the often intricate genetic mechanisms that regulate swarming, there are also several ways in which physico-chemical phenomena could play a role in the dynamics of swarming and biofilm formation. Possible parameters intervening in these are the heterogeneity of substrates, the surface-active nature of signaling molecules, and the dependence of viscosity on the concentration of bacteria and its effect on thin film hydrodynamics. Likewise, the extracellular slime is a non-Newtonian fluid whose viscosity strongly depends on local deformation rates that will affect the spreading dynamics of the bacterial film. Finally, at high concentrations of bacteria, large-scale coherent movements of bacteria with vortex-like motions might appear due to hydrodynamic coupling, in which the collective motion of bacteria through the viscous slime drives the fluid flow. In particular, the striking ‘fingering’ patterns, formed by some swarmer colonies on relatively soft subphases, have attracted attention as they could be the signatures of instability

 

   

تصویری از استافیلوکوک مقاوم به دیسک متی سیلین در محیط  مولر هینتون اگار

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacterium responsible for difficult-to-treat infections in humans. It may also be referred to as multidrug-resistant Staphylococcus aureus or oxacillin-resistant Staphylococcus aureus (ORSA). MRSA is by definition a strain of Staphylococcus aureus that is resistant to a large group of antibiotics called the beta-lactams, which include the penicillins and the cephalosporins.

The organism is often sub-categorized as Community-Associated MRSA (CA-MRSA) or Health Care-Associated MRSA (HA-MRSA) although this distinction is complex. Some have defined CA-MRSA by criteria related to patients suffering from an MRSA infection while other authors have defined CA-MRSA by genetic characteristics of the bacteria themselves. CA-MRSA strains were first reported in the late 1990s; these cases were defined by a lack of exposure to the health care setting. In the next several years, it became clear that CA-MRSA infections were caused by strains of MRSA that differed from the older and better studied healthcare-associated strains.^[1] The new CA-MRSA strains have rapidly spread in the United States to become the most common cause of cultured skin infections among individuals seeking medical care for these infections at emergency rooms in cities. These strains also commonly cause skin infections in athletes, jail and prison detainees, and soldiers.

MRSA is a resistant variation of the common bacterium Staphylococcus aureus. It has evolved an ability to survive treatment with beta-lactamase resistant beta-lactam antibiotics, including methicillin, dicloxacillin, nafcillin, and oxacillin. MRSA is especially troublesome in hospital-associated (nosocomial) infections. In hospitals, patients with open wounds, invasive devices, and weakened immune systems are at greater risk for infection than the general public. Hospital staff who do not follow proper sanitary procedures may transfer bacteria from patient to patient. Visitors to patients with MRSA infections or MRSA colonization are advised to follow hospital isolation protocol by using the provided gloves, gowns, and masks if indicated. Visitors who do not follow such protocols are capable of spreading the bacteria to cafeterias, bathrooms, and elevators.

In microbiology, McFarland standards are used as a reference to adjust the turbidity of bacterial suspensions so that the number of bacteria will be within a given range

Original McFarland standards were made by mixing specified amounts of barium chloride and sulfuric acid together. Mixing the two compounds forms a barium sulfate precipitate, which causes turbidity in the solution. A 0.5 McFarland standard is prepared by mixing 0.05 mL of 1.175% barium chloride dihydrate (BaCl₂•2H₂O), with 9.95 mL of 1% sulfuric acid (H₂SO₄).

Now there are McFarland standards prepared from suspensions of latex particles, which lengthens the shelf life and stability of the suspensions.

The standard can be compared visually to a suspension of bacteria in sterile saline or nutrient broth. If the bacterial suspension is too turbid, it can be diluted with more diluent. If the suspension is not turbid enough, more bacteria can be added.

McFarland Nephelometer Standards^{[citation needed]}:

*at wavelength of 600 nm

ترجمه :

در میکروبیولوژی اندازه های مک فارلند به عنوان مرجعی برای مطابقت دادن کدورت ناشی ازسوسپانسیون  باکتری  با شمار باکتریهایی که در یک حیطه داده شده خواهد بود به کاربرده میشود.

نسخه های اصلی اندازه های  مک فارلند با مخلوط کردن مقدار مشخصی از کلرید باریم واسید سولفوریک بدست می اید.مخلوط کردن این دو ترکیب رسوب سولفات باریم را تشکیل میدهد که سبب کدورت و تیرگی محلول میشود.اندازه 0.5مک فارلند از مخلوط کردن0.05 mL از کلرید باریم دهیدرات  1.175% با 9.95 mL از اسید سولفوریک 1% تهیه میشود.

 اکنون اندازه های مک فارلندی موجود هستند که از تعلیق ذرات لاتکس تهیه میشوند که طول عمر بیشتری دارند و ثبات ذرات معلق در انها بیشتر است.

 این استاندارد میتواند با چشم با سوسپانسیون باکتری در یک محیط نمکی ضد عفونی یا نوترینت براث مقایسه شود.اگر سوسپانسیون خیلی تیره یا کدر باشد( یعنی کدورت بیشتری نسبت به میزان مک فارلند داشته باشد) میتواند با رقیق کننده بیشتر رقیق شود و اگر سوسپانسیون باکتری  کدورت کمتری داشته باشد باکتری بیشتری باید اضافه گردد.

 منبع :ویکی پدیا

گروه بزرگی از باکتریهای نا همگون و مارپیچی شکل هستند که متحرک میباشند .

برخی مانند فنرپیچیده و برخی مانند فنر باز شده دیده میشوند. حرکت انها به وسیله یک رشته محوری انجام میگیرد .

اندازه اسپیروکتها از چند تا ۵۰۰میکرون میرسد .

این باکتریها هوازی و بی هوازی اختیاری بوده و فاقد تاژه ازاد و اندوسپور هستند و همگی با شکاف عرضی تقسیم میشوند.

اسپیروکت ها در ابهای الوده . فاضلابها . خاک . مواد الی در حال پوسیدن و در بدن انسان و حیوانات یافت میشوند .

نکته مهم از نظر پزشکی حساسیت اکثر اسپیرو کتها نسبت به فلزات سنگین (ارسنیک . قلع و بیسموت )و به مقدار کم انتی بیوتیک پنی سیلین میباشد .

اسپیروکتها فوق العاده نازک بوده و به اسانی توسط میکروسکوپ نوری عادی دیده نمیشوند .

رنگ امیزی معمولی نظیر رنگ امیزی گرم باعث تغییر شکل سلول میگردد . اسپیروکتها را به وسیله میکروسکوپ زمینه تاریک بدون رنگ امیزی میتوان به بهترین وجه مطالعه کرد.