Whether the machine is top or front loading, uses an agitator, a drum, a pulsator, a pair of electromechanical robot hands etc really makes no difference in terms of bacteria killing. If anything, a front loader is potentially more hygienic as it has the possibility of a "boil wash" cycle to sanitise the drum completely. However, you can achieve similar results in any machine by adding chemicals to the water.
There are a few things to remember.
The majority of bacteria and viruses will actually be taken care of by a warm wash with a good detergent in either front or top loading machines. It's just really if you have a specific concern, such as a family member with some kind of contageous skin disorder, or someone in your household who is immune suppressed e.g. has had a transplant and is on anti-rejection medication, is currently undergoing certain types of chemotherapy for cancer or has AIDS and would be highly vulnerable to bacteria/viruses.
In those cases, in any type of washing machine you should use a proper laundry sanitizer in the correct concentration.
It might also be a consideration to isolate their laundry.
Floor cloths, dirty rags etc should only be washed in a disinfectant solution or, if your machine allows, boiled. They are not normal clothes, and shouldn't be washed with them.
The reality of modern fabrics means that it is not possible to boil everything nor is it advisable to use the concentrations of chlorine bleach that would be necessary to kill off the bugs.
There are perfectly good laundry sanitising products available for such situation.
If you're in the UK/Ireland you can use Dettol clear disinfectant in your front loader without any problems. Just follow the dosage instructions on the back of the bottle. It will wipe out EVERYTHING and leave the laundry perfectly hygenically clean.
The concern for washing machine health and laundry hygeine is where people do very short washes with very low temps with very little detergent. This applies to both types of washing machine.
I know I came across someone in Boston who had black mould growing in their toploader. She ran all her washes on cold/cool and used 1/4 the recommended dose and used an eco-detergent. The machine was full of undisolved detergent 'gunk' and was horrible.
To fix the problem, we ran long hot wash without clothes and on heavy agitation full to the top with a strong detergent. It readily broke down the residues and most of the gunk in the machine. We followed that off with a wash with bleach.
"stinky washing machine syndrome" is generally avoidable in either type of washing machine with the simplest of steps and really has nothing whatsoever to do with the choice of wash action used by the machine i.e. H-axis drum or V-axis agitator.
In Europe, Chlorine bleach is simply not used at all for laundry. This is because detergent manufacturers moved towards longer acting peroxide bleaching methods as it was possible to create 'universal' powders that were safe to use with coloured clothes at lower temps and then took on a more aggressive bleaching action when heated up.
When automatic washing machines became the norm in the 60s and 70s, there was a huge leap forward in enzyme technology. The result was that the new 'automatic' detergents i.e. for h-axis washing machines didn't need bleach to produce very good cleaning results. The machines all have cycles which are designed to wash the clothes at temps that are optimised for enzyme activity.
Whiteness is achieved with milder oxygen-based bleaching formulas and optical brighteners.
If you want to absolutely sanitise, you add something like Dettol or similar sanitisors to the wash and they will destroy every bacterium and virus known to man!
Alternatively, you wash at a high temp.
Regardless of what washing method you use, you really just have to be aware of what you're doing if you're laundering potentially contaminated materials.
Also, your tumble dryer or even line drying will go a long way towards killing bacteria too by heating them and drying them out.
